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Deployment Guide

Deployment Guide

Deployment, Configuration and Administration of Red Hat Enterprise Linux 6

Edition 1

Link to Original Document

Legal Notice

Copyright © 2010 Red Hat, Inc.
The text of and illustrations in this document are licensed by Red Hat under a Creative Commons Attribution–Share Alike 3.0 Unported license ("CC-BY-SA"). An explanation of CC-BY-SA is available at http://creativecommons.org/licenses/by-sa/3.0/. In accordance with CC-BY-SA, if you distribute this document or an adaptation of it, you must provide the URL for the original version.
Red Hat, as the licensor of this document, waives the right to enforce, and agrees not to assert, Section 4d of CC-BY-SA to the fullest extent permitted by applicable law.
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Abstract
The Deployment Guide documents relevant information regarding the deployment, configuration and administration of Red Hat Enterprise Linux 6.

Preface
1. Document Conventions
1.1. Typographic Conventions
1.2. Pull-quote Conventions
1.3. Notes and Warnings
2. We Need Feedback!
2.1. Technical Review Requests
3. Acknowledgements
Introduction
I. Package Management
1. Yum
1.1. Checking For and Updating Packages
1.1.1. Checking For Updates
1.1.2. Updating Packages
1.1.3. Updating Security-Related Packages
1.1.4. Preserving Configuration File Changes
1.2. Packages and Package Groups
1.2.1. Searching, Listing and Displaying Package Information
1.2.2. Installing
1.2.3. Removing
1.3. Configuring Yum and Yum Repositories
1.3.1. Setting [main] Options
1.3.2. Setting [repository] Options
1.3.3. Using Yum Variables
1.3.4. Creating a Yum Repository
1.4. Yum Plugins
1.4.1. Enabling, Configuring and Disabling Yum Plugins
1.4.2. Installing More Yum Plugins
1.4.3. Plugin Descriptions
1.5. Additional Resources
2. PackageKit
2.1. Updating Packages with Software Update
2.2. Using Add/Remove Software
2.2.1. Refreshing Software Sources (Yum Repositories)
2.2.2. Finding Packages with Filters
2.2.3. Installing and Removing Packages (and Dependencies)
2.2.4. Installing and Removing Package Groups
2.2.5. Viewing the Transaction Log
2.3. PackageKit Architecture
2.4. Additional Resources
3. RPM
3.1. RPM Design Goals
3.2. Using RPM
3.2.1. Finding RPM Packages
3.2.2. Installing and Upgrading
3.2.3. Configuration File Changes
3.2.4. Uninstalling
3.2.5. Freshening
3.2.6. Querying
3.2.7. Verifying
3.3. Checking a Package's Signature
3.3.1. Importing Keys
3.3.2. Verifying Signature of Packages
3.4. Practical and Common Examples of RPM Usage
3.5. Additional Resources
3.5.1. Installed Documentation
3.5.2. Useful Websites
3.5.3. Related Books
II. Network-Related Configuration
4. Network Interfaces
4.1. Network Configuration Files
4.2. Interface Configuration Files
4.2.1. Ethernet Interfaces
4.2.2. Channel Bonding Interfaces
4.2.3. Alias and Clone Files
4.2.4. Dialup Interfaces
4.2.5. Other Interfaces
4.3. Interface Control Scripts
4.4. Configuring Static Routes
4.5. Network Function Files
4.6. Additional Resources
4.6.1. Installed Documentation
5. Network Configuration
5.1. The NetworkManager Daemon
5.2. Interacting with NetworkManager
5.2.1. Connecting to a Network
5.2.2. Configuring New and Editing Existing Connections
5.2.3. Connecting to a Network Automatically
5.2.4. User and System Connections
5.3. Configuring Connection Settings
5.3.1. Configuring IPv4 Settings
6. Dynamic Host Configuration Protocol (DHCP)
6.1. Why Use DHCP?
6.2. Configuring a DHCP Server
6.2.1. Configuration File
6.2.2. Lease Database
6.2.3. Starting and Stopping the Server
6.2.4. DHCP Relay Agent
6.3. Configuring a DHCP Client
6.4. Configuring a Multihomed DHCP Server
6.4.1. Host Configuration
6.5. DHCP for IPv6 (DHCPv6)
6.6. Additional Resources
6.6.1. Installed Documentation
7. Controlling Access to Services
7.1. Configuring the Default Runlevel
7.2. Configuring the Services
7.2.1. Using the Service Configuration Utility
7.2.2. Using the ntsysv Utility
7.2.3. Using the chkconfig Utility
7.3. Running the Services
7.3.1. Using the service Utility
7.4. Additional Resources
7.4.1. Installed Documentation
7.4.2. Related Books
8. Authentication Configuration
8.1. The Authentication Configuration Tool
8.1.1. Identity & Authentication
8.1.2. Advanced Options
8.1.3. Command Line Version
8.2. The System Security Services Daemon (SSSD)
8.2.1. What is SSSD?
8.2.2. SSSD Features
8.2.3. Setting Up SSSD
8.2.4. Configuring Services
8.2.5. Configuring Domains
8.2.6. Setting Up Kerberos Authentication
8.2.7. Troubleshooting
8.2.8. SSSD Configuration File Format
9. OpenSSH
9.1. The SSH Protocol
9.1.1. Why Use SSH?
9.1.2. Main Features
9.1.3. Protocol Versions
9.1.4. Event Sequence of an SSH Connection
9.2. An OpenSSH Configuration
9.2.1. Configuration Files
9.2.2. Starting an OpenSSH Server
9.2.3. Requiring SSH for Remote Connections
9.2.4. Using a Key-Based Authentication
9.3. OpenSSH Clients
9.3.1. Using the ssh Utility
9.3.2. Using the scp Utility
9.3.3. Using the sftp Utility
9.4. More Than a Secure Shell
9.4.1. X11 Forwarding
9.4.2. Port Forwarding
9.5. Additional Resources
9.5.1. Installed Documentation
9.5.2. Useful Websites
10. The BIND DNS Server
10.1. Introduction to DNS
10.1.1. Nameserver Zones
10.1.2. Nameserver Types
10.1.3. BIND as a Nameserver
10.2. Configuring the named Service
10.2.1. Common Statement Types
10.2.2. Other Statement Types
10.2.3. Comment Tags
10.3. Editing Zone Files
10.3.1. Common Directives
10.3.2. Common Resource Records
10.3.3. Comment Tags
10.3.4. Example Usage
10.4. Using the rndc Utility
10.4.1. Configuring the Utility
10.4.2. Checking the Service Status
10.4.3. Reloading the Configuration and Zones
10.4.4. Updating Zone Keys
10.4.5. Enabling the DNSSEC Validation
10.4.6. Enabling the Query Logging
10.5. Using the dig Utility
10.5.1. Looking Up a Nameserver
10.5.2. Looking Up an IP Address
10.5.3. Looking Up a Hostname
10.6. Advanced Features of BIND
10.6.1. Multiple Views
10.6.2. Incremental Zone Transfers (IXFR)
10.6.3. Transaction SIGnatures (TSIG)
10.6.4. DNS Security Extensions (DNSSEC)
10.6.5. Internet Protocol version 6 (IPv6)
10.7. Common Mistakes to Avoid
10.8. Additional Resources
10.8.1. Installed Documentation
10.8.2. Useful Websites
10.8.3. Related Books
11. The Apache HTTP Server
11.1. The Apache HTTP Server 2.2
11.1.1. New Features
11.1.2. Notable Changes
11.1.3. Updating the Configuration
11.2. Running the httpd Service
11.2.1. Starting the Service
11.2.2. Stopping the Service
11.2.3. Restarting the Service
11.2.4. Checking the Service Status
11.3. Editing the Configuration Files
11.3.1. Common httpd.conf Directives
11.3.2. Common ssl.conf Directives
11.3.3. Common Multi-Processing Module Directives
11.4. Working with Modules
11.4.1. Loading a Module
11.4.2. Writing a Module
11.5. Setting Up Virtual Hosts
11.6. Setting Up an SSL Server
11.6.1. An Overview of Certificates and Security
11.6.2. Enabling the mod_ssl Module
11.6.3. Using an Existing Key and Certificate
11.6.4. Generating a New Key and Certificate
11.7. Additional Resources
11.7.1. Installed Documentation
11.7.2. Useful Websites
12. Email
12.1. Email Protocols
12.1.1. Mail Transport Protocols
12.1.2. Mail Access Protocols
12.2. Email Program Classifications
12.2.1. Mail Transport Agent
12.2.2. Mail Delivery Agent
12.2.3. Mail User Agent
12.3. Mail Transport Agents
12.3.1. Postfix
12.3.2. Sendmail
12.3.3. Fetchmail
12.3.4. Mail Transport Agent (MTA) Configuration
12.4. Mail Delivery Agents
12.4.1. Procmail Configuration
12.4.2. Procmail Recipes
12.5. Mail User Agents
12.5.1. Securing Communication
12.6. Additional Resources
12.6.1. Installed Documentation
12.6.2. Useful Websites
12.6.3. Related Books
III. System Configuration
13. Date and Time Configuration
13.1. Date/Time Properties Tool
13.1.1. Date and Time Properties
13.1.2. Network Time Protocol Properties
13.1.3. Time Zone Properties
13.2. Command Line Configuration
13.2.1. Date and Time Setup
13.2.2. Network Time Protocol Setup
14. Keyboard Configuration
14.1. Changing the Keyboard Layout
14.2. Adding the Keyboard Layout Indicator
14.3. Setting Up a Typing Break
15. Users and Groups
15.1. User and Group Configuration
15.1.1. Adding a New User
15.1.2. Adding a New Group
15.1.3. Modifying Group Properties
15.2. User and Group Management Tools
15.2.1. Command Line Configuration
15.2.2. Explaining the Process
15.3. Standard Users
15.4. Standard Groups
15.5. User Private Groups
15.5.1. Group Directories
15.6. Shadow Passwords
15.7. Additional Resources
15.7.1. Installed Documentation
16. Automated Tasks
16.1. Cron and Anacron
16.1.1. Starting and Stopping the Service
16.1.2. Configuring Anacron Jobs
16.1.3. Configuring Cron Jobs
16.1.4. Controlling Access to Cron
16.1.5. Black/White Listing of Cron Jobs
16.2. At and Batch
16.2.1. Configuring At Jobs
16.2.2. Configuring Batch Jobs
16.2.3. Viewing Pending Jobs
16.2.4. Additional Command Line Options
16.2.5. Controlling Access to At and Batch
16.2.6. Starting and Stopping the Service
16.3. Additional Resources
16.3.1. Installed Documentation
17. Log Files
17.1. Configuring rsyslog
17.1.1. Modules
17.1.2. Global Directives
17.1.3. Rules
17.1.4. Templates
17.1.5. Filter Conditions
17.1.6. Output Channels
17.2. rsyslog Performance
17.3. Locating Log Files
17.3.1. Configuring logrotate
17.4. Viewing Log Files
17.5. Adding a Log File
17.6. Monitoring Log Files
17.7. Additional Resources
17.7.1. Installed Documentation
17.7.2. Useful Websites
18. The sysconfig Directory
18.1. Files in the /etc/sysconfig/ Directory
18.1.1. /etc/sysconfig/arpwatch
18.1.2. /etc/sysconfig/authconfig
18.1.3. /etc/sysconfig/autofs
18.1.4. /etc/sysconfig/clock
18.1.5. /etc/sysconfig/dhcpd
18.1.6. /etc/sysconfig/firstboot
18.1.7. /etc/sysconfig/i18n
18.1.8. /etc/sysconfig/init
18.1.9. /etc/sysconfig/ip6tables-config
18.1.10. /etc/sysconfig/keyboard
18.1.11. /etc/sysconfig/ldap
18.1.12. /etc/sysconfig/named
18.1.13. /etc/sysconfig/network
18.1.14. /etc/sysconfig/ntpd
18.1.15. /etc/sysconfig/quagga
18.1.16. /etc/sysconfig/radvd
18.1.17. /etc/sysconfig/samba
18.1.18. /etc/sysconfig/selinux
18.1.19. /etc/sysconfig/sendmail
18.1.20. /etc/sysconfig/spamassassin
18.1.21. /etc/sysconfig/squid
18.1.22. /etc/sysconfig/system-config-users
18.1.23. /etc/sysconfig/vncservers
18.1.24. /etc/sysconfig/xinetd
18.2. Directories in the /etc/sysconfig/ Directory
18.3. Additional Resources
18.3.1. Installed Documentation
19. The proc File System
19.1. A Virtual File System
19.1.1. Viewing Virtual Files
19.1.2. Changing Virtual Files
19.2. Top-level Files within the proc File System
19.2.1. /proc/buddyinfo
19.2.2. /proc/cmdline
19.2.3. /proc/cpuinfo
19.2.4. /proc/crypto
19.2.5. /proc/devices
19.2.6. /proc/dma
19.2.7. /proc/execdomains
19.2.8. /proc/fb
19.2.9. /proc/filesystems
19.2.10. /proc/interrupts
19.2.11. /proc/iomem
19.2.12. /proc/ioports
19.2.13. /proc/kcore
19.2.14. /proc/kmsg
19.2.15. /proc/loadavg
19.2.16. /proc/locks
19.2.17. /proc/mdstat
19.2.18. /proc/meminfo
19.2.19. /proc/misc
19.2.20. /proc/modules
19.2.21. /proc/mounts
19.2.22. /proc/mtrr
19.2.23. /proc/partitions
19.2.24. /proc/slabinfo
19.2.25. /proc/stat
19.2.26. /proc/swaps
19.2.27. /proc/sysrq-trigger
19.2.28. /proc/uptime
19.2.29. /proc/version
19.3. Directories within /proc/
19.3.1. Process Directories
19.3.2. /proc/bus/
19.3.3. /proc/bus/pci
19.3.4. /proc/driver/
19.3.5. /proc/fs
19.3.6. /proc/irq/
19.3.7. /proc/net/
19.3.8. /proc/scsi/
19.3.9. /proc/sys/
19.3.10. /proc/sysvipc/
19.3.11. /proc/tty/
19.3.12. /proc/PID/
19.4. Using the sysctl Command
19.5. References
IV. System Monitoring
20. Gathering System Information
20.1. System Processes
20.2. Memory Usage
20.3. File Systems
20.4. Hardware
20.5. Additional Resources
20.5.1. Installed Documentation
21. ABRT
21.1. Overview
21.2. Installing and Running ABRT
21.3. ABRT Plugins
21.3.1. Analyzer Plugins
21.3.2. Reporter Plugins
21.3.3. Plugin Configuration in the GUI
21.4. Generating Backtraces
21.4.1. Troubleshooting Backtrace Generation
21.5. Using the Command Line Interface
21.5.1. Viewing Crashes
21.5.2. Reporting Crashes
21.5.3. Deleting Crashes
21.6. Configuring ABRT
21.7. Configuring Centralized Crash Collection
21.7.1. Testing ABRT's Crash Detection
21.7.2. Testing the Upload Method
V. Kernel, Module and Driver Configuration
22. Working with Kernel Modules
22.1. Listing Currently-Loaded Modules
22.2. Displaying Information About a Module
22.3. Loading a Module
22.4. Unloading a Module
22.5. Setting Module Parameters
22.6. Persistent Module Loading
22.7. Specific Kernel Module Capabilities
22.7.1. Using Multiple Ethernet Cards
22.7.2. Using Channel Bonding
22.8. Additional Resources
23. Manually Upgrading the Kernel
23.1. Overview of Kernel Packages
23.2. Preparing to Upgrade
23.3. Downloading the Upgraded Kernel
23.4. Performing the Upgrade
23.5. Verifying the Initial RAM Disk Image
23.6. Verifying the Boot Loader
23.6.1. Configuring the GRUB Boot Loader
23.6.2. Configuring the OS/400® Boot Loader
23.6.3. Configuring the YABOOT Boot Loader
24. The kdump Crash Recovery Service
24.1. Configuring the kdump Service
24.1.1. Configuring the kdump at First Boot
24.1.2. Using the Kernel Dump Configuration Utility
24.1.3. Configuring kdump on the Command Line
24.1.4. Testing the Configuration
24.2. Analyzing the Core Dump
24.2.1. Displaying the Message Buffer
24.2.2. Displaying a Backtrace
24.2.3. Displaying a Process Status
24.2.4. Displaying Virtual Memory Information
24.2.5. Displaying Open Files
24.3. Additional Resources
24.3.1. Installed Documentation
24.3.2. Useful Websites
A. Revision History
Index

Preface

1. Document Conventions

This manual uses several conventions to highlight certain words and phrases and draw attention to specific pieces of information.
In PDF and paper editions, this manual uses typefaces drawn from the Liberation Fonts set. The Liberation Fonts set is also used in HTML editions if the set is installed on your system. If not, alternative but equivalent typefaces are displayed. Note: Red Hat Enterprise Linux 5 and later includes the Liberation Fonts set by default.

1.1. Typographic Conventions

Four typographic conventions are used to call attention to specific words and phrases. These conventions, and the circumstances they apply to, are as follows.
Mono-spaced Bold
Used to highlight system input, including shell commands, file names and paths. Also used to highlight keycaps and key combinations. For example:
To see the contents of the file my_next_bestselling_novel in your current working directory, enter the cat my_next_bestselling_novel command at the shell prompt and press Enter to execute the command.
The above includes a file name, a shell command and a keycap, all presented in mono-spaced bold and all distinguishable thanks to context.
Key combinations can be distinguished from keycaps by the hyphen connecting each part of a key combination. For example:
Press Enter to execute the command.
Press Ctrl+Alt+F2 to switch to the first virtual terminal. Press Ctrl+Alt+F1 to return to your X-Windows session.
The first paragraph highlights the particular keycap to press. The second highlights two key combinations (each a set of three keycaps with each set pressed simultaneously).
If source code is discussed, class names, methods, functions, variable names and returned values mentioned within a paragraph will be presented as above, in mono-spaced bold. For example:
File-related classes include filesystem for file systems, file for files, and dir for directories. Each class has its own associated set of permissions.
Proportional Bold
This denotes words or phrases encountered on a system, including application names; dialog box text; labeled buttons; check-box and radio button labels; menu titles and sub-menu titles. For example:
Choose System → Preferences → Mouse from the main menu bar to launch Mouse Preferences. In the Buttons tab, click the Left-handed mouse check box and click Close to switch the primary mouse button from the left to the right (making the mouse suitable for use in the left hand).
To insert a special character into a gedit file, choose Applications → Accessories → Character Map from the main menu bar. Next, choose Search → Find… from the Character Map menu bar, type the name of the character in the Search field and click Next. The character you sought will be highlighted in the Character Table. Double-click this highlighted character to place it in the Text to copy field and then click the Copy button. Now switch back to your document and choose Edit → Paste from the gedit menu bar.
The above text includes application names; system-wide menu names and items; application-specific menu names; and buttons and text found within a GUI interface, all presented in proportional bold and all distinguishable by context.
Mono-spaced Bold Italic or Proportional Bold Italic
Whether mono-spaced bold or proportional bold, the addition of italics indicates replaceable or variable text. Italics denotes text you do not input literally or displayed text that changes depending on circumstance. For example:
To connect to a remote machine using ssh, type ssh username@domain.name at a shell prompt. If the remote machine is example.com and your username on that machine is john, type ssh john@example.com.
The mount -o remount file-system command remounts the named file system. For example, to remount the /home file system, the command is mount -o remount /home.
To see the version of a currently installed package, use the rpm -q package command. It will return a result as follows: package-version-release.
Note the words in bold italics above — username, domain.name, file-system, package, version and release. Each word is a placeholder, either for text you enter when issuing a command or for text displayed by the system.
Aside from standard usage for presenting the title of a work, italics denotes the first use of a new and important term. For example:
Publican is a DocBook publishing system.

1.2. Pull-quote Conventions

Terminal output and source code listings are set off visually from the surrounding text.
Output sent to a terminal is set in mono-spaced roman and presented thus: 
books        Desktop   documentation  drafts  mss    photos   stuff  svn
books_tests  Desktop1  downloads      images  notes  scripts  svgs
Source-code listings are also set in mono-spaced roman but add syntax highlighting as follows: 
package org.jboss.book.jca.ex1;

import javax.naming.InitialContext;

public class ExClient
{
   public static void main(String args[]) 
       throws Exception
   {
      InitialContext iniCtx = new InitialContext();
      Object         ref    = iniCtx.lookup("EchoBean");
      EchoHome       home   = (EchoHome) ref;
      Echo           echo   = home.create();

      System.out.println("Created Echo");

      System.out.println("Echo.echo('Hello') = " + echo.echo("Hello"));
   }
}

1.3. Notes and Warnings

Finally, we use three visual styles to draw attention to information that might otherwise be overlooked.

Note

Notes are tips, shortcuts or alternative approaches to the task at hand. Ignoring a note should have no negative consequences, but you might miss out on a trick that makes your life easier.

Important

Important boxes detail things that are easily missed: configuration changes that only apply to the current session, or services that need restarting before an update will apply. Ignoring a box labeled 'Important' will not cause data loss but may cause irritation and frustration.

Warning

Warnings should not be ignored. Ignoring warnings will most likely cause data loss.

2. We Need Feedback!

If you find a typographical error in this manual, or if you have thought of a way to make this manual better, we would love to hear from you! Please submit a report in Bugzilla: http://bugzilla.redhat.com/ against the product Red Hat Enterprise Linux 6.
When submitting a bug report, be sure to mention the manual's identifier: doc-Deployment_Guide and version number: 6.
If you have a suggestion for improving the documentation, try to be as specific as possible when describing it. If you have found an error, please include the section number and some of the surrounding text so we can find it easily.

2.1. Technical Review Requests

All review requests are classified into one of the following five categories:
New Content
content documented for the first time — an entirely new feature, procedure, or concept. For example: "Section now describes the new procedure for creating bootable USB devices."
Correction
a factual error previously present in the text has been corrected. For example: "Section previously stated (incorrectly) that IPv4 and IPv6 were both supported; section now states that IPv6 has never been supported."
Clarification
material that was already factually correct but is now better explained. Clarifications are usually in response to reader feedback that the previous content was confusing or misleading in some way. For example: "Paths described in Example 1.2.3 now better reflect the directory structure of an actual installed system."
Obsoletion
a description of a feature or a procedure has been dropped. Material might be obsolete because of a feature that is no longer supported, a known issue that has been corrected, or hardware that is now obsolete. For example, "Section no longer describes how to update kernel modules using a floppy disk."
Verification
a request to check a fact, procedure, or whether material should be obsoleted. For example, "Section describes how to connect to a generic iSCSI storage device. Please verify this on your hardware" or "Section still describes how to update kernel modules using a LS-120 SuperDisk; please verify that we still need to tell readers about this obsolete hardware."

3. Acknowledgements

Certain portions of this text first appeared in the Deployment Guide, copyright © 2007 Red Hat, Inc., available at http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Deployment_Guide/index.html.
The authors of this book would like to thank the following people for their valuable contributions: Adam Tkáč, Andrew Fitzsimon, Andrius Benokraitis, Brian Cleary Edward Bailey, Garrett LeSage, Jeffrey Fearn, Joe Orton, Joshua Wulf, KarstenWade, Lucy Ringland, Marcela Mašláňová, Mark Johnson, Michael Behm, Michael Behm, Miroslav Lichvár, Radek Vokál, Rahul Kavalapara, Rahul Sundaram, Sandra Moore, and Zbyšek Mráz, among many others.

Introduction

Welcome to the Red Hat Enterprise Linux 6 Deployment Guide.
The Deployment Guide contains information on how to customize your Red Hat Enterprise Linux 6 system to fit your needs. If you are looking for a comprehensive, task-oriented guide for configuring and customizing your system, this is the manual for you.
This manual discusses many intermediate topics such as the following:
  • Installing and managing packages using the graphical PackageKit and command line Yum package managers
  • Setting up a network—from establishing an Ethernet connection using NetworkManager to configuring channel bonding interfaces to increase server bandwidth
  • Configuring DHCP, BIND, Apache, Postfix, Sendmail and other enterprise-class servers and software
  • Gathering information about your system, including obtaining user-space crash data with the Automatic Bug Reporting Tool, and kernel-space crash data with kdump
  • Easily working with kernel modules and upgrading the kernel
This manual is divided into the following main categories:
This guide assumes you have a basic understanding of your Red Hat Enterprise Linux system. If you need help installing Red Hat Enterprise Linux, refer to the Red Hat Enterprise Linux 6 Installation Guide.

Part I. Package Management

All software on a Red Hat Enterprise Linux system is divided into RPM packages, which can be installed, upgraded, or removed. This part describes how to manage packages on Red Hat Enterprise Linux using the Yum and RPM package managers and the PackageKit suite of graphical package management tools.

Table of Contents

1. Yum
1.1. Checking For and Updating Packages
1.1.1. Checking For Updates
1.1.2. Updating Packages
1.1.3. Updating Security-Related Packages
1.1.4. Preserving Configuration File Changes
1.2. Packages and Package Groups
1.2.1. Searching, Listing and Displaying Package Information
1.2.2. Installing
1.2.3. Removing
1.3. Configuring Yum and Yum Repositories
1.3.1. Setting [main] Options
1.3.2. Setting [repository] Options
1.3.3. Using Yum Variables
1.3.4. Creating a Yum Repository
1.4. Yum Plugins
1.4.1. Enabling, Configuring and Disabling Yum Plugins
1.4.2. Installing More Yum Plugins
1.4.3. Plugin Descriptions
1.5. Additional Resources
2. PackageKit
2.1. Updating Packages with Software Update
2.2. Using Add/Remove Software
2.2.1. Refreshing Software Sources (Yum Repositories)
2.2.2. Finding Packages with Filters
2.2.3. Installing and Removing Packages (and Dependencies)
2.2.4. Installing and Removing Package Groups
2.2.5. Viewing the Transaction Log
2.3. PackageKit Architecture
2.4. Additional Resources
3. RPM
3.1. RPM Design Goals
3.2. Using RPM
3.2.1. Finding RPM Packages
3.2.2. Installing and Upgrading
3.2.3. Configuration File Changes
3.2.4. Uninstalling
3.2.5. Freshening
3.2.6. Querying
3.2.7. Verifying
3.3. Checking a Package's Signature
3.3.1. Importing Keys
3.3.2. Verifying Signature of Packages
3.4. Practical and Common Examples of RPM Usage
3.5. Additional Resources
3.5.1. Installed Documentation
3.5.2. Useful Websites
3.5.3. Related Books

Chapter 1. Yum

1.1. Checking For and Updating Packages
1.1.1. Checking For Updates
1.1.2. Updating Packages
1.1.3. Updating Security-Related Packages
1.1.4. Preserving Configuration File Changes
1.2. Packages and Package Groups
1.2.1. Searching, Listing and Displaying Package Information
1.2.2. Installing
1.2.3. Removing
1.3. Configuring Yum and Yum Repositories
1.3.1. Setting [main] Options
1.3.2. Setting [repository] Options
1.3.3. Using Yum Variables
1.3.4. Creating a Yum Repository
1.4. Yum Plugins
1.4.1. Enabling, Configuring and Disabling Yum Plugins
1.4.2. Installing More Yum Plugins
1.4.3. Plugin Descriptions
1.5. Additional Resources
Yum is the Red Hat package manager that is able to query for information about packages, fetch packages from repositories, install and uninstall packages using automatic dependency resolution, and update an entire system to the latest available packages. Yum performs automatic dependency resolution on packages you are updating, installing or removing, and thus is able to automatically determine, fetch and install all available dependent packages. Yum can be configured with new, additional repositories, or package sources, and also provides many plugins which enhance and extend its capabilities. Yum is able to perform many of the same tasks that RPM can; additionally, many of the command line options are similar. Yum enables easy and simple package management on a single machine or on groups of them.

Secure Package Management with GPG-Signed Packages

Yum provides secure package management by enabling GPG (Gnu Privacy Guard; also known as GnuPG) signature verification on GPG-signed packages to be turned on for all package repositories (i.e. package sources), or for individual repositories. When signature verification is enabled, Yum will refuse to install any packages not GPG-signed with the correct key for that repository. This means that you can trust that the RPM packages you download and install on your system are from a trusted source, such as Red Hat, and were not modified during transfer. Refer to Section 1.3, “Configuring Yum and Yum Repositories” for details on enabling signature-checking with Yum, or Section 3.3, “Checking a Package's Signature” for information on working with and verifying GPG-signed RPM packages in general.
Yum also enables you to easily set up your own repositories of RPM packages for download and installation on other machines.
Learning Yum is a worthwhile investment because it is often the fastest way to perform system administration tasks, and it provides capabilities beyond those provided by the PackageKit graphical package management tools. Refer to Chapter 2, PackageKit for details on using PackageKit.

1.1. Checking For and Updating Packages

1.1.1. Checking For Updates

You can use the yum check-update command to see which installed packages on your system have updates available.

Note: Yum and Superuser Privileges

You must have superuser privileges in order to use yum to install, update or remove packages on your system. All examples in this chapter assume that you have already obtained superuser privileges by using either the su or sudo command. 
~]# yum check-update
Loaded plugins: presto, refresh-packagekit, security
PackageKit.x86_64                  0.5.8-2.el6                rhel
PackageKit-glib.x86_64             0.5.8-2.el6                rhel
PackageKit-yum.x86_64              0.5.8-2.el6                rhel
PackageKit-yum-plugin.x86_64       0.5.8-2.el6                rhel
glibc.x86_64                       2.11.90-20.el6             rhel
glibc-common.x86_64                2.10.90-22                 rhel
kernel.x86_64                      2.6.31-14.el6              rhel
kernel-firmware.noarch             2.6.31-14.el6              rhel
rpm.x86_64                         4.7.1-5.el6                rhel
rpm-libs.x86_64                    4.7.1-5.el6                rhel
rpm-python.x86_64                  4.7.1-5.el6                rhel
udev.x86_64                        147-2.15.el6               rhel
yum.noarch                         3.2.24-4.el6               rhel
These packages are listed as having updates available. The first package in the list is PackageKit, the graphical package manager. The first line of the above output tells us:
  • PackageKit — the name of the package
  • x86_64 — the CPU architecture the package was built for
  • 0.5.8 — the version of the updated package to be installed
  • rhel — the repository in which the updated package is located
The output also shows us that we can update the kernel (the kernel package), Yum and RPM themselves (the yum and rpm packages), as well as their dependencies (such as the kernel-firmware, rpm-libs and rpm-python packages), all using yum.

1.1.2. Updating Packages

You can choose to update a single package, multiple packages, or all packages at once. If any dependencies of the package (or packages) you update have updates available themselves, then they are updated too. To update a single package , enter yum update <package_name>: 
~]# yum update udev
Loaded plugins: presto, refresh-packagekit, rhnplugin, security
Setting up Update Process
Resolving Dependencies
--> Running transaction check
---> Package udev.x86_64 0:147-2.15.el6 set to be updated
--> Finished Dependency Resolution
Dependencies Resolved
===========================================================================
 Package       Arch            Version                 Repository     Size
===========================================================================
Updating:
 udev          x86_64          147-2.15.el6            rhel          337 k
Transaction Summary
===========================================================================
Install       0 Package(s)
Upgrade       1 Package(s)
Total download size: 337 k
Is this ok [y/N]:
This output contains several items of interest:
  1. Loaded plugins: presto, refresh-packagekit, security — yum always informs you which Yum plugins are installed and enabled. Here, yum is using the presto, refresh-packagekit and security plugins. Refer to Section 1.4, “Yum Plugins” for general information on Yum plugins, or to Section 1.4.3, “Plugin Descriptions” for descriptions of specific plugins.
  2. kernel.x86_64 — you can download and install new kernels safely with yum.

    Important: Updating and Installing Kernels with Yum

    yum always installs a new kernel in the same sense that RPM installs a new kernel when you use the command rpm -i kernel. Therefore, you do not need to worry about the distinction between installing and upgrading a kernel package when you use yum: it will do the right thing, regardless of whether you are using the yum update or yum install command.
    When using RPM, on the other hand, it is important to use the rpm -i kernel command (which installs a new kernel) instead of rpm -u kernel (which replaces the current kernel). Refer to Section 3.2.2, “Installing and Upgrading” for more information on installing/updating kernels with RPM.
  3. yum presents the update information and then prompts you as to whether you want it to perform the update; yum runs interactively by default. If you already know which transactions yum plans to perform, you can use the -y option to automatically answer yes to any questions yum may ask (in which case it runs non-interactively). However, you should always examine which changes yum plans to make to the system so that you can easily troubleshoot any problems that might arise.
    If a transaction does go awry, you can view Yum's log of transactions by entering cat /var/log/yum.log at the shell prompt. The most recent transactions are listed at the end of the log file.

Updating All Packages and Their Dependencies

To update all packages and their dependencies, simply enter yum update (without any arguments):
Example 1.1. Updating all packages at once
~]# yum update

1.1.4. Preserving Configuration File Changes

You will inevitably make changes to the configuration files installed by packages as you use your Red Hat Enterprise Linux system. RPM, which Yum uses to perform changes to the system, provides a mechanism for ensuring their integrity. Refer to Section 3.2.2, “Installing and Upgrading” for details on how to manage changes to configuration files across package upgrades.

1.2. Packages and Package Groups

1.2.1. Searching, Listing and Displaying Package Information

You can search all RPM package names, descriptions and summaries by using the yum search <term> [more_terms] command. yum displays the list of matches for each term: 
~]# yum search meld kompare
Loaded plugins: presto, refresh-packagekit, rhnplugin, security
============================ Matched: kompare =============================
kdesdk.x86_64 : The KDE Software Development Kit (SDK)
Warning: No matches found for: meld
yum search is useful for searching for packages you do not know the name of, but for which you know a related term.

Listing Packages

yum list and related commands provide information about packages, package groups, and repositories.

Tip: Filtering Results with Glob Expressions

All of Yum's various list commands allow you to filter the results by appending one or more glob expressions as arguments. Glob expressions are normal strings of characters which contain one or more of the wildcard characters * (which expands to match any character multiple times) and ? (which expands to match any one character). Be careful to escape both of these glob characters when passing them as arguments to a yum command. If you do not, the bash shell will interpret the glob expressions as pathname expansions, and potentially pass all files in the current directory that match the globs to yum, which is not what you want. Instead, you want to pass the glob expressions themselves to yum, which you can do by either:
  • escaping the wildcard characters
  • double-quoting or single-quoting the entire glob expression.
The following examples show both methods:
Example 1.2. Filtering results using a single glob expression with two escaped wildcard characters
~]# yum list available gstreamer\*plugin\*
Loaded plugins: presto, refresh-packagekit, rhnplugin, security
Available Packages
gstreamer-plugins-bad-free.i686               0.10.17-4.el6            rhel
gstreamer-plugins-base.i686                   0.10.26-1.el6            rhel
gstreamer-plugins-base-devel.i686             0.10.26-1.el6            rhel
gstreamer-plugins-base-devel.x86_64           0.10.26-1.el6            rhel
gstreamer-plugins-good.i686                   0.10.18-1.el6            rhel

Example 1.3. Filtering results using a double-quoted glob expression
~]# yum list installed "krb?-*"
Loaded plugins: presto, refresh-packagekit, rhnplugin, security
Installed Packages
krb5-libs.x86_64                         1.8.1-3.el6                  @rhel
krb5-workstation.x86_64                  1.8.1-3.el6                  @rhel

  • yum list <glob_expr> [more_glob_exprs] — List information on installed and available packages matching all glob expressions.
    Example 1.4. Listing all ABRT addons and plugins using glob expressions
    ~]# yum list abrt-addon\* abrt-plugin\*
Loaded plugins: presto, refresh-packagekit, rhnplugin, security
Installed Packages
abrt-addon-ccpp.x86_64                        1.0.7-5.el6             @rhel
abrt-addon-kerneloops.x86_64                  1.0.7-5.el6             @rhel
abrt-addon-python.x86_64                      1.0.7-5.el6             @rhel
abrt-plugin-bugzilla.x86_64                   1.0.7-5.el6             @rhel
abrt-plugin-logger.x86_64                     1.0.7-5.el6             @rhel
abrt-plugin-sosreport.x86_64                  1.0.7-5.el6             @rhel
abrt-plugin-ticketuploader.x86_64             1.0.7-5.el6             @rhel

  • yum list all — List all installed and available packages.
  • yum list installed — List all packages installed on your system. The rightmost column in the output lists the repository from which the package was retrieved.
  • yum list available — List all available packages in all enabled repositories.
  • yum grouplist — List all package groups.
  • yum repolist — List the repository ID, name, and number of packages it provides for each enabled repository.

Displaying Package Info

yum info <package_name> [more_names] displays information about one or more packages (glob expressions are valid here as well): 
~]# yum info abrt
Loaded plugins: presto, refresh-packagekit, rhnplugin, security
Installed Packages
Name       : abrt
Arch       : x86_64
Version    : 1.0.7
Release    : 5.el6
Size       : 578 k
Repo       : installed
From repo  : rhel
Summary    : Automatic bug detection and reporting tool
URL        : https://fedorahosted.org/abrt/
License    : GPLv2+
Description: abrt is a tool to help users to detect defects in applications
           : and to create a bug report with all informations needed by
           : maintainer to fix it. It uses plugin system to extend its
           : functionality.
yum info <package_name> is similar to the rpm -q --info <package_name> command, but provides as additional information the ID of the Yum repository the RPM package is found in (look for the From repo: line in the output).
yumdb info <package_name> [more_names] can be used to query the Yum database for alternative and useful information about a package, including the checksum of the package (and algorithm used to produce it, such as SHA-256), the command given on the command line that was invoked to install the package (if any), and the reason that the package is installed on the system (where user indicates it was installed by the user, and dep means it was brought in as a dependency): 
~]# yumdb info yum
yum-3.2.27-4.el6.noarch
     checksum_data = 15c8eaf583fabad6974a35b9f6c6527e49362fe4e23baec1682ef51a598e4abb
     checksum_type = sha256
     command_line = update
     from_repo = rhel
     from_repo_revision = 1271991599
     from_repo_timestamp = 1271991721
     reason = user
     releasever = 6
See man yumdb for more information on the yumdb command.
Finally, the yum history command, which is new in Red Hat Enterprise Linux 6, can be used to show a timeline of Yum transactions, the dates and times on when they occurred, the number of packages affected, whether transactions succeeded or were aborted, and if the RPM database was changed between transactions. Refer to the history section of man yum for details.

1.2.2. Installing

You can install a package and all of its non-installed dependencies by entering: 
~]# yum install <package_name>
You can install multiple packages simultaneously by appending their names as arguments: yum install <package_name> [more_names] .
If you are installing packages on a multilib system, such as an AMD64 or Intel64 machine, you can specify the architecture of the package (as long as it's available in an enabled repository) by appending .arch to the package name: 
~]# yum install sqlite2.i586
You can use glob expressions to quickly install multiple similarly-named packages: 
~]# yum install audacious-plugins-\*
In addition to package names and glob expressions, you can also provide file names to yum install. If you know the name of the binary you want to install, but not its package name, you can give yum install the path name: 
~]# yum install /usr/sbin/named
yum then searches through its package lists, finds the package which provides /usr/sbin/named, if any, and prompts you as to whether you want to install it.
What if you know you want to install the package that contains the named binary, but don't know in which bin or sbin directory that file lives? In that situation, you can give yum provides a glob expression:
Example 1.5. Finding which package owns a file and installing it
~]# yum provides "*bin/named"
Loaded plugins: presto, refresh-packagekit, rhnplugin, security
32:bind-9.7.0-4.P1.el6.x86_64 : The Berkeley Internet Name Domain (BIND)
                              : DNS (Domain Name System) server
Repo        : rhel
Matched from:
Filename    : /usr/sbin/named
~]# yum install bind

Note

yum provides is the same as yum whatprovides.

Tip: yum provides/whatprovides and Glob Expressions

yum provides "*/<file_name>" is a common and useful trick to quickly find the package(s) that contain <file_name>.

Installing a Package Group

A package group is similar to a package: it is not useful by itself, but installing one pulls a group of dependent packages that serve a common purpose. A package group has a name and a groupid. The yum grouplist -v command lists the names of all package groups, and, next to each of them, their groupid in parentheses. The groupid is always the term in the last pair of parentheses, such as kde-desktop and kde-software-development in this example:

Not all packages used in examples may be available on RHN

Some of the software packages—or package groups—queried for and installed with Yum in this chapter may not be available from Red Hat Network. Their use in examples is purely to demonstrate Yum's command usage.
Note that obtaining and installing software packages from unverified or untrusted software sources other than Red Hat Network constitutes a potential security risk, and could lead to security, stability, compatibility maintainability issues. 
~]# yum -v grouplist kde\*
KDE (K Desktop Environment) (kde-desktop)
KDE Software Development (kde-software-development)
You can install a package group by passing its full group name (without the groupid part) to groupinstall: 
~]# yum groupinstall "KDE (K Desktop Environment)"
You can also install by groupid: 
~]# yum groupinstall kde-desktop
You can even pass the groupid (or quoted name) to the install command if you prepend it with an @-symbol (which tells yum that you want to perform a groupinstall): 
~]# yum install @kde-desktop

1.2.3. Removing

yum remove <package_name> uninstalls (removes in RPM and Yum terminology) the package, as well as any packages that depend on it. As when you install multiple packages, you can remove several at once by adding more package names to the command: 
 yum remove foo bar baz
Similar to install, remove can take these arguments:
  • package names
  • glob expressions
  • file lists
  • package provides

Warning: Removing a Package when Other Packages Depend On It

Yum is not able to remove a package without also removing packages which depend on it. This type of operation can only be performed by RPM, is not advised, and can potentially leave your system in a non-functioning state or cause applications to misbehave and/or crash. For further information, refer to Section 3.2.4, “Uninstalling” in the RPM chapter.

Removing a Package Group

You can remove a package group using syntax congruent with the install syntax.
Example 1.6. Alternative but equivalent ways of removing a package group
~]# yum groupremove "KDE (K Desktop Environment)"
~]# yum groupremove kde-desktop
~]# yum remove @kde-desktop

Smart package group removal

When you tell yum to remove a package group, it will remove every package in that group, even if those packages are members of other package groups or dependencies of other installed packages. However, you can instruct yum to remove only those packages which are not required by any other packages or groups by adding the groupremove_leaf_only=1 directive to the [main] section of the /etc/yum.conf configuration file. For more information on this directive, refer to Section 1.3.1, “Setting [main] Options”.

1.3. Configuring Yum and Yum Repositories

This section shows you how to:
  • set global Yum options by editing the [main] section of the /etc/yum.conf configuration file;
  • set options for individual repositories by editing the [repository] sections in /etc/yum.conf and .repo files in the /etc/yum.repos.d/ directory;
  • use Yum variables in /etc/yum.conf and files in /etc/yum.repos.d/so that dynamic version and architecture values are handled correctly; and,
  • set up your own custom Yum repository.
The /etc/yum.conf configuration file contains one mandatory [main] section under which you can set Yum options. The values that you define in the [main] section of yum.conf have global effect, and may override values set any individual [repository] sections. You can also add [repository] sections to /etc/yum.conf; however, best practice is to define individual repositories in new or existing .repo files in the /etc/yum.repos.d/directory. Refer to Section 1.3.2, “Setting [repository] Options” if you need to add or edit repository-specific information.

1.3.1. Setting [main] Options

The /etc/yum.conf configuration file contains exactly one [main] section. You can add many additional options under the [main] section heading in /etc/yum.conf. Some of the key-value pairs in the [main] section affect how yum operates; others affect how Yum treats repositories. The best source of information for all Yum options is in the [main] OPTIONS and [repository] OPTIONS sections of man yum.conf.
Here is a sample /etc/yum.conf configuration file: 
[main]
cachedir=/var/cache/yum/$basearch/$releasever
keepcache=0
debuglevel=2
logfile=/var/log/yum.log
exactarch=1
obsoletes=1
gpgcheck=1
plugins=1
installonly_limit=3
[comments abridged]
# PUT YOUR REPOS HERE OR IN separate files named file.repo
# in /etc/yum.repos.d
Here is a list of the most commonly-used options in the [main] section, and descriptions for each:
assumeyes=<value>
...where <value> is one of:
0 — yum should prompt for confirmation of critical actions it performs. This is the default.
1 — Do not prompt for confirmation of critical yum actions. If assumeyes=1 is set, yum behaves in the same way that the command line option -y does.
cachedir=/var/cache/yum/$basearch/$releasever
This option specifies the directory where Yum should store its cache and database files. By default, Yum's cache directory is /var/cache/yum/$basearch/$releasever. See Section 1.3.3, “Using Yum Variables” for descriptions of the $basearch and $releasever Yum variables.
debuglevel=value
...where <value> is an integer between 1 and 10. Setting a higher debuglevel value causes yum to display more detailed debugging output. debuglevel=0 disables debugging output, while debuglevel=2 is the default.
exactarch=<value>
...where <value> is one of:
0 — Do not take into account the exact architecture when updating packages.
1 — Consider the exact architecture when updating packages. With this setting, yum will not install an i686 package to update an i386 package already installed on the system. This is the default.
exclude=<package_name> [more_package_names ]
This option allows you to exclude packages by keyword during installation/updates. Listing multiple packages for exclusion can be accomplished by quoting a space-delimited list of packages. Shell globs using wildcards (for example, * and ?) are allowed.
gpgcheck=<value>
...where <value> is one of:
0 — Disable GPG signature-checking on packages in all repositories, including local package installation.
1 — Enable GPG signature-checking on all packages in all repositories, including local package installation. gpgcheck=1 is the default, and thus all packages' signatures are checked.
If this option is set in the [main] section of the /etc/yum.conf file, it sets the GPG-checking rule for all repositories. However, you can also set gpgcheck= <value> for individual repositories instead; i.e., you can enable GPG-checking on one repository while disabling it on another. Setting gpgcheck=<value> for an individual repository in its correpsonding .repo file overrides the default if it is present in /etc/yum.conf. Refer to Section 3.3, “Checking a Package's Signature” for further information on GPG signature-checking.
groupremove_leaf_only=<value>
...where <value> is one of:
0 — yum should not check the dependencies of each package when removing a package group. With this setting, yum removes all packages in a package group, regardless of whether those packages are required by other packages or groups. groupremove_leaf_only=0 is the default.
1 — yum should check the dependencies of each package when removing a package group, and remove only those packages which are not not required by any other package or group.
For more information on removing packages, refer to Smart package group removal.
installonlypkgs=<space> <separated> <list> <of> <packages>
Here you can provide a space-separated list of packages which yum can install, but will never update. Refer to man yum.conf for the list of packages which are install-only by default. If you add the installonlypkgs directive to /etc/yum.conf, you should ensure that you list all of the packages that should be install-only, including any of those listed under the installonlypkgs section of man yum.conf. In particular, kernel packages should always be listed in installonlypkgs (as they are by default), and installonly_limit should always be set to a value greater than 2 so that a backup kernel is always available in case the default one fails to boot. Refer to installonly_limit=<value> for details on the installonly_limit directive.
installonly_limit=<value>
...where <value> is an integer representing the maximum number of versions that can be installed simultaneously for any single package listed in the installonlypkgs directive. The defaults for the installonlypkgs directive include several different kernel packages, so be aware that changing the value of installonly_limit will also affect the maximum number of installed versions of any single kernel package. The default value listed in /etc/yum.conf is installonly_limit=3, and it is not recommended to decrease this value, particularly below 2.
keepcache=<value>
...where value is one of:
0 — Do not retain the cache of headers and packages after a successful installation. This is the default.
1 — Retain the cache after a successful installation.
logfile=/var/log/yum.log
This option specifies where yum should send its logging output. By default, yum logs to /var/log/yum.log.
multilib_policy=<value>
...where <value> is one of:
best — install the best-choice architecture for this system. For example, setting multilib_policy=best on an AMD64 system causes yum to install 64-bit versions of all packages.
all — always install every possible architecture for every package. For example, with multilib_policy set to all on an AMD64 system, yum would install both the i586 and AMD64 versions of a package, if both were available.
obsoletes=<value>
...where <value> is one of:
0 — Disable yum's obsoletes processing logic when performing updates.
1 — Enable yum's obsoletes processing logic when performing updates. When one package declares in its spec file that it obsoletes another package, the latter package will be replaced by the former package when the former package is installed. Obsoletes are declared, for example, when a package is renamed. obsoletes=1 the default.
plugins=<value>
...where <value> is one of:
0 — Disable all Yum plugins globally.

Disabling plugins is not advised

Disabling all plugins is not advised because certain plugins provide important Yum services. In particular, rhnplugin enables connecting to Red Hat Network, and the security plugin allows system administrators to easily update the system with (sometimes critical) security updates. Disabling plugins globally is provided as a convenience option, and is generally only recommended when diagnosing a potential problem with Yum.
1 — Enable all Yum plugins globally. With plugins=1, you can still disable a specific Yum plugin by setting enabled=0 in that plugin's configuration file. Refer to Section 1.4, “Yum Plugins” for more information about various Yum plugins, or to Section 1.4.1, “Enabling, Configuring and Disabling Yum Plugins” for further information on controlling plugins.
reposdir=</absolute/path/to/directory/containing/repo/files>
This option allows you to specify a directory where .repo files are located. All .repo files contain repository information (similar to the [repository] section(s) of /etc/yum.conf). yum collects all repository information from .repo files and the [repository] section of the /etc/yum.conf file to create a master list of repositories to use for transactions. Refer to Section 1.3.2, “Setting [repository] Options” for more information about options you can use for both the [repository] section and .repo files. If reposdir is not set, yum uses the default directory /etc/yum.repos.d/.
retries=<value>
...where <value> is an integer 0 or greater. This value sets the number of times yum should attempt to retrieve a file before returning an error. Setting this to 0 makes yum retry forever. The default value is 10.

1.3.2. Setting [repository] Options

You can define individual Yum repositories by adding [repository] sections (where repository is a unique repository ID, such as [my_personal_repo]) to /etc/yum.conf or to .repo files in the /etc/yum.repos.d/directory. All .repo files in /etc/yum.repos.d/are read by yum; best practice is to define your repositories here instead of in /etc/yum.conf. You can create new, custom .repo files in this directory, add [repository] sections to those files, and the next time you run a yum command, it will take all newly-added repositories into account.
Here is a (bare-minimum) example of the form a .repo file should take: 
[repository_ID]
name=A Repository Name
baseurl=http://path/to/repo or ftp://path/to/repo or file://path/to/local/repo
Every [repository] section must contain the following minimum parts:
[repository_ID]
The repository ID is a unique, one-word (no spaces; underscores are allowed) string of characters (enclosed by brackets) that serves as a repository identifier.
name=<My Repository Name>
This is a human-readable string describing the repository.
baseurl=http://path/to/repo, ftp://path/to/repo, file://path/to/local/repo
This is a URL to the directory where the repodata directory of a repository is located. Usually this URL is an HTTP link, such as: 
baseurl=http://path/to/repo/releases/$releasever/server/$basearch/os/
Yum always expands the $releasever, $arch and $basearch variables in URLs. See the following section for explanations of all Yum variables: Section 1.3.3, “Using Yum Variables”.
  • If the repository is available over FTP, use: ftp://path/to/repo
  • If the repository is local to the machine, use file://path/to/local/repo
  • If a specific online repository requires basic HTTP authentication, you can specify your username and password in the http://path/to/repo by prepending it as username:password@link. For example, if a repository on http://www.example.com/repo/ requires a username of "user" and a password of "password", then the baseurl link could be specified as: 
    baseurl=http://user:password@www.example.com/repo/
The following is another useful [repository] directive:
enabled=<value>
...where <value> is one of:
0 — do not include this repository as a package source when performing updates and installs. This is an easy way of quickly turning repositories on and off, which is useful when you desire a single package from a repository that you do not want to enable for updates or installs.
1 — include this repository as a package source.
Turning repositories on and off can also be performed quickly by passing either the --enablerepo=<repo_name> or --disablerepo=<repo_name> option to yum, or easily through PackageKit's Add/Remove Software window.
Many more [repository] options exist. Refer to the [repository] OPTIONS section of man yum.conf for the exhaustive list and descriptions for each.

1.3.3. Using Yum Variables

You can use and reference the following variables in yum commands and in all Yum configuration files (/etc/yum.conf and all .repo files in /etc/yum.repos.d/.
$releasever
You can use this variable to reference the release version of Red Hat Enterprise Linux. Yum obtains the value of $releasever from the distroverpkg=<value> line in the /etc/yum.conf configuration file. If there is no such line in /etc/yum.conf, then yum infers the correct value by deriving the version number from the redhat-release package.
$arch
You can use this variable to refer to the system's CPU architecture as returned when calling Python's os.uname() function. Valid values for $arch include: i586, i686 and x86_64.
$basearch
You can use $basearch to reference the base architecture of the system. For example, i686 and i586 machines both have a base architecture of i386, and AMD64 and Intel64 machines have a base architecture of x86_64.
$YUM0-9
These ten variables are each replaced with the value of any shell environment variables with the same name. If one of these variables is referenced (in /etc/yum.conf for example) and a shell environment variable with the same name does not exist, then the configuration file variable is not replaced.

1.3.4. Creating a Yum Repository

To set up a Yum repository, follow these steps:
Procedure 1.1. Setting Up a Yum repository
  1. Install the createrepo package: 
    ~]# yum install createrepo
  2. Copy all of the packages into one directory, such as /mnt/local_repo/.
  3. Run the createrepo --database command on that directory: 
    ~]# createrepo --database /mnt/local_repo

    Important

    Because RPM packages for Red Hat Enterprise Linux 6 are compressed using the XZ lossless data compression format, and may also be signed using alternative (and stronger) hash algorithms such as SHA-256, it is not possible to run createrepo on Red Hat Enterprise Linux 5 to create the package metadata for Red Hat Enterprise Linux 6 packages. The createrepo command relies on rpm to open and inspect the packages, and rpm on Red Hat Enterprise Linux 5 is not able to open the improved Red Hat Enterprise Linux 6 RPM package format.
This will create the necessary metadata for your Yum repository, as well as the sqlite database for speeding up yum operations.

1.4. Yum Plugins

Yum provides plugins that extend and enhance its operations. Certain plugins are installed by default. Yum always informs you which plugins, if any, are loaded and active whenever you call any yum command: 
~]# yum info yum
Loaded plugins: presto, refresh-packagekit, security
[output truncated]
Note that the plugin names which follow Loaded plugins are the names you can provide to the --disableplugins=<plugin_name> option.

1.4.1. Enabling, Configuring and Disabling Yum Plugins

To enable Yum plugins, ensure that a line beginning with plugins= is present in the [main] section of /etc/yum.conf, and that its value is set to 1: 
plugins=1
You can disable all plugins by changing this line to plugins=0.

Disabling plugins is not advised

Disabling all plugins is not advised because certain plugins provide important Yum services. In particular, rhnplugin enables connecting to Red Hat Network, and the security plugin allows system administrators to easily update the system with (sometimes critical) security updates. Disabling plugins globally is provided as a convenience option, and is generally only recommended when diagnosing a potential problem with Yum.
Every installed plugin has its own configuration file in the /etc/yum/pluginconf.d/ directory. You can set plugin-specific options in these files. For example, here is the security plugin's security.conf configuration file:
Example 1.7. A minimal Yum plugin configuration file
[main]
enabled=1

Plugin configuration files always contain a [main] section (similar to Yum's /etc/yum.conf file) in which there is (or you can place if it is missing) an enabled= option that controls whether the plugin is enabled when you run yum commands.
If you disable all plugins by setting enabled=0 in /etc/yum.conf, then all plugins are disabled regardless of whether they are enabled in their individual configuration files.
If you merely want to disable all Yum plugins for a single yum command, use the --noplugins option.
If you simply want to disable one or more Yum plugins for a single yum command, then you can add the --disableplugin=<plugin_name> option to the command:
Example 1.8. Disabling the presto plugin while running yum update
~]# yum update --disableplugin=presto

The plugin names you provide to the --disableplugin= option are the same names listed after the Loaded plugins: line in the output of any yum command. You can disable multiple plugins by separating their names with commas. In addition, you can match multiple similarly-named plugin names or simply shorten long ones by using glob expressions: --disableplugin=presto,refresh-pack*.

1.4.2. Installing More Yum Plugins

Yum plugins usually adhere to the yum-plugin-<plugin_name> package-naming convention, but not always: the package which provides the presto plugin is named yum-presto, for example. You can install a Yum plugin in the same way you install other packages: 
~]# yum install yum-plugin-security

1.4.3. Plugin Descriptions

Here are descriptions of a few useful Yum plugins:

presto (yum-presto)

The presto plugin adds support to Yum for downloading delta RPM packages, during updates, from repositories which have presto metadata enabled. Delta RPMs contain only the differences between the version of the package installed on the client requesting the RPM package and the updated version in the repository. Downloading a delta RPM is much quicker than downloading the entire updated package, and can speed up updates considerably. Once the delta RPMs are downloaded, they must be rebuilt (the difference applied to the currently-installed package to create the full updated package) on the installing machine, which takes CPU time. Using delta RPMs is therefore a tradeoff between time-to-download, which depends on the network connection, and time-to-rebuild, which is CPU-bound. Using the presto plugin is recommended for fast machines and systems with slower network connections, while slower machines on very fast connections may benefit more from downloading normal RPM packages, i.e. by disabling presto. The presto plugin is enabled by default.

protect-packages (yum-plugin-protect-packages)

The protect-packages plugin prevents the yum package and all packages it depends on from being purposefully or accidentally removed. This simple scheme prevents many of the most important packages necessary for your system to run from being removed. In addition, you can list more packages, one per line, in the /etc/sysconfig/protected-packages file[1] (which you should create if it does not exist), and protect-packages will extend protection-from-removal to those packages as well. To temporarily override package protection, use the --override-protection option with an applicable yum command.

rhnplugin (yum-rhn-plugin)

The rhnplugin for Yum provides support for connecting to Red Hat Network (RHN). Systems registered with RHN are able to update and install packages from Red Hat Network.
Refer to man rhnplugin for more information.

refresh-packagekit (PackageKit-yum-plugin)

This plugin updates metadata for PackageKit whenever yum is run. The refresh-packagekit plugin is installed by default.

security (yum-plugin-security)

Discovering information about and applying security updates easily and often is important to all system administrators. For this reason Yum provides the security plugin, which extends yum with a set of highly-useful security-related commands, subcommands and options.
You can check for all security-related updates as follows: 
~]# yum check-update --security
Loaded plugins: presto, refresh-packagekit, security
Limiting package lists to security relevant ones
Needed 3 of 7 packages, for security
elinks.x86_64                   0.12-0.13.el6               rhel
kernel.x86_64                   2.6.30.8-64.el6             rhel
kernel-headers.x86_64           2.6.30.8-64.el6             rhel
You can then use either yum update --security or yum update-minimal --security to update those packages which are affected by security advisories. Both of these commands update all packages on the system for which a security advisiory has been issued. yum update-minimal --security updates them to the latest packages which were released as part of a security advisory, while yum update --security will update all packages affected by a security advisory to the latest version of that package available.
In other words, if:
  • the kernel-2.6.30.8-16 package is installed on your system;
  • the kernel-2.6.30.8-32 package was released as a security update;
  • then kernel-2.6.30.8-64 was released as a bug fix update,
...then yum update-minimal --security will update you to kernel-2.6.30.8-32, and yum update --security will update you to kernel-2.6.30.8-64. Conservative system administrators may want to use update-minimal to reduce the risk incurred by updating packages as much as possible.
Refer to man yum-security for usage details and further explanation of the enhancements the security plugin adds to yum.

1.5. Additional Resources

The Yum home page and wiki — http://yum.baseurl.org/wiki/Guides
The Yum Guides section of the wiki contains more Yum documentation.
Managing Software with Yum — http://docs.fedoraproject.org/en-US/Fedora_Core/5/html-single/Software_Management_Guide/
A useful resource that provides additional information about using the Yum package manager.

[1] You can also place files with the extension .list in the /etc/sysconfig/protected-packages.d/ directory (which you should create if it does not exist), and list packages—one per line—in these files. protect-packages will protect these too.

Chapter 2. PackageKit

2.1. Updating Packages with Software Update
2.2. Using Add/Remove Software
2.2.1. Refreshing Software Sources (Yum Repositories)
2.2.2. Finding Packages with Filters
2.2.3. Installing and Removing Packages (and Dependencies)
2.2.4. Installing and Removing Package Groups
2.2.5. Viewing the Transaction Log
2.3. PackageKit Architecture
2.4. Additional Resources
Red Hat provides PackageKit for viewing, managing, updating, installing and uninstalling packages compatible with your system. PackageKit consists of several graphical interfaces that can be opened from the GNOME panel menu, or from the Notification Area when PackageKit alerts you that updates are available. For more information on PackageKit's architecture and available front ends, refer to Section 2.3, “PackageKit Architecture”.

2.1. Updating Packages with Software Update

PackageKit displays a starburst icon in the Notification Area whenever updates are available to be installed on your system.
Clicking on the notification icon opens the Software Update window. Alternatively, you can open Software Updates by clicking System → Administration → Software Update from the GNOME panel, or running the gpk-update-viewer command at the shell prompt. In the Software Updates window, all available updates are listed along with the names of the packages being updated (minus the .rpm suffix, but including the CPU architecture), a short summary of the package, and, usually, short descriptions of the changes the update provides. Any updates you do not wish to install can be de-selected here by unchecking the checkbox corresponding to the update.
Installing updates with Software Update
installing 12 updates with packagekit's software update window
Figure 2.1. Installing updates with Software Update

The updates presented in the Software Updates window only represent the currently-installed packages on your system for which updates are available; dependencies of those packages, whether they are existing packages on your system or new ones, are not shown until you click Install Updates.
PackageKit utilizes the fine-grained user authentication capabilities provided by the PolicyKit toolkit whenever you request it to make changes to the system. Whenever you instruct PackageKit to update, install or remove packages, you will be prompted to enter the superuser password before changes are made to the system.
PackageKit uses PolicyKit to authenticate
packagekit defers to policykit to provide authentication in order to make changes to the system
Figure 2.2. PackageKit uses PolicyKit to authenticate

If you instruct PackageKit to update the kernel package, then it will prompt you after installation, asking you whether you want to reboot the system and thereby boot into the newly-installed kernel.

Setting the Update-Checking Interval

Right-clicking on PackageKit's Notification Area icon and clicking Preferences opens the Software Update Preferences window, where you can define the interval at which PackageKit checks for package updates, as well as whether or not to automatically install all updates or only security updates, and how often to check for major upgrades. Leaving the Check for updates when using mobile broadband box unchecked is handy for avoiding extraneous bandwidth usage when using a wireless connection on which you are charged for the amount of data you download.
Setting PackageKit's update-checking interval
Setting the update-checking interval for packagekit by right-clicking on the notification area applet
Figure 2.3. Setting PackageKit's update-checking interval

2.2. Using Add/Remove Software

PackageKit's Software Update GUI window is a separate application from its Add/Remove Software application, although the two have intuitively similar interfaces. To find and install a new package, on the GNOME panel click on System → Administration → Add/Remove Software, or run the gpk-application command at the shell prompt.
PackageKit's Add/Remove Software window
viewing packagekit's add/remove softvware window
Figure 2.4. PackageKit's Add/Remove Software window

2.2.1. Refreshing Software Sources (Yum Repositories)

PackageKit refers to Yum repositories as software sources. It obtains all packages from enabled software sources. You can view the list of all configured and unfiltered (see below) Yum repositories by opening Add/Remove Software and clicking System → Software sources. The Software Sources dialog shows the repository name, as written on the name=<My Repository Name> field of all [repository] sections in the /etc/yum.conf configuration file, and in all repository.repo files in the /etc/yum.repos.d/ directory.
Entries which are checked in the Enabled column indicate that the corresponding repository will be used to locate packages to satisfy all update and installation requests (including dependency resolution). The Enabled column corresponds to the enabled=<1 or 0> field in [repository] sections. Checking an unchecked box enables the Yum repository, and unchecking it disables it. Performing either function causes PolicyKit to prompt for superuser authentication to enable or disable the repository. PackageKit actually inserts the enabled=<1 or 0> line into the correct [repository] section if it does not exist, or changes the value if it does. This means that enabling or disabling a repository through the Software Sources window causes that change to persist after closing the window or rebooting the system. The ability to quickly enable and disable repositories based on our needs is a highly-convenient feature of PackageKit.
Note that it is not possible to add or remove Yum repositories through PackageKit.

Showing Source RPM, Test and Debuginfo Repositories

Checking the box at the bottom of the Software Sources window causes PackageKit to display source RPM, testing and debuginfo repositories as well. This box is unchecked by defaut.
After enabling and/or disabling the correct Yum repositories, ensure that you have the latest list of available packages. Click on System → Refresh package lists and PackageKit will obtain the latest lists of packages from all enabled software sources, i.e. Yum repositories.

2.2.2. Finding Packages with Filters

Once the software sources have been updated, it is often beneficial to apply some filters so that PackageKit retrieves the results of our Find queries faster. This is especially helpful when performing many package searches. Four of the filters in the Filters drop-down menu are used to split results by matching or not matching a single criterion. By default when PackageKit starts, these filters are all unapplied (No filter), but once you do filter by one of them, that filter remains set until you either change it or close PackageKit.
Because you are usually searching for available packages that are not installed on the system, click Filters → Installed and select the Only available radio button.
Filtering out already-installed packages
filtering out packages which are already installed
Figure 2.5. Filtering out already-installed packages

Also, unless we require development files such as C header files, we can filter for Only end user files and, in doing so, filter out all of the <package_name>-devel packages we are not interested in.
Filtering out development packages from the list of Find results
filtering out development packages from our results
Figure 2.6. Filtering out development packages from the list of Find results

The two remaining filters with submenus are:
Graphical
Narrows the search to either applications which provide a GUI interface or those that do not (Only text). This filter is useful when browsing for GUI applications that perform a specific function.
Free
Search for packages which are considered to be free software Refer to the Fedora Licensing List for details on approved licenses.
The remaining checkbox filters are always either checked or unchecked. They are:
Hide subpackages
Checking the Hide subpackages checkbox filters out generally-uninteresting packages that are typically only dependencies of other packages that we want. For example, checking Hide subpackages and searching for <package> would cause the following related packages to be filtered out of the Find results (if it exists):
  • <package>-devel
  • <package>-libs
  • <package>-libs-devel
  • <package>-debuginfo
Only newest items
Checking Only newest items filters out all older versions of the same package from the list of results, which is generally what we want.

Important: Using the Only newest items filter

Checking Only newest items filters out all but the most recent version of any package from the results list. This filter is often combined with the Only available filter to search for the latest available versions of new (not installed) packages.
Only native packages
Checking the Only native packages box on a multilib system causes PackageKit to omit listing results for packages compiled for the architecture that runs in compatibility mode. For example, enabling this filter on a 64-bit system with an AMD64 CPU would cause all packages built for the 32-bit x86 CPU architecture not to be shown in the list of results, even though those packages are able to run on an AMD64 machine. Packages which are architecture-agnostic (i.e. noarch packages such as crontabs-1.10-32.1.el6.noarch.rpm) are never filtered out by checking Only native packages. This filter has no affect on non-multilib systems, such as x86 machines.

2.2.3. Installing and Removing Packages (and Dependencies)

With the two filters selected, Only available and Only end user files, search for the htop interactive process viewer and highlight the package. You now have access to some very useful information about it, including: a clickable link to the project homepage; the Yum package group it is found in, if any; the license of the package; a pointer to the GNOME menu location from where the application can be opened, if applicable (Applications → System Tools → Htop in our case); and the size of the package, which is relevant when we download and install it.
Viewing and installing a package with PackageKit's Add/Remove Software window
Viewing and installing a package with PackageKit's Add/Remove Software window
Figure 2.7. Viewing and installing a package with PackageKit's Add/Remove Software window

When the checkbox next to a package or group is checked, then that item is already installed on the system. Checking an unchecked box causes it to be marked for installation, which only occurs when the Apply button is clicked. In this way, you can search for and select multiple packages or package groups before performing the actual installation transactions. Additionally, you can remove installed packages by unchecking the checked box, and the removal will occur along with any pending installations when Apply is pressed. Dependency resolution , which may add additional packages to be installed or removed, is performed after pressing Apply. PackageKit will then display a window listing those additional packages to install or remove, and ask for confirmation to proceed.
Check htop and click the Apply button. You will then be prompted for the superuser password; enter it, and PackageKit will install htop. One nice feature of PackageKit is that, following installation, it sometimes presents you with a list of your newly-installed applications and offer you the choice of running them immediately. Alternatively, you will remember that finding a package and selecting it in the Add/Remove Software window shows you the Location of where in the GNOME menus its application shortcut is located, which is helpful when you want to run it.
Once it is installed, you can run htop, an colorful and enhanced version of the top process viewer, by opening a shell prompt and entering: 
~]$ htop
Viewing processes with htop!
htop is nifty, but we decide that top is good enough for us and we want to uninstall it. Remembering that we need to change the Only available filter we recently used to install it to Only installed in Filters → Installed, we search for htop again and uncheck it. The program did not install any dependencies of its own; if it had, those would be automatically removed as well, as long as they were not also dependencies of any other packages still installed on our system.

Warning: Removing a Package when Other Packages Depend On It

Although PackageKit automatically resolves dependencies during package installation and removal, it is unable to remove a package without also removing packages which depend on it. This type of operation can only be performed by RPM, is not advised, and can potentially leave your system in a non-functioning state or cause applications to misbehave and/or crash.
Removing a package with PackageKit's Add/Remove Software window
removing the htop package with packagekit's add/remove software window
Figure 2.8. Removing a package with PackageKit's Add/Remove Software window

2.2.4. Installing and Removing Package Groups

PackageKit also has the ability to install Yum package groups, which it calls Package collections. Clicking on Package collections in the top-left list of categories in the Software Updates window allows us to scroll through and find the package group we want to install. In this case, we want to install Czech language support (the Czech Support group). Checking the box and clicking apply informs us how many additional packages must be installed in order to fulfill the dependencies of the package group.
Installing the Czech Support package group
using PackageKit to install czech language support with PackageKit's add/remove software window
Figure 2.9. Installing the Czech Support package group

Similarly, installed package groups can be uninstalled by selecting Package collections, unchecking the appropriate checkbox, and applying.

2.2.5. Viewing the Transaction Log

PackageKit maintains a log of the transactions that it performs. To view the log, from the Add/Remove Software window, click System → Software log, or run the gpk-log command at the shell prompt.
The Software Log Viewer shows the Action, such as Updated System or Installed Packages, the Date on which that action was performed, the Username of the user who performed the action, and the front end Application the user used (such as Update Icon, or kpackagekit). The Details column provides the types of the transactions, such as Updated, Installed or Removed, as well as the list of packages the transactions were performed on.
Viewing the log of package management transactions with the Software Log Viewer
viewing the log of package management transactions with packagekit's loftware log viewer window
Figure 2.10. Viewing the log of package management transactions with the Software Log Viewer

Typing the name of a package in the top text entry field filters the list of transactions to those which affected that package.

2.3. PackageKit Architecture

Red Hat provides the PackageKit suite of applications for viewing, updating, installing and uninstalling packages and package groups compatible with your system. Architecturally, PackageKit consists of several graphical front ends that communicate with the packagekitd daemon back end, which communicates with a package manager-specific back end that utilizes Yum to perform the actual transactions, such as installing and removing packages, etc.
Table 2.1, “PackageKit GUI Windows, Menu Locations, and Shell Prompt Commands” shows the name of the GUI window, how to start the window from the GNOME desktop or from the Add/Remove Software window, and the name of the command line application that opens that window.
Table 2.1. PackageKit GUI Windows, Menu Locations, and Shell Prompt Commands
Window Title Function How to Open Shell Command
Add/Remove Software Install, remove or view package info
From the GNOME panel: System → Administration → Add/Remove Software
gpk-application
Software Update Perform package updates
From the GNOME panel: System → Administration → Software Update
gpk-update-viewer
Software Sources Enable and disable Yum repositories
From Add/Remove Software: System → Software sources
gpk-repo
Software Log Viewer View the transaction log
From Add/Remove Software: System → Software log
gpk-log
Software Update Preferences Set PackageKit preferences gpk-prefs
(Notification Area Alert) Alerts you when updates are available
From the GNOME panel: System → Preferences → Startup Applications, Startup Programs tab
gpk-update-icon

The packagekitd daemon runs outside the user session and communicates with the various graphical front ends. The packagekitd daemon[2] communicates via the DBus system message bus with another back end, which utilizes Yum's Python API to perform queries and make changes to the sytem. On Linux systems other than Red Hat and Fedora, packagekitd can communicate with other back ends that are able to utilize the native package manager for that system. This modular architecture provides the abstraction necessary for the graphical interfaces to work with many different package managers to perform essentially the same types of package management tasks. Learning how to use the PackageKit front ends means that you can use the same familiar graphical interface across many different Linux distributions, even when they utilize a native package manager other than Yum.
In addition, PackageKit's separation of concerns provides reliability in that a crash of one of the GUI windows—or even the user's X Window session—will not affect any package management tasks being supervised by the packagekitd daemon, which runs outside of the user session.
All of the front end graphical applications discussed in this chapter are provided by the gnome-packagekit package instead of by PackageKit and its dependencies. Users working in a KDE environment may prefer to install the kpackagekit package, which provides a KDE interface for PackageKit.
Finally, PackageKit also comes with a console-based frontend called pkcon.

2.4. Additional Resources

PackageKit home page — http://www.packagekit.org/index.html
Information about and mailing lists for PackageKit.
PackageKit FAQ — http://www.packagekit.org/pk-faq.html
An informative list of Frequently Asked Questions for the PackageKit software suite.
PackageKit Feature Matrix — http://www.packagekit.org/pk-matrix.html
Cross-reference PackageKit-provided features with the long list of package manager back ends.

[2] System daemons are typically long-running processes that provide services to the user or to other programs, and which are started, often at boot time, by special initialization scripts (often shortened to init scripts). Daemons respond to the service command and can be turned on or off permanently by using the chkconfig on or chkconfig offcommands. They can typically be recognized by a “d ” appended to their name, such as the packagekitd daemon. Refer to Chapter 7, Controlling Access to Services for information about system services.

Chapter 3. RPM

3.1. RPM Design Goals
3.2. Using RPM
3.2.1. Finding RPM Packages
3.2.2. Installing and Upgrading
3.2.3. Configuration File Changes
3.2.4. Uninstalling
3.2.5. Freshening
3.2.6. Querying
3.2.7. Verifying
3.3. Checking a Package's Signature
3.3.1. Importing Keys
3.3.2. Verifying Signature of Packages
3.4. Practical and Common Examples of RPM Usage
3.5. Additional Resources
3.5.1. Installed Documentation
3.5.2. Useful Websites
3.5.3. Related Books
The RPM Package Manager (RPM) is an open packaging system , which runs on Red Hat Enterprise Linux as well as other Linux and UNIX systems. Red Hat, Inc. and the Fedora Project encourage other vendors to use RPM for their own products. RPM is distributed under the terms of the GPL (GNU General Public License).
The RPM Package Manager only works with packages built to work with the RPM format. RPM is itself provided as a pre-installed rpm package. For the end user, RPM makes system updates easy. Installing, uninstalling and upgrading RPM packages can be accomplished with short commands. RPM maintains a database of installed packages and their files, so you can invoke powerful queries and verifications on your system.
The RPM package format has been improved for Red Hat Enterprise Linux 6. RPM packages are now compressed using the XZ lossless data compression format, which has the benefit of greater compression and less CPU usage during decompression, and support multiple strong hash algorithms, such as SHA-256, for package signing and verification.

Use Yum Instead of RPM Whenever Possible

For most package management tasks, the Yum package manager offers equal and often greater capabilities and utility than RPM . Yum also performs and tracks complicated system dependency resolution, and will complain and force system integrity checks if you use RPM as well to install and remove packages. For these reasons, it is highly recommended that you use Yum instead of RPM whenever possible to perform package management tasks. Refer to Chapter 1, Yum.
If you prefer a graphical interface, you can use the PackageKit GUI application, which uses Yum as its back end, to manage your system's packages. Refer to Chapter 2, PackageKit for details.

Important

When installing a package, ensure it is compatible with your operating system and processor architecture. This can usually be determined by checking the package name. Many of the following examples show RPM packages compiled for the AMD64/Intel 64 computer architectures; thus, the RPM file name ends in x86_64.rpm.
During upgrades, RPM handles configuration files carefully, so that you never lose your customizations—something that you cannot accomplish with regular .tar.gz files.
For the developer, RPM allows you to take software source code and package it into source and binary packages for end users. This process is quite simple and is driven from a single file and optional patches that you create. This clear delineation between pristine sources and your patches along with build instructions eases the maintenance of the package as new versions of the software are released.

Note

Because RPM makes changes to your system, you must be logged in as root to install, remove, or upgrade an RPM package.

3.1. RPM Design Goals

To understand how to use RPM, it can be helpful to understand the design goals of RPM:
Upgradability
With RPM, you can upgrade individual components of your system without completely reinstalling. When you get a new release of an operating system based on RPM, such as Red Hat Enterprise Linux, you do not need to reinstall a fresh copy of the operating system your machine (as you might need to with operating systems based on other packaging systems). RPM allows intelligent, fully-automated, in-place upgrades of your system. In addition, configuration files in packages are preserved across upgrades, so you do not lose your customizations. There are no special upgrade files needed to upgrade a package because the same RPM file is used to both install and upgrade the package on your system.
Powerful Querying
RPM is designed to provide powerful querying options. You can perform searches on your entire database for packages or even just certain files. You can also easily find out what package a file belongs to and from where the package came. The files an RPM package contains are in a compressed archive, with a custom binary header containing useful information about the package and its contents, allowing you to query individual packages quickly and easily.
System Verification
Another powerful RPM feature is the ability to verify packages. If you are worried that you deleted an important file for some package, you can verify the package. You are then notified of anomalies, if any—at which point you can reinstall the package, if necessary. Any configuration files that you modified are preserved during reinstallation.
Pristine Sources
A crucial design goal was to allow the use of pristine software sources, as distributed by the original authors of the software. With RPM, you have the pristine sources along with any patches that were used, plus complete build instructions. This is an important advantage for several reasons. For instance, if a new version of a program is released, you do not necessarily have to start from scratch to get it to compile. You can look at the patch to see what you might need to do. All the compiled-in defaults, and all of the changes that were made to get the software to build properly, are easily visible using this technique.
The goal of keeping sources pristine may seem important only for developers, but it results in higher quality software for end users, too.

3.2. Using RPM

RPM has five basic modes of operation (not counting package building): installing, uninstalling, upgrading, querying, and verifying. This section contains an overview of each mode. For complete details and options, try rpm --help or man rpm. You can also refer to Section 3.5, “Additional Resources” for more information on RPM.

3.2.1. Finding RPM Packages

Before using any RPM packages, you must know where to find them. An Internet search returns many RPM repositories, but if you are looking for Red Hat RPM packages, they can be found at the following locations:
  • The Red Hat Enterprise Linux installation media contain many installable RPMs.
  • The initial RPM repositories provided with the YUM package manager . Refer to Chapter 1, Yum for details on how to use the official Red Hat Enterprise Linux package repositories.
  • The Extra Packages for Enterprise Linux (EPEL) is a community effort to provide high-quality add-on packages for Red Hat Enterprise Linux . Refer to http://fedoraproject.org/wiki/EPEL for details on EPEL RPM packages.
  • Unofficial, third-party repositories not ahffiliated Red Hat also provide RPM packages.

    Important

    When considering third-party repositories for use with your Red Hat Enterprise Linux system, pay close attention to the repository's web site with regard to package compatibility before adding the repository as a package source. Alternate package repositories may offer different, incompatible versions of the same software, including packages already included in the Red Hat Enterprise Linux repositories.
  • The Red Hat Errata Page, available at http://www.redhat.com/apps/support/errata/

3.2.2. Installing and Upgrading

RPM packages typically have file names like tree-1.5.3-2.el6.x86_64.rpm. The file name includes the package name (tree), version (1.5.3), release (2), operating system major version (el6) and CPU architecture (x86_64).
You can use rpm's -U option to:
  • upgrade an existing but older package on the system to a newer version, or
  • install the package even if an older version is not already installed.
That is, rpm -U <rpm_file> is able to perform the function of either upgrading or installing as is appropriate for the package.
Assuming the tree-1.5.3-2.el6.x86_64.rpm package is in the current directory, log in as root and type the following command at a shell prompt to either upgrade or install the tree package as determined by rpm: 
rpm -Uvh tree-1.5.3-2.el6.x86_64.rpm

Use -Uvh for nicely-formatted RPM installs

The -v and -h options (which are combined with -U) cause rpm to print more verbose output and display a progress meter using hash signs.
If the upgrade/installation is successful, the following output is displayed: 
Preparing...                ########################################### [100%]
   1:tree                   ########################################### [100%]

Always use the -i (install) option to install new kernel packages!

rpm provides two different options for installing packages: the aforementioned -U option (which historically stands for upgrade), and the -i option, historically standing for install. Because the -U option subsumes both install and upgrade functions, we recommend to use rpm -Uvh with all packages except kernel packages.
You should always use the -i option to simply install a new kernel package instead of upgrading it. This is because using the -U option to upgrade a kernel package removes the previous (older) kernel package, which could render the system unable to boot if there is a problem with the new kernel. Therefore, use the rpm -i <kernel_package> command to install a new kernel without replacing any older kernel packages. For more information on installing kernel packages, refer to Chapter 23, Manually Upgrading the Kernel.
The signature of a package is checked automatically when installing or upgrading a package. The signature confirms that the package was signed by an authorized party. For example, if the verification of the signature fails, an error message such as the following is displayed: 
error: tree-1.5.3-2.el6.x86_64.rpm: Header V3 RSA/SHA256 signature: BAD, key ID
d22e77f2
If it is a new, header-only, signature, an error message such as the following is displayed: 
error: tree-1.5.3-2.el6.x86_64.rpm: Header V3 RSA/SHA256 signature: BAD,
key ID d22e77f2
If you do not have the appropriate key installed to verify the signature, the message contains the word NOKEY: 
warning: tree-1.5.3-2.el6.x86_64.rpm: Header V3 RSA/SHA1 signature: NOKEY, key ID 57bbccba
Refer to Section 3.3, “Checking a Package's Signature” for more information on checking a package's signature.

3.2.2.1. Package Already Installed

If a package of the same name and version is already installed , the following output is displayed: 
Preparing...                ########################################### [100%]
	package tree-1.5.3-2.el6.x86_64 is already installed
However, if you want to install the package anyway, you can use the --replacepkgs option, which tells RPM to ignore the error: 
rpm -Uvh --replacepkgs tree-1.5.3-2.el6.x86_64.rpm
This option is helpful if files installed from the RPM were deleted or if you want the original configuration files from the RPM to be installed.

3.2.2.2. Conflicting Files

If you attempt to install a package that contains a file which has already been installed by another package , the following is displayed: 
Preparing... ##################################################
 file /usr/bin/foobar from install of foo-1.0-1.el6.x86_64 conflicts
with file from package bar-3.1.1.el6.x86_64
To make RPM ignore this error, use the --replacefiles option: 
rpm -Uvh --replacefiles foo-1.0-1.el6.x86_64.rpm

3.2.2.3. Unresolved Dependency

RPM packages may sometimes depend on other packages , which means that they require other packages to be installed to run properly. If you try to install a package which has an unresolved dependency, output similar to the following is displayed: 
error: Failed dependencies:
	bar.so.3()(64bit) is needed by foo-1.0-1.el6.x86_64
If you are installing a package from the Red Hat Enterprise Linux installation media, such as from a CD-ROM or DVD, the dependencies may be available. Find the suggested package(s) on the Red Hat Enterprise Linux installation media or on one of the active Red Hat Enterprise Linux mirrors and add it to the command: 
rpm -Uvh foo-1.0-1.el6.x86_64.rpm    bar-3.1.1.el6.x86_64.rpm
If installation of both packages is successful, output similar to the following is displayed: 
Preparing...                ########################################### [100%]
   1:foo                   ########################################### [ 50%]
   2:bar                   ########################################### [100%]
You can try the --whatprovides option to determine which package contains the required file. 
rpm -q --whatprovides "bar.so.3"
If the package that contains bar.so.3 is in the RPM database, the name of the package is displayed: 
bar-3.1.1.el6.i586.rpm

Warning: Forcing Package Installation

Although we can force rpm to install a package that gives us a Failed dependencies error (using the --nodeps option), this is not recommended, and will usually result in the installed package failing to run. Installing or removing packages with rpm --nodeps can cause applications to misbehave and/or crash, and can cause serious package management problems or, possibly, system failure. For these reasons, it is best to heed such warnings; the package manager—whether RPM, Yum or PackageKit—shows us these warnings and suggests possible fixes because accounting for dependencies is critical. The Yum package manager can perform dependency resolution and fetch dependencies from online repositories, making it safer, easier and smarter than forcing rpm to carry out actions without regard to resolving dependencies.

3.2.3. Configuration File Changes

Because RPM performs intelligent upgrading of packages with configuration files , you may see one or the other of the following messages: 
saving /etc/foo.conf as /etc/foo.conf.rpmsave
This message means that changes you made to the configuration file may not be forward-compatible with the new configuration file in the package, so RPM saved your original file and installed a new one. You should investigate the differences between the two configuration files and resolve them as soon as possible, to ensure that your system continues to function properly.
Alternatively, RPM may save the package's new configuration file as, for example, foo.conf.rpmnew, and leave the configuration file you modified untouched. You should still resolve any conflicts between your modified configuration file and the new one, usually by merging changes from the old one to the new one with a diff program.
If you attempt to upgrade to a package with an older version number (that is, if a higher version of the package is already installed), the output is similar to the following: 
package foo-2.0-1.el6.x86_64.rpm (which is newer than foo-1.0-1) is already installed
To force RPM to upgrade anyway, use the --oldpackage option: 
rpm -Uvh --oldpackage foo-1.0-1.el6.x86_64.rpm

3.2.4. Uninstalling

Uninstalling a package is just as simple as installing one. Type the following command at a shell prompt: 
rpm -e foo

Note

Notice that we used the package name foo, not the name of the original package file, foo-1.0-1.el6.x86_64. If you attempt to uninstall a package using the rpm -e command and the original full file name, you will receive a package name error.
You can encounter dependency errors when uninstalling a package if another installed package depends on the one you are trying to remove. For example: 
rpm -e ghostscript
error: Failed dependencies:
	libgs.so.8()(64bit) is needed by (installed) libspectre-0.2.2-3.el6.x86_64
	libgs.so.8()(64bit) is needed by (installed) foomatic-4.0.3-1.el6.x86_64
	libijs-0.35.so()(64bit) is needed by (installed) gutenprint-5.2.4-5.el6.x86_64
	ghostscript is needed by (installed) printer-filters-1.1-4.el6.noarch
Similar to how we searched for a shared object library (i.e. a <library_name>.so.<number> file) in Section 3.2.2.3, “Unresolved Dependency”, we can search for a 64-bit shared object library using this exact syntax (and making sure to quote the file name): 
~]# rpm -q --whatprovides "libgs.so.8()(64bit)"
ghostscript-8.70-1.el6.x86_64

Warning: Forcing Package Installation

Although we can force rpm to remove a package that gives us a Failed dependencies error (using the --nodeps option), this is not recommended, and may cause harm to other installed applications. Installing or removing packages with rpm --nodeps can cause applications to misbehave and/or crash, and can cause serious package management problems or, possibly, system failure. For these reasons, it is best to heed such warnings; the package manager—whether RPM, Yum or PackageKit—shows us these warnings and suggests possible fixes because accounting for dependencies is critical. The Yum package manager can perform dependency resolution and fetch dependencies from online repositories, making it safer, easier and smarter than forcing rpm to carry out actions without regard to resolving dependencies.

3.2.5. Freshening

Freshening is similar to upgrading, except that only existent packages are upgraded. Type the following command at a shell prompt: 
rpm -Fvh foo-2.0-1.el6.x86_64.rpm
RPM's freshen option checks the versions of the packages specified on the command line against the versions of packages that have already been installed on your system. When a newer version of an already-installed package is processed by RPM's freshen option, it is upgraded to the newer version. However, RPM's freshen option does not install a package if no previously-installed package of the same name exists. This differs from RPM's upgrade option, as an upgrade does install packages whether or not an older version of the package was already installed.
Freshening works for single packages or package groups. If you have just downloaded a large number of different packages, and you only want to upgrade those packages that are already installed on your system, freshening does the job. Thus, you do not have to delete any unwanted packages from the group that you downloaded before using RPM.
In this case, issue the following with the *.rpm glob: 
rpm -Fvh *.rpm
RPM then automatically upgrades only those packages that are already installed.

3.2.6. Querying

The RPM database stores information about all RPM packages installed in your system. It is stored in the directory /var/lib/rpm/, and is used to query what packages are installed, what versions each package is, and to calculate any changes to any files in the package since installation, among other use cases.
To query this database, use the -q option. The rpm -q package name command displays the package name, version, and release number of the installed package <package_name>. For example, using rpm -q tree to query installed package tree might generate the following output: 
tree-1.5.2.2-4.el6.x86_64
You can also use the following Package Selection Options (which is a subheading in the RPM man page: see man rpm for details) to further refine or qualify your query:
  • -a — queries all currently installed packages.
  • -f <file_name> — queries the RPM database for which package owns <file_name> . Specify the absolute path of the file (for example, rpm -qf /bin/ls instead of rpm -qf ls).
  • -p <package_file> — queries the uninstalled package <package_file> .
There are a number of ways to specify what information to display about queried packages. The following options are used to select the type of information for which you are searching. These are called the Package Query Options.
  • -i displays package information including name, description, release, size, build date, install date, vendor, and other miscellaneous information.
  • -l displays the list of files that the package contains.
  • -s displays the state of all the files in the package.
  • -d displays a list of files marked as documentation (man pages, info pages, READMEs, etc.) in the package.
  • -c displays a list of files marked as configuration files. These are the files you edit after installation to adapt and customize the package to your system (for example, sendmail.cf, passwd, inittab, etc.).
For options that display lists of files, add -v to the command to display the lists in a familiar ls -l format.

3.2.7. Verifying

Verifying a package compares information about files installed from a package with the same information from the original package. Among other things, verifying compares the file size, MD5 sum, permissions, type, owner, and group of each file.
The command rpm -V verifies a package. You can use any of the Verify Options listed for querying to specify the packages you wish to verify. A simple use of verifying is rpm -V tree, which verifies that all the files in the tree package are as they were when they were originally installed. For example:
  • To verify a package containing a particular file: 
    rpm -Vf /usr/bin/tree
    In this example, /usr/bin/tree is the absolute path to the file used to query a package.
  • To verify ALL installed packages throughout the system (which will take some time): 
    rpm -Va
  • To verify an installed package against an RPM package file: 
    rpm -Vp tree-1.5.3-2.el6.x86_64.rpm
    This command can be useful if you suspect that your RPM database is corrupt.
If everything verified properly, there is no output. If there are any discrepancies, they are displayed. The format of the output is a string of eight characters (a "c" denotes a configuration file) and then the file name. Each of the eight characters denotes the result of a comparison of one attribute of the file to the value of that attribute recorded in the RPM database. A single period (.) means the test passed. The following characters denote specific discrepancies:
  • 5 — MD5 checksum
  • S — file size
  • L — symbolic link
  • T — file modification time
  • D — device
  • U — user
  • G — group
  • M — mode (includes permissions and file type)
  • ? — unreadable file (file permission errors, for example)
If you see any output, use your best judgment to determine if you should remove the package, reinstall it, or fix the problem in another way.

3.3. Checking a Package's Signature

If you wish to verify that a package has not been corrupted or tampered with, examine only the md5sum by typing the following command at a shell prompt (where <rpm_file> is the file name of the RPM package): 
rpm -K --nosignature <rpm_file>
The message <rpm_file>: rsa sha1 (md5) pgp md5 OK (specifically the OK part of it) is displayed. This brief message means that the file was not corrupted during download. To see a more verbose message, replace -K with -Kvv in the command.
On the other hand, how trustworthy is the developer who created the package? If the package is signed with the developer's GnuPG key, you know that the developer really is who they say they are.
An RPM package can be signed using Gnu Privacy Guard (or GnuPG), to help you make certain your downloaded package is trustworthy.
GnuPG is a tool for secure communication; it is a complete and free replacement for the encryption technology of PGP, an electronic privacy program. With GnuPG, you can authenticate the validity of documents and encrypt/decrypt data to and from other recipients. GnuPG is capable of decrypting and verifying PGP 5.x files as well.
During installation, GnuPG is installed by default. That way you can immediately start using GnuPG to verify any packages that you receive from Red Hat. Before doing so, you must first import Red Hat's public key.

3.3.1. Importing Keys

To verify Red Hat packages, you must import the Red Hat GPG key. To do so, execute the following command at a shell prompt: 
rpm --import /usr/share/rhn/RPM-GPG-KEY
To display a list of all keys installed for RPM verification, execute the command: 
rpm -qa gpg-pubkey*
For the Red Hat key, the output includes: 
gpg-pubkey-db42a60e-37ea5438
To display details about a specific key, use rpm -qi followed by the output from the previous command: 
rpm -qi gpg-pubkey-db42a60e-37ea5438

3.3.2. Verifying Signature of Packages

To check the GnuPG signature of an RPM file after importing the builder's GnuPG key, use the following command (replace <rpm-file> with the filename of the RPM package): 
rpm -K <rpm-file>
If all goes well, the following message is displayed: md5 gpg OK. This means that the signature of the package has been verified, that it is not corrupt, and therefore is safe to install and use.

3.4. Practical and Common Examples of RPM Usage

RPM is a useful tool for both managing your system and diagnosing and fixing problems. The best way to make sense of all its options is to look at some examples.
  • Perhaps you have deleted some files by accident, but you are not sure what you deleted. To verify your entire system and see what might be missing, you could try the following command: 
    rpm -Va
    If some files are missing or appear to have been corrupted, you should probably either re-install the package or uninstall and then re-install the package.
  • At some point, you might see a file that you do not recognize. To find out which package owns it, enter: 
    rpm -qf /usr/bin/ghostscript
    The output would look like the following: 
    ghostscript-8.70-1.el6.x86_64
  • We can combine the above two examples in the following scenario. Say you are having problems with /usr/bin/paste. You would like to verify the package that owns that program, but you do not know which package owns paste. Enter the following command, 
    rpm -Vf /usr/bin/paste
    and the appropriate package is verified.
  • Do you want to find out more information about a particular program? You can try the following command to locate the documentation which came with the package that owns that program: 
    rpm -qdf /usr/bin/free
    The output would be similar to the following: 
    /usr/share/doc/procps-3.2.8/BUGS
/usr/share/doc/procps-3.2.8/FAQ
/usr/share/doc/procps-3.2.8/NEWS
/usr/share/doc/procps-3.2.8/TODO
/usr/share/man/man1/free.1.gz
/usr/share/man/man1/pgrep.1.gz
/usr/share/man/man1/pkill.1.gz
/usr/share/man/man1/pmap.1.gz
/usr/share/man/man1/ps.1.gz
/usr/share/man/man1/pwdx.1.gz
/usr/share/man/man1/skill.1.gz
/usr/share/man/man1/slabtop.1.gz
/usr/share/man/man1/snice.1.gz
/usr/share/man/man1/tload.1.gz
/usr/share/man/man1/top.1.gz
/usr/share/man/man1/uptime.1.gz
/usr/share/man/man1/w.1.gz
/usr/share/man/man1/watch.1.gz
/usr/share/man/man5/sysctl.conf.5.gz
/usr/share/man/man8/sysctl.8.gz
/usr/share/man/man8/vmstat.8.gz
  • You may find a new RPM, but you do not know what it does. To find information about it, use the following command: 
    rpm -qip crontabs-1.10-32.1.el6.noarch.rpm
    The output would be similar to the following: 
    Name        : crontabs                     Relocations: (not relocatable)
Version     : 1.10                              Vendor: Red Hat, Inc.
Release     : 32.1.el6                      Build Date: Thu 03 Dec 2009 02:17:44 AM CET
Install Date: (not installed)               Build Host: js20-bc1-11.build.redhat.com
Group       : System Environment/Base       Source RPM: crontabs-1.10-32.1.el6.src.rpm
Size        : 2486                             License: Public Domain and GPLv2
Signature   : RSA/8, Wed 24 Feb 2010 08:46:13 PM CET, Key ID 938a80caf21541eb
Packager    : Red Hat, Inc. <http://bugzilla.redhat.com/bugzilla>
Summary     : Root crontab files used to schedule the execution of programs
Description :
The crontabs package contains root crontab files and directories.
You will need to install cron daemon to run the jobs from the crontabs.
The cron daemon such as cronie or fcron checks the crontab files to
see when particular commands are scheduled to be executed.  If commands
are scheduled, it executes them.
Crontabs handles a basic system function, so it should be installed on
your system.
  • Perhaps you now want to see what files the crontabs RPM package installs. You would enter the following: 
    rpm -qlp crontabs-1.10-32.1.el6.noarch.rpm
    The output is similar to the following: 
    /etc/cron.daily
/etc/cron.hourly
/etc/cron.monthly
/etc/cron.weekly
/etc/crontab
/usr/bin/run-parts
/usr/share/man/man4/crontabs.4.gz
These are just a few examples. As you use RPM, you may find more uses for it.

3.5. Additional Resources

RPM is an extremely complex utility with many options and methods for querying, installing, upgrading, and removing packages. Refer to the following resources to learn more about RPM.

3.5.1. Installed Documentation

  • rpm --help — This command displays a quick reference of RPM parameters.
  • man rpm — The RPM man page gives more detail about RPM parameters than the rpm --help command.

3.5.2. Useful Websites

Part III. System Configuration

Part of a system administrator's job is configuring the system for various tasks, types of users, and hardware configurations. This section explains how to configure a Red Hat Enterprise Linux system.

Table of Contents

13. Date and Time Configuration
13.1. Date/Time Properties Tool
13.1.1. Date and Time Properties
13.1.2. Network Time Protocol Properties
13.1.3. Time Zone Properties
13.2. Command Line Configuration
13.2.1. Date and Time Setup
13.2.2. Network Time Protocol Setup
14. Keyboard Configuration
14.1. Changing the Keyboard Layout
14.2. Adding the Keyboard Layout Indicator
14.3. Setting Up a Typing Break
15. Users and Groups
15.1. User and Group Configuration
15.1.1. Adding a New User
15.1.2. Adding a New Group
15.1.3. Modifying Group Properties
15.2. User and Group Management Tools
15.2.1. Command Line Configuration
15.2.2. Explaining the Process
15.3. Standard Users
15.4. Standard Groups
15.5. User Private Groups
15.5.1. Group Directories
15.6. Shadow Passwords
15.7. Additional Resources
15.7.1. Installed Documentation
16. Automated Tasks
16.1. Cron and Anacron
16.1.1. Starting and Stopping the Service
16.1.2. Configuring Anacron Jobs
16.1.3. Configuring Cron Jobs
16.1.4. Controlling Access to Cron
16.1.5. Black/White Listing of Cron Jobs
16.2. At and Batch
16.2.1. Configuring At Jobs
16.2.2. Configuring Batch Jobs
16.2.3. Viewing Pending Jobs
16.2.4. Additional Command Line Options
16.2.5. Controlling Access to At and Batch
16.2.6. Starting and Stopping the Service
16.3. Additional Resources
16.3.1. Installed Documentation
17. Log Files
17.1. Configuring rsyslog
17.1.1. Modules
17.1.2. Global Directives
17.1.3. Rules
17.1.4. Templates
17.1.5. Filter Conditions
17.1.6. Output Channels
17.2. rsyslog Performance
17.3. Locating Log Files
17.3.1. Configuring logrotate
17.4. Viewing Log Files
17.5. Adding a Log File
17.6. Monitoring Log Files
17.7. Additional Resources
17.7.1. Installed Documentation
17.7.2. Useful Websites
18. The sysconfig Directory
18.1. Files in the /etc/sysconfig/ Directory
18.1.1. /etc/sysconfig/arpwatch
18.1.2. /etc/sysconfig/authconfig
18.1.3. /etc/sysconfig/autofs
18.1.4. /etc/sysconfig/clock
18.1.5. /etc/sysconfig/dhcpd
18.1.6. /etc/sysconfig/firstboot
18.1.7. /etc/sysconfig/i18n
18.1.8. /etc/sysconfig/init
18.1.9. /etc/sysconfig/ip6tables-config
18.1.10. /etc/sysconfig/keyboard
18.1.11. /etc/sysconfig/ldap
18.1.12. /etc/sysconfig/named
18.1.13. /etc/sysconfig/network
18.1.14. /etc/sysconfig/ntpd
18.1.15. /etc/sysconfig/quagga
18.1.16. /etc/sysconfig/radvd
18.1.17. /etc/sysconfig/samba
18.1.18. /etc/sysconfig/selinux
18.1.19. /etc/sysconfig/sendmail
18.1.20. /etc/sysconfig/spamassassin
18.1.21. /etc/sysconfig/squid
18.1.22. /etc/sysconfig/system-config-users
18.1.23. /etc/sysconfig/vncservers
18.1.24. /etc/sysconfig/xinetd
18.2. Directories in the /etc/sysconfig/ Directory
18.3. Additional Resources
18.3.1. Installed Documentation
19. The proc File System
19.1. A Virtual File System
19.1.1. Viewing Virtual Files
19.1.2. Changing Virtual Files
19.2. Top-level Files within the proc File System
19.2.1. /proc/buddyinfo
19.2.2. /proc/cmdline
19.2.3. /proc/cpuinfo
19.2.4. /proc/crypto
19.2.5. /proc/devices
19.2.6. /proc/dma
19.2.7. /proc/execdomains
19.2.8. /proc/fb
19.2.9. /proc/filesystems
19.2.10. /proc/interrupts
19.2.11. /proc/iomem
19.2.12. /proc/ioports
19.2.13. /proc/kcore
19.2.14. /proc/kmsg
19.2.15. /proc/loadavg
19.2.16. /proc/locks
19.2.17. /proc/mdstat
19.2.18. /proc/meminfo
19.2.19. /proc/misc
19.2.20. /proc/modules
19.2.21. /proc/mounts
19.2.22. /proc/mtrr
19.2.23. /proc/partitions
19.2.24. /proc/slabinfo
19.2.25. /proc/stat
19.2.26. /proc/swaps
19.2.27. /proc/sysrq-trigger
19.2.28. /proc/uptime
19.2.29. /proc/version
19.3. Directories within /proc/
19.3.1. Process Directories
19.3.2. /proc/bus/
19.3.3. /proc/bus/pci
19.3.4. /proc/driver/
19.3.5. /proc/fs
19.3.6. /proc/irq/
19.3.7. /proc/net/
19.3.8. /proc/scsi/
19.3.9. /proc/sys/
19.3.10. /proc/sysvipc/
19.3.11. /proc/tty/
19.3.12. /proc/PID/
19.4. Using the sysctl Command
19.5. References

Chapter 13. Date and Time Configuration

13.1. Date/Time Properties Tool
13.1.1. Date and Time Properties
13.1.2. Network Time Protocol Properties
13.1.3. Time Zone Properties
13.2. Command Line Configuration
13.2.1. Date and Time Setup
13.2.2. Network Time Protocol Setup
This chapter covers setting the system date and time in Red Hat Enterprise Linux, both manually and using the Network Time Protocol (NTP), as well as setting the adequate time zone. Two methods are covered: setting the date and time using the Date/Time Properties tool, and doing so on the command line.

13.1. Date/Time Properties Tool

The Date/Time Properties tool allows the user to change the system date and time, to configure the time zone used by the system, and to set up the Network Time Protocol daemon to synchronize the system clock with a time server. Note that to use this application, you must be running the X Window System.
To start the tool, select System → Administration → Date & Time from the panel, or type the system-config-date command at a shell prompt (e.g., xterm or GNOME Terminal). Unless you are already authenticated, you will be prompted to enter the superuser password.
Authentication Query
Figure 13.1. Authentication Query

13.1.1. Date and Time Properties

As shown in Figure 13.2, “Date and Time Properties”, the Date/Time Properties tool is divided into two separate tabs. The tab containing the configuration of the current date and time is shown by default.
Date and Time Properties
Date and Time Properties
Figure 13.2. Date and Time Properties

To set up your system manually, follow these steps:
  1. Change the current date. Use the arrows to the left and right of the month and year to change the month and year respectively. Then click inside the calendar to select the day of the month.
  2. Change the current time. Use the up and down arrow buttons beside the Hour, Minute, and Second, or replace the values directly.
Click the OK button to apply the changes and exit the application.

13.1.2. Network Time Protocol Properties

If you prefer an automatic setup, select the checkbox labeled Synchronize date and time over the network instead. This will display the list of available NTP servers as shown in Figure 13.3, “Network Time Protocol Properties”.
Network Time Protocol Properties
Network Time Protocol Properties
Figure 13.3. Network Time Protocol Properties

Here you can choose one of the predefined servers, edit a predefined server by clicking the Edit button, or add a new server name by clicking Add. In the Advanced Options, you can also select whether you want to synchronize the system clock before starting the service, and if you wish to use a local time source.

Note

Your system does not start synchronizing with the NTP server until you click the OK button at the bottom of the window to confirm your changes.
Click the OK button to apply any changes made to the date and time settings and exit the application.

13.1.3. Time Zone Properties

To configure the system time zone, click the Time Zone tab as shown in Figure 13.4, “Time Zone Properties”.
Time Zone Properties
Time Zone Properties
Figure 13.4. Time Zone Properties

There are two common approaches to the time zone selection:
  1. Using the interactive map. Click “zoom in” and “zoom out” buttons next to the map, or click on the map itself to zoom into the selected region. Then choose the city specific to your time zone. A red X appears and the time zone selection changes in the list below the map.
  2. Use the list below the map. To make the selection easier, cities and countries are grouped within their specific continents. Note that non-geographic time zones have also been added to address needs in the scientific community.
If your system clock is set to use UTC, select the System clock uses UTC option. UTC stands for the Universal Time, Coordinated, also known as Greenwich Mean Time (GMT). Other time zones are determined by adding or subtracting from the UTC time.
Click OK to apply the changes and exit the program.

13.2. Command Line Configuration

In case your system does not have the Date/Time Properties tool installed, or the X Window Server is not running, you will have to change the system date and time on the command line. Note that in order to perform actions described in this section, you have to be logged in as a superuser: 
~]$ su -
Password:

13.2.1. Date and Time Setup

The date command allows the superuser to set the system date and time manually:
  1. Change the current date. Type the command in the following form at a shell prompt, replacing the YYYY with a four-digit year, MM with a two-digit month, and DD with a two-digit day of the month: 
    ~]# date +%D -s YYYY-MM-DD
    For example, to set the date to 2 June 2010, type: 
    ~]# date +%D -s 2010-06-02
  2. Change the current time. Use the following command, where HH stands for an hour, MM is a minute, and SS is a second, all typed in a two-digit form: 
    ~]# date +%T -s HH:MM:SS
    If your system clock is set to use UTC (Coordinated Universal Time), add the following option: 
    ~]# date +%T -s HH:MM:SS -u
    For instance, to set the system clock to 11:26 PM using the UTC, type: 
    ~]# date +%T -s 23:26:00 -u
You can check your current settings by typing date without any additional argument:
Example 13.1. Displaying the current date and time
~]$ date
Wed Jun  2 11:58:48 CEST 2010

13.2.2. Network Time Protocol Setup

As opposed to the manual setup described above, you can also synchronize the system clock with a remote server over the Network Time Protocol (NTP). For the one-time synchronization only, use the ntpdate command:
  1. Firstly, check whether the selected NTP server is accessible: 
    ~]# ntpdate -q server_address
    For example: 
    ~]# ntpdate -q 0.rhel.pool.ntp.org
  2. When you find a satisfactory server, run the ntpdate command followed with on or more server addresses: 
    ~]# ntpdate server_address...
    For instance: 
    ~]# ntpdate 0.rhel.pool.ntp.org 1.rhel.pool.ntp.org
    Unless an error message is displayed, the system time should now be set. You can check the current by setting typing date without any additional arguments as shown in Section 13.2.1, “Date and Time Setup”.
  3. In most cases, these steps are sufficient. Only if you really need one or more system services to always use the correct time, enable running the ntpdate at boot time: 
    ~]# chkconfig ntpdate on
    For more information about system services and their setup, see Chapter 7, Controlling Access to Services.

    Note

    If the synchronization with the time server at boot time keeps failing, i.e., you find a relevant error message in the /var/log/boot.log system log, try to add the following line to /etc/sysconfig/network: 
    NETWORKWAIT=1
However, the more convenient way is to set the ntpd daemon to synchronize the time at boot time automatically:
  1. Open the NTP configuration file /etc/ntp.conf in a text editor such as vi or nano, or create a new one if it does not already exist: 
    ~]# nano /etc/ntp.conf
  2. Now add or edit the list of public NTP servers. If you are using Red Hat Enterprise Linux 6, the file should already contain the following lines, but feel free to change or expand these according to your needs: 
    server 0.rhel.pool.ntp.org
server 1.rhel.pool.ntp.org
server 2.rhel.pool.ntp.org

    Tip

    To speed the initial synchronization up, add the iburst directive at the end of each server line: 
    server 0.rhel.pool.ntp.org iburst
server 1.rhel.pool.ntp.org iburst
server 2.rhel.pool.ntp.org iburst
  3. Once you have the list of servers complete, in the same file, set the proper permissions, giving the unrestricted access to localhost only: 
    restrict default kod nomodify notrap nopeer noquery
restrict -6 default kod nomodify notrap nopeer noquery
restrict 127.0.0.1
restrict -6 ::1
  4. Save all changes, exit the editor, and restart the NTP daemon: 
    ~]# service ntpd restart
  5. Make sure that ntpd daemon is started at boot time: 
    ~]# chkconfig ntpd on

Chapter 14. Keyboard Configuration

14.1. Changing the Keyboard Layout
14.2. Adding the Keyboard Layout Indicator
14.3. Setting Up a Typing Break
This chapter describes how to change the keyboard layout, as well as how to add the Keyboard Indicator applet to the panel. It also covers the option to enforce a typing break, and explains both advantages and disadvantages of doing so.

14.1. Changing the Keyboard Layout

The installation program allowed you to configure a keyboard layout for your system. However, the default settings may not always suit your current needs. To configure a different keyboard layout after the installation, use the Keyboard Preferences tool.
To open Keyboard Layout Preferences, select System → Preferences → Keyboard from the panel, and click the Layouts tab.
Keybord Layout Preferences
Keyboard Layout Preferences
Figure 14.1. Keybord Layout Preferences

You will be presented with a list of available layouts. To add a new one, click the Add... button below the list, and you will be prompted to chose which layout you want to add.
Choosing a layout
Choosing a layout
Figure 14.2. Choosing a layout

Currently, there are two ways how to chose the keyboard layout: you can either find it by the country it is associated with (the By country tab), or you can select it by the language (the By language tab). In either case, first select the desired country or language from the Country or Language pulldown menu, then specify the variant from the Variants menu. The preview of the layout changes immediately. To confirm the selection, click Add.
Selecting the default layout
Selecting the default layout
Figure 14.3. Selecting the default layout

The layout should appear in the list. To make it the default, select the radio button next to its name. The changes take effect immediately. Note that there is a text-entry field at the bottom of the window where you can safely test your settings. Once you are satisfied, click Close to close the window.
Testing the layout
Testing the layout
Figure 14.4. Testing the layout

Suggestion: Disable Separate Layout for Each Window

By default, changing the keyboard layout affects the active window only. This means that if you change the layout and switch to another window, this window will use the old one, which might be confusing. To turn this unfortunate behavior off, unselect the Separate layout for each window check box.
Disabling separate layout for each window
Doing this has its drawbacks though, as you will no longer be able to chose the default layout by selecting the radio button as shown in Figure 14.3, “Selecting the default layout”. To make the layout the default, simply drag it at the beginning of the list.
Changing the order of layouts

14.2. Adding the Keyboard Layout Indicator

If you want to see what keyboard layout you are currently using, or you would like to switch between different layouts with a single mouse click, add the Keyboard Indicator applet to the panel. To do so, right-click the empty space on the main panel, and select the Add to Panel... option from the pulldown menu.
Adding a new applet
Adding a New Applet
Figure 14.5. Adding a new applet

You will be presented with a list of available applets. Scroll through the list (or start typing “keyboard” to the search field at the top of the window), select Keyboard Indicator, and click the Add button.
Selecting the Keyboard Indicator
Selecting the Keyboard Indicator
Figure 14.6. Selecting the Keyboard Indicator

The applet appears immediately, displaying the shortened name of the country the current layout is associated with. To display the actual variant, hover the pointer over the applet icon.
The Keyboard Indicator applet
The Keyboard Indicator applet
Figure 14.7. The Keyboard Indicator applet

14.3. Setting Up a Typing Break

Typing for a long period of time can be not only tiresome, but it can also increase the risk of serious health problems, such as the carpal tunnel syndrome. One way of preventing this is to configure the system to enforce the typing break. Simply select System → Preferences → Keyboard from the panel, click the Typing Break tab, and select the Lock screen to enforce typing break check box.
Typing Break Properties
Typing Break Properties
Figure 14.8. Typing Break Properties

To increase or decrease the amount of time you want to be allowed to type before the break is enforced, click the up or down button next to the Work interval lasts label respectively. You can do the same with the Break interval lasts setting to alter the length of the break itself. Finally, select the Allow postponing of breaks check box if you want to be able to delay the break in case you need to finish the work. The changes take effect immediately.
Taking a break
Taking a break
Figure 14.9. Taking a break

Next time you reach the time limit, you will be presented with a screen advising you to take a break, and a clock displaying the remaining time. If you enabled it, the Postpone Break button will be located at the bottom right corner of the screen.

Chapter 15. Users and Groups

15.1. User and Group Configuration
15.1.1. Adding a New User
15.1.2. Adding a New Group
15.1.3. Modifying Group Properties
15.2. User and Group Management Tools
15.2.1. Command Line Configuration
15.2.2. Explaining the Process
15.3. Standard Users
15.4. Standard Groups
15.5. User Private Groups
15.5.1. Group Directories
15.6. Shadow Passwords
15.7. Additional Resources
15.7.1. Installed Documentation
The control of users and groups is a core element of Red Hat Enterprise Linux system administration.
Users can be either people (meaning accounts tied to physical users) or accounts which exist for specific applications to use.
Groups are logical expressions of organization, tying users together for a common purpose. Users within a group can read, write, or execute files owned by that group.
Each user is associated with a unique numerical identification number called a userid (UID); likewise, each group is associated with a groupid (GID).
A user who creates a file is also the owner and group owner of that file. The file is assigned separate read, write, and execute permissions for the owner, the group, and everyone else. The file owner can be changed only by the root user, and access permissions can be changed by both the root user and file owner.
Red Hat Enterprise Linux also supports access control lists (ACLs) for files and directories which allow permissions for specific users outside of the owner to be set. For more information about ACLs, refer to chapterACLS.

15.1. User and Group Configuration

The User Manager allows you to view, modify, add, and delete local users and groups.
The GNOME User Manager
the gnome user manager lets you manage users
Figure 15.1. The GNOME User Manager

You can start the User Manager by clicking System → Administration → Users and Groups. Alternatively, you can enter system-config-users at the shell prompt to open the User Manager. Viewing and modifying user and group information requires superuser privileges. If you are not the superuser when you open the User Manager, it will prompt you for the superuser password.
To view a list of local users on the system, click the Users tab. To view a list of local groups on the system, click the Groups tab.
To find a specific user or group, type the first few letters of the name in the Search filter field. Press Enter or click the Apply filter button. The filtered list is displayed.
To sort the users, click on the column User Name and for groups click on Group Name. The users or groups are sorted according to the value of that column.
Red Hat Enterprise Linux reserves user IDs below 500 for system users. By default, the User Manager does not display system users. To view all users, including the system users, go to Edit > Preferences and uncheck Hide system users and groups from the dialog box.

15.1.1. Adding a New User

To add a new user, click the Add User button. A window as shown in Figure 15.2, “Creating a new user” appears. Type the username and full name for the new user in the appropriate fields. Type the user's password in the Password and Confirm Password fields. The password must be at least six characters.

Tip

It is advisable to use a much longer password, as this makes it more difficult for an intruder to guess it and access the account without permission. It is also recommended that the password not be based on a dictionary term; use a combination of letters, numbers and special characters.
Select a login shell from the pulldown list. If you are not sure which shell to select, accept the default value of /bin/bash. The default home directory is /home/<username>/. You can change the home directory that is created for the user, or you can choose not to create the home directory by unselecting Create home directory.
If you select to create the home directory, default configuration files are copied from the /etc/skel/ directory into the new home directory.
Red Hat Enterprise Linux uses a user private group (UPG) scheme. The UPG scheme does not add or change anything in the standard UNIX way of handling groups; it offers a new convention. Whenever you create a new user, by default, a unique group with the same name as the user is created. If you do not want to create this group, unselect Create a private group for the user.
To specify a user ID for the user, select Specify user ID manually. If the option is not selected, the next available user ID above 500 is assigned to the new user. Because Red Hat Enterprise Linux reserves user IDs below 500 for system users, it is not advisable to manually assign user IDs 1-499.
Click OK to create the user.
Creating a new user
creating a new user with the create new user dialog
Figure 15.2. Creating a new user

To configure more advanced user properties, such as password expiration, modify the user's properties after adding the user.

Modifying User Properties

To view the properties of an existing user, click on the Users tab, select the user from the user list, and click Properties from the menu (or choose File > Properties from the pulldown menu). A window similar to Figure 15.3, “User Properties” appears.
User Properties
Modifying user properties
Figure 15.3. User Properties

The User Properties window is divided into multiple tabbed pages:
  • User Data — Shows the basic user information configured when you added the user. Use this tab to change the user's full name, password, home directory, or login shell.
  • Account Info — Select Enable account expiration if you want the account to expire on a certain date. Enter the date in the provided fields. Select Local password is locked to lock the user account and prevent the user from logging into the system.
  • Password Info — Displays the date that the user's password last changed. To force the user to change passwords after a certain number of days, select Enable password expiration and enter a desired value in the Days before change required: field. The number of days before the user's password expires, the number of days before the user is warned to change passwords, and days before the account becomes inactive can also be changed.
  • Groups — Allows you to view and configure the Primary Group of the user, as well as other groups that you want the user to be a member of.

15.1.2. Adding a New Group

To add a new user group, select Add Group from the toolbar. A window similar to Figure 15.4, “New Group” appears. Type the name of the new group. To specify a group ID for the new group, select Specify group ID manually and select the GID. Note that Red Hat Enterprise Linux also reserves group IDs lower than 500 for system groups.
New Group
Creating a new group
Figure 15.4. New Group

Click OK to create the group. The new group appears in the group list.

15.1.3. Modifying Group Properties

To view the properties of an existing group, select the group from the group list and click Properties from the menu (or choose File > Properties from the pulldown menu). A window similar to Figure 15.5, “Group Properties” appears.
Group Properties
Modifying group properties
Figure 15.5. Group Properties

The Group Users tab displays which users are members of the group. Use this tab to add or remove users from the group. Click OK to save your changes.

15.2. User and Group Management Tools

Managing users and groups can be tiresome; this is why Red Hat Enterprise Linux provides tools and conventions to make this task easier to manage.
The easiest way to manage users and groups is through the graphical application, User Manager (system-config-users). For more information on User Manager, refer to Section 15.1, “User and Group Configuration”.
The following command line tools can also be used to manage users and groups:
  • useradd, usermod, and userdel — Industry-standard methods of adding, deleting and modifying user accounts
  • groupadd, groupmod, and groupdel — Industry-standard methods of adding, deleting, and modifying user groups
  • gpasswd — Industry-standard method of administering the /etc/group file
  • pwck, grpck — Tools used for the verification of the password, group, and associated shadow files
  • pwconv, pwunconv — Tools used for the conversion of passwords to shadow passwords and back to standard passwords

15.2.1. Command Line Configuration

If you prefer command line tools or do not have the X Window System installed, use following to configure users and groups.

Adding a User

To add a user to the system:
  1. Issue the useradd command to create a locked user account: 
    useradd <username>
  2. Unlock the account by issuing the passwd command to assign a password and set password aging guidelines: 
    passwd <username>
Command line options for useradd are detailed in Table 15.1, “ useradd Command Line Options”.
Table 15.1.  useradd Command Line Options
Option Description
-c '<comment>' <comment> can be replaced with any string. This option is generally used to specify the full name of a user.
-d <home-dir> Home directory to be used instead of default /home/<username>/
-e <date> Date for the account to be disabled in the format YYYY-MM-DD
-f <days> Number of days after the password expires until the account is disabled. If 0 is specified, the account is disabled immediately after the password expires. If -1 is specified, the account is not be disabled after the password expires.
-g <group-name> Group name or group number for the user's default group. The group must exist prior to being specified here.
-G <group-list> List of additional (other than default) group names or group numbers, separated by commas, of which the user is a member. The groups must exist prior to being specified here.
-m Create the home directory if it does not exist.
-M Do not create the home directory.
-N Do not create a user private group for the user.
-p <password> The password encrypted with crypt
-r Create a system account with a UID less than 500 and without a home directory
-s User's login shell, which defaults to /bin/bash
-u <uid> User ID for the user, which must be unique and greater than 499

Adding a Group

To add a group to the system, use the command groupadd: 
groupadd <group-name>
Command line options for groupadd are detailed in Table 15.2, “ groupadd Command Line Options”.
Table 15.2.  groupadd Command Line Options
Option Description
-f, --force When used with -g <gid> and <gid> already exists, groupadd will choose another unique <gid> for the group.
-g <gid> Group ID for the group, which must be unique and greater than 499
-K, --key KEY=VALUE override /etc/login.defs defaults
-o, --non-unique allow to create groups with duplicate
-p, --password PASSWORD use this encrypted password for the new group
-r Create a system group with a GID less than 500

Password Aging

For security reasons, it is advisable to require users to change their passwords periodically. This can be done when adding or editing a user on the Password Info tab of the User Manager.
To configure password expiration for a user from a shell prompt, use the chage command with an option from Table 15.3, “ chage Command Line Options”, followed by the username.

Important

Shadow passwords must be enabled to use the chage command. For more information, see Section 15.6, “Shadow Passwords”.
Table 15.3.  chage Command Line Options
Option Description
-d <days> Specifies the number of days since January 1, 1970 the password was changed
-E <date> Specifies the date on which the account is locked, in the format YYYY-MM-DD. Instead of the date, the number of days since January 1, 1970 can also be used.
-I <days> Specifies the number of inactive days after the password expiration before locking the account. If the value is 0, the account is not locked after the password expires.
-l Lists current account aging settings.
-m <days> Specify the minimum number of days after which the user must change passwords. If the value is 0, the password does not expire.
-M <days> Specify the maximum number of days for which the password is valid. When the number of days specified by this option plus the number of days specified with the -d option is less than the current day, the user must change passwords before using the account.
-W <days> Specifies the number of days before the password expiration date to warn the user.

Tip

If the chage command is followed directly by a username (with no options), it displays the current password aging values and allows them to be changed interactively.
You can configure a password to expire the first time a user logs in. This forces users to change passwords immediately.
  1. Set up an initial password — There are two common approaches to this step. The administrator can assign a default password or assign a null password.
    To assign a default password, use the following steps:
    • Start the command line Python interpreter with the python command. It displays the following: 
      Python 2.4.3 (#1, Jul 21 2006, 08:46:09)
[GCC 4.1.1 20060718 (Application Stack 4.1.1-9)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>
    • At the prompt, type the following commands. Replace <password> with the password to encrypt and <salt> with a random combination of at least 2 of the following: any alphanumeric character, the slash (/) character or a dot (.): 
      import crypt; print crypt.crypt("<password>","<salt>")
      The output is the encrypted password, similar to '12CsGd8FRcMSM'.
    • Press Ctrl-D to exit the Python interpreter.
    • At the shell, enter the following command (replacing <encrypted-password> with the encrypted output of the Python interpreter): 
      usermod -p "<encrypted-password>" <username>
    Alternatively, you can assign a null password instead of an initial password. To do this, use the following command: 
    usermod -p "" username

    Caution

    Using a null password, while convenient, is a highly unsecure practice, as any third party can log in first and access the system using the unsecure username. Always make sure that the user is ready to log in before unlocking an account with a null password.
  2. Force immediate password expiration — Type the following command: 
    chage -d 0 username
    This command sets the value for the date the password was last changed to the epoch (January 1, 1970). This value forces immediate password expiration no matter what password aging policy, if any, is in place.
Upon the initial log in, the user is now prompted for a new password.

15.2.2. Explaining the Process

The following steps illustrate what happens if the command useradd juan is issued on a system that has shadow passwords enabled:
  1. A new line for juan is created in /etc/passwd. 
    juan:x:501:501::/home/juan:/bin/bash
    The line has the following characteristics:
    • It begins with the username juan.
    • There is an x for the password field indicating that the system is using shadow passwords.
    • A UID greater than 499 is created. Under Red Hat Enterprise Linux. UIDs and GIDs below 500 are reserved for system use. These should not be assigned to users.
    • A GID greater than 499 is created.
    • The optional GECOS information is left blank.
    • The home directory for juan is set to /home/juan/.
    • The default shell is set to /bin/bash.
  2. A new line for juan is created in /etc/shadow. 
    juan:!!:14798:0:99999:7:::
    The line has the following characteristics:
    • It begins with the username juan.
    • Two exclamation points (!!) appear in the password field of the /etc/shadow file, which locks the account.

      Note

      If an encrypted password is passed using the -p flag, it is placed in the /etc/shadow file on the new line for the user.
    • The password is set to never expire.
  3. A new line for a group named juan is created in /etc/group. 
    juan:x:501:
    A group with the same name as a user is called a user private group. For more information on user private groups, refer to Section 15.1.1, “Adding a New User”.
    The line created in /etc/group has the following characteristics:
    • It begins with the group name juan.
    • An x appears in the password field indicating that the system is using shadow group passwords.
    • The GID matches the one listed for user juan in /etc/passwd.
  4. A new line for a group named juan is created in /etc/gshadow. 
    juan:!::
    The line has the following characteristics:
    • It begins with the group name juan.
    • An exclamation point (!) appears in the password field of the /etc/gshadow file, which locks the group.
    • All other fields are blank.
  5. A directory for user juan is created in the /home/ directory. 
    ls -l /home
              drwx------. 4 juan juan 4096 Jul 9 14:55 juan
    This directory is owned by user juan and group juan. It has read, write, and execute privileges only for the user juan. All other permissions are denied.
  6. The files within the /etc/skel/ directory (which contain default user settings) are copied into the new /home/juan/ directory.
At this point, a locked account called juan exists on the system. To activate it, the administrator must next assign a password to the account using the passwd command and, optionally, set password aging guidelines.

15.3. Standard Users

Table 15.4, “Standard Users” lists the standard users configured in the /etc/passwd file by an Everything installation. The groupid (GID) in this table is the primary group for the user. See Section 15.4, “Standard Groups” for a listing of standard groups.
Table 15.4. Standard Users
User UID GID Home Directory Shell Packages
root 0 0 /root /bin/bash setup
bin 1 1 /bin /sbin/nologin setup
daemon 2 2 /sbin /sbin/nologin setup
sys - 3 - - setup
adm 3 4 /var/adm /bin/bash setup
tty - 5 - - setup
disk - 6 - - setup
lp 4 7 /var/spool/lpd /sbin/nologin setup
mem - 8 - - setup
kmem - 9 - - setup
wheel - 10 - - setup
cdrom - 11 - - udev,MAKEDEV
sync 5 (0) /sbin /bin/sync setup
shutdown 6 (0) /sbin /sbin/shutdown setup
halt 7 (0) /sbin /sbin/halt setup
mail 8 12 /var/spool/mail /sbin/nologin setup
news 9 13 /var/spool/news /sbin/nologin setup
uucp 10 14 /var/spool/uucp /sbin/nologin setup
operator 11 (0) /root /sbin/nologin setup
games 12 (100) /usr/games /sbin/nologin setup
gopher 13 30 /usr/lib/gopher-data /sbin/nologin setup
ftp 14 50 /var/ftp /sbin/nologin setup
man - 15 - - setup
oprofile 16 16 /home/oprofile /sbin/nologin oprofile
pkiuser 17 17 /usr/share/pki /sbin/nologin pki-ca,rhpki-ca
dialout - 18 - - udev,MAKEDEV
floppy - 19 - - dev,MAKEDEV
games - 20 - - setup
slocate - 21 - - slocate
utmp - 22 - - initscripts,libutempter
squid 23 23 /var/spool/squid /dev/null squid
pvm 24 24 /usr/share/pvm3 /bin/bash pvm
named 25 25 /var/named /bin/false bind
postgres 26 26 /var/lib/pgsql /bin/bash postgresql-server
mysql 27 27 /var/lib/mysql /bin/bash mysql
nscd 28 28 / /bin/false nscd
rpcuser 29 29 /var/lib/nfs /bin/false nfs-utils
console - 31 - - dev
rpc 32 32 / /bin/false portmap
amanda 33 (6) /var/lib/amanda /bin/false amanda
tape - 33 - - udev,MAKEDEV
netdump 34 34 /var/crash /bin/bash netdump-client, netdump-server
utempter - 35 - - libutempter
vdsm 36 - / /bin/bash kvm, vdsm
kvm - 36 - - kvm, vdsm, libvirt
rpm 37 37 /var/lib/rpm /bin/bash rpm
ntp 38 38 /etc/ntp /sbin/nologin ntp
video - 39 - - setup
dip - 40 - - setup
mailman 41 41 /var/mailman /bin/false mailman
gdm 42 42 /var/gdm /bin/bash gdm
xfs 43 43 /etc/X11/fs /bin/false XFree86-xfs
pppusers - 44 - - linuxconf
popusers - 45 - - linuxconf
slipusers - 46 - - linuxconf
mailnull 47 47 /var/spool/mqueue /dev/null sendmail
apache 48 48 /var/www /bin/false apache
wnn 49 49 /home/wnn /bin/bash FreeWnn
smmsp 51 51 /var/spool/mqueue /dev/null sendmail
puppet 52 52 /var/lib/puppet /sbin/nologin puppet
tomcat 53 53 /var/lib/tomcat /sbin/nologin tomcat
lock - 54 - - lockdev
ldap 55 55 /var/lib/ldap /bin/false openldap-servers
frontpage 56 56 /var/www /bin/false mod_frontpage
nut 57 57 /var/lib/ups /bin/false nut
beagleindex 58 58 /var/cache/beagle /bin/false beagle
tss 59 59 - /sbin/nologin trousers
piranha 60 60 /etc/sysconfig/ha /dev/null piranha
prelude-manager 61 61 - /sbin/nologin prelude-manager
snortd 62 62 - /sbin/nologin snortd
audio - 63 - - setup
condor 64 64 /var/lib/condor /sbin/nologin condord
nslcd 65 (55) / /sbin/nologin nslcd
wine - 66 - - wine
pegasus 66 65 /var/lib/Pegasus /sbin/nologin tog-pegasus
webalizer 67 67 /var/www/html/usage /sbin/nologin webalizer
haldaemon 68 68 / /sbin/nologin hal
vcsa 69 69 - /sbin/nologin dev,MAKEDEV
avahi 70 70 /var/run/avahi-daemon /sbin/nologin avahi
realtime - 71 - - -
tcpdump 72 72 / /sbin/nologin tcpdump
privoxy 73 73 /etc/privoxy /bin/bash privoxy
sshd 74 74 /var/empty/sshd /sbin/nologin openssh-server
radvd 75 75 / /bin/false radvd
cyrus 76 (12) /var/imap /bin/bash cyrus-imapd
saslauth - 76 - - cyrus-imapd
arpwatch 77 77 /var/lib/arpwatch /sbin/nologin arpwatch
fax 78 78 /var/spool/fax /sbin/nologin mgetty
nocpulse 79 79 /etc/sysconfig/nocpulse /bin/bash nocpulse
desktop 80 80 - /sbin/nologin desktop-file-utils
dbus 81 81 / /sbin/nologin dbus
jonas 82 82 /var/lib/jonas /sbin/nologin jonas
clamav 83 83 /tmp /sbin/nologin clamav
screen - 84 - - screen
quaggavt - 85 - - quagga
sabayon 86 86 - /sbin/nologin sabayon
polkituser 87 87 / /sbin/nologin PolicyKit
wbpriv - 88 - - samba-common
postfix 89 89 /var/spool/postfix /bin/true postfix
postdrop - 90 - - postfix
majordomo 91 91 /usr/lib/majordomo /bin/bash majordomo
quagga 92 92 / /sbin/nologin quagga
exim 93 93 /var/spool/exim /sbin/nologin exim
distcache 94 94 / /sbin/nologin distcache
radiusd 95 95 / /bin/false freeradius
hsqldb 96 96 /var/lib/hsqldb /sbin/nologin hsqldb
dovecot 97 97 /usr/libexec/dovecot /sbin/nologin dovecot
ident 98 98 / /sbin/nologin ident
nobody 99 99 / /sbin/nologin setup
users - 100 - - setup
qemu 107 107 / /sbin/nologin libvirt
ovirt 108 108 / /sbin/nologin libvirt
saned 111 111 / /sbin/nologin sane-backends
vhostmd 112 112 /usr/share/vhostmd /sbin/nologin vhostmd
usbmuxd 113 113 / /sbin/nologin usbmuxd
bacula 133 133 /var/spool/bacula /sbin/nologin bacula
ricci 140 140 /var/lib/ricci /sbin/nologin ricci
luci 141 141 /var/lib/luci /sbin/nologin luci
stap-server 155 155 /var/lib/stap-server /sbin/nologin systemtap
avahi-autoipd 170 170 /var/lib/avahi-autoipd /sbin/nologin avahi
pulse 171 171 /var/run/pulse /sbin/nologin pulseaudio
rtkit 172 172 /proc /sbin/nologin rtkit
nfsnobody 65534[a] 65534 /var/lib/nfs /sbin/nologin nfs-utils

[a] nfsnobdy is 4294967294 on 64-bit platforms


15.4. Standard Groups

Table 15.5, “Standard Groups” lists the standard groups configured by an Everything installation. Groups are stored in the /etc/group file.
Table 15.5. Standard Groups
Group GID Members
root 0 root
bin 1 root, bin, daemon
daemon 2 root, bin, daemon
sys 3 root, bin, adm
adm 4 root, adm, daemon
tty 5
disk 6 root
lp 7 daemon, lp
mem 8
kmem 9
wheel 10 root
mail 12 mail, postfix
uucp 14 uucp
man 15
games 20
gopher 30
video 39
dip 40
ftp 50
lock 54
audio 63
nobody 99
users 100
dbus 81
usbmuxd 113
utmp 22
utempter 35
avahi-autoipd 170
floppy 19
vcsa 69
rpc 32
rtkit 499
abrt 498
nscd 28
desktop_admin_r 497
desktop_user_r 496
cdrom 11
tape 33
dialout 18
haldaemon 68 haldaemon
apache 48
ldap 55
saslauth 495
postdrop 90
postfix 89
avahi 70
ntp 38
rpcuser 29
nfsnobody 4294967294
pulse 494
pulse-access 493
fuse 492
gdm 42
stapdev 491
stapusr 490
sshd 74
tcpdump 72
slocate 21
dovecot 97
dovenull 489
mailnull 47
smmsp 51

15.5. User Private Groups

Red Hat Enterprise Linux uses a user private group (UPG) scheme, which makes UNIX groups easier to manage.
A UPG is created whenever a new user is added to the system. A UPG has the same name as the user for which it was created and that user is the only member of the UPG.
UPGs make it safe to set default permissions for a newly created file or directory, allowing both the user and the group of that user to make modifications to the file or directory.
The setting which determines what permissions are applied to a newly created file or directory is called a umask and is configured in the /etc/bashrc file. Traditionally on UNIX systems, the umask is set to 022, which allows only the user who created the file or directory to make modifications. Under this scheme, all other users, including members of the creator's group, are not allowed to make any modifications. However, under the UPG scheme, this "group protection" is not necessary since every user has their own private group.

15.5.1. Group Directories

System administrators usually like to create a group for each major project and assign people to the group when they need to access that project's files. With this traditional scheme, file managing is difficult; when someone creates a file, it is associated with the primary group to which they belong. When a single person works on multiple projects, it becomes difficult to associate the right files with the right group. However, with the UPG scheme, groups are automatically assigned to files created within a directory with the setgid bit set. The setgid bit makes managing group projects that share a common directory very simple because any files a user creates within the directory are owned by the group which owns the directory.
For example, a group of people need to work on files in the /usr/share/emacs/site-lisp/ directory. Some people are trusted to modify the directory, but not everyone. First create an emacs group, as in the following command: 
/usr/sbin/groupadd emacs
To associate the contents of the directory with the emacs group, type: 
chown -R root.emacs /usr/share/emacs/site-lisp
Now, it is possible to add the right users to the group with the gpasswd command: 
/usr/bin/gpasswd -a <username> emacs
To allow users to create files within the directory, use the following command: 
chmod 775 /usr/share/emacs/site-lisp
When a user creates a new file, it is assigned the group of the user's default private group. Next, set the setgid bit, which assigns everything created in the directory the same group permission as the directory itself (emacs). Use the following command: 
chmod 2775 /usr/share/emacs/site-lisp
At this point, because the default umask of each user is 002, all members of the emacs group can create and edit files in the /usr/share/emacs/site-lisp/ directory without the administrator having to change file permissions every time users write new files.
The command ls -l /usr/share/emacs/ displays the current settings: 
        total 4
drwxrwsr-x. 2 root emacs 4096 May 18 15:41 site-lisp

15.6. Shadow Passwords

In multiuser environments it is very important to use shadow passwords (provided by the shadow-utils package). Doing so enhances the security of system authentication files. For this reason, the installation program enables shadow passwords by default.
The following list shows the advantages shadow passwords have over the traditional way of storing passwords on UNIX-based systems:
  • Improves system security by moving encrypted password hashes from the world-readable /etc/passwd file to /etc/shadow, which is readable only by the root user.
  • Stores information about password aging.
  • Allows the /etc/login.defs file to enforce security policies.
Most utilities provided by the shadow-utils package work properly whether or not shadow passwords are enabled. However, since password aging information is stored exclusively in the /etc/shadow file, any commands which create or modify password aging information do not work.
The following is a list of commands which do not work without first enabling shadow passwords:
  • chage
  • gpasswd
  • /usr/sbin/usermod -e or -f options
  • /usr/sbin/useradd -e or -f options

15.7. Additional Resources

For more information about users and groups, and tools to manage them, refer to the following resources.

15.7.1. Installed Documentation

  • Related man pages — There are a number of man pages for the various applications and configuration files involved with managing users and groups. Some of the more important man pages have been listed here:
    User and Group Administrative Applications
    • man chage — A command to modify password aging policies and account expiration.
    • man gpasswd — A command to administer the /etc/group file.
    • man groupadd — A command to add groups.
    • man grpck — A command to verify the /etc/group file.
    • man groupdel — A command to remove groups.
    • man groupmod — A command to modify group membership.
    • man pwck — A command to verify the /etc/passwd and /etc/shadow files.
    • man pwconv — A tool to convert standard passwords to shadow passwords.
    • man pwunconv — A tool to convert shadow passwords to standard passwords.
    • man useradd — A command to add users.
    • man userdel — A command to remove users.
    • man usermod — A command to modify users.
    Configuration Files
    • man 5 group — The file containing group information for the system.
    • man 5 passwd — The file containing user information for the system.
    • man 5 shadow — The file containing passwords and account expiration information for the system.

Chapter 16. Automated Tasks

16.1. Cron and Anacron
16.1.1. Starting and Stopping the Service
16.1.2. Configuring Anacron Jobs
16.1.3. Configuring Cron Jobs
16.1.4. Controlling Access to Cron
16.1.5. Black/White Listing of Cron Jobs
16.2. At and Batch
16.2.1. Configuring At Jobs
16.2.2. Configuring Batch Jobs
16.2.3. Viewing Pending Jobs
16.2.4. Additional Command Line Options
16.2.5. Controlling Access to At and Batch
16.2.6. Starting and Stopping the Service
16.3. Additional Resources
16.3.1. Installed Documentation
In Linux, tasks, which are also known as jobs, can be configured to run automatically within a specified period of time, on a specified date, or when the system load average is below a specified number. Red Hat Enterprise Linux is pre-configured to run important system tasks to keep the system updated. For example, the slocate database used by the locate command is updated daily. A system administrator can use automated tasks to perform periodic backups, monitor the system, run custom scripts, and more.
Red Hat Enterprise Linux comes with several automated tasks utilities: cron, at, and batch.

16.1. Cron and Anacron

Both, Cron and Anacron, are daemons that can be used to schedule the execution of recurring tasks according to a combination of the time, day of the month, month, day of the week, and week.
Cron assumes that the system is on continuously. If the system is not on when a job is scheduled, it is not executed. Cron allows jobs to be run as often as every minute. Anacron does not assume the system is always on, remembers every scheduled job, and executes it the next time the system is up. However, Anacron can only run a job once a day. To schedule reccurring jobs, refer to Section 16.1.2, “Configuring Anacron Jobs” or Section 16.1.3, “Configuring Cron Jobs”. To schedule one-time jobs, refer to Section 16.2, “At and Batch”.
To use the cron service, the cronie RPM package must be installed and the crond service must be running. anacron is a sub-package of cronie. To determine if these packages are installed, use the rpm -q cronie cronie-anacron command.

16.1.1. Starting and Stopping the Service

To determine if the service is running, use the command /sbin/service crond status. To start the cron service, use the command /sbin/service crond start. To stop the service, use the command /sbin/service crond stop. It is recommended that you start the service at boot time. Refer to Chapter 7, Controlling Access to Services for details on starting the cron service automatically at boot time.

16.1.2. Configuring Anacron Jobs

The main configuration file to schedule jobs is /etc/anacrontab (only root is allowed to modify this file), which contains the following lines: 
SHELL=/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
# the maximal random delay added to the base delay of the jobs
RANDOM_DELAY=45
# the jobs will be started during the following hours only
START_HOURS_RANGE=3-22

#period in days   delay in minutes   job-identifier   command
1         5     cron.daily    nice run-parts /etc/cron.daily
7         25    cron.weekly   nice run-parts /etc/cron.weekly
@monthly  45    cron.monthly  nice run-parts /etc/cron.monthly
The first three lines are variables used to configure the environment in which the anacron tasks are run. The SHELL variable tells the system which shell environment to use (in this example the bash shell). The PATH variable defines the path used to execute commands. The output of the anacron jobs are emailed to the username defined with the MAILTO variable. If the MAILTO variable is not defined, (i.e. is empty, MAILTO=), email is not sent.
The next two lines are variables that modify the time for each scheduled job. The RANDOM_DELAY variable denotes the maximum number of minutes that will be added to the delay in minutes variable which is specified for each job. The minimum delay value is set, by default, to 6 minutes. A RANDOM_DELAY set to 12 would therefore add, randomly, between 6 and 12 minutes to the delay in minutes for each job in that particular anacrontab. RANDOM_DELAY can also be set to a value below 6, or even 0. When set to 0, no random delay is added. This proves to be useful when, for example, more computers that share one network connection need to download the same data every day. The START_HOURS_RANGE variable defines an interval (in hours) when scheduled jobs can be run. In case this time interval is missed, for example, due to a power down, then scheduled jobs are not executed that day.
The rest of the lines in the /etc/anacrontab file represent scheduled jobs and have the following format: 
period in days   delay in minutes   job-identifier   command
  • period in days — specifies the frequency of execution of a job in days. This variable can be represented by an integer or a macro (@daily, @weekly, @monthly), where @daily denotes the same value as the integer 1, @weekly the same as 7, and @monthly specifies that the job is run once a month, independent on the length of the month.
  • delay in minutes — specifies the number of minutes anacron waits, if necessary, before executing a job. This variable is represented by an integer where 0 means no delay.
  • job-identifier — specifies a unique name of a job which is used in the log files.
  • command — specifies the command to execute. The command can either be a command such as ls /proc >> /tmp/proc or a command to execute a custom script.
Any lines that begin with a hash sign (#) are comments and are not processed.

16.1.2.1. Examples of Anacron Jobs

The following example shows a simple /etc/anacrontab file: 
SHELL=/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root

# the maximal random delay added to the base delay of the jobs
RANDOM_DELAY=30
# the jobs will be started during the following hours only
START_HOURS_RANGE=16-20

#period in days   delay in minutes   job-identifier   command
1         20    dailyjob      nice run-parts /etc/cron.daily
7         25    weeklyjob     /etc/weeklyjob.bash
@monthly  45    monthlyjob    ls /proc >> /tmp/proc
All jobs defined in this anacrontab file are randomly delayed by 6-30 minutes and can be executed between 16:00 and 20:00. Thus, the first defined job will run anywhere between 16:26 and 16:50 every day. The command specified for this job will execute all present programs in the /etc/cron.daily directory (using the run-parts script which takes a directory as a command-line argument and sequentially executes every program within that directory). The second specified job will be executed once a week and will execute the weeklyjob.bash script in the /etc directory. The third job is executed once a month and runs a command to write the contents of the /proc to the /tmp/proc file (e.g. ls /proc >> /tmp/proc).
16.1.2.1.1. Disabling Anacron
In case your system is continuously on and you do not require anacron to run your scheduled jobs, you may uninstall the cronie-anacron package. Thus, you will be able to define jobs using crontabs only.

16.1.3. Configuring Cron Jobs

The configuration file to configure cron jobs, /etc/crontab (only root is allowed to modify this file), contains the following lines: 
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/
# For details see man 4 crontabs
# Example of job definition:
# .---------------- minute (0 - 59)
# | .------------- hour (0 - 23)
# | | .---------- day of month (1 - 31)
# | | | .------- month (1 - 12) OR jan,feb,mar,apr ...
# | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# | | | | |
# * * * * * user command to be executed
The first three lines contain the same variables as an anacrontab file, SHELL, PATH and MAILTO. For more information about these variables, refer to Section 16.1.2, “Configuring Anacron Jobs”. The fourth line contains the HOME variable. The HOME variable can be used to set the home directory to use when executing commands or scripts.
The rest of the lines in the /etc/crontab file represent scheduled jobs and have the following format: 
minute   hour   day   month   day of week   user   command
  • minute — any integer from 0 to 59
  • hour — any integer from 0 to 23
  • day — any integer from 1 to 31 (must be a valid day if a month is specified)
  • month — any integer from 1 to 12 (or the short name of the month such as jan or feb)
  • day of week — any integer from 0 to 7, where 0 or 7 represents Sunday (or the short name of the week such as sun or mon)
  • user — specifies the user under which the jobs are run
  • command — the command to execute (the command can either be a command such as ls /proc >> /tmp/proc or the command to execute a custom script)
For any of the above values, an asterisk (*) can be used to specify all valid values. For example, an asterisk for the month value means execute the command every month within the constraints of the other values.
A hyphen (-) between integers specifies a range of integers. For example, 1-4 means the integers 1, 2, 3, and 4.
A list of values separated by commas (,) specifies a list. For example, 3, 4, 6, 8 indicates those four specific integers.
The forward slash (/) can be used to specify step values. The value of an integer can be skipped within a range by following the range with /<integer>. For example, 0-59/2 can be used to define every other minute in the minute field. Step values can also be used with an asterisk. For instance, the value */3 can be used in the month field to run the task every third month.
Any lines that begin with a hash sign (#) are comments and are not processed.
Users other than root can configure cron tasks by using the crontab utility. All user-defined crontabs are stored in the /var/spool/cron/ directory and are executed using the usernames of the users that created them. To create a crontab as a user, login as that user and type the command crontab -e to edit the user's crontab using the editor specified by the VISUAL or EDITOR environment variable. The file uses the same format as /etc/crontab. When the changes to the crontab are saved, the crontab is stored according to username and written to the file /var/spool/cron/username . To list the contents of your own personal crontab file, use the crontab -l command.

Note

When using the crontab utility, there is no need to specify a user when defining a job.
The /etc/cron.d/ directory contains files that have the same syntax as the /etc/crontab file. Only root is allowed to create and modify files in this directory.

Note

The cron daemon checks the /etc/anacrontab file, the /etc/crontab file, the /etc/cron.d/ directory, and the /var/spool/cron/ directory every minute for any changes. If any changes are found, they are loaded into memory. Thus, the daemon does not need to be restarted if an anacrontab or a crontab file is changed.

16.1.4. Controlling Access to Cron

The /etc/cron.allow and /etc/cron.deny files are used to restrict access to cron. The format of both access control files is one username on each line. Whitespace is not permitted in either file. The cron daemon (crond) does not have to be restarted if the access control files are modified. The access control files are checked each time a user tries to add or delete a cron job.
The root user can always use cron, regardless of the usernames listed in the access control files.
If the file cron.allow exists, only users listed in it are allowed to use cron, and the cron.deny file is ignored.
If cron.allow does not exist, users listed in cron.deny are not allowed to use cron.
Access can also be controlled through Pluggable Authentication Modules (PAM). These settings are stored in /etc/security/access.conf. For example, adding the following line in this file forbids creating crontabs for all users except the root user: 
-:ALL EXCEPT root :cron
The forbidden jobs are logged in an appropriate log file or, when using “crontab -e”, returned to the standard output. For more information, refer to access.conf.5 (i.e. man 5 access.conf).

16.1.5. Black/White Listing of Cron Jobs

Black/White listing of jobs is used to omit parts of the defined jobs that do not need to be executed. When calling the run-parts script on a cron folder, such as /etc/cron.daily, we can define which of the programs in this folder will not be executed by run-parts.
To define a black list, create a jobs.deny file in the folder that run-parts will be executing from. For example, if we need to omit a particular program from /etc/cron.daily, then, a file /etc/cron.daily/jobs.deny has to be created. In this file, specify the names of the omitted programs from the same directory. These will not be executed when a command, such as run-parts /etc/cron.daily, is executed by a specific job.
To define a white list, create a jobs.allow file.
The principles of jobs.deny and jobs.allow are the same as those of cron.deny and cron.allow described in section Section 16.1.4, “Controlling Access to Cron”.

16.2. At and Batch

While cron is used to schedule recurring tasks, the at command is used to schedule a one-time task at a specific time and the batch command is used to schedule a one-time task to be executed when the systems load average drops below 0.8.
To use at or batch, the at RPM package must be installed, and the atd service must be running. To determine if the package is installed, use the rpm -q at command. To determine if the service is running, use the command /sbin/service atd status.

16.2.1. Configuring At Jobs

To schedule a one-time job at a specific time, type the command at time , where time is the time to execute the command.
The argument time can be one of the following:
  • HH:MM format — For example, 04:00 specifies 4:00 a.m. If the time is already past, it is executed at the specified time the next day.
  • midnight — Specifies 12:00 a.m.
  • noon — Specifies 12:00 p.m.
  • teatime — Specifies 4:00 p.m.
  • month-name day year format — For example, January 15 2002 specifies the 15th day of January in the year 2002. The year is optional.
  • MMDDYY, MM/DD/YY, or MM.DD.YY formats — For example, 011502 for the 15th day of January in the year 2002.
  • now + time — time is in minutes, hours, days, or weeks. For example, now + 5 days specifies that the command should be executed at the same time five days from now.
The time must be specified first, followed by the optional date. For more information about the time format, read the /usr/share/doc/at-<version>/timespec text file.
After typing the at command with the time argument, the at> prompt is displayed. Type the command to execute, press Enter, and press Ctrl+D . Multiple commands can be specified by typing each command followed by the Enter key. After typing all the commands, press Enter to go to a blank line and press Ctrl+D . Alternatively, a shell script can be entered at the prompt, pressing Enter after each line in the script, and pressing Ctrl+D on a blank line to exit. If a script is entered, the shell used is the shell set in the user's SHELL environment, the user's login shell, or /bin/sh (whichever is found first).
If the set of commands or script tries to display information to standard output, the output is emailed to the user.
Use the command atq to view pending jobs. Refer to Section 16.2.3, “Viewing Pending Jobs” for more information.
Usage of the at command can be restricted. For more information, refer to Section 16.2.5, “Controlling Access to At and Batch” for details.

16.2.2. Configuring Batch Jobs

To execute a one-time task when the load average is below 0.8, use the batch command.
After typing the batch command, the at> prompt is displayed. Type the command to execute, press Enter, and press Ctrl+D . Multiple commands can be specified by typing each command followed by the Enter key. After typing all the commands, press Enter to go to a blank line and press Ctrl+D . Alternatively, a shell script can be entered at the prompt, pressing Enter after each line in the script, and pressing Ctrl+D on a blank line to exit. If a script is entered, the shell used is the shell set in the user's SHELL environment, the user's login shell, or /bin/sh (whichever is found first). As soon as the load average is below 0.8, the set of commands or script is executed.
If the set of commands or script tries to display information to standard out, the output is emailed to the user.
Use the command atq to view pending jobs. Refer to Section 16.2.3, “Viewing Pending Jobs” for more information.
Usage of the batch command can be restricted. For more information, refer to Section 16.2.5, “Controlling Access to At and Batch” for details.

16.2.3. Viewing Pending Jobs

To view pending at and batch jobs, use the atq command. The atq command displays a list of pending jobs, with each job on a line. Each line follows the job number, date, hour, job class, and username format. Users can only view their own jobs. If the root user executes the atq command, all jobs for all users are displayed.

16.2.4. Additional Command Line Options

Additional command line options for at and batch include:
Table 16.1.  at and batch Command Line Options
Option Description
-f Read the commands or shell script from a file instead of specifying them at the prompt.
-m Send email to the user when the job has been completed.
-v Display the time that the job is executed.

16.2.5. Controlling Access to At and Batch

The /etc/at.allow and /etc/at.deny files can be used to restrict access to the at and batch commands. The format of both access control files is one username on each line. Whitespace is not permitted in either file. The at daemon (atd) does not have to be restarted if the access control files are modified. The access control files are read each time a user tries to execute the at or batch commands.
The root user can always execute at and batch commands, regardless of the access control files.
If the file at.allow exists, only users listed in it are allowed to use at or batch, and the at.deny file is ignored.
If at.allow does not exist, users listed in at.deny are not allowed to use at or batch.

16.2.6. Starting and Stopping the Service

To start the at service, use the command /sbin/service atd start. To stop the service, use the command /sbin/service atd stop. It is recommended that you start the service at boot time. Refer to Chapter 7, Controlling Access to Services for details on starting the cron service automatically at boot time.

16.3. Additional Resources

To learn more about configuring automated tasks, refer to the following resources.

16.3.1. Installed Documentation

  • cron man page — contains an overview of cron.
  • crontab man pages in sections 1 and 5 — The man page in section 1 contains an overview of the crontab file. The man page in section 5 contains the format for the file and some example entries.
  • anacron man page — contains an overview of anacron.
  • anacrontab man page — contains an overview of the anacrontab file.
  • /usr/share/doc/at-<version>/timespec contains more detailed information about the times that can be specified for cron jobs.
  • at man page — description of at and batch and their command line options.

Chapter 17. Log Files

17.1. Configuring rsyslog
17.1.1. Modules
17.1.2. Global Directives
17.1.3. Rules
17.1.4. Templates
17.1.5. Filter Conditions
17.1.6. Output Channels
17.2. rsyslog Performance
17.3. Locating Log Files
17.3.1. Configuring logrotate
17.4. Viewing Log Files
17.5. Adding a Log File
17.6. Monitoring Log Files
17.7. Additional Resources
17.7.1. Installed Documentation
17.7.2. Useful Websites
Log files are files that contain messages about the system, including the kernel, services, and applications running on it. There are different log files for different information. For example, there is a default system log file, a log file just for security messages, and a log file for cron tasks.
Log files can be very useful when trying to troubleshoot a problem with the system such as trying to load a kernel driver or when looking for unauthorized log in attempts to the system. This chapter discusses where to find log files, how to view log files, and what to look for in log files.
Some log files are controlled by a daemon called rsyslogd. A list of log messages maintained by rsyslogd can be found in the /etc/rsyslog.conf configuration file.
rsyslog replaced syslogd as the default program for forwarding syslog messages over the network. rsyslog uses the basic syslog protocol and extends its functionality with enhanced filtering, encryption protected relaying of messages, various configuration options, or support for transportation via the TCP or UDP protocols.

17.1. Configuring rsyslog

The main configuration file for rsyslog is /etc/rsyslog.conf. It is essentially divided in the following parts:
  • Modules
  • Global directives
  • Rules
  • Templates
  • Filter conditions
  • Output channels
Each of these segments of the /etc/rsyslog.conf configuration file is described in the sections below.

Note

In your /etc/rsyslog.conf configuration file, any empty lines or any text following a hash sign (#) are comments and are not processed.

17.1.1. Modules

Due to its modular design, rsyslog offers a variety of modules which provide dynamic functionality. Note that modules can be written by third parties. Essentially, modules are comprised of various configuration directives that become available when a module is loaded. To load a module, use the following syntax: 
$ModLoad <MODULE>
where <MODULE> represents your desired module. For example, if you want to load the Text File Input Module (imfile — enables rsyslog to convert any standard text files into a syslog messages), specify the following line in your /etc/rsyslog.conf configuration file: 
$ModLoad imfile
rsyslog offers a number of modules which are split into these main categories:
  • Input Modules — Input modules gather messages from various sources. The name of an input module always starts with the im prefix, such as imfile, imrelp, etc.
  • Output Modules — Output modules process messages into different formats or perform various actions on them. The name of an output module always starts with the om prefix, such as omsnmp, omrelp, etc.
  • Filter Modules — Filter modules provide the ability to filter messages according to specified rules. The name of a filter module always starts with the fm prefix.
  • Parser Modules — Parser modules use the message parsers to parse message content of any received messages. The name of a parser module always starts with the pm prefix, such as pmrfc5424, pmrfc3164, etc.
  • Message Modification Modules — Message modification modules change the content of asyslog message. The message modification modules only differ in their implementation from the output and filter modules but share the same interface.
  • String Generator Modules — String generator modules generate strings based on the message content and strongly cooperate with the template feature provided by rsyslog. For more information on templates, refer to . The name of a string generator module always starts with the sm prefix, such as smfile, smtradfile, etc.
  • Library Modules — Library modules provide the ability to load and handle other loadable modules. These modules are loaded automatically by rsyslog when needed and cannot be configured by the user.
A comprehensive list of all available modules and their detailed description can be found at http://www.rsyslog.com/doc/rsyslog_conf_modules.html

Warning

Note that when rsyslog loads any modules, it provides them with access to some of its functions and data. This poses a possible security threat. To minimize security risks, use trustworthy modules only.

17.1.2. Global Directives

Global directives specify configuration options that apply to the rsyslogd daemon. All of the global directives must start with a dollar sign ($). Only one directive can be specified per line. The following is an example of a global directive that specifies the maximum size of the syslog message queue: 
$MainMsgQueueSize
The default size defined for this directive (10,000 messages) can be overridden by specifying a different value.
A comprehensive list of all available configuration directives and their detailed description can be found in /usr/share/doc/rsyslog-4.4.2/rsyslog_conf_global.html or online at http://www.rsyslog.com/doc/rsyslog_conf_global.html.

17.1.3. Rules

A rule specifies the cooperation of a selector with an action. To define a rule in your /etc/rsyslog.conf configuration file, define both, a selector and an action, on one line and separate them with one or more spaces or tabs. For more information on selectors, refer to Section 17.1.3.1, “Selectors” and for information on actions, refer to Section 17.1.3.2, “Actions”.

17.1.3.1. Selectors

Selectors filter syslog messages based on two conditions: facility and priority. The following is an example of a selector: 
<FACILITY>.<PRIORITY>
where:
  • <FACILITY> specifies the subsystem that produces a specific syslog message. For example, the mail subsystem handles all mail related syslog messages. <FACILITY> can be represented by one of these keywords: auth, authpriv, cron, daemon, kern, lpr, mail, news, syslog, user, uucp, and local0 through local7.
  • <PRIORITY> specifies a priority of a syslog message. <PRIORITY> can be represented by one of these keywords: debug, info, notice, warning, err, crit, alert, and emerg.
    By preceding any priority with an equal sign (=), you specify that only syslog messages with that priority will be selected. All other priorities will be ignored. Conversely, preceding a priority with an exclamation mark (!) selects all syslog messages but those with the defined priority. By not using either of these two extensions, you specify a selection of syslog messages with the defined priority and higher.
In addition to the keywords specified above, you may also use an asterisk (*) to define all facilities or priorities (depending on where you place the asterisk, before or after the dot). Specifying the keyword none serves for facilities with no given priorities.
To define multiple facilities and priorities, simply separate them with a comma (,). To define multiple selectors on one line, separate them with a semi-colon (;).
The following are a few examples of simple selectors: 
kern.*    # Selects all kernel syslog messages with any priority

mail.crit    # Selects all mail syslog messages with priority crit and higher.

cron.!info,!debug    # Selects all cron syslog messages except those with the info or debug priority.

17.1.3.2. Actions

Actions specify what is to be done with the messages filtered out by the defined selector. The following are some of the actions you can define in your rule:
Syslog message placement
The majority of actions specify to which log file a syslog message is saved. This is done by specifying a file path after your already defined selector. The following is a rule comprised of a selector that selects all cron syslog messages and an action that saves them into the /var/log/cron log file: 
cron.* /var/log/cron
Use a dash mark (-) as a prefix of the file path you specified if you want to omit syncing the desired log file after every syslog message is generated.
Your specified file path can be either static or dynamic. Static files are represented by a simple file path as was shown in the example above. Dynamic files are represented by a template and a question mark (?) prefix. For more information on templates, refer to Section 17.1.4, “Templates”.
Sending syslog messages over the network
rsyslog allows you to send and receive syslog messages over the network. This feature allows to administer syslog messages of multiple hosts on one machine. To forward syslog messages to a remote machine, use the following syntax: 
@[(<OPTION>,<MORE OPTIONS>)]<HOST>:[<PORT>]
where:
  • The at sign (@) indicates that the syslog messages are forwarded to a host using the UDP protocol. To use the TCP protocol, use two at signs with no space between them (@@).
  • The <OPTION> and <MORE OPTIONS> attributes can be replaced with an option such as z<NUMBER>. This option enables zlib compression for syslog messages; the <NUMBER> attribute specifies the level of compression.
  • The <HOST> attribute specifies the host which receives the selected syslog messages.
  • The <PORT> attribute specifies the host machine's port.
When specifying an IPv6 address as the hoset, enclose the address in square brackets ([, ]).
The following are some examples of actions that forward syslog messages over the network (note that all actions are preceded with a selector that selects all messages with any priority): 
*.* @192.168.0.1    # Forwards messages to 192.168.0.1 via the UDP protocol
*.* @@example.com:18    # Forwards messages to "example.com" using port 18 and the TCP protocol
*.* @(z9)[2001::1]    # Compresses messages with zlib (level 9 compression)
                      # and forwards them to 2001::1 using the UDP protocol
Sending syslog messages to specific users
rsyslog can send syslog messages to specific users by simply specifying a username of the user you wish to send the messages to. To specify more than one user, separate each username with a comma (,). To send messages to every user that is currently logged on, use an asterisk (*).
Discarding syslog messages
To discard your selected messages, use the tilde character (~). The following rule discards any cron syslog messages: 
cron.* ~
Note that any action can be followed by a template that formats the message. To specify a template, suffix an action with a semicolon (;) and specify the name of the template.

Caution

A template must be defined before it is used in an action.
For more information on templates, refer to Section 17.1.4, “Templates”.
For more information on various rsyslog actions, refer to /usr/share/doc/rsyslog-4.4.2/rsyslog_conf_actions.html.

17.1.4. Templates

17.1.5. Filter Conditions

17.1.6. Output Channels

17.2. rsyslog Performance

17.3. Locating Log Files

Most log files are located in the /var/log/ directory. Some applications such as httpd and samba have a directory within /var/log/ for their log files.
You may notice multiple files in the /var/log/ directory with numbers after them (e.g.: cron-20100906). These numbers represent a timestamp that has been added to a rotated log file. Log files are rotated so their file sizes do not become too large. The logrotate package contains a cron task that automatically rotates log files according to the /etc/logrotate.conf configuration file and the configuration files in the /etc/logrotate.d/ directory.

17.3.1. Configuring logrotate

The following is a sample /etc/logrotate.conf configuration file: 
# rotate log files weekly
weekly
# keep 4 weeks worth of backlogs
rotate 4
# uncomment this if you want your log files compressed
compress
All of the lines in the sample configuration file define global options that apply to every log file. In our example, log files are rotated weekly, rotated log files are kept for the duration of 4 weeks, and all rotated log files are compressed by gzip into the .gz format. Any lines that begin with a hash sign (#) are comments and are not processed
You may define configuration options for a specific log file and place it under the global options. However, it is advisable to create a separate configuration file for any specific log file in the /etc/logrotate.d/ directory and define any configuration options there.
The following is an example of a configuration file placed in the /etc/logrotate.d/ directory: 
/var/log/messages {
    rotate 5
    weekly
    postrotate
    /usr/bin/killall -HUP syslogd
    endscript
}
The configuration options in this file are specific for the /var/log/messages log file only. The settings specified here override the global settings where possible. Thus the rotated /var/log/messages log file will be kept for five weeks instead of four weeks as was defined in the global options.
The following is a list of some of the directives you can specify in your logrotate configuration file:
  • weekly — Specifies the rotation of log files on a weekly basis. Similar directives include:
    • daily
    • monthly
    • yearly
  • compress — Enables compression of rotated log files. Similar directives include:
    • nocompress
    • compresscmd — Specifies the command to be used for compressing.
    • uncompresscmd
    • compressext — Specifies what extension is to be used for compressing.
    • compressoptions — Lets you specify any options that may be passed to the used compression program.
    • delaycompress — Postpones the compression of log files to the next rotation of log files.
  • rotate <INTEGER> — Specifies the number of rotations a log file undergoes before it is removed or mailed to a specific address. If the value 0 is specified, old log files are removed instead of rotated.
  • mail <ADDRESS> — This option enables mailing of log files that have been rotated as many times as is defined by the rotate directive to the specified address. Similar directives include:
    • nomail
    • mailfirst — Specifies that the just-rotated log files are to be mailed, instead of the about-to-expire log files.
    • maillast — Specifies that the just-rotated log files are to be mailed, instead of the about-to-expire log files. This is the default option when mail is enabled.
For the full list of directives and various configuration options, refer to the logrotate man page (man logrotate).

17.4. Viewing Log Files

Most log files are in plain text format. You can view them with any text editor such as Vi or Emacs. Some log files are readable by all users on the system; however, root privileges are required to read most log files.
To view system log files in an interactive, real-time application, use the Log File Viewer.

Note: Installing the gnome-system-log package

In order to use the Log File Viewer, first ensure the gnome-system-log package is installed on your system by running, as root: 
~]# yum install gnome-system-log
For more information on installing packages with Yum, refer to Section 1.2.2, “Installing”.
After you have installed the gnome-system-log package, you can open the Log File Viewer by clicking on Applications → System → Log File Viewer, or type the following command at a shell prompt: 
~]$ gnome-system-log
The application only displays log files that exist; thus, the list might differ from the one shown in Figure 17.1, “ Log File Viewer ”.
Log File Viewer
Log File Viewer
Figure 17.1.  Log File Viewer

The Log File Viewer application lets you filter any existing log file. Click on Filters from the menu and select Manage Filters to define or edit your desired filter.
Log File Viewer - Filters
Log File Viewer - Filters
Figure 17.2.  Log File Viewer - Filters

Adding or editing a filter lets you define its parameters as is shown in Figure 17.3, “ Log File Viewer - Defining a Filter ”.
Log File Viewer - Defining a Filter
Log File Viewer - Defining a Filter
Figure 17.3.  Log File Viewer - Defining a Filter

When defining a filter, you can edit the following parameters:
  • Name — Specifies the name of the filter.
  • Regular Expression — Specifies the regular expression that will be applied to the log file and will attempt to match any possible strings of text in it.
  • Effect
    • Highlight — If checked, the found results will be highlighted with the selected color. You may select whether to highlight the background or the foreground of the text.
    • Hide — If checked, the found results will be hidden from the log file you are viewing.
When you have at least one filter defined, you may select it from the Filters menu and it will automatically search for the strings you have defined in the filter and highlight/hide every successful match in the log file you are currently viewing.
Log File Viewer - Enabling a Filter
Log File Viewer - Enabling a Filter
Figure 17.4.  Log File Viewer - Enabling a Filter

When you check the Show matches only option, only the matched strings will be shown in the log file you are currently viewing.

17.5. Adding a Log File

To add a log file you wish to view in the list, select File → Open. This will display the Open Log window where you can select the directory and filename of the log file you wish to view.Figure 17.5, “Log File Viewer - Adding a Log File” illustrates the Open Log window.
Log File Viewer - Adding a Log File
Log File Viewer - Adding a Log File
Figure 17.5. Log File Viewer - Adding a Log File

Click on the Open button to open the file. The file is immediately added to the viewing list where you can select it and view its contents.

Note

The Log File Viewer also allows you to open log files zipped in the .gz format.

17.6. Monitoring Log Files

Log File Viewer monitors all opened logs by default. If a new line is added to a monitored log file, the log name appears in bold in the log list. If the log file is selected or displayed, the new lines appear in bold at the bottom of the log file. Figure 17.6, “Log File Viewer - New Log Alert” illustrates a new alert in the cron log file and in the messages log file. Clicking on the cron log file displays the logs in the file with the new lines in bold.
Log File Viewer - New Log Alert
Log File Viewer - New Log Alert
Figure 17.6. Log File Viewer - New Log Alert

17.7. Additional Resources

To learn more about rsyslog, logrotate, and log files in general, refer to the following resources.

17.7.1. Installed Documentation

  • rsyslogd manual page — Type man rsyslogd to learn more about rsyslogd and its many options.
  • rsyslog.conf manual page — Type man rsyslog.conf to learn more about the /etc/rsyslog.conf configuration file and its many options.
  • /usr/share/doc/rsyslog-<version-number> — After installing the rsyslog package, this directory contains extensive documentation in the html format.
  • logrotate manual page — Type man logrotate to learn more about logrotate and its many options.

17.7.2. Useful Websites

Chapter 18. The sysconfig Directory

18.1. Files in the /etc/sysconfig/ Directory
18.1.1. /etc/sysconfig/arpwatch
18.1.2. /etc/sysconfig/authconfig
18.1.3. /etc/sysconfig/autofs
18.1.4. /etc/sysconfig/clock
18.1.5. /etc/sysconfig/dhcpd
18.1.6. /etc/sysconfig/firstboot
18.1.7. /etc/sysconfig/i18n
18.1.8. /etc/sysconfig/init
18.1.9. /etc/sysconfig/ip6tables-config
18.1.10. /etc/sysconfig/keyboard
18.1.11. /etc/sysconfig/ldap
18.1.12. /etc/sysconfig/named
18.1.13. /etc/sysconfig/network
18.1.14. /etc/sysconfig/ntpd
18.1.15. /etc/sysconfig/quagga
18.1.16. /etc/sysconfig/radvd
18.1.17. /etc/sysconfig/samba
18.1.18. /etc/sysconfig/selinux
18.1.19. /etc/sysconfig/sendmail
18.1.20. /etc/sysconfig/spamassassin
18.1.21. /etc/sysconfig/squid
18.1.22. /etc/sysconfig/system-config-users
18.1.23. /etc/sysconfig/vncservers
18.1.24. /etc/sysconfig/xinetd
18.2. Directories in the /etc/sysconfig/ Directory
18.3. Additional Resources
18.3.1. Installed Documentation
This chapter outlines some of the files and directories found in the /etc/sysconfig/ directory, their function, and their contents. The information in this chapter is not intended to be complete, as many of these files have a variety of options that are only used in very specific or rare circumstances.

Note

The actual content of your /etc/sysconfig/ directory depends on the programs you have installed on your machine. To find the name of the package the configuration file belongs to, type the following at a shell prompt: 
~]$ yum provides /etc/sysconfig/filename
Refer to Section 1.2.2, “Installing” for more information on how to install new packages in Red Hat Enterprise Linux.

18.1. Files in the /etc/sysconfig/ Directory

The following sections offer descriptions of files normally found in the /etc/sysconfig/ directory.

18.1.1.  /etc/sysconfig/arpwatch

The /etc/sysconfig/arpwatch file is used to pass arguments to the arpwatch daemon at boot time. By default, it contains the following option:
OPTIONS=value
Additional options to be passed to the arpwatch daemon. For example: 
OPTIONS="-u arpwatch -e root -s 'root (Arpwatch)'"

18.1.2.  /etc/sysconfig/authconfig

The /etc/sysconfig/authconfig file sets the authorization to be used on the host. By default, it contains the following options:
USEMKHOMEDIR=boolean
A boolean to enable (yes) or disable (no) creating a home directory for a user on the first login. For example: 
USEMKHOMEDIR=no
USEPAMACCESS=boolean
A boolean to enable (yes) or disable (no) the PAM authentication. For example: 
USEPAMACCESS=no
USESSSDAUTH=boolean
A boolean to enable (yes) or disable (no) the SSSD authentication. For example: 
USESSSDAUTH=no
USESHADOW=boolean
A boolean to enable (yes) or disable (no) shadow passwords. For example: 
USESHADOW=yes
USEWINBIND=boolean
A boolean to enable (yes) or disable (no) using Winbind for user account configuration. For example: 
USEWINBIND=no
USEDB=boolean
A boolean to enable (yes) or disable (no) the FAS authentication. For example: 
USEDB=no
USEFPRINTD=boolean
A boolean to enable (yes) or disable (no) the fingerprint authentication. For example: 
USEFPRINTD=yes
FORCESMARTCARD=boolean
A boolean to enable (yes) or disable (no) enforcing the smart card authentication. For example: 
FORCESMARTCARD=no
PASSWDALGORITHM=value
The password algorithm. The value can be bigcrypt, descrypt, md5, sha256, or sha512. For example: 
PASSWDALGORITHM=sha512
USELDAPAUTH=boolean
A boolean to enable (yes) or disable (no) the LDAP authentication. For example: 
USELDAPAUTH=no
USELOCAUTHORIZE=boolean
A boolean to enable (yes) or disable (no) the local authorization for local users. For example: 
USELOCAUTHORIZE=yes
USECRACKLIB=boolean
A boolean to enable (yes) or disable (no) using the CrackLib. For example: 
USECRACKLIB=yes
USEWINBINDAUTH=boolean
A boolean to enable (yes) or disable (no) the Winbind authentication. For example: 
USEWINBINDAUTH=no
USESMARTCARD=boolean
A boolean to enable (yes) or disable (no) the smart card authentication. For example: 
USESMARTCARD=no
USELDAP=boolean
A boolean to enable (yes) or disable (no) using LDAP for user account configuration. For example: 
USELDAP=no
USENIS=boolean
A boolean to enable (yes) or disable (no) using NIS for user account configuration. For example: 
USENIS=no
USEKERBEROS=boolean
A boolean to enable (yes) or disable (no) the Kerberos authentication. For example: 
USEKERBEROS=no
USESYSNETAUTH=boolean
A boolean to enable (yes) or disable (no) authenticating system accounts with network services. For example: 
USESYSNETAUTH=no
USESMBAUTH=boolean
A boolean to enable (yes) or disable (no) the SMB authentication. For example: 
USESMBAUTH=no
USESSSD=boolean
A boolean to enable (yes) or disable (no) using SSSD for obtaining user information. For example: 
USESSSD=no
USEHESIOD=boolean
A boolean to enable (yes) or disable (no) using the Hesoid name service. For example: 
USEHESIOD=no
Refer to Chapter 8, Authentication Configuration for more information on this topic.

18.1.3.  /etc/sysconfig/autofs

The /etc/sysconfig/autofs file defines custom options for the automatic mounting of devices. This file controls the operation of the automount daemons, which automatically mount file systems when you use them and unmount them after a period of inactivity. File systems can include network file systems, CD-ROM drives, diskettes, and other media.
By default, it contains the following options:
MASTER_MAP_NAME=value
The default name for the master map. For example: 
MASTER_MAP_NAME="auto.master"
TIMEOUT=value
The default mount timeout. For example: 
TIMEOUT=300
NEGATIVE_TIMEOUT=value
The default negative timeout for unsuccessful mount attempts. For example: 
NEGATIVE_TIMEOUT=60
MOUNT_WAIT=value
The time to wait for a response from mount. For example: 
MOUNT_WAIT=-1
UMOUNT_WAIT=value
The time to wait for a response from umount. For example: 
UMOUNT_WAIT=12
BROWSE_MODE=boolean
A boolean to enable (yes) or disable (no) browsing the maps. For example: 
BROWSE_MODE="no"
MOUNT_NFS_DEFAULT_PROTOCOL=value
The default protocol to be used by mount.nfs. For example: 
MOUNT_NFS_DEFAULT_PROTOCOL=4
APPEND_OPTIONS=boolean
A boolean to enable (yes) or disable (no) appending the global options instead of replacing them. For example: 
APPEND_OPTIONS="yes"
LOGGING=value
The default logging level. The value has to be either none, verbose, or debug. For example: 
LOGGING="none"
LDAP_URI=value
A space-separated list of server URIs in the form of protocol://server . For example: 
LDAP_URI="ldaps://ldap.example.com/"
LDAP_TIMEOUT=value
The synchronous API calls timeout. For example: 
LDAP_TIMEOUT=-1
LDAP_NETWORK_TIMEOUT=value
The network response timeout. For example: 
LDAP_NETWORK_TIMEOUT=8
SEARCH_BASE=value
The base Distinguished Name (DN) for the map search. For example: 
SEARCH_BASE=""
AUTH_CONF_FILE=value
The default location of the SASL authentication configuration file. For example: 
AUTH_CONF_FILE="/etc/autofs_ldap_auth.conf"
MAP_HASH_TABLE_SIZE=value
The hash table size for the map cache. For example: 
MAP_HASH_TABLE_SIZE=1024
USE_MISC_DEVICE=boolean
A boolean to enable (yes) or disable (no) using the autofs miscellaneous device. For example: 
USE_MISC_DEVICE="yes"
OPTIONS=value
Additional options to be passed to the LDAP daemon. For example: 
OPTIONS=""

18.1.4.  /etc/sysconfig/clock

The /etc/sysconfig/clock file controls the interpretation of values read from the system hardware clock. It is used by the Date/Time Properties tool, and should not be edited by hand. By default, it contains the following option:
ZONE=value
The time zone file under /usr/share/zoneinfo that /etc/localtime is a copy of. For example: 
ZONE="Europe/Prague"
Refer to Section 13.1, “Date/Time Properties Tool” for more information on the Date/Time Properties tool and its usage.

18.1.5.  /etc/sysconfig/dhcpd

The /etc/sysconfig/dhcpd file is used to pass arguments to the dhcpd daemon at boot time. By default, it contains the following options:
DHCPDARGS=value
Additional options to be passed to the dhcpd daemon. For example: 
DHCPDARGS=
Refer to Chapter 6, Dynamic Host Configuration Protocol (DHCP) for more information on DHCP and its usage.

18.1.6.  /etc/sysconfig/firstboot

The /etc/sysconfig/firstboot file defines whether to run the firstboot utility. By default, it contains the following option:
RUN_FIRSTBOOT=boolean
A boolean to enable (YES) or disable (NO) running the firstboot program. For example: 
RUN_FIRSTBOOT=NO
The first time the system boots, the init program calls the /etc/rc.d/init.d/firstboot script, which looks for the /etc/sysconfig/firstboot file. If this file does not contain the RUN_FIRSTBOOT=NO option, the firstboot program is run, guiding a user through the initial configuration of the system.

Tip: You Can Run the firstboot Program Again

To start the firstboot program the next time the system boots, change the value of RUN_FIRSTBOOT option to YES, and type the following at a shell prompt: 
~]# chkconfig firstboot on

18.1.7.  /etc/sysconfig/i18n

The /etc/sysconfig/i18n configuration file defines the default language, any supported languages, and the default system font. By default, it contains the following options:
LANG=value
The default language. For example: 
LANG="en_US.UTF-8"
SUPPORTED=value
A colon-separated list of supported languages. For example: 
SUPPORTED="en_US.UTF-8:en_US:en"
SYSFONT=value
The default system font. For example: 
SYSFONT="latarcyrheb-sun16"

18.1.8.  /etc/sysconfig/init

The /etc/sysconfig/init file controls how the system appears and functions during the boot process. By default, it contains the following options:
BOOTUP=value
The bootup style. The value has to be either color (the standard color boot display), verbose (an old style display which provides more information), or anything else for the new style display, but without ANSI formatting. For example: 
BOOTUP=color
RES_COL=value
The number of the column in which the status labels start. For example: 
RES_COL=60
MOVE_TO_COL=value
The terminal sequence to move the cursor to the column specified in RES_COL (see above). For example: 
MOVE_TO_COL="echo -en \\033[${RES_COL}G"
SETCOLOR_SUCCESS=value
The terminal sequence to set the success color. For example: 
SETCOLOR_SUCCESS="echo -en \\033[0;32m"
SETCOLOR_FAILURE=value
The terminal sequence to set the failure color. For example: 
SETCOLOR_FAILURE="echo -en \\033[0;31m"
SETCOLOR_WARNING=value
The terminal sequence to set the warning color. For example: 
SETCOLOR_WARNING="echo -en \\033[0;33m"
SETCOLOR_NORMAL=value
The terminal sequence to set the default color. For example: 
SETCOLOR_NORMAL="echo -en \\033[0;39m"
LOGLEVEL=value
The initial console logging level. The value has to be in the range from 1 (kernel panics only) to 8 (everything, including the debugging information). For example: 
LOGLEVEL=3
PROMPT=boolean
A boolean to enable (yes) or disable (no) the hotkey interactive startup. For example: 
PROMPT=yes
AUTOSWAP=boolean
A boolean to enable (yes) or disable (no) probing for devices with swap signatures. For example: 
AUTOSWAP=no
ACTIVE_CONSOLES=value
The list of active consoles. For example: 
ACTIVE_CONSOLES=/dev/tty[1-6]
SINGLE=value
The single-user mode type. The value has to be either /sbin/sulogin (a user will be prompted for a password to log in), or /sbin/sushell (the user will be logged in directly). For example: 
SINGLE=/sbin/sushell

18.1.9.  /etc/sysconfig/ip6tables-config

The /etc/sysconfig/ip6tables-config file stores information used by the kernel to set up IPv6 packet filtering at boot time or whenever the ip6tables service is started. Note that you should not modify it unless you are familiar with ip6tables rules. By default, it contains the following options:
IP6TABLES_MODULES=value
A space-separated list of helpers to be loaded after the firewall rules are applied. For example: 
IP6TABLES_MODULES="ip_nat_ftp ip_nat_irc"
IP6TABLES_MODULES_UNLOAD=boolean
A boolean to enable (yes) or disable (no) module unloading when the firewall is stopped or restarted. For example: 
IP6TABLES_MODULES_UNLOAD="yes"
IP6TABLES_SAVE_ON_STOP=boolean
A boolean to enable (yes) or disable (no) saving the current firewall rules when the firewall is stopped. For example: 
IP6TABLES_SAVE_ON_STOP="no"
IP6TABLES_SAVE_ON_RESTART=boolean
A boolean to enable (yes) or disable (no) saving the current firewall rules when the firewall is restarted. For example: 
IP6TABLES_SAVE_ON_RESTART="no"
IP6TABLES_SAVE_COUNTER=boolean
A boolean to enable (yes) or disable (no) saving the rule and chain counters. For example: 
IP6TABLES_SAVE_COUNTER="no"
IP6TABLES_STATUS_NUMERIC=boolean
A boolean to enable (yes) or disable (no) printing IP addresses and port numbers in a numeric format in the status output. For example: 
IP6TABLES_STATUS_NUMERIC="yes"
IP6TABLES_STATUS_VERBOSE=boolean
A boolean to enable (yes) or disable (no) printing information about the number of packets and bytes in the status output. For example: 
IP6TABLES_STATUS_VERBOSE="no"
IP6TABLES_STATUS_LINENUMBERS=boolean
A boolean to enable (yes) or disable (no) printing line numbers in the status output. For example: 
IP6TABLES_STATUS_LINENUMBERS="yes"

Tip: Use the ip6tables Command to Create the Rules

You can create the rules manually using the ip6tables command. Once created, type the following at a shell prompt: 
~]# service ip6tables save
This will add the rules to /etc/sysconfig/ip6tables. Once this file exists, any firewall rules saved in it persist through a system reboot or a service restart.

18.1.10.  /etc/sysconfig/keyboard

The /etc/sysconfig/keyboard file controls the behavior of the keyboard. By default, it contains the following options:
KEYTABLE=value
The name of a keytable file. The files that can be used as keytables start in the /lib/kbd/keymaps/i386/ directory, and branch into different keyboard layouts from there, all labeled value.kmap.gz. The first filename that matches the KEYTABLE setting is used. For example: 
KEYTABLE="us"
MODEL=value
The keyboard model. For example: 
MODEL="pc105+inet"
LAYOUT=value
The keyboard layout. For example: 
LAYOUT="us"
KEYBOARDTYPE=value
The keyboard type. Allowed values are pc (a PS/2 keyboard), or sun (a Sun keyboard). For example: 
KEYBOARDTYPE="pc"

18.1.11.  /etc/sysconfig/ldap

The /etc/sysconfig/ldap file holds the basic configuration for the LDAP server. By default, it contains the following options:
SLAPD_OPTIONS=value
Additional options to be passed to the slapd daemon. For example: 
SLAPD_OPTIONS="-4"
SLURPD_OPTIONS=value
Additional options to be passed to the slurpd daemon. For example: 
SLURPD_OPTIONS=""
SLAPD_LDAP=boolean
A boolean to enable (yes) or disable (no) using the LDAP over TCP (that is, ldap:///). For example: 
SLAPD_LDAP="yes"
SLAPD_LDAPI=boolean
A boolean to enable (yes) or disable (no) using the LDAP over IPC (that is, ldapi:///). For example: 
SLAPD_LDAPI="no"
SLAPD_LDAPS=boolean
A boolean to enable (yes) or disable (no) using the LDAP over TLS (that is, ldaps:///). For example: 
SLAPD_LDAPS="no"
SLAPD_URLS=value
A space-separated list of URLs. For example: 
SLAPD_URLS="ldapi:///var/lib/ldap_root/ldapi ldapi:/// ldaps:///"
SLAPD_SHUTDOWN_TIMEOUT=value
The time to wait for slapd to shut down. For example: 
SLAPD_SHUTDOWN_TIMEOUT=3
SLAPD_ULIMIT_SETTINGS=value
The parameters to be passed to ulimit before the slapd daemon is started. For example: 
SLAPD_ULIMIT_SETTINGS=""

18.1.12.  /etc/sysconfig/named

The /etc/sysconfig/named file is used to pass arguments to the named daemon at boot time. By default, it contains the following options:
ROOTDIR=value
The chroot environment under which the named daemon runs. The value has to be a full directory path. For example: 
ROOTDIR="/var/named/chroot"
Note that the chroot environment has to be configured first (type info chroot at a shell prompt for more information).
OPTIONS=value
Additional options to be passed to named. For example: 
OPTIONS="-6"
Note that you should not use the -t option. Instead, use ROOTDIR as described above.
KEYTAB_FILE=value
The keytab filename. For example: 
KEYTAB_FILE="/etc/named.keytab"
Refer to Chapter 10, The BIND DNS Server for more information on the BIND DNS server and its configuration.

18.1.13.  /etc/sysconfig/network

The /etc/sysconfig/network file is used to specify information about the desired network configuration. By default, it contains the following options:
NETWORKING=boolean
A boolean to enable (yes) or disable (no) the networking. For example: 
NETWORKING=yes
HOSTNAME=value
The hostname of the machine. For example: 
HOSTNAME=penguin.example.com
GATEWAY=value
The IP address of the network's gateway. For example: 
GATEWAY=192.168.1.0

Warning: Avoid Using Custom Init Scripts

Do not use custom init scripts to configure network settings. When performing a post-boot network service restart, custom init scripts configuring network settings that are run outside of the network init script lead to unpredictable results.

18.1.14.  /etc/sysconfig/ntpd

The /etc/sysconfig/ntpd file is used to pass arguments to the ntpd daemon at boot time. By default, it contains the following option:
OPTIONS=value
Additional options to be passed to ntpd. For example: 
OPTIONS="-u ntp:ntp -p /var/run/ntpd.pid -g"
Refer to Section 13.1.2, “Network Time Protocol Properties” or Section 13.2.2, “Network Time Protocol Setup” for more information on how to configure the ntpd daemon.

18.1.15.  /etc/sysconfig/quagga

The /etc/sysconfig/quagga file holds the basic configuration for Quagga daemons. By default, it contains the following options:
QCONFDIR=value
The directory with the configuration files for Quagga daemons. For example: 
QCONFDIR="/etc/quagga"
BGPD_OPTS=value
Additional options to be passed to the bgpd daemon. For example: 
BGPD_OPTS="-A 127.0.0.1 -f ${QCONFDIR}/bgpd.conf"
OSPF6D_OPTS=value
Additional options to be passed to the ospf6d daemon. For example: 
OSPF6D_OPTS="-A ::1 -f ${QCONFDIR}/ospf6d.conf"
OSPFD_OPTS=value
Additional options to be passed to the ospfd daemon. For example: 
OSPFD_OPTS="-A 127.0.0.1 -f ${QCONFDIR}/ospfd.conf"
RIPD_OPTS=value
Additional options to be passed to the ripd daemon. For example: 
RIPD_OPTS="-A 127.0.0.1 -f ${QCONFDIR}/ripd.conf"
RIPNGD_OPTS=value
Additional options to be passed to the ripngd daemon. For example: 
RIPNGD_OPTS="-A ::1 -f ${QCONFDIR}/ripngd.conf"
ZEBRA_OPTS=value
Additional options to be passed to the zebra daemon. For example: 
ZEBRA_OPTS="-A 127.0.0.1 -f ${QCONFDIR}/zebra.conf"
ISISD_OPTS=value
Additional options to be passed to the isisd daemon. For example: 
ISISD_OPTS="-A ::1 -f ${QCONFDIR}/isisd.conf"
WATCH_OPTS=value
Additional options to be passed to the watchquagga daemon. For example: 
WATCH_OPTS="-Az -b_ -r/sbin/service_%s_restart -s/sbin/service_%s_start -k/sbin/service_%s_stop"
WATCH_DAEMONS=value
A space separated list of monitored daemons. For example: 
WATCH_DAEMONS="zebra bgpd ospfd ospf6d ripd ripngd"

18.1.16.  /etc/sysconfig/radvd

The /etc/sysconfig/radvd file is used to pass arguments to the radvd daemon at boot time. By default, it contains the following option:
OPTIONS=value
Additional options to be passed to the radvd daemon. For example: 
OPTIONS="-u radvd"

18.1.17.  /etc/sysconfig/samba

The /etc/sysconfig/samba file is used to pass arguments to the Samba daemons at boot time. By default, it contains the following options:
SMBDOPTIONS=value
Additional options to be passed to smbd. For example: 
SMBDOPTIONS="-D"
NMBDOPTIONS=value
Additional options to be passed to nmbd. For example: 
NMBDOPTIONS="-D"
WINBINDOPTIONS=value
Additional options to be passed to winbindd. For example: 
WINBINDOPTIONS=""

18.1.18.  /etc/sysconfig/selinux

The /etc/sysconfig/selinux file contains the basic configuration options for SELinux. It is a symbolic link to /etc/selinux/config, and by default, it contains the following options:
SELINUX=value
The security policy. The value can be either enforcing (the security policy is always enforced), permissive (instead of enforcing the policy, appropriate warnings are displayed), or disabled (no policy is used). For example: 
SELINUX=enforcing
SELINUXTYPE=value
The protection type. The value can be either targeted (the targeted processes are protected), or mls (the Multi Level Security protection). For example: 
SELINUXTYPE=targeted

18.1.19.  /etc/sysconfig/sendmail

The /etc/sysconfig/sendmail is used to set the default values for the Sendmail application. By default, it contains the following values:
DAEMON=boolean
A boolean to enable (yes) or disable (no) running sendmail as a daemon. For example: 
DAEMON=yes
QUEUE=value
The interval at which the messages are to be processed. For example: 
QUEUE=1h
Refer to Section 12.3.2, “Sendmail” for more information on Sendmail and its configuration.

18.1.20.  /etc/sysconfig/spamassassin

The /etc/sysconfig/spamassassin file is used to pass arguments to the spamd daemon (a daemonized version of Spamassassin) at boot time. By default, it contains the following option:
SPAMDOPTIONS=value
Additional options to be passed to the spamd daemon. For example: 
SPAMDOPTIONS="-d -c -m5 -H"
Refer to Section 12.4.2.6, “Spam Filters” for more information on Spamassassin and its configuration.

18.1.21.  /etc/sysconfig/squid

The /etc/sysconfig/squid file is used to pass arguments to the squid daemon at boot time. By default, it contains the following options:
SQUID_OPTS=value
Additional options to be passed to the squid daemon. For example: 
SQUID_OPTS=""
SQUID_SHUTDOWN_TIMEOUT=value
The time to wait for squid daemon to shut down. For example: 
SQUID_SHUTDOWN_TIMEOUT=100
SQUID_CONF=value
The default configuration file. For example: 
SQUID_CONF="/etc/squid/squid.conf"

18.1.22.  /etc/sysconfig/system-config-users

The /etc/sysconfig/system-config-users file is the configuration file for the User Manager utility, and should not be edited by hand. By default, it contains the following options:
FILTER=boolean
A boolean to enable (true) or disable (false) filtering of system users. For example: 
FILTER=true
ASSIGN_HIGHEST_UID=boolean
A boolean to enable (true) or disable (false) assigning the highest available UID to newly added users. For example: 
ASSIGN_HIGHEST_UID=true
ASSIGN_HIGHEST_GID=boolean
A boolean to enable (true) or disable (false) assigning the highest available GID to newly added groups. For example: 
ASSIGN_HIGHEST_GID=true
PREFER_SAME_UID_GID=boolean
A boolean to enable (true) or disable (false) using the same UID and GID for newly added users when possible. For example: 
PREFER_SAME_UID_GID=true
Refer to Section 15.1, “User and Group Configuration” for more information on User Manager and its usage.

18.1.23.  /etc/sysconfig/vncservers

The /etc/sysconfig/vncservers file configures the way the Virtual Network Computing (VNC) server starts up. By default, it contains the following options:
VNCSERVERS=value
A list of space separated display:username pairs. For example: 
VNCSERVERS="2:myusername"
VNCSERVERARGS[display]=value
Additional arguments to be passed to the VNC server running on the specified display. For example: 
VNCSERVERARGS[2]="-geometry 800x600 -nolisten tcp -localhost"

18.1.24.  /etc/sysconfig/xinetd

The /etc/sysconfig/xinetd file is used to pass arguments to the xinetd daemon at boot time. By default, it contains the following options:
EXTRAOPTIONS=value
Additional options to be passed to xinetd. For example: 
EXTRAOPTIONS=""
XINETD_LANG=value
The locale information to be passed to every service started by xinetd. Note that to remove locale information from the xinetd environment, you can use an empty string ("") or none. For example: 
XINETD_LANG="en_US"
Refer to Chapter 7, Controlling Access to Services for more information on how to configure the xinetd services.

18.2. Directories in the /etc/sysconfig/ Directory

The following directories are normally found in /etc/sysconfig/.
/etc/sysconfig/cbq/
This directory contains the configuration files needed to do Class Based Queuing for bandwidth management on network interfaces. CBQ divides user traffic into a hierarchy of classes based on any combination of IP addresses, protocols, and application types.
/etc/sysconfig/networking/
This directory is used by the Network Administration Tool (system-config-network), and its contents should not be edited manually. For more information about configuring network interfaces using the Network Administration Tool, refer to Chapter 5, Network Configuration.
/etc/sysconfig/network-scripts/
This directory contains the following network-related configuration files:
  • Network configuration files for each configured network interface, such as ifcfg-eth0 for the eth0 Ethernet interface.
  • Scripts used to bring network interfaces up and down, such as ifup and ifdown.
  • Scripts used to bring ISDN interfaces up and down, such as ifup-isdn and ifdown-isdn.
  • Various shared network function scripts which should not be edited directly.
For more information on the /etc/sysconfig/network-scripts/ directory, refer to Chapter 4, Network Interfaces.
/etc/sysconfig/rhn/
This directory contains the configuration files and GPG keys for Red Hat Network. No files in this directory should be edited by hand. For more information on Red Hat Network, refer to the Red Hat Network website online at https://rhn.redhat.com/.

18.3. Additional Resources

This chapter is only intended as an introduction to the files in the /etc/sysconfig/ directory. The following source contains more comprehensive information.

18.3.1. Installed Documentation

/usr/share/doc/initscripts-version/sysconfig.txt
A more authoritative listing of the files found in the /etc/sysconfig/ directory and the configuration options available for them.

Chapter 19. The proc File System

19.1. A Virtual File System
19.1.1. Viewing Virtual Files
19.1.2. Changing Virtual Files
19.2. Top-level Files within the proc File System
19.2.1. /proc/buddyinfo
19.2.2. /proc/cmdline
19.2.3. /proc/cpuinfo
19.2.4. /proc/crypto
19.2.5. /proc/devices
19.2.6. /proc/dma
19.2.7. /proc/execdomains
19.2.8. /proc/fb
19.2.9. /proc/filesystems
19.2.10. /proc/interrupts
19.2.11. /proc/iomem
19.2.12. /proc/ioports
19.2.13. /proc/kcore
19.2.14. /proc/kmsg
19.2.15. /proc/loadavg
19.2.16. /proc/locks
19.2.17. /proc/mdstat
19.2.18. /proc/meminfo
19.2.19. /proc/misc
19.2.20. /proc/modules
19.2.21. /proc/mounts
19.2.22. /proc/mtrr
19.2.23. /proc/partitions
19.2.24. /proc/slabinfo
19.2.25. /proc/stat
19.2.26. /proc/swaps
19.2.27. /proc/sysrq-trigger
19.2.28. /proc/uptime
19.2.29. /proc/version
19.3. Directories within /proc/
19.3.1. Process Directories
19.3.2. /proc/bus/
19.3.3. /proc/bus/pci
19.3.4. /proc/driver/
19.3.5. /proc/fs
19.3.6. /proc/irq/
19.3.7. /proc/net/
19.3.8. /proc/scsi/
19.3.9. /proc/sys/
19.3.10. /proc/sysvipc/
19.3.11. /proc/tty/
19.3.12. /proc/PID/
19.4. Using the sysctl Command
19.5. References
The Linux kernel has two primary functions: to control access to physical devices on the computer and to schedule when and how processes interact with these devices. The /proc/ directory (also called the proc file system) contains a hierarchy of special files which represent the current state of the kernel, allowing applications and users to peer into the kernel's view of the system.
The /proc/ directory contains a wealth of information detailing system hardware and any running processes. In addition, some of the files within /proc/ can be manipulated by users and applications to communicate configuration changes to the kernel.

Note

Later versions of the 2.6 kernel have made the /proc/ide/ and /proc/pci/ directories obsolete. The /proc/ide/ file system is now superseded by files in sysfs; to retrieve information on PCI devices, use lspci instead. For more information on sysfs or lspci, refer to their respective man pages.

19.1. A Virtual File System

Linux systems store all data as files. Most users are familiar with the two primary types of files: text and binary. But the /proc/ directory contains another type of file called a virtual file. As such, /proc/ is often referred to as a virtual file system.
Virtual files have unique qualities. Most of them are listed as zero bytes in size, but can still contain a large amount of information when viewed. In addition, most of the time and date stamps on virtual files reflect the current time and date, indicative of the fact they are constantly updated.
Virtual files such as /proc/interrupts, /proc/meminfo, /proc/mounts, and /proc/partitions provide an up-to-the-moment glimpse of the system's hardware. Others, like the /proc/filesystems file and the /proc/sys/ directory provide system configuration information and interfaces.
For organizational purposes, files containing information on a similar topic are grouped into virtual directories and sub-directories. Process directories contain information about each running process on the system.

19.1.1. Viewing Virtual Files

Most files within /proc/ files operate similarly to text files, storing useful system and hardware data in human-readable text format. As such, you can use cat, more, or less to view them. For example, to display information about the system's CPU, run cat /proc/cpuinfo. This will return output similar to the following: 
processor	: 0
vendor_id	: AuthenticAMD
cpu family	: 5
model		: 9
model name	: AMD-K6(tm) 3D+
Processor stepping	: 1 cpu
MHz		: 400.919
cache size	: 256 KB
fdiv_bug	: no
hlt_bug		: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 1
wp		: yes
flags		: fpu vme de pse tsc msr mce cx8 pge mmx syscall 3dnow k6_mtrr
bogomips	: 799.53
Some files in /proc/ contain information that is not human-readable. To retrieve information from such files, use tools such as lspci, apm, free, and top.

Note

Some of the virtual files in the /proc/ directory are readable only by the root user.

19.1.2. Changing Virtual Files

As a general rule, most virtual files within the /proc/ directory are read-only. However, some can be used to adjust settings in the kernel. This is especially true for files in the /proc/sys/ subdirectory.
To change the value of a virtual file, use the following command:
echo value > /proc/file
For example, to change the hostname on the fly, run:
echo www.example.com > /proc/sys/kernel/hostname
Other files act as binary or Boolean switches. Typing cat /proc/sys/net/ipv4/ip_forward returns either a 0 (off or false) or a 1 (on or true). A 0 indicates that the kernel is not forwarding network packets. To turn packet forwarding on, run echo 1 > /proc/sys/net/ipv4/ip_forward.

Tip

Another command used to alter settings in the /proc/sys/ subdirectory is /sbin/sysctl. For more information on this command, refer to Section 19.4, “Using the sysctl Command”
For a listing of some of the kernel configuration files available in the /proc/sys/ subdirectory, refer to Section 19.3.9, “ /proc/sys/ ”.

19.2. Top-level Files within the proc File System

Below is a list of some of the more useful virtual files in the top-level of the /proc/ directory.

Note

In most cases, the content of the files listed in this section are not the same as those installed on your machine. This is because much of the information is specific to the hardware on which Red Hat Enterprise Linux is running for this documentation effort.

19.2.1.  /proc/buddyinfo

This file is used primarily for diagnosing memory fragmentation issues. Using the buddy algorithm, each column represents the number of pages of a certain order (a certain size) that are available at any given time. For example, for zone direct memory access (DMA), there are 90 of 2(0*PAGE_SIZE) chunks of memory. Similarly, there are 6 of 2(1*PAGE_SIZE) chunks, and 2 of 2(2*PAGE_SIZE) chunks of memory available.
The DMA row references the first 16 MB on a system, the HighMem row references all memory greater than 4 GB on a system, and the Normal row references all memory in between.
The following is an example of the output typical of /proc/buddyinfo: 
Node 0, zone      DMA     90      6      2      1      1      ...
Node 0, zone   Normal   1650    310      5      0      0      ...
Node 0, zone  HighMem      2      0      0      1      1      ...

19.2.2.  /proc/cmdline

This file shows the parameters passed to the kernel at the time it is started. A sample /proc/cmdline file looks like the following: 
ro root=/dev/VolGroup00/LogVol00 rhgb quiet 3
This tells us that the kernel is mounted read-only (signified by (ro)), located on the first logical volume (LogVol00) of the first volume group (/dev/VolGroup00). LogVol00 is the equivalent of a disk partition in a non-LVM system (Logical Volume Management), just as /dev/VolGroup00 is similar in concept to /dev/hda1, but much more extensible.
For more information on LVM used in Red Hat Enterprise Linux, refer to http://www.tldp.org/HOWTO/LVM-HOWTO/index.html.
Next, rhgb signals that the rhgb package has been installed, and graphical booting is supported, assuming /etc/inittab shows a default runlevel set to id:5:initdefault:.
Finally, quiet indicates all verbose kernel messages are suppressed at boot time.

19.2.3.  /proc/cpuinfo

This virtual file identifies the type of processor used by your system. The following is an example of the output typical of /proc/cpuinfo: 
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 15
model		: 2
model name	: Intel(R) Xeon(TM) CPU 2.40GHz
stepping	: 7 cpu
MHz		: 2392.371
cache size	: 512 KB
physical id	: 0
siblings	: 2
runqueue	: 0
fdiv_bug	: no
hlt_bug		: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 2
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca  cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
bogomips	: 4771.02
  • processor — Provides each processor with an identifying number. On systems that have one processor, only a 0 is present.
  • cpu family — Authoritatively identifies the type of processor in the system. For an Intel-based system, place the number in front of "86" to determine the value. This is particularly helpful for those attempting to identify the architecture of an older system such as a 586, 486, or 386. Because some RPM packages are compiled for each of these particular architectures, this value also helps users determine which packages to install.
  • model name — Displays the common name of the processor, including its project name.
  • cpu MHz — Shows the precise speed in megahertz for the processor to the thousandths decimal place.
  • cache size — Displays the amount of level 2 memory cache available to the processor.
  • siblings — Displays the number of sibling CPUs on the same physical CPU for architectures which use hyper-threading.
  • flags — Defines a number of different qualities about the processor, such as the presence of a floating point unit (FPU) and the ability to process MMX instructions.

19.2.4.  /proc/crypto

This file lists all installed cryptographic ciphers used by the Linux kernel, including additional details for each. A sample /proc/crypto file looks like the following: 
name         : sha1
module       : kernel
type         : digest
blocksize    : 64
digestsize   : 20
name         : md5
module       : md5
type         : digest
blocksize    : 64
digestsize   : 16

19.2.5.  /proc/devices

This file displays the various character and block devices currently configured (not including devices whose modules are not loaded). Below is a sample output from this file: 
Character devices:
  1 mem
  4 /dev/vc/0
  4 tty
  4 ttyS
  5 /dev/tty
  5 /dev/console
  5 /dev/ptmx
  7 vcs
  10 misc
  13 input
  29 fb
  36 netlink
  128 ptm
  136 pts
  180 usb

Block devices:
  1 ramdisk
  3 ide0
  9 md
  22 ide1
  253 device-mapper
  254 mdp
The output from /proc/devices includes the major number and name of the device, and is broken into two major sections: Character devices and Block devices.
Character devices are similar to block devices, except for two basic differences:
  1. Character devices do not require buffering. Block devices have a buffer available, allowing them to order requests before addressing them. This is important for devices designed to store information — such as hard drives — because the ability to order the information before writing it to the device allows it to be placed in a more efficient order.
  2. Character devices send data with no preconfigured size. Block devices can send and receive information in blocks of a size configured per device.
For more information about devices refer to the following installed documentation: 
/usr/share/doc/kernel-doc-<kernel_version>/Documentation/devices.txt

19.2.6.  /proc/dma

This file contains a list of the registered ISA DMA channels in use. A sample /proc/dma files looks like the following: 
4: cascade

19.2.7.  /proc/execdomains

This file lists the execution domains currently supported by the Linux kernel, along with the range of personalities they support. 
0-0   Linux           [kernel]
Think of execution domains as the "personality" for an operating system. Because other binary formats, such as Solaris, UnixWare, and FreeBSD, can be used with Linux, programmers can change the way the operating system treats system calls from these binaries by changing the personality of the task. Except for the PER_LINUX execution domain, different personalities can be implemented as dynamically loadable modules.

19.2.8.  /proc/fb

This file contains a list of frame buffer devices, with the frame buffer device number and the driver that controls it. Typical output of /proc/fb for systems which contain frame buffer devices looks similar to the following: 
0 VESA VGA

19.2.9.  /proc/filesystems

This file displays a list of the file system types currently supported by the kernel. Sample output from a generic /proc/filesystems file looks similar to the following: 
nodev   sysfs
nodev   rootfs
nodev   bdev
nodev   proc
nodev   sockfs
nodev   binfmt_misc
nodev   usbfs
nodev   usbdevfs
nodev   futexfs
nodev   tmpfs
nodev   pipefs
nodev   eventpollfs
nodev   devpts
	ext2
nodev   ramfs
nodev   hugetlbfs
	iso9660
nodev   mqueue
	ext3
nodev   rpc_pipefs
nodev   autofs
The first column signifies whether the file system is mounted on a block device. Those beginning with nodev are not mounted on a device. The second column lists the names of the file systems supported.
The mount command cycles through the file systems listed here when one is not specified as an argument.

19.2.10.  /proc/interrupts

This file records the number of interrupts per IRQ on the x86 architecture. A standard /proc/interrupts looks similar to the following: 
  CPU0
  0:   80448940          XT-PIC  timer
  1:     174412          XT-PIC  keyboard
  2:          0          XT-PIC  cascade
  8:          1          XT-PIC  rtc
 10:     410964          XT-PIC  eth0
 12:      60330          XT-PIC  PS/2 Mouse
 14:    1314121          XT-PIC  ide0
 15:    5195422          XT-PIC  ide1
NMI:          0
ERR:          0
For a multi-processor machine, this file may look slightly different: 
	   CPU0       CPU1
  0: 1366814704          0          XT-PIC  timer
  1:        128        340    IO-APIC-edge  keyboard
  2:          0          0          XT-PIC  cascade
  8:          0          1    IO-APIC-edge  rtc
 12:       5323       5793    IO-APIC-edge  PS/2 Mouse
 13:          1          0          XT-PIC  fpu
 16:   11184294   15940594   IO-APIC-level  Intel EtherExpress Pro 10/100 Ethernet
 20:    8450043   11120093   IO-APIC-level  megaraid
 30:      10432      10722   IO-APIC-level  aic7xxx
 31:         23         22   IO-APIC-level  aic7xxx
NMI:          0
ERR:          0
The first column refers to the IRQ number. Each CPU in the system has its own column and its own number of interrupts per IRQ. The next column reports the type of interrupt, and the last column contains the name of the device that is located at that IRQ.
Each of the types of interrupts seen in this file, which are architecture-specific, mean something different. For x86 machines, the following values are common:
  • XT-PIC — This is the old AT computer interrupts.
  • IO-APIC-edge — The voltage signal on this interrupt transitions from low to high, creating an edge, where the interrupt occurs and is only signaled once. This kind of interrupt, as well as the IO-APIC-level interrupt, are only seen on systems with processors from the 586 family and higher.
  • IO-APIC-level — Generates interrupts when its voltage signal is high until the signal is low again.

19.2.11.  /proc/iomem

This file shows you the current map of the system's memory for each physical device: 
00000000-0009fbff : System RAM
0009fc00-0009ffff : reserved
000a0000-000bffff : Video RAM area
000c0000-000c7fff : Video ROM
000f0000-000fffff : System ROM
00100000-07ffffff : System RAM
00100000-00291ba8 : Kernel code
00291ba9-002e09cb : Kernel data
e0000000-e3ffffff : VIA Technologies, Inc. VT82C597 [Apollo VP3] e4000000-e7ffffff : PCI Bus #01
e4000000-e4003fff : Matrox Graphics, Inc. MGA G200 AGP
e5000000-e57fffff : Matrox Graphics, Inc. MGA G200 AGP
e8000000-e8ffffff : PCI Bus #01
e8000000-e8ffffff : Matrox Graphics, Inc. MGA G200 AGP
ea000000-ea00007f : Digital Equipment Corporation DECchip 21140 [FasterNet]
ea000000-ea00007f : tulip ffff0000-ffffffff : reserved
The first column displays the memory registers used by each of the different types of memory. The second column lists the kind of memory located within those registers and displays which memory registers are used by the kernel within the system RAM or, if the network interface card has multiple Ethernet ports, the memory registers assigned for each port.

19.2.12.  /proc/ioports

The output of /proc/ioports provides a list of currently registered port regions used for input or output communication with a device. This file can be quite long. The following is a partial listing: 
0000-001f : dma1
0020-003f : pic1
0040-005f : timer
0060-006f : keyboard
0070-007f : rtc
0080-008f : dma page reg
00a0-00bf : pic2
00c0-00df : dma2
00f0-00ff : fpu
0170-0177 : ide1
01f0-01f7 : ide0
02f8-02ff : serial(auto)
0376-0376 : ide1
03c0-03df : vga+
03f6-03f6 : ide0
03f8-03ff : serial(auto)
0cf8-0cff : PCI conf1
d000-dfff : PCI Bus #01
e000-e00f : VIA Technologies, Inc. Bus Master IDE
e000-e007 : ide0
e008-e00f : ide1
e800-e87f : Digital Equipment Corporation DECchip 21140 [FasterNet]
e800-e87f : tulip
The first column gives the I/O port address range reserved for the device listed in the second column.

19.2.13.  /proc/kcore

This file represents the physical memory of the system and is stored in the core file format. Unlike most /proc/ files, kcore displays a size. This value is given in bytes and is equal to the size of the physical memory (RAM) used plus 4 KB.
The contents of this file are designed to be examined by a debugger, such as gdb, and is not human readable.

Caution

Do not view the /proc/kcore virtual file. The contents of the file scramble text output on the terminal. If this file is accidentally viewed, press Ctrl+C to stop the process and then type reset to bring back the command line prompt.

19.2.14.  /proc/kmsg

This file is used to hold messages generated by the kernel. These messages are then picked up by other programs, such as /sbin/klogd or /bin/dmesg.

19.2.15.  /proc/loadavg

This file provides a look at the load average in regard to both the CPU and IO over time, as well as additional data used by uptime and other commands. A sample /proc/loadavg file looks similar to the following: 
0.20 0.18 0.12 1/80 11206
The first three columns measure CPU and IO utilization of the last one, five, and 15 minute periods. The fourth column shows the number of currently running processes and the total number of processes. The last column displays the last process ID used.
In addition, load average also refers to the number of processes ready to run (i.e. in the run queue, waiting for a CPU share.

19.2.16.  /proc/locks

This file displays the files currently locked by the kernel. The contents of this file contain internal kernel debugging data and can vary tremendously, depending on the use of the system. A sample /proc/locks file for a lightly loaded system looks similar to the following: 
1: POSIX  ADVISORY  WRITE 3568 fd:00:2531452 0 EOF
2: FLOCK  ADVISORY  WRITE 3517 fd:00:2531448 0 EOF
3: POSIX  ADVISORY  WRITE 3452 fd:00:2531442 0 EOF
4: POSIX  ADVISORY  WRITE 3443 fd:00:2531440 0 EOF
5: POSIX  ADVISORY  WRITE 3326 fd:00:2531430 0 EOF
6: POSIX  ADVISORY  WRITE 3175 fd:00:2531425 0 EOF
7: POSIX  ADVISORY  WRITE 3056 fd:00:2548663 0 EOF
Each lock has its own line which starts with a unique number. The second column refers to the class of lock used, with FLOCK signifying the older-style UNIX file locks from a flock system call and POSIX representing the newer POSIX locks from the lockf system call.
The third column can have two values: ADVISORY or MANDATORY. ADVISORY means that the lock does not prevent other people from accessing the data; it only prevents other attempts to lock it. MANDATORY means that no other access to the data is permitted while the lock is held. The fourth column reveals whether the lock is allowing the holder READ or WRITE access to the file. The fifth column shows the ID of the process holding the lock. The sixth column shows the ID of the file being locked, in the format of MAJOR-DEVICE:MINOR-DEVICE:INODE-NUMBER . The seventh and eighth column shows the start and end of the file's locked region.

19.2.17.  /proc/mdstat

This file contains the current information for multiple-disk, RAID configurations. If the system does not contain such a configuration, then /proc/mdstat looks similar to the following: 
Personalities :  read_ahead not set unused devices: <none>
This file remains in the same state as seen above unless a software RAID or md device is present. In that case, view /proc/mdstat to find the current status of mdX RAID devices.
The /proc/mdstat file below shows a system with its md0 configured as a RAID 1 device, while it is currently re-syncing the disks: 
Personalities : [linear] [raid1] read_ahead 1024 sectors
md0: active raid1 sda2[1] sdb2[0] 9940 blocks [2/2] [UU] resync=1% finish=12.3min algorithm 2 [3/3] [UUU]
unused devices: <none>

19.2.18.  /proc/meminfo

This is one of the more commonly used files in the /proc/ directory, as it reports a large amount of valuable information about the systems RAM usage.
The following sample /proc/meminfo virtual file is from a system with 256 MB of RAM and 512 MB of swap space: 
MemTotal:       255908 kB
MemFree:         69936 kB
Buffers:         15812 kB
Cached:         115124 kB
SwapCached:          0 kB
Active:          92700 kB
Inactive:        63792 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:       255908 kB
LowFree:         69936 kB
SwapTotal:      524280 kB
SwapFree:       524280 kB
Dirty:               4 kB
Writeback:           0 kB
Mapped:          42236 kB
Slab:            25912 kB
Committed_AS:   118680 kB
PageTables:       1236 kB
VmallocTotal:  3874808 kB
VmallocUsed:      1416 kB
VmallocChunk:  3872908 kB
HugePages_Total:     0
HugePages_Free:      0
Hugepagesize:     4096 kB
Much of the information here is used by the free, top, and ps commands. In fact, the output of the free command is similar in appearance to the contents and structure of /proc/meminfo. But by looking directly at /proc/meminfo, more details are revealed:
  • MemTotal — Total amount of physical RAM, in kilobytes.
  • MemFree — The amount of physical RAM, in kilobytes, left unused by the system.
  • Buffers — The amount of physical RAM, in kilobytes, used for file buffers.
  • Cached — The amount of physical RAM, in kilobytes, used as cache memory.
  • SwapCached — The amount of swap, in kilobytes, used as cache memory.
  • Active — The total amount of buffer or page cache memory, in kilobytes, that is in active use. This is memory that has been recently used and is usually not reclaimed for other purposes.
  • Inactive — The total amount of buffer or page cache memory, in kilobytes, that are free and available. This is memory that has not been recently used and can be reclaimed for other purposes.
  • HighTotal and HighFree — The total and free amount of memory, in kilobytes, that is not directly mapped into kernel space. The HighTotal value can vary based on the type of kernel used.
  • LowTotal and LowFree — The total and free amount of memory, in kilobytes, that is directly mapped into kernel space. The LowTotal value can vary based on the type of kernel used.
  • SwapTotal — The total amount of swap available, in kilobytes.
  • SwapFree — The total amount of swap free, in kilobytes.
  • Dirty — The total amount of memory, in kilobytes, waiting to be written back to the disk.
  • Writeback — The total amount of memory, in kilobytes, actively being written back to the disk.
  • Mapped — The total amount of memory, in kilobytes, which have been used to map devices, files, or libraries using the mmap command.
  • Slab — The total amount of memory, in kilobytes, used by the kernel to cache data structures for its own use.
  • Committed_AS — The total amount of memory, in kilobytes, estimated to complete the workload. This value represents the worst case scenario value, and also includes swap memory.
  • PageTables — The total amount of memory, in kilobytes, dedicated to the lowest page table level.
  • VMallocTotal — The total amount of memory, in kilobytes, of total allocated virtual address space.
  • VMallocUsed — The total amount of memory, in kilobytes, of used virtual address space.
  • VMallocChunk — The largest contiguous block of memory, in kilobytes, of available virtual address space.
  • HugePages_Total — The total number of hugepages for the system. The number is derived by dividing Hugepagesize by the megabytes set aside for hugepages specified in /proc/sys/vm/hugetlb_pool. This statistic only appears on the x86, Itanium, and AMD64 architectures.
  • HugePages_Free — The total number of hugepages available for the system. This statistic only appears on the x86, Itanium, and AMD64 architectures.
  • Hugepagesize — The size for each hugepages unit in kilobytes. By default, the value is 4096 KB on uniprocessor kernels for 32 bit architectures. For SMP, hugemem kernels, and AMD64, the default is 2048 KB. For Itanium architectures, the default is 262144 KB. This statistic only appears on the x86, Itanium, and AMD64 architectures.

19.2.19.  /proc/misc

This file lists miscellaneous drivers registered on the miscellaneous major device, which is device number 10: 
63 device-mapper 175 agpgart 135 rtc 134 apm_bios
The first column is the minor number of each device, while the second column shows the driver in use.

19.2.20.  /proc/modules

This file displays a list of all modules loaded into the kernel. Its contents vary based on the configuration and use of your system, but it should be organized in a similar manner to this sample /proc/modules file output:

Note

This example has been reformatted into a readable format. Most of this information can also be viewed via the /sbin/lsmod command. 
nfs      170109  0 -          Live 0x129b0000
lockd    51593   1 nfs,       Live 0x128b0000
nls_utf8 1729    0 -          Live 0x12830000
vfat     12097   0 -          Live 0x12823000
fat      38881   1 vfat,      Live 0x1287b000
autofs4  20293   2 -          Live 0x1284f000
sunrpc   140453  3 nfs,lockd, Live 0x12954000
3c59x    33257   0 -          Live 0x12871000
uhci_hcd 28377   0 -          Live 0x12869000
md5      3777    1 -          Live 0x1282c000
ipv6     211845 16 -          Live 0x128de000
ext3     92585   2 -          Live 0x12886000
jbd      65625   1 ext3,      Live 0x12857000
dm_mod   46677   3 -          Live 0x12833000
The first column contains the name of the module.
The second column refers to the memory size of the module, in bytes.
The third column lists how many instances of the module are currently loaded. A value of zero represents an unloaded module.
The fourth column states if the module depends upon another module to be present in order to function, and lists those other modules.
The fifth column lists what load state the module is in: Live, Loading, or Unloading are the only possible values.
The sixth column lists the current kernel memory offset for the loaded module. This information can be useful for debugging purposes, or for profiling tools such as oprofile.

19.2.21.  /proc/mounts

This file provides a list of all mounts in use by the system: 
rootfs / rootfs rw 0 0
/proc /proc proc rw,nodiratime 0 0 none
/dev ramfs rw 0 0
/dev/mapper/VolGroup00-LogVol00 / ext3 rw 0 0
none /dev ramfs rw 0 0
/proc /proc proc rw,nodiratime 0 0
/sys /sys sysfs rw 0 0
none /dev/pts devpts rw 0 0
usbdevfs /proc/bus/usb usbdevfs rw 0 0
/dev/hda1 /boot ext3 rw 0 0
none /dev/shm tmpfs rw 0 0
none /proc/sys/fs/binfmt_misc binfmt_misc rw 0 0
sunrpc /var/lib/nfs/rpc_pipefs rpc_pipefs rw 0 0
The output found here is similar to the contents of /etc/mtab, except that /proc/mounts is more up-to-date.
The first column specifies the device that is mounted, the second column reveals the mount point, and the third column tells the file system type, and the fourth column tells you if it is mounted read-only (ro) or read-write (rw). The fifth and sixth columns are dummy values designed to match the format used in /etc/mtab.

19.2.22.  /proc/mtrr

This file refers to the current Memory Type Range Registers (MTRRs) in use with the system. If the system architecture supports MTRRs, then the /proc/mtrr file may look similar to the following: 
reg00: base=0x00000000 (   0MB), size= 256MB: write-back, count=1
reg01: base=0xe8000000 (3712MB), size=  32MB: write-combining, count=1
MTRRs are used with the Intel P6 family of processors (Pentium II and higher) and control processor access to memory ranges. When using a video card on a PCI or AGP bus, a properly configured /proc/mtrr file can increase performance more than 150%.
Most of the time, this value is properly configured by default. More information on manually configuring this file can be found locally at the following location: 
/usr/share/doc/kernel-doc-<kernel_version>/Documentation/<arch>/mtrr.txt

19.2.23.  /proc/partitions

This file contains partition block allocation information. A sampling of this file from a basic system looks similar to the following: 
major minor  #blocks  name
  3     0   19531250 hda
  3     1     104391 hda1
  3     2   19422585 hda2
253     0   22708224 dm-0
253     1     524288 dm-1
Most of the information here is of little importance to the user, except for the following columns:
  • major — The major number of the device with this partition. The major number in the /proc/partitions, (3), corresponds with the block device ide0, in /proc/devices.
  • minor — The minor number of the device with this partition. This serves to separate the partitions into different physical devices and relates to the number at the end of the name of the partition.
  • #blocks — Lists the number of physical disk blocks contained in a particular partition.
  • name — The name of the partition.

19.2.24.  /proc/slabinfo

This file gives full information about memory usage on the slab level. Linux kernels greater than version 2.2 use slab pools to manage memory above the page level. Commonly used objects have their own slab pools.
Instead of parsing the highly verbose /proc/slabinfo file manually, the /usr/bin/slabtop program displays kernel slab cache information in real time. This program allows for custom configurations, including column sorting and screen refreshing.
A sample screen shot of /usr/bin/slabtop usually looks like the following example: 
Active / Total Objects (% used)    : 133629 / 147300 (90.7%)
Active / Total Slabs (% used)      : 11492 / 11493 (100.0%)
Active / Total Caches (% used)     : 77 / 121 (63.6%)
Active / Total Size (% used)       : 41739.83K / 44081.89K (94.7%)
Minimum / Average / Maximum Object : 0.01K / 0.30K / 128.00K
OBJS   ACTIVE USE      OBJ   SIZE     SLABS OBJ/SLAB CACHE SIZE NAME
44814  43159  96%    0.62K   7469      6     29876K ext3_inode_cache
36900  34614  93%    0.05K    492     75      1968K buffer_head
35213  33124  94%    0.16K   1531     23      6124K dentry_cache
7364   6463  87%    0.27K    526      14      2104K radix_tree_node
2585   1781  68%    0.08K     55      47       220K vm_area_struct
2263   2116  93%    0.12K     73      31       292K size-128
1904   1125  59%    0.03K     16      119        64K size-32
1666    768  46%    0.03K     14      119        56K anon_vma
1512   1482  98%    0.44K    168       9       672K inode_cache
1464   1040  71%    0.06K     24      61        96K size-64
1320    820  62%    0.19K     66      20       264K filp
678    587  86%    0.02K      3      226        12K dm_io
678    587  86%    0.02K      3      226        12K dm_tio
576    574  99%    0.47K     72        8       288K proc_inode_cache
528    514  97%    0.50K     66        8       264K size-512
492    372  75%    0.09K     12       41        48K bio
465    314  67%    0.25K     31       15       124K size-256
452    331  73%    0.02K      2      226         8K biovec-1
420    420 100%    0.19K     21       20        84K skbuff_head_cache
305    256  83%    0.06K      5       61        20K biovec-4
290      4   1%    0.01K      1      290         4K revoke_table
264    264 100%    4.00K    264        1      1056K size-4096
260    256  98%    0.19K     13       20        52K biovec-16
260    256  98%    0.75K     52        5       208K biovec-64
Some of the more commonly used statistics in /proc/slabinfo that are included into /usr/bin/slabtop include:
  • OBJS — The total number of objects (memory blocks), including those in use (allocated), and some spares not in use.
  • ACTIVE — The number of objects (memory blocks) that are in use (allocated).
  • USE — Percentage of total objects that are active. ((ACTIVE/OBJS)(100))
  • OBJ SIZE — The size of the objects.
  • SLABS — The total number of slabs.
  • OBJ/SLAB — The number of objects that fit into a slab.
  • CACHE SIZE — The cache size of the slab.
  • NAME — The name of the slab.
For more information on the /usr/bin/slabtop program, refer to the slabtop man page.

19.2.25.  /proc/stat

This file keeps track of a variety of different statistics about the system since it was last restarted. The contents of /proc/stat, which can be quite long, usually begins like the following example: 
cpu  259246 7001 60190 34250993 137517 772 0
cpu0 259246 7001 60190 34250993 137517 772 0
intr 354133732 347209999 2272 0 4 4 0 0 3 1 1249247 0 0 80143 0 422626 5169433
ctxt 12547729
btime 1093631447
processes 130523
procs_running 1
procs_blocked 0
preempt 5651840
cpu  209841 1554 21720 118519346 72939 154 27168
cpu0 42536 798 4841 14790880 14778 124 3117
cpu1 24184 569 3875 14794524 30209 29 3130
cpu2 28616 11 2182 14818198 4020 1 3493
cpu3 35350 6 2942 14811519 3045 0 3659
cpu4 18209 135 2263 14820076 12465 0 3373
cpu5 20795 35 1866 14825701 4508 0 3615
cpu6 21607 0 2201 14827053 2325 0 3334
cpu7 18544 0 1550 14831395 1589 0 3447
intr 15239682 14857833 6 0 6 6 0 5 0 1 0 0 0 29 0 2 0 0 0 0 0 0 0 94982 0 286812
ctxt 4209609
btime 1078711415
processes 21905
procs_running 1
procs_blocked 0
Some of the more commonly used statistics include:
  • cpu — Measures the number of jiffies (1/100 of a second for x86 systems) that the system has been in user mode, user mode with low priority (nice), system mode, idle task, I/O wait, IRQ (hardirq), and softirq respectively. The IRQ (hardirq) is the direct response to a hardware event. The IRQ takes minimal work for queuing the "heavy" work up for the softirq to execute. The softirq runs at a lower priority than the IRQ and therefore may be interrupted more frequently. The total for all CPUs is given at the top, while each individual CPU is listed below with its own statistics. The following example is a 4-way Intel Pentium Xeon configuration with multi-threading enabled, therefore showing four physical processors and four virtual processors totaling eight processors.
  • page — The number of memory pages the system has written in and out to disk.
  • swap — The number of swap pages the system has brought in and out.
  • intr — The number of interrupts the system has experienced.
  • btime — The boot time, measured in the number of seconds since January 1, 1970, otherwise known as the epoch.

19.2.26.  /proc/swaps

This file measures swap space and its utilization. For a system with only one swap partition, the output of /proc/swaps may look similar to the following: 
Filename                          Type        Size     Used    Priority
/dev/mapper/VolGroup00-LogVol01   partition   524280   0       -1
While some of this information can be found in other files in the /proc/ directory, /proc/swap provides a snapshot of every swap file name, the type of swap space, the total size, and the amount of space in use (in kilobytes). The priority column is useful when multiple swap files are in use. The lower the priority, the more likely the swap file is to be used.

19.2.27.  /proc/sysrq-trigger

Using the echo command to write to this file, a remote root user can execute most System Request Key commands remotely as if at the local terminal. To echo values to this file, the /proc/sys/kernel/sysrq must be set to a value other than 0. For more information about the System Request Key, refer to Section 19.3.9.3, “ /proc/sys/kernel/ ”.
Although it is possible to write to this file, it cannot be read, even by the root user.

19.2.28.  /proc/uptime

This file contains information detailing how long the system has been on since its last restart. The output of /proc/uptime is quite minimal: 
350735.47 234388.90
The first number is the total number of seconds the system has been up. The second number is how much of that time the machine has spent idle, in seconds.

19.2.29.  /proc/version

This file specifies the version of the Linux kernel, the version of gcc used to compile the kernel, and the time of kernel compilation. It also contains the kernel compiler's user name (in parentheses). 
Linux version 2.6.8-1.523 (user@foo.redhat.com) (gcc version 3.4.1 20040714 \  (Red Hat Enterprise Linux 3.4.1-7)) #1 Mon Aug 16 13:27:03 EDT 2004
This information is used for a variety of purposes, including the version data presented when a user logs in.

19.3. Directories within /proc/

Common groups of information concerning the kernel are grouped into directories and subdirectories within the /proc/ directory.

19.3.1. Process Directories

Every /proc/ directory contains a number of directories with numerical names. A listing of them may be similar to the following: 
dr-xr-xr-x    3 root     root            0 Feb 13 01:28 1
dr-xr-xr-x    3 root     root            0 Feb 13 01:28 1010
dr-xr-xr-x    3 xfs      xfs             0 Feb 13 01:28 1087
dr-xr-xr-x    3 daemon   daemon          0 Feb 13 01:28 1123
dr-xr-xr-x    3 root     root            0 Feb 13 01:28 11307
dr-xr-xr-x    3 apache   apache          0 Feb 13 01:28 13660
dr-xr-xr-x    3 rpc      rpc             0 Feb 13 01:28 637
dr-xr-xr-x    3 rpcuser  rpcuser         0 Feb 13 01:28 666
These directories are called process directories, as they are named after a program's process ID and contain information specific to that process. The owner and group of each process directory is set to the user running the process. When the process is terminated, its /proc/ process directory vanishes.
Each process directory contains the following files:
  • cmdline — Contains the command issued when starting the process.
  • cwd — A symbolic link to the current working directory for the process.
  • environ — A list of the environment variables for the process. The environment variable is given in all upper-case characters, and the value is in lower-case characters.
  • exe — A symbolic link to the executable of this process.
  • fd — A directory containing all of the file descriptors for a particular process. These are given in numbered links: 
    total 0
lrwx------    1 root     root           64 May  8 11:31 0 -> /dev/null
lrwx------    1 root     root           64 May  8 11:31 1 -> /dev/null
lrwx------    1 root     root           64 May  8 11:31 2 -> /dev/null
lrwx------    1 root     root           64 May  8 11:31 3 -> /dev/ptmx
lrwx------    1 root     root           64 May  8 11:31 4 -> socket:[7774817]
lrwx------    1 root     root           64 May  8 11:31 5 -> /dev/ptmx
lrwx------    1 root     root           64 May  8 11:31 6 -> socket:[7774829]
lrwx------    1 root     root           64 May  8 11:31 7 -> /dev/ptmx
  • maps — A list of memory maps to the various executables and library files associated with this process. This file can be rather long, depending upon the complexity of the process, but sample output from the sshd process begins like the following: 
    08048000-08086000 r-xp 00000000 03:03 391479     /usr/sbin/sshd
08086000-08088000 rw-p 0003e000 03:03 391479	/usr/sbin/sshd
08088000-08095000 rwxp 00000000 00:00 0
40000000-40013000 r-xp 0000000 03:03 293205	/lib/ld-2.2.5.so
40013000-40014000 rw-p 00013000 03:03 293205	/lib/ld-2.2.5.so
40031000-40038000 r-xp 00000000 03:03 293282	/lib/libpam.so.0.75
40038000-40039000 rw-p 00006000 03:03 293282	/lib/libpam.so.0.75
40039000-4003a000 rw-p 00000000 00:00 0
4003a000-4003c000 r-xp 00000000 03:03 293218	/lib/libdl-2.2.5.so
4003c000-4003d000 rw-p 00001000 03:03 293218	/lib/libdl-2.2.5.so
  • mem — The memory held by the process. This file cannot be read by the user.
  • root — A link to the root directory of the process.
  • stat — The status of the process.
  • statm — The status of the memory in use by the process. Below is a sample /proc/statm file: 
    263 210 210 5 0 205 0
    The seven columns relate to different memory statistics for the process. From left to right, they report the following aspects of the memory used:
    1. Total program size, in kilobytes.
    2. Size of memory portions, in kilobytes.
    3. Number of pages that are shared.
    4. Number of pages that are code.
    5. Number of pages of data/stack.
    6. Number of library pages.
    7. Number of dirty pages.
  • status — The status of the process in a more readable form than stat or statm. Sample output for sshd looks similar to the following: 
    Name:	sshd
State:	S (sleeping)
Tgid:	797
Pid:	797
PPid:	1
TracerPid:	0
Uid:	0	0	0	0
Gid:	0	0	0	0
FDSize:	32
Groups:
VmSize:	    3072 kB
VmLck:	       0 kB
VmRSS:	     840 kB
VmData:	     104 kB
VmStk:	      12 kB
VmExe:	     300 kB
VmLib:	    2528 kB
SigPnd:	0000000000000000
SigBlk:	0000000000000000
SigIgn:	8000000000001000
SigCgt:	0000000000014005
CapInh:	0000000000000000
CapPrm:	00000000fffffeff
CapEff:	00000000fffffeff
    The information in this output includes the process name and ID, the state (such as S (sleeping) or R (running)), user/group ID running the process, and detailed data regarding memory usage.

19.3.1.1.  /proc/self/

The /proc/self/ directory is a link to the currently running process. This allows a process to look at itself without having to know its process ID.
Within a shell environment, a listing of the /proc/self/ directory produces the same contents as listing the process directory for that process.

19.3.2.  /proc/bus/

This directory contains information specific to the various buses available on the system. For example, on a standard system containing PCI and USB buses, current data on each of these buses is available within a subdirectory within /proc/bus/ by the same name, such as /proc/bus/pci/.
The subdirectories and files available within /proc/bus/ vary depending on the devices connected to the system. However, each bus type has at least one directory. Within these bus directories are normally at least one subdirectory with a numerical name, such as 001, which contain binary files.
For example, the /proc/bus/usb/ subdirectory contains files that track the various devices on any USB buses, as well as the drivers required for them. The following is a sample listing of a /proc/bus/usb/ directory: 
total 0 dr-xr-xr-x    1 root     root            0 May  3 16:25 001
-r--r--r--    1 root     root            0 May  3 16:25 devices
-r--r--r--    1 root     root            0 May  3 16:25 drivers
The /proc/bus/usb/001/ directory contains all devices on the first USB bus and the devices file identifies the USB root hub on the motherboard.
The following is a example of a /proc/bus/usb/devices file: 
T:  Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=12  MxCh= 2
B:  Alloc=  0/900 us ( 0%), #Int=  0, #Iso=  0
D:  Ver= 1.00 Cls=09(hub  ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
P:  Vendor=0000 ProdID=0000 Rev= 0.00
S:  Product=USB UHCI Root Hub
S:  SerialNumber=d400
C:* #Ifs= 1 Cfg#= 1 Atr=40 MxPwr=  0mA
I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
E:  Ad=81(I) Atr=03(Int.) MxPS=   8 Ivl=255ms

19.3.3.  /proc/bus/pci

Later versions of the 2.6 Linux kernel have obsoleted the /proc/pci directory in favor of the /proc/bus/pci directory. Although you can get a list of all PCI devices present on the system using the command cat /proc/bus/pci/devices, the output is difficult to read and interpret.
For a human-readable list of PCI devices, run the following command: 
~]# /sbin/lspci -vb
00:00.0 Host bridge: Intel Corporation 82X38/X48 Express DRAM Controller
        Subsystem: Hewlett-Packard Company Device 1308
        Flags: bus master, fast devsel, latency 0
        Capabilities: [e0] Vendor Specific Information <?>
        Kernel driver in use: x38_edac
        Kernel modules: x38_edac

00:01.0 PCI bridge: Intel Corporation 82X38/X48 Express Host-Primary PCI Express Bridge (prog-if 00 [Normal decode])
        Flags: bus master, fast devsel, latency 0
        Bus: primary=00, secondary=01, subordinate=01, sec-latency=0
        I/O behind bridge: 00001000-00001fff
        Memory behind bridge: f0000000-f2ffffff
        Capabilities: [88] Subsystem: Hewlett-Packard Company Device 1308
        Capabilities: [80] Power Management version 3
        Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
        Capabilities: [a0] Express Root Port (Slot+), MSI 00
        Capabilities: [100] Virtual Channel <?>
        Capabilities: [140] Root Complex Link <?>
        Kernel driver in use: pcieport
        Kernel modules: shpchp

00:1a.0 USB Controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #4 (rev 02) (prog-if 00 [UHCI])
        Subsystem: Hewlett-Packard Company Device 1308
        Flags: bus master, medium devsel, latency 0, IRQ 5
        I/O ports at 2100
        Capabilities: [50] PCI Advanced Features
        Kernel driver in use: uhci_hcd
[output truncated]
The output is a sorted list of all IRQ numbers and addresses as seen by the cards on the PCI bus instead of as seen by the kernel. Beyond providing the name and version of the device, this list also gives detailed IRQ information so an administrator can quickly look for conflicts.

19.3.4.  /proc/driver/

This directory contains information for specific drivers in use by the kernel.
A common file found here is rtc which provides output from the driver for the system's Real Time Clock (RTC), the device that keeps the time while the system is switched off. Sample output from /proc/driver/rtc looks like the following: 
rtc_time        : 16:21:00
rtc_date        : 2004-08-31
rtc_epoch       : 1900
alarm           : 21:16:27
DST_enable      : no
BCD             : yes
24hr            : yes
square_wave     : no
alarm_IRQ       : no
update_IRQ      : no
periodic_IRQ    : no
periodic_freq   : 1024
batt_status     : okay
For more information about the RTC, refer to the following installed documentation:
/usr/share/doc/kernel-doc-<kernel_version>/Documentation/rtc.txt.

19.3.5.  /proc/fs

This directory shows which file systems are exported. If running an NFS server, typing cat /proc/fs/nfsd/exports displays the file systems being shared and the permissions granted for those file systems. For more on file system sharing with NFS, refer to the Network File System (NFS) chapter of the Storage Administration Guide.

19.3.6.  /proc/irq/

This directory is used to set IRQ to CPU affinity, which allows the system to connect a particular IRQ to only one CPU. Alternatively, it can exclude a CPU from handling any IRQs.
Each IRQ has its own directory, allowing for the individual configuration of each IRQ. The /proc/irq/prof_cpu_mask file is a bitmask that contains the default values for the smp_affinity file in the IRQ directory. The values in smp_affinity specify which CPUs handle that particular IRQ.
For more information about the /proc/irq/ directory, refer to the following installed documentation: 
/usr/share/doc/kernel-doc-kernel_version/Documentation/filesystems/proc.txt

19.3.7.  /proc/net/

This directory provides a comprehensive look at various networking parameters and statistics. Each directory and virtual file within this directory describes aspects of the system's network configuration. Below is a partial list of the /proc/net/ directory:
  • arp — Lists the kernel's ARP table. This file is particularly useful for connecting a hardware address to an IP address on a system.
  • atm/ directory — The files within this directory contain Asynchronous Transfer Mode (ATM) settings and statistics. This directory is primarily used with ATM networking and ADSL cards.
  • dev — Lists the various network devices configured on the system, complete with transmit and receive statistics. This file displays the number of bytes each interface has sent and received, the number of packets inbound and outbound, the number of errors seen, the number of packets dropped, and more.
  • dev_mcast — Lists Layer2 multicast groups on which each device is listening.
  • igmp — Lists the IP multicast addresses which this system joined.
  • ip_conntrack — Lists tracked network connections for machines that are forwarding IP connections.
  • ip_tables_names — Lists the types of iptables in use. This file is only present if iptables is active on the system and contains one or more of the following values: filter, mangle, or nat.
  • ip_mr_cache — Lists the multicast routing cache.
  • ip_mr_vif — Lists multicast virtual interfaces.
  • netstat — Contains a broad yet detailed collection of networking statistics, including TCP timeouts, SYN cookies sent and received, and much more.
  • psched — Lists global packet scheduler parameters.
  • raw — Lists raw device statistics.
  • route — Lists the kernel's routing table.
  • rt_cache — Contains the current routing cache.
  • snmp — List of Simple Network Management Protocol (SNMP) data for various networking protocols in use.
  • sockstat — Provides socket statistics.
  • tcp — Contains detailed TCP socket information.
  • tr_rif — Lists the token ring RIF routing table.
  • udp — Contains detailed UDP socket information.
  • unix — Lists UNIX domain sockets currently in use.
  • wireless — Lists wireless interface data.

19.3.8.  /proc/scsi/

The primary file in this directory is /proc/scsi/scsi, which contains a list of every recognized SCSI device. From this listing, the type of device, as well as the model name, vendor, SCSI channel and ID data is available.
For example, if a system contains a SCSI CD-ROM, a tape drive, a hard drive, and a RAID controller, this file looks similar to the following: 
Attached devices:
Host: scsi1
Channel: 00
Id: 05
Lun: 00
Vendor: NEC
Model: CD-ROM DRIVE:466
Rev: 1.06
Type:   CD-ROM
ANSI SCSI revision: 02
Host: scsi1
Channel: 00
Id: 06
Lun: 00
Vendor: ARCHIVE
Model: Python 04106-XXX
Rev: 7350
Type:   Sequential-Access
ANSI SCSI revision: 02
Host: scsi2
Channel: 00
Id: 06
Lun: 00
Vendor: DELL
Model: 1x6 U2W SCSI BP
Rev: 5.35
Type:   Processor
ANSI SCSI revision: 02
Host: scsi2
Channel: 02
Id: 00
Lun: 00
Vendor: MegaRAID
Model: LD0 RAID5 34556R
Rev: 1.01
Type:   Direct-Access
ANSI SCSI revision: 02
Each SCSI driver used by the system has its own directory within /proc/scsi/, which contains files specific to each SCSI controller using that driver. From the previous example, aic7xxx/ and megaraid/ directories are present, since two drivers are in use. The files in each of the directories typically contain an I/O address range, IRQ information, and statistics for the SCSI controller using that driver. Each controller can report a different type and amount of information. The Adaptec AIC-7880 Ultra SCSI host adapter's file in this example system produces the following output: 
Adaptec AIC7xxx driver version: 5.1.20/3.2.4
Compile Options:
TCQ Enabled By Default : Disabled
AIC7XXX_PROC_STATS     : Enabled
AIC7XXX_RESET_DELAY    : 5
Adapter Configuration:
SCSI Adapter: Adaptec AIC-7880 Ultra SCSI host adapter
Ultra Narrow Controller     PCI MMAPed
I/O Base: 0xfcffe000
Adapter SEEPROM Config: SEEPROM found and used.
Adaptec SCSI BIOS: Enabled
IRQ: 30
SCBs: Active 0, Max Active 1, Allocated 15, HW 16, Page 255
Interrupts: 33726
BIOS Control Word: 0x18a6
Adapter Control Word: 0x1c5f
Extended Translation: Enabled
Disconnect Enable Flags: 0x00ff
Ultra Enable Flags: 0x0020
Tag Queue Enable Flags: 0x0000
Ordered Queue Tag Flags: 0x0000
Default Tag Queue Depth: 8
Tagged Queue By Device array for aic7xxx
host instance 1:       {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
Actual queue depth per device for aic7xxx host instance 1:       {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
Statistics:

(scsi1:0:5:0) Device using Narrow/Sync transfers at 20.0 MByte/sec, offset 15
Transinfo settings: current(12/15/0/0), goal(12/15/0/0), user(12/15/0/0)
Total transfers 0 (0 reads and 0 writes)
		< 2K      2K+     4K+     8K+    16K+    32K+    64K+   128K+
Reads:        0       0       0       0       0       0       0       0
Writes:       0       0       0       0       0       0       0       0

(scsi1:0:6:0) Device using Narrow/Sync transfers at 10.0 MByte/sec, offset 15
Transinfo settings: current(25/15/0/0), goal(12/15/0/0), user(12/15/0/0)
Total transfers 132 (0 reads and 132 writes)
		< 2K      2K+     4K+     8K+    16K+    32K+    64K+   128K+
Reads:        0       0       0       0       0       0       0       0
Writes:       0       0       0       1     131       0       0       0
This output reveals the transfer speed to the SCSI devices connected to the controller based on channel ID, as well as detailed statistics concerning the amount and sizes of files read or written by that device. For example, this controller is communicating with the CD-ROM at 20 megabytes per second, while the tape drive is only communicating at 10 megabytes per second.

19.3.9.  /proc/sys/

The /proc/sys/ directory is different from others in /proc/ because it not only provides information about the system but also allows the system administrator to immediately enable and disable kernel features.

Caution

Use caution when changing settings on a production system using the various files in the /proc/sys/ directory. Changing the wrong setting may render the kernel unstable, requiring a system reboot.
For this reason, be sure the options are valid for that file before attempting to change any value in /proc/sys/.
A good way to determine if a particular file can be configured, or if it is only designed to provide information, is to list it with the -l option at the shell prompt. If the file is writable, it may be used to configure the kernel. For example, a partial listing of /proc/sys/fs looks like the following: 
-r--r--r--    1 root     root            0 May 10 16:14 dentry-state
-rw-r--r--    1 root     root            0 May 10 16:14 dir-notify-enable
-rw-r--r--    1 root     root            0 May 10 16:14 file-max
-r--r--r--    1 root     root            0 May 10 16:14 file-nr
In this listing, the files dir-notify-enable and file-max can be written to and, therefore, can be used to configure the kernel. The other files only provide feedback on current settings.
Changing a value within a /proc/sys/ file is done by echoing the new value into the file. For example, to enable the System Request Key on a running kernel, type the command: 
echo 1 > /proc/sys/kernel/sysrq
This changes the value for sysrq from 0 (off) to 1 (on).
A few /proc/sys/ configuration files contain more than one value. To correctly send new values to them, place a space character between each value passed with the echo command, such as is done in this example: 
echo 4 2 45 > /proc/sys/kernel/acct

Note

Any configuration changes made using the echo command disappear when the system is restarted. To make configuration changes take effect after the system is rebooted, refer to Section 19.4, “Using the sysctl Command”.
The /proc/sys/ directory contains several subdirectories controlling different aspects of a running kernel.

19.3.9.1.  /proc/sys/dev/

This directory provides parameters for particular devices on the system. Most systems have at least two directories, cdrom/ and raid/. Customized kernels can have other directories, such as parport/, which provides the ability to share one parallel port between multiple device drivers.
The cdrom/ directory contains a file called info, which reveals a number of important CD-ROM parameters: 
CD-ROM information, Id: cdrom.c 3.20 2003/12/17
drive name:             hdc
drive speed:            48
drive # of slots:       1
Can close tray:         1
Can open tray:          1
Can lock tray:          1
Can change speed:       1
Can select disk:        0
Can read multisession:  1
Can read MCN:           1
Reports media changed:  1
Can play audio:         1
Can write CD-R:         0
Can write CD-RW:        0
Can read DVD:           0
Can write DVD-R:        0
Can write DVD-RAM:      0
Can read MRW:           0
Can write MRW:          0
Can write RAM:          0
This file can be quickly scanned to discover the qualities of an unknown CD-ROM. If multiple CD-ROMs are available on a system, each device is given its own column of information.
Various files in /proc/sys/dev/cdrom, such as autoclose and checkmedia, can be used to control the system's CD-ROM. Use the echo command to enable or disable these features.
If RAID support is compiled into the kernel, a /proc/sys/dev/raid/ directory becomes available with at least two files in it: speed_limit_min and speed_limit_max. These settings determine the acceleration of RAID devices for I/O intensive tasks, such as resyncing the disks.

19.3.9.2.  /proc/sys/fs/

This directory contains an array of options and information concerning various aspects of the file system, including quota, file handle, inode, and dentry information.
The binfmt_misc/ directory is used to provide kernel support for miscellaneous binary formats.
The important files in /proc/sys/fs/ include:
  • dentry-state — Provides the status of the directory cache. The file looks similar to the following: 
    57411	52939	45	0	0	0
    The first number reveals the total number of directory cache entries, while the second number displays the number of unused entries. The third number tells the number of seconds between when a directory has been freed and when it can be reclaimed, and the fourth measures the pages currently requested by the system. The last two numbers are not used and display only zeros.
  • file-max — Lists the maximum number of file handles that the kernel allocates. Raising the value in this file can resolve errors caused by a lack of available file handles.
  • file-nr — Lists the number of allocated file handles, used file handles, and the maximum number of file handles.
  • overflowgid and overflowuid — Defines the fixed group ID and user ID, respectively, for use with file systems that only support 16-bit group and user IDs.

19.3.9.3.  /proc/sys/kernel/

This directory contains a variety of different configuration files that directly affect the operation of the kernel. Some of the most important files include:
  • acct — Controls the suspension of process accounting based on the percentage of free space available on the file system containing the log. By default, the file looks like the following: 
    4	2	30
    The first value dictates the percentage of free space required for logging to resume, while the second value sets the threshold percentage of free space when logging is suspended. The third value sets the interval, in seconds, that the kernel polls the file system to see if logging should be suspended or resumed.
  • ctrl-alt-del — Controls whether Ctrl+Alt+Delete gracefully restarts the computer using init (0) or forces an immediate reboot without syncing the dirty buffers to disk (1).
  • domainname — Configures the system domain name, such as example.com.
  • exec-shield — Configures the Exec Shield feature of the kernel. Exec Shield provides protection against certain types of buffer overflow attacks.
    There are two possible values for this virtual file:
    • 0 — Disables Exec Shield.
    • 1 — Enables Exec Shield. This is the default value.

    Important

    If a system is running security-sensitive applications that were started while Exec Shield was disabled, these applications must be restarted when Exec Shield is enabled in order for Exec Shield to take effect.
  • hostname — Configures the system hostname, such as www.example.com.
  • hotplug — Configures the utility to be used when a configuration change is detected by the system. This is primarily used with USB and Cardbus PCI. The default value of /sbin/hotplug should not be changed unless testing a new program to fulfill this role.
  • modprobe — Sets the location of the program used to load kernel modules. The default value is /sbin/modprobe which means kmod calls it to load the module when a kernel thread calls kmod.
  • msgmax — Sets the maximum size of any message sent from one process to another and is set to 8192 bytes by default. Be careful when raising this value, as queued messages between processes are stored in non-swappable kernel memory. Any increase in msgmax would increase RAM requirements for the system.
  • msgmnb — Sets the maximum number of bytes in a single message queue. The default is 16384.
  • msgmni — Sets the maximum number of message queue identifiers. The default is 4008.
  • osrelease — Lists the Linux kernel release number. This file can only be altered by changing the kernel source and recompiling.
  • ostype — Displays the type of operating system. By default, this file is set to Linux, and this value can only be changed by changing the kernel source and recompiling.
  • overflowgid and overflowuid — Defines the fixed group ID and user ID, respectively, for use with system calls on architectures that only support 16-bit group and user IDs.
  • panic — Defines the number of seconds the kernel postpones rebooting when the system experiences a kernel panic. By default, the value is set to 0, which disables automatic rebooting after a panic.
  • printk — This file controls a variety of settings related to printing or logging error messages. Each error message reported by the kernel has a loglevel associated with it that defines the importance of the message. The loglevel values break down in this order:
    • 0 — Kernel emergency. The system is unusable.
    • 1 — Kernel alert. Action must be taken immediately.
    • 2 — Condition of the kernel is considered critical.
    • 3 — General kernel error condition.
    • 4 — General kernel warning condition.
    • 5 — Kernel notice of a normal but significant condition.
    • 6 — Kernel informational message.
    • 7 — Kernel debug-level messages.
    Four values are found in the printk file: 
    6     4     1     7
    Each of these values defines a different rule for dealing with error messages. The first value, called the console loglevel, defines the lowest priority of messages printed to the console. (Note that, the lower the priority, the higher the loglevel number.) The second value sets the default loglevel for messages without an explicit loglevel attached to them. The third value sets the lowest possible loglevel configuration for the console loglevel. The last value sets the default value for the console loglevel.
  • random/ directory — Lists a number of values related to generating random numbers for the kernel.
  • sem — Configures semaphore settings within the kernel. A semaphore is a System V IPC object that is used to control utilization of a particular process.
  • shmall — Sets the total amount of shared memory that can be used at one time on the system, in bytes. By default, this value is 2097152.
  • shmmax — Sets the largest shared memory segment size allowed by the kernel, in bytes. By default, this value is 33554432. However, the kernel supports much larger values than this.
  • shmmni — Sets the maximum number of shared memory segments for the whole system, in bytes. By default, this value is 4096
  • sysrq — Activates the System Request Key, if this value is set to anything other than zero (0), the default.
    The System Request Key allows immediate input to the kernel through simple key combinations. For example, the System Request Key can be used to immediately shut down or restart a system, sync all mounted file systems, or dump important information to the console. To initiate a System Request Key, type Alt+SysRq+ system request code . Replace system request code with one of the following system request codes:
    • r — Disables raw mode for the keyboard and sets it to XLATE (a limited keyboard mode which does not recognize modifiers such as Alt, Ctrl, or Shift for all keys).
    • k — Kills all processes active in a virtual console. Also called Secure Access Key (SAK), it is often used to verify that the login prompt is spawned from init and not a trojan copy designed to capture usernames and passwords.
    • b — Reboots the kernel without first unmounting file systems or syncing disks attached to the system.
    • c — Crashes the system without first unmounting file systems or syncing disks attached to the system.
    • o — Shuts off the system.
    • s — Attempts to sync disks attached to the system.
    • u — Attempts to unmount and remount all file systems as read-only.
    • p — Outputs all flags and registers to the console.
    • t — Outputs a list of processes to the console.
    • m — Outputs memory statistics to the console.
    • 0 through 9 — Sets the log level for the console.
    • e — Kills all processes except init using SIGTERM.
    • i — Kills all processes except init using SIGKILL.
    • l — Kills all processes using SIGKILL (including init). The system is unusable after issuing this System Request Key code.
    • h — Displays help text.
    This feature is most beneficial when using a development kernel or when experiencing system freezes.

    Caution

    The System Request Key feature is considered a security risk because an unattended console provides an attacker with access to the system. For this reason, it is turned off by default.
    Refer to /usr/share/doc/kernel-doc-kernel_version/Documentation/sysrq.txt for more information about the System Request Key.
  • tainted — Indicates whether a non-GPL module is loaded.
    • 0 — No non-GPL modules are loaded.
    • 1 — At least one module without a GPL license (including modules with no license) is loaded.
    • 2 — At least one module was force-loaded with the command insmod -f.
  • threads-max — Sets the maximum number of threads to be used by the kernel, with a default value of 2048.
  • version — Displays the date and time the kernel was last compiled. The first field in this file, such as #3, relates to the number of times a kernel was built from the source base.

19.3.9.4.  /proc/sys/net/

This directory contains subdirectories concerning various networking topics. Various configurations at the time of kernel compilation make different directories available here, such as ethernet/, ipv4/, ipx/, and ipv6/. By altering the files within these directories, system administrators are able to adjust the network configuration on a running system.
Given the wide variety of possible networking options available with Linux, only the most common /proc/sys/net/ directories are discussed.
The /proc/sys/net/core/ directory contains a variety of settings that control the interaction between the kernel and networking layers. The most important of these files are:
  • message_burst — Sets the amount of time in tenths of a second required to write a new warning message. This setting is used to mitigate Denial of Service (DoS) attacks. The default setting is 10.
  • message_cost — Sets a cost on every warning message. The higher the value of this file (default of 5), the more likely the warning message is ignored. This setting is used to mitigate DoS attacks.
    The idea of a DoS attack is to bombard the targeted system with requests that generate errors and fill up disk partitions with log files or require all of the system's resources to handle the error logging. The settings in message_burst and message_cost are designed to be modified based on the system's acceptable risk versus the need for comprehensive logging.
  • netdev_max_backlog — Sets the maximum number of packets allowed to queue when a particular interface receives packets faster than the kernel can process them. The default value for this file is 1000.
  • optmem_max — Configures the maximum ancillary buffer size allowed per socket.
  • rmem_default — Sets the receive socket buffer default size in bytes.
  • rmem_max — Sets the receive socket buffer maximum size in bytes.
  • wmem_default — Sets the send socket buffer default size in bytes.
  • wmem_max — Sets the send socket buffer maximum size in bytes.
The /proc/sys/net/ipv4/ directory contains additional networking settings. Many of these settings, used in conjunction with one another, are useful in preventing attacks on the system or when using the system to act as a router.

Caution

An erroneous change to these files may affect remote connectivity to the system.
The following is a list of some of the more important files within the /proc/sys/net/ipv4/ directory:
  • icmp_echo_ignore_all and icmp_echo_ignore_broadcasts — Allows the kernel to ignore ICMP ECHO packets from every host or only those originating from broadcast and multicast addresses, respectively. A value of 0 allows the kernel to respond, while a value of 1 ignores the packets.
  • ip_default_ttl — Sets the default Time To Live (TTL), which limits the number of hops a packet may make before reaching its destination. Increasing this value can diminish system performance.
  • ip_forward — Permits interfaces on the system to forward packets to one other. By default, this file is set to 0. Setting this file to 1 enables network packet forwarding.
  • ip_local_port_range — Specifies the range of ports to be used by TCP or UDP when a local port is needed. The first number is the lowest port to be used and the second number specifies the highest port. Any systems that expect to require more ports than the default 1024 to 4999 should use a range from 32768 to 61000.
  • tcp_syn_retries — Provides a limit on the number of times the system re-transmits a SYN packet when attempting to make a connection.
  • tcp_retries1 — Sets the number of permitted re-transmissions attempting to answer an incoming connection. Default of 3.
  • tcp_retries2 — Sets the number of permitted re-transmissions of TCP packets. Default of 15.
The file called 
/usr/share/doc/kernel-doc-kernel_version/Documentation/networking/ip-sysctl.txt
contains a complete list of files and options available in the /proc/sys/net/ipv4/ directory.
A number of other directories exist within the /proc/sys/net/ipv4/ directory and each covers a different aspect of the network stack. The /proc/sys/net/ipv4/conf/ directory allows each system interface to be configured in different ways, including the use of default settings for unconfigured devices (in the /proc/sys/net/ipv4/conf/default/ subdirectory) and settings that override all special configurations (in the /proc/sys/net/ipv4/conf/all/ subdirectory).
The /proc/sys/net/ipv4/neigh/ directory contains settings for communicating with a host directly connected to the system (called a network neighbor) and also contains different settings for systems more than one hop away.
Routing over IPV4 also has its own directory, /proc/sys/net/ipv4/route/. Unlike conf/ and neigh/, the /proc/sys/net/ipv4/route/ directory contains specifications that apply to routing with any interfaces on the system. Many of these settings, such as max_size, max_delay, and min_delay, relate to controlling the size of the routing cache. To clear the routing cache, write any value to the flush file.
Additional information about these directories and the possible values for their configuration files can be found in: 
/usr/share/doc/kernel-doc-kernel_version/Documentation/filesystems/proc.txt

19.3.9.5.  /proc/sys/vm/

This directory facilitates the configuration of the Linux kernel's virtual memory (VM) subsystem. The kernel makes extensive and intelligent use of virtual memory, which is commonly referred to as swap space.
The following files are commonly found in the /proc/sys/vm/ directory:
  • block_dump — Configures block I/O debugging when enabled. All read/write and block dirtying operations done to files are logged accordingly. This can be useful if diagnosing disk spin up and spin downs for laptop battery conservation. All output when block_dump is enabled can be retrieved via dmesg. The default value is 0.

    Tip

    If block_dump is enabled at the same time as kernel debugging, it is prudent to stop the klogd daemon, as it generates erroneous disk activity caused by block_dump.
  • dirty_background_ratio — Starts background writeback of dirty data at this percentage of total memory, via a pdflush daemon. The default value is 10.
  • dirty_expire_centisecs — Defines when dirty in-memory data is old enough to be eligible for writeout. Data which has been dirty in-memory for longer than this interval is written out next time a pdflush daemon wakes up. The default value is 3000, expressed in hundredths of a second.
  • dirty_ratio — Starts active writeback of dirty data at this percentage of total memory for the generator of dirty data, via pdflush. The default value is 20.
  • dirty_writeback_centisecs — Defines the interval between pdflush daemon wakeups, which periodically writes dirty in-memory data out to disk. The default value is 500, expressed in hundredths of a second.
  • laptop_mode — Minimizes the number of times that a hard disk needs to spin up by keeping the disk spun down for as long as possible, therefore conserving battery power on laptops. This increases efficiency by combining all future I/O processes together, reducing the frequency of spin ups. The default value is 0, but is automatically enabled in case a battery on a laptop is used.
    This value is controlled automatically by the acpid daemon once a user is notified battery power is enabled. No user modifications or interactions are necessary if the laptop supports the ACPI (Advanced Configuration and Power Interface) specification.
    For more information, refer to the following installed documentation:
    /usr/share/doc/kernel-doc-kernel_version/Documentation/laptop-mode.txt
  • max_map_count — Configures the maximum number of memory map areas a process may have. In most cases, the default value of 65536 is appropriate.
  • min_free_kbytes — Forces the Linux VM (virtual memory manager) to keep a minimum number of kilobytes free. The VM uses this number to compute a pages_min value for each lowmem zone in the system. The default value is in respect to the total memory on the machine.
  • nr_hugepages — Indicates the current number of configured hugetlb pages in the kernel.
    For more information, refer to the following installed documentation:
    /usr/share/doc/kernel-doc-kernel_version/Documentation/vm/hugetlbpage.txt
  • nr_pdflush_threads — Indicates the number of pdflush daemons that are currently running. This file is read-only, and should not be changed by the user. Under heavy I/O loads, the default value of two is increased by the kernel.
  • overcommit_memory — Configures the conditions under which a large memory request is accepted or denied. The following three modes are available:
    • 0 — The kernel performs heuristic memory over commit handling by estimating the amount of memory available and failing requests that are blatantly invalid. Unfortunately, since memory is allocated using a heuristic rather than a precise algorithm, this setting can sometimes allow available memory on the system to be overloaded. This is the default setting.
    • 1 — The kernel performs no memory over commit handling. Under this setting, the potential for memory overload is increased, but so is performance for memory intensive tasks (such as those executed by some scientific software).
    • 2 — The kernel fails requests for memory that add up to all of swap plus the percent of physical RAM specified in /proc/sys/vm/overcommit_ratio. This setting is best for those who desire less risk of memory overcommitment.

      Note

      This setting is only recommended for systems with swap areas larger than physical memory.
  • overcommit_ratio — Specifies the percentage of physical RAM considered when /proc/sys/vm/overcommit_memory is set to 2. The default value is 50.
  • page-cluster — Sets the number of pages read in a single attempt. The default value of 3, which actually relates to 16 pages, is appropriate for most systems.
  • swappiness — Determines how much a machine should swap. The higher the value, the more swapping occurs. The default value, as a percentage, is set to 60.
All kernel-based documentation can be found in the following locally installed location:
/usr/share/doc/kernel-doc-kernel_version/Documentation/, which contains additional information.

19.3.10.  /proc/sysvipc/

This directory contains information about System V IPC resources. The files in this directory relate to System V IPC calls for messages (msg), semaphores (sem), and shared memory (shm).

19.3.11.  /proc/tty/

This directory contains information about the available and currently used tty devices on the system. Originally called teletype devices, any character-based data terminals are called tty devices.
In Linux, there are three different kinds of tty devices. Serial devices are used with serial connections, such as over a modem or using a serial cable. Virtual terminals create the common console connection, such as the virtual consoles available when pressing Alt+<F-key> at the system console. Pseudo terminals create a two-way communication that is used by some higher level applications, such as XFree86. The drivers file is a list of the current tty devices in use, as in the following example: 
serial               /dev/cua        5  64-127 serial:callout
serial               /dev/ttyS       4  64-127 serial
pty_slave            /dev/pts      136   0-255 pty:slave
pty_master           /dev/ptm      128   0-255 pty:master
pty_slave            /dev/ttyp       3   0-255 pty:slave
pty_master           /dev/pty        2   0-255 pty:master
/dev/vc/0            /dev/vc/0       4       0 system:vtmaster
/dev/ptmx            /dev/ptmx       5       2 system
/dev/console         /dev/console    5       1 system:console
/dev/tty             /dev/tty        5       0 system:/dev/tty
unknown              /dev/vc/%d      4    1-63 console
The /proc/tty/driver/serial file lists the usage statistics and status of each of the serial tty lines.
In order for tty devices to be used as network devices, the Linux kernel enforces line discipline on the device. This allows the driver to place a specific type of header with every block of data transmitted over the device, making it possible for the remote end of the connection to a block of data as just one in a stream of data blocks. SLIP and PPP are common line disciplines, and each are commonly used to connect systems to one other over a serial link.

19.3.12.  /proc/PID/

Out of Memory (OOM) refers to a computing state where all available memory, including swap space, has been allocated. When this situation occurs, it will cause the system to panic and stop functioning as expected. There is a switch that controls OOM behavior in /proc/sys/vm/panic_on_oom. When set to 1 the kernel will panic on OOM. A setting of 0 instructs the kernel to call a function named oom_killer on an OOM. Usually, oom_killer can kill rogue processes and the system will survive.
The easiest way to change this is to echo the new value to /proc/sys/vm/panic_on_oom. 
# cat /proc/sys/vm/panic_on_oom
1

# echo 0 > /proc/sys/vm/panic_on_oom

# cat /proc/sys/vm/panic_on_oom
0
It is also possible to prioritize which processes get killed by adjusting the oom_killer score. In /proc/PID/ there are two tools labelled oom_adj and oom_score. Valid scores for oom_adj are in the range -16 to +15. To see the current oom_killer score, view the oom_score for the process. oom_killer will kill processes with the highest scores first.
This example adjusts the oom_score of a process with a PID of 12465 to make it less likely that oom_killer will kill it. 
# cat /proc/12465/oom_score
79872

# echo -5 > /proc/12465/oom_adj

# cat /proc/12465/oom_score
78
There is also a special value of -17, which disables oom_killer for that process. In the example below, oom_score returns a value of 0, indicating that this process would not be killed. 
# cat /proc/12465/oom_score
78

# echo -17 > /proc/12465/oom_adj

# cat /proc/12465/oom_score
0
A function called badness() is used to determine the actual score for each process. This is done by adding up 'points' for each examined process. The process scoring is done in the following way:
  1. The basis of each process's score is its memory size.
  2. The memory size of any of the process's children (not including a kernel thread) is also added to the score
  3. The process's score is increased for 'niced' processes and decreased for long running processes.
  4. Processes with the CAP_SYS_ADMIN and CAP_SYS_RAWIO capabilities have their scores reduced.
  5. The final score is then bitshifted by the value saved in the oom_adj file.
Thus, a process with the highest oom_score value will most probably be a non-priviliged, recently started process that, along with its children, uses a large amount of memory, has been 'niced', and handles no raw I/O.

19.4. Using the sysctl Command

The /sbin/sysctl command is used to view, set, and automate kernel settings in the /proc/sys/ directory.
For a quick overview of all settings configurable in the /proc/sys/ directory, type the /sbin/sysctl -a command as root. This creates a large, comprehensive list, a small portion of which looks something like the following: 
net.ipv4.route.min_delay = 2 kernel.sysrq = 0 kernel.sem = 250     32000     32     128
This is the same information seen if each of the files were viewed individually. The only difference is the file location. For example, the /proc/sys/net/ipv4/route/min_delay file is listed as net.ipv4.route.min_delay, with the directory slashes replaced by dots and the proc.sys portion assumed.
The sysctl command can be used in place of echo to assign values to writable files in the /proc/sys/ directory. For example, instead of using the command 
echo 1 > /proc/sys/kernel/sysrq
use the equivalent sysctl command as follows: 
sysctl -w kernel.sysrq="1"
kernel.sysrq = 1
While quickly setting single values like this in /proc/sys/ is helpful during testing, this method does not work as well on a production system as special settings within /proc/sys/ are lost when the machine is rebooted. To preserve custom settings, add them to the /etc/sysctl.conf file.
Each time the system boots, the init program runs the /etc/rc.d/rc.sysinit script. This script contains a command to execute sysctl using /etc/sysctl.conf to determine the values passed to the kernel. Any values added to /etc/sysctl.conf therefore take effect each time the system boots.

19.5. References

Below are additional sources of information about proc file system.

Installed Documentation

Some of the best documentation about the proc file system is installed on the system by default.
  • /usr/share/doc/kernel-doc-kernel_version/Documentation/filesystems/proc.txt — Contains assorted, but limited, information about all aspects of the /proc/ directory.
  • /usr/share/doc/kernel-doc-kernel_version/Documentation/sysrq.txt — An overview of System Request Key options.
  • /usr/share/doc/kernel-doc-kernel_version/Documentation/sysctl/ — A directory containing a variety of sysctl tips, including modifying values that concern the kernel (kernel.txt), accessing file systems (fs.txt), and virtual memory use (vm.txt).
  • /usr/share/doc/kernel-doc-kernel_version/Documentation/networking/ip-sysctl.txt — A detailed overview of IP networking options.

Useful Websites

  • http://www.linuxhq.com/ — This website maintains a complete database of source, patches, and documentation for various versions of the Linux kernel.

Part IV. System Monitoring

Chapter 20. Gathering System Information

20.1. System Processes
20.2. Memory Usage
20.3. File Systems
20.4. Hardware
20.5. Additional Resources
20.5.1. Installed Documentation
Before you learn how to configure your system, you should learn how to gather essential system information. For example, you should know how to find the amount of free memory, the amount of available hard drive space, how your hard drive is partitioned, and what processes are running. This chapter discusses how to retrieve this type of information from your Red Hat Enterprise Linux system using simple commands and a few simple programs.

20.1. System Processes

The ps ax command displays a list of current system processes, including processes owned by other users. To display the owner alongside each process, use the ps aux command. This list is a static list; in other words, it is a snapshot of what was running when you invoked the command. If you want a constantly updated list of running processes, use top as described below.
The ps output can be long. To prevent it from scrolling off the screen, you can pipe it through less: 
ps aux | less
You can use the ps command in combination with the grep command to see if a process is running. For example, to determine if Emacs is running, use the following command: 
ps ax | grep emacs
The top command displays currently running processes and important information about them including their memory and CPU usage. The list is both real-time and interactive. An example of output from the top command is provided as follows: 
top - 18:11:48 up 1 min,  1 user,  load average: 0.68, 0.30, 0.11
Tasks: 122 total,   1 running, 121 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.0%us,  0.5%sy,  0.0%ni, 93.4%id,  5.7%wa,  0.2%hi,  0.2%si,  0.0
Mem:    501924k total,   376496k used,   125428k free,    29664k buffers
Swap:  1015800k total,        0k used,  1015800k free,   189008k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND       
 1601 root      40   0 20172 1084  920 S  0.3  0.2   0:00.08 hald-addon-sto
 1998 silas     40   0 14984 1160  880 R  0.3  0.2   0:00.13 top           
    1 root      40   0 19160 1412 1156 S  0.0  0.3   0:00.96 init          
    2 root      40   0     0    0    0 S  0.0  0.0   0:00.01 kthreadd      
    3 root      RT   0     0    0    0 S  0.0  0.0   0:00.05 migration/0   
    4 root      20   0     0    0    0 S  0.0  0.0   0:00.00 ksoftirqd/0   
    5 root      RT   0     0    0    0 S  0.0  0.0   0:00.00 watchdog/0    
    6 root      RT   0     0    0    0 S  0.0  0.0   0:00.04 migration/1   
    7 root      20   0     0    0    0 S  0.0  0.0   0:00.00 ksoftirqd/1   
    8 root      RT   0     0    0    0 S  0.0  0.0   0:00.00 watchdog/1    
    9 root      20   0     0    0    0 S  0.0  0.0   0:00.00 events/0      
   10 root      20   0     0    0    0 S  0.0  0.0   0:00.01 events/1      
   11 root      20   0     0    0    0 S  0.0  0.0   0:00.00 cpuset        
   12 root      20   0     0    0    0 S  0.0  0.0   0:00.00 khelper       
[output truncated]
To exit top, press the q key.
Table 20.1, “Interactive top commands” contains useful interactive commands that you can use with top. For more information, refer to the top(1) manual page.
Table 20.1. Interactive top commands
Command Description
Space Immediately refresh the display
h Display a help screen
k Kill a process. You are prompted for the process ID and the signal to send to it.
n Change the number of processes displayed. You are prompted to enter the number.
u Sort by user.
M Sort by memory usage.
P Sort by CPU usage.

If you prefer a graphical interface for top, you can use the GNOME System Monitor. To start it from the desktop, select Applications → System Tools → System Monitor or execute gnome-system-monitor at a shell prompt. Select the Processes tab.
The GNOME System Monitor allows you to search for a process in the list of running processes. Using the GNOME System Monitor, you can also view all processes, your processes, or active processes.
The Edit menu item allows you to:
  • Stop a process.
  • Continue or start a process.
  • End a processes.
  • Kill a process.
  • Change the priority of a selected process.
  • Edit the System Monitor preferences. These include changing the interval seconds to refresh the list and selecting process fields to display in the System Monitor window.
The View menu item allows you to:
  • View only active processes.
  • View all processes.
  • View my processes.
  • View process dependencies.
  • View a memory map of a selected process.
  • View the files opened by the selected process.
  • Refresh the list of processes.
To stop a process, select it and click End Process. Alternatively you can also stop a process by selecting it, clicking Edit on your menu and selecting Stop Process.
To sort the information by a specific column, click on the name of the column. This sorts the information by the selected column in ascending order. Click on the name of the column again to toggle the sort between ascending and descending order.
GNOME System Monitor - Processes tab
Processes tab of the gnome-system-monitor
Figure 20.1.  GNOME System Monitor - Processes tab

20.2. Memory Usage

The free command displays the total amount of physical memory and swap space for the system as well as the amount of memory that is used, free, shared, in kernel buffers, and cached. 
             total       used       free     shared    buffers     cached
Mem:       4017660    1619044    2398616          0      59864     637968
-/+ buffers/cache:     921212    3096448
Swap:      3071996          0    3071996
The command free -m shows the same information in megabytes, which are easier to read. 
             total       used       free     shared    buffers     cached
Mem:          3923       1569       2353          0         58        626
-/+ buffers/cache:        884       3038
Swap:         2999          0       2999
If you prefer a graphical interface for free, you can use the GNOME System Monitor. To start it from the desktop, select Applications → System Tools → System Monitor or execute gnome-system-monitor at a shell prompt. Click on the Resources tab.
GNOME System Monitor - Resources tab
Resources tab of the gnome-system-monitor
Figure 20.2.  GNOME System Monitor - Resources tab

20.3. File Systems

The df command reports the system's disk space usage. If you Execute the command df at a shell prompt, the output looks similar to the following: 
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/volgrp1-lvroot
                      14127024   6868092   6541316  52% /
tmpfs                  2008828       592   2008236   1% /dev/shm
/dev/sda1               495844     65047    405197  14% /boot
/dev/mapper/luks-b20f8f7a-7f0f-4497-8de4-81bfa3e541cf
                     122046576  12111420 103735552  11% /home
By default, this utility shows the partition size in 1 kilobyte blocks and the amount of used and available disk space in kilobytes. To view the information in megabytes and gigabytes, use the command df -h. The -h argument stands for human-readable format. The output looks similar to the following: 
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/volgrp1-lvroot
                       14G  6.6G  6.3G  52% /
tmpfs                 2.0G  592K  2.0G   1% /dev/shm
/dev/sda1             485M   64M  396M  14% /boot
/dev/mapper/luks-b20f8f7a-7f0f-4497-8de4-81bfa3e541cf
                      117G   12G   99G  11% /home
In the list of mounted partitions, there is an entry for /dev/shm. This entry represents the system's virtual memory file system.
The du command displays the estimated amount of space being used by files in a directory. If you execute du at a shell prompt, the disk usage for each of the subdirectories is displayed in a list. The grand total for the current directory and subdirectories are also shown as the last line in the list. If you do not want to see the totals for all the subdirectories, use the command du -hs to see only the grand total for the directory in human-readable format. Use the du --help command to see more options.
To view the system's partitions and disk space usage in a graphical format, use the Gnome System Monitor by clicking on Applications → System Tools → System Monitor or executing the gnome-system-monitor command at a shell prompt. Select the File Systems tab to view the system's partitions. The figure below illustrates the File Systems tab.
GNOME System Monitor - File Systems tab
File systems tab of the gnome-system-monitor
Figure 20.3.  GNOME System Monitor - File Systems tab

20.4. Hardware

If you are having trouble configuring your hardware or just want to know what hardware is in your system, you can use the Hardware Browser application to display the hardware that can be probed. To start the program from the desktop, select System (the main menu on the panel) > Administration > Hardware or type hwbrowser at a shell prompt. As shown in Figure 20.4, “ Hardware Browser ”, it displays your CD-ROM devices, diskette drives, hard drives and their partitions, network devices, pointing devices, system devices, and video cards. Click on the category name in the left menu, and the information is displayed.
Hardware Browser
hwbrowser
Figure 20.4.  Hardware Browser

The Device Manager application can also be used to display your system hardware. This application can be started by selecting System (the main menu on the panel) > Administration > Hardware like the Hardware Browser. To start the application from a terminal, type hal-device-manager. Depending on your installation preferences, the graphical menu above may start this application or the Hardware Browser when clicked. The figure below illustrates the Device Manager window.
Device Manager
Device Manager
Figure 20.5.  Device Manager

You can also use the lspci command to list all PCI devices. Use the command lspci -v for more verbose information or lspci -vv for very verbose output.
For example, lspci can be used to determine the manufacturer, model, and memory size of a system's video card: 
 
00:02.1 Display controller: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 07)
        Subsystem: Lenovo Device 20e4
        Flags: bus master, fast devsel, latency 0
        Memory at f4200000 (64-bit, non-prefetchable) [size=1M]
        Capabilities: [d0] Power Management version 3
The lspci is also useful to determine the network card in your system if you do not know the manufacturer or model number.

20.5. Additional Resources

To learn more about gathering system information, refer to the following resources.

20.5.1. Installed Documentation

  • ps --help — Displays a list of options that can be used with ps.
  • top manual page — Execute man top to learn more about top and its many options.
  • free manual page — Execute man free to learn more about free and its many options.
  • df manual page — Execute man df to learn more about the df command and its many options.
  • du manual page — Execute man du to learn more about the du command and its many options.
  • lspci manual page — Execute man lspci to learn more about the lspci command and its many options.
  • /proc/ directory — The contents of the /proc/ directory can also be used to gather more detailed system information.

Chapter 21. ABRT

21.1. Overview
21.2. Installing and Running ABRT
21.3. ABRT Plugins
21.3.1. Analyzer Plugins
21.3.2. Reporter Plugins
21.3.3. Plugin Configuration in the GUI
21.4. Generating Backtraces
21.4.1. Troubleshooting Backtrace Generation
21.5. Using the Command Line Interface
21.5.1. Viewing Crashes
21.5.2. Reporting Crashes
21.5.3. Deleting Crashes
21.6. Configuring ABRT
21.7. Configuring Centralized Crash Collection
21.7.1. Testing ABRT's Crash Detection
21.7.2. Testing the Upload Method

21.1. Overview

ABRT is the Automatic Bug-Reporting Tool. ABRT consists of a daemon that runs silently in the background most of the time. It springs into action when an application crashes. It then collects the relevant crash data such as a core file if there is one, the crashing application's command line parameters, and other contextual puzzle pieces of forensic utility. Finally, ABRT is capable of reporting crash data to a relevant issue tracker, such as RHTSupport. Reporting crash data to a relevant issue tracker can be configured to happen automatically at every detected crash, or crash dumps can be stored locally, reviewed, reported, and deleted manually by a user. ABRT's various plugins analyze crash data from applications written in the C, C++ and Python language, as well as report crashes to relevant issue trackers.
The ABRT package consists of:
  • abrtd, the system service
  • abrt-applet, which runs in the user's Notification Area
  • abrt-gui, the GUI application that shows collected crash dumps and allows you to edit, report, and delete them
  • abrt-cli, the command line interface with functionality similar to abrt-gui.
You can open the ABRT GUI application by clicking Applications → System Tools → Automatic Bug Reporting Tool.
Automatic Bug Reporting Tool Main Window
A number of additional packages can be installed to provide ABRT plugins and addons. To view all the available ABRT packages, type the following command: 
~]$ yum list all | grep abrt

21.2. Installing and Running ABRT

By default, ABRT should be installed on your system, the abrtd daemon configured to run at boot time, and abrt-applet to run in the Notification Area of your desktop session.

Note: Installing the ABRT packages

In order to use ABRT, first ensure the abrt-desktop package is installed on your system by running, as root: 
~]# yum install abrt-desktop
For more information on installing packages with Yum, refer to Section 1.2.2, “Installing”.
ABRT is typically configured to start up at boot time. You can check that the abrtd daemon is running by running the following command, as root: 
~]# service abrtd status
abrt (pid  1559) is running...
If you receive abrt is stopped, you can start the abrtd service by running, as root: 
~]# service abrtd start
Starting abrt daemon:                                      [  OK  ]
You can ensure that the abrtd service initializes at startup time by running the following command, as root: 
~]# chkconfig abrtd on
ABRT's applet can be started by hand by running the abrt-applet program as a normal user when logged into your desktop session, or by arranging for it to be started when the GUI session is initialized. For example, on the GNOME desktop, this can be configured in System → Preferences → Startup Applications.
The ABRT alarm icon
When a crash is detected and saved, a broadcast D-Bus message is sent about this crash. If abrt-applet is running, it receives this message and displays a red alarm icon in the Notification Area. You can open the GUI application by clicking on this icon.
Alternatively, you can open the ABRT GUI application by clicking Applications → System Tools → Automatic Bug Reporting Tool.

21.3.  ABRT Plugins

ABRT offers a variety of analyzer plugins and reporter plugins. These plugins are described in the following two sections. Not all of the plugins mentioned in the following sections are installed by default. To view all available plugins, run the following command: 
]$ yum list all | grep abrt-plugin-*

21.3.1. Analyzer Plugins

These plugins serve as analyzers and crash information collectors for specific types of crashes. For example, the Kerneloops analyzer plugin checks for crashes in the kernel only. These plugins can be enabled/disabled from loading at start-up in their corresponding configuration files placed in the /etc/abrt/plugins/ directory. The following is a list of all analyzer plugins.
Kerneloops
— Checks for crashes in the kernel and consequently collects kernel crash information. It can be enabled/disabled from loading at start-up in the /etc/abrt/plugins/Kerneloops.conf file.
Python
— Checks for crashes in Python programs and consequently collects the crash information. It can be enabled/disabled from loading at start-up in the /etc/abrt/plugins/Python.conf file.
CCpp
— Checks for crashes in C and C++ programs and consequently collects the crash information. It can be enabled/disabled from loading at start-up in the /etc/abrt/plugins/CCpp.conf file.

21.3.2. Reporter Plugins

These plugins gather the crash data acquired by the analyzer plugins, combine the data with any user input (such as comments about the crash, reproducibility, etc.), and provide a specific output. Each of these plugins is configurable in its corresponding configuration file placed in the /etc/abrt/plugins/ directory or in the ABRT GUI application (for more information on reporter plugin configuration in the ABRT GUI application, refer to Section 21.3.3, “Plugin Configuration in the GUI”).
RHTSupport
— Reports crashes into the Red Hat Technical Support system. Intended for users of Red Hat Enterprise Linux.
MailX
— Sends a crash report via the mailx utility to a specified email address.
Report Uploader
— Uploads a tarball with crash data into a FTP/SCP server
Bugzilla
— Reports crashes into Bugzilla in the form of Bugzilla database entries.

Note

The use of the Bugzilla plugin to report crashes into Bugzilla in the form of Bugzilla database entries is strongly discouraged. Please use the RHTSupport plugin to report crashes into the Red Hat Ticketing System instead.
Logger
— Creates a crash report and saves it to a specified local file.

21.3.3. Plugin Configuration in the GUI

You can override the system-wide plugin configuration in the /etc/abrt/plugins/*.conf configuration files on a per-user basis. Each of the plugins specified in section Section 21.3.2, “Reporter Plugins” can be configured in the ABRT GUI application. Open the plugins window by clicking Edit → Plugins. This window shows a list of all installed plugins. You can also view each of the plugins' details by selecting one and expanding Plugin Details. When you select one of the configurable plugins, you can click the Configure plugin button and you will be able to configure your desired plugin. If you change any of the plugins' parameters, they are saved in the Gnome keyring and will be used in the future GUI sessions.

Note

All of the /etc/abrt/plugins/*.conf configuration files are world readable and are meant to be used as global settings. Thus, it is not advisable to store usernames, passwords or any other sensitive data in them. The per-user settings (set in the GUI application and readable by the owner of $HOME only) are stored in the Gnome keyring or can be stored in a text file in $HOME/.abrt/*.conf for use in abrt-cli.
ABRT Plugins
The following is a list of all configuration options available for each configurable plugin in the ABRT GUI application.
RHTSupport
In the RHTSupport plugin configuration, you can configure the following parameters:
  • RHTSupport URL — Specifies the RHTSupport URL where crash dumps are sent (by default, set to https://api.access.redhat.com/rs).
  • Login — User login which is used to log into RHTSupport and create a RHTSupport database entry for a reported crash.
  • Password — Password used to log into RHTSupport.
When the SSL verify option is checked, the SSL protocol is used when sending the data over the network.
MailX
In the MailX plugin configuration, you can configure the following parameters:
  • Subject — A string that appears in the Subject field of a crash report email sent by mailx (by default, set to "[abrt] crash report").
  • Your Email — A string that appears in the From field of a crash report email.
  • Recipient's Email — Email address of the recipient of a crash report email.
When the Send Binary Data option is checked, the crash report email will also contain all binary files associated with the crash in an attachment. The core dump file is also sent as an attachment.
ReportUploader
In the ReportUploader plugin configuration, you can configure the following parameters:
  • Customer — Specifies customer's identification.
  • Ticket — Specifies the Ticket ID number in a specific issue tracker that collects crash reports.
  • URL — Specifies the URL of the issue tracker used to collect crash reports.
  • Retry count — Specifies the number of retries should an upload fail.
  • Retry delay — Specifies the number or seconds between two retries.
When the Use encryption option is checked, the crash report sent to the issue tracker is encrypted.
When the Upload option is checked, all crash reports are uploaded to the specified issue tracker. If the option is unchecked, all crash reports are saved locally.
Bugzilla
In the Bugzilla plugin configuration, you can configure the following parameters:
  • Bugzilla URL — Specifies the Bugzilla URL where crash dumps are sent (by default, set to https://bugzilla.redhat.com).
  • Login (email) — User login which is used to log into Bugzilla and create a Bugzilla database entry for a reported crash.
  • Password — Password used to log into Bugzilla.
When the SSL verify option is checked, the SSL protocol is used when sending the data over the network.
Logger
In the Logger plugin configuration, you can configure the following parameter:
  • Logger file — Specifies a file into which the crash reports are saved (by default, set to /var/log/abrt.log).
When the Append new logs option is checked, the Logger plugin will append new crash reports to the log file specified in the Logger file option. When unchecked, the new crash report always replaces the previous one.

21.4. Generating Backtraces

In order to analyze a reported crash, developers need as much detail about the crash as possible. A stack backtrace is an important source of information when a crash in a binary program (caught by the CCpp analyzer plugin) occurs.
ABRT is configured to generate a backtrace whenever a crash is reported through the ABRT GUI application or the ABRT command line interface.
ABRT completes the following steps to generate a backtrace:
  • It examines the core dump (which consists of the recorded contents of the memory of an application at a specific time), which is saved in the crash dump directory. From this file, ABRT extracts the information about the crashed binary program and information about every loaded dynamic library.
  • It queries Yum to determine which debuginfo packages correspond to all the files extracted from the crash dump. This is the first potentially slow operation. Yum may need to refresh the filelists of various repositories in order to find the correct package names. This process may take a few minutes.
  • It downloads the needed debuginfo packages, and extracts and saves the debuginfo files. In order to speed up future backtrace generation, debuginfo files are cached in the /var/cache/abrt-di directory.
  • It generates a backtrace using GDB (the GNU Debugger) and saves it into the crash dump directory.
You can change the following backtrace generation parameters in the /etc/abrt/plugins/CCpp.conf file:
  • Backtrace = <yes/no> — Enables/Disables backtrace generation.
  • BacktraceRemotes = <yes/no> — For more information about this parameter, refer to Section 21.7, “Configuring Centralized Crash Collection”.
  • InstallDebugInfo = <yes/no> — Enables/Disables the installation of debuginfo packages (useful if your network is not available or it is firewalled).
  • ReadonlyLocalDebugInfoDirs = /path1:/path2:... — Specifies the paths of local repositories (available, for example, through a network mount) that contain pre-downloaded debuginfo packages.
  • DebugInfoCacheMB = 4000 — Specifies the maximum size of the cached debuginfo packages in the /var/cache/abrt-di directory.

21.4.1. Troubleshooting Backtrace Generation

In some cases, a long delay in the ABRT GUI application occurs after choosing a crash and pressing the Report button. In this case, open the Details in the Generating backtrace window and examine the messages.
The following is a typical output seen in the Generating backtrace window: 
Starting the debuginfo installation
Getting list of build IDs
12 missing debuginfos, getting package list from cache
12 missing debuginfos, getting package list from repositories
Downloading 7 packages
Download 1/7: acl-debuginfo-2.2.49-6.fc13.x86_64
Unpacking: acl-debuginfo-2.2.49-6.fc13.x86_64.rpm
Caching debuginfo:
usr/lib/debug/.build-id/3d/e20df1db609bd9313b1dc440796004f95911fd.debug
Download 2/7: firefox-debuginfo-3.6.7-1.fc13.x86_64
Unpacking: firefox-debuginfo-3.6.7-1.fc13.x86_64.rpm
Caching debuginfo:
usr/lib/debug/.build-id/3d/b29c9308cb276431ce8854a2d88cf83518afc6.debug
Caching debuginfo:
usr/lib/debug/.build-id/a3/86884285365c8288e4e761ec034fafaa1daee1.debug
⋮
Download 7/7: zlib-debuginfo-1.2.3-23.fc12.x86_64
Unpacking: zlib-debuginfo-1.2.3-23.fc12.x86_64.rpm
Caching debuginfo:
usr/lib/debug/.build-id/f7/933750da80f555321576e72b375caf7a3cc075.debug
All needed debuginfos are present
Generating backtrace
This process is performed by the /usr/bin/abrt-debuginfo-install shell script. This script uses a temporary directory (e.g. /var/run/abrt/tmp-29177-1283344373) for its operations. Normally, this directory is removed when abrt-debuginfo-install exits.
If the debuginfo installation hangs, or is unable to download anything, you may debug the problem by editing the abrt-debuginfo-install script. Change the following parameters: 
debug=false
keep_tmp=false
at the top of the script to: 
debug=true
keep_tmp=true
The first parameter instructs abrt-debuginfo-install to be verbose, the second parameter instructs abrt-debuginfo-install to not delete the /var/run/abrt/tmp-NNN-NNN directory. You can examine the log files in this directory, they may contain useful error messages.
abrt-debuginfo-install uses yum and yumdownloader to handle the debuginfo packages. In order to quickly check that your yum configuration does not cause any problems which prevent abrt-debuginfo-install from working properly, change to the /tmp directory and run the following commands, as root: 
tmp]# yum --enablerepo=*debuginfo* --quiet provides /usr/bin/true
tmp]# yumdownloader --enablerepo=*debuginfo* --quiet coreutils
Both of these commands should complete successfully, with no error messages. The second command should download the coreutils-*.rpm file. If any error messages appear, check your yum configuration files in the /etc/yum.repos.d/* directory and the /etc/yum/* directory. If any of these commands hang, check that you do not have another instance of yum running, and that your network connection is working properly.

21.5. Using the Command Line Interface

Crashes detected by ABRT can be viewed, reported, and deleted using the command line interface.

21.5.1. Viewing Crashes

To get a list of all crashes, simply enter abrt-cli --list or abrt-cli -l: 
~]$ abrt-cli --list
0.
   UID        : 500
   UUID       : 784b06666020e9f43718d99bf2649f19b4f251a9
   Package    : bash-4.1.2-3.el6
   Executable : /bin/bash
   Crash Time : Tue 20 Jul 2010 03:22:52 PM CEST
   Crash Count: 2
1.
   UID        : 500
   UUID       : 48007b98d65cca4530d99a564379e2609169239d
   Package    : coreutils-8.4-9.el6
   Executable : /bin/sleep
   Crash Time : Tue 20 Jul 2010 03:22:00 PM CEST
   Crash Count: 1
This output contains basic information for every crash. The UID: field shows the ID of the user which ran the program that caused the crash. The Package field shows the name and version of the Red Hat Enterprise Linux package that contains the program, and the Executable field shows the location of the binary or script that crashed. The Crash Count field indicates how many times the same crash happened.

21.5.2. Reporting Crashes

To report a certain crash, enter abrt-cli --report <UUID> or abrt-cli --r <UUID>, where UUID is a Universally Unique Identifier of a crash from the list of crashes; to view this list, execute the abrt-cli --list command. You do not need to remember the exact UUID; either use a mouse to copy and paste it, or enter a unique prefix and press <ENTER>. 
~]$ abrt-cli --report 480
        <ENTER>
>> Starting report creation...
ABRT analyzes the crash and creates a report about it. This might take a while. When the report is ready, abrt-cli opens a text editor with the content of the report. You can see what is being reported, and you can fill in instructions on how to reproduce the crash and other comments. You should also check the backtrace, because the backtrace might be sent to a public server and viewed by anyone, depending on the plugin settings.

Preferred Text Editor

You can choose which text editor is used to check the reports. abrt-cli uses the editor defined in the ABRT_EDITOR environment variable. If the variable is not defined, it checks the VISUAL and EDITOR variables. If none of these variables is set, vi is used. You can set the preferred editor in your .bashrc configuration file. For example, if you prefer GNU Emacs, add the following line to the file: 
export VISUAL=emacs
When you are done with the report, save your changes and close the editor. You will be asked which of the enabled ABRT plugins you want to use to send the report. Respond Y to send the report using your desired plugin or N to skip a plugin you wish not to use.

21.5.3. Deleting Crashes

If you know that you do not want to report a certain crash dump, you can delete it from the crash list. To delete a certain crash dump, enter the command: abrt-cli --delete <UUID> .
Note that ABRT performs a detection of duplicate crashes by comparing new crashes with all locally saved crashes. For a repeating crash, ABRT requires you to act upon it only once. However, if you delete the crash dump of that crash, the next time this specific crash occurs, ABRT will treat it as a new crash: ABRT will alert you about it, prompt you to fill in a description, and report it. This can be redundant, therefore, deleting a crash is not advisable.

21.6. Configuring ABRT

ABRT's main configuration file is /etc/abrt/abrt.conf. ABRT plugins can be configured through their config files, located in the /etc/abrt/plugins/ directory.
After changing and saving the abrt.conf configuration file, you must restart the abrtd daemon—as root—for the new settings to take effect: 
~]# service abrtd restart
The following configuration directives are currently supported in /etc/abrt/abrt.conf.
[ Common ] Section Directives
OpenGPGCheck = <yes/no>
Setting the OpenGPGCheck directive to yes (the default setting) tells ABRT to only analyze and handle crashes in applications provided by packages which are signed by the GPG keys whose locations are listed in the /etc/abrt/gpg_keys file. Setting OpenGPGCheck to no tells ABRT to catch crashes in all programs.
BlackList = nspluginwrapper, valgrind, strace, avant-window-navigator, [<additional_packages> ]
Crashes in packages and binaries listed after the BlackList directive will not be handled by ABRT. If you want ABRT to ignore other packages and binaries, list them here separated by commas.
ProcessUnpackaged = <yes/no>
This directive tells ABRT whether to process crashes in executables that do not belong to any package.
BlackListedPaths = /usr/share/doc/*, */example*
Crashes in executables in these paths will be ignored by ABRT.
Database = SQLite3
This directive instructs ABRT to store its crash data in the SQLite3 database. Other databases are not currently supported. However, ABRT's plugin architecture allows for future support for alternative databases.
#WatchCrashdumpArchiveDir = /var/spool/abrt-upload/
This directive is commented out by default. Enable (uncomment) it if you want abrtd to auto-unpack crashdump tarballs which appear in the specified directory — in this case /var/spool/abrt-upload/ — (for example, uploaded via ftp, scp, etc.). You must ensure that whatever directory you specify in this directive exists and is writable for abrtd. abrtd will not create it automatically.
MaxCrashReportsSize = <size_in_megabytes>
This option sets the amount of storage space, in megabytes, used by ABRT to store all crash information from all users. The default setting is 1000 MB. Once the quota specified here has been met, ABRT will continue catching crashes, and in order to make room for the new crash dumps, it will delete the oldest and largest ones.
ActionsAndReporters = SOSreport, [<additional_plugins> ]
This option tells ABRT to run the specified plugin(s) immediately after a crash is detected and saved. For example, the SOSreport plugin runs the sosreport tool which adds the data collected by it to the created crash dump. You can turn this behavior off by commenting out this line. For further fine-tuning, you can add SOSreport (or any other specified plugin) to either the CCpp or Python options to make ABRT run sosreport (or any other specified plugin) after any C and C++ or Python applications crash, respectively. For more information on various Action and Reporter plugins, refer to Section 21.3, “ ABRT Plugins”
[ AnalyzerActionsAndReporters ] Section Directives
This section allows you to associate certain analyzer actions and reporter actions to run when ABRT catches kernel oopses or crashes in C, C++ or Python programs. The actions and reporters specified in any of the directives below will run only if you run abrt-gui or abrt-cli and report the crash that occurred. If you do not specify any actions and reporters in these directives, you will not be able to report a crash via abrt-gui or abrt-cli. The order of actions and reporters is important. Commenting out a directive, will cause ABRT not to catch the crashes associated with that directive. For example, commenting out the Kerneloops line will cause ABRT not to catch kernel oopses.
Kerneloops = RHTSupport, Logger
This directive specifies that, for kernel oopses, both the RHTSupport and Logger reporters will be run.
CCpp = RHTSupport, Logger
This directive specifies that, when C or C++ program crashes occur, both the RHTSupport and Logger reporters will be run.
Python = RHTSupport, Logger
This directive specifies that, when Python program crashes occur, both the RHTSupport and Logger reporters will be run.
Each of these destinations' details can be specified in the corresponding plugins/*.conf file. For example, plugins/RHTSupport.conf specifies which RHTSupport URL to use (set to https://api.access.redhat.com/rs by default), the user's login name, password for logging in to the RHTSupport site, etc. All these options can also be configured through the abrt-gui application (for more information on plugin configuration refer to Section 21.3, “ ABRT Plugins”).
[ Cron ] Section Directives
<time> = <action_to_run>
The [ Cron ] section of abrt.conf allows you to specify the exact time, or elapsed amount of time between, when ABRT should run a certain action, such as scanning for kernel oopses or performing file transfers. You can list further actions to run by appending them to the end of this section.
Example 21.1. [ Cron ] section of /etc/abrt/abrt.conf
# Which Action plugins to run repeatedly
[ Cron ]
# h:m - at h:m
# s - every s seconds
120 = KerneloopsScanner
#02:00 = FileTransfer

The format for an entry is either <time_in_seconds> = <action_to_run> or <hh:mm> = <action_to_run> , where hh (hour) is in the range 00-23 (all hours less than 10 should be zero-filled, i.e. preceded by a 0), and mm (minute) is 00-59, zero-filled likewise.

21.7. Configuring Centralized Crash Collection

You can set up ABRT so that crash reports are collected from multiple systems and sent to a dedicated system for further processing. This is useful when an administrator does not want to log into hundreds of systems and manually check for crashes found by ABRT. In order to use this method, you need to install the abrt-plugin-reportuploader plugin (yum install abrt-plugin-reportuploader).
The steps to configure ABRT's centralized crash collection are:
  1. Complete the following steps on a dedicated system ("server system"):
    • Create a directory to which you want the crash reports to be uploaded to. Usually, /var/spool/abrt-upload/ is used (the rest of the document assumes you are using /var/spool/abrt-upload/). Make sure this directory is writable by the abrt user.

      Note

      When the abrt-desktop package is installed, it creates a new system user and and a group, both named abrt. This user is used by the abrtd daemon for various things, for example, as the owner:group of /var/spool/abrt/* directories.
    • In the /etc/abrt/abrt.conf configuration file, set the WatchCrashdumpArchiveDir directive to the following: 
      WatchCrashdumpArchiveDir = /var/spool/abrt-upload/
    • Determine your preferred upload mechanism; for example, FTP or SCP. For more information on how to configure SCP, refer to Section 9.3.2, “Using the scp Utility”.
      For security reasons, make sure that uploads can only be performed by a specific user and with a password. The rest of the document assumes that the username used for uploads is USERNAME and the password is PASSWORD. If you do not already have a suitable username which can be used to perform uploads under, you may use the abrt user which already exists on every system where ABRT is installed.
      It is advisable to check whether your upload method works. For more information, refer to Section 21.7.2, “Testing the Upload Method”.
    • It is advisable to check and modify the following parameters if needed:
      • The MaxCrashReportsSize directive (in /etc/abrt/abrt.conf) needs to be set to a larger value if the expected volume of crash data is larger than the default 1000 MB.
      • The ProcessUnpackaged directive (in /etc/abrt/abrt.conf) needs to be set to yes and the BacktraceRemotes (in /etc/abrt/plugins/CCpp.conf) needs to be set to no if the client system and the server system have significantly different sets of installed packages.
  2. Complete the following steps on every client system which will use the central management method:
    • Modify the /etc/abrt/plugins/ReportUploader.conf configuration file so that the ReportUploader plugin knows where to copy the saved crash reports in the following way: 
      Enabled = yes
Upload = yes
URL = ftp://USERNAME:PASSWORD@SERVERNAME/var/spool/abrt-upload/
    • To automatically send the crash reports to the server system immediately after the crash occurs, is detected, and saved, set the [ ActionsAndReporters ] directive in the /etc/abrt/abrt.conf configuration file to the following: 
      ActionsAndReporters = ReportUploader
    • # Alternatively, if user interaction is required before the crash dump is sent to the server system, set the ReportUploader to be a reporter plugin for a specific crash type in the [ AnalyzerActionsAndReporters ] section of the /etc/abrt/abrt.conf configuration file. The user will be required to run abrt-cli or abrt-gui and instruct the abrtd daemon to report the crash and send it to the server system. For example, if you want all crash types to use this method, edit the [ AnalyzerActionsAndReporters ] section in your /etc/abrt/abrt.conf configuration file in the following way: 
      Kerneloops = ReportUploader
CCpp = ReportUploader
Python = ReportUploader

21.7.1. Testing ABRT's Crash Detection

After completing all the steps of the configuration process, the basic setup is finished. To test that this setup works properly use the kill -s SEGV PID command to terminate a process on a client system. For example, start a sleep process and terminate it with the kill command in the following way: 
~]$ sleep 100 &
[1] 2823
~]$ kill -s SEGV 2823
ABRT should detect a crash shortly after executing the kill command. Check that the crash was detected by ABRT on the client system (this can be checked by examining the appropriate syslog file, by running the abrt-cli --list --full command, or by examining the crash dump created in the /var/spool/abrt directory), copied to the server system, unpacked on the server system and can be seen and acted upon using abrt-cli or abrt-gui on the server system.

21.7.2. Testing the Upload Method

Test your upload method from a client system to ensure that it works. For example, upload a file using the interactive FTP client: 
~]$ ftp
ftp> open SERVERNAME
Name: USERNAME
Password: PASSWORD
ftp> cd /var/spool/abrt-upload
250 Operation successful 
ftp> put TESTFILE
ftp> quit
Check whether TESTFILE appeared in the correct directory on the server system.

Part V. Kernel, Module and Driver Configuration

Chapter 22. Working with Kernel Modules

22.1. Listing Currently-Loaded Modules
22.2. Displaying Information About a Module
22.3. Loading a Module
22.4. Unloading a Module
22.5. Setting Module Parameters
22.6. Persistent Module Loading
22.7. Specific Kernel Module Capabilities
22.7.1. Using Multiple Ethernet Cards
22.7.2. Using Channel Bonding
22.8. Additional Resources
The Linux kernel is modular, which means it can extend its capabilities through the use of dynamically-loaded kernel modules. A Kernel module can provide:
  • a device driver which adds support for new hardware; or,
  • support for a file system such as btrfs orNFS.
Like the kernel itself, modules can take parameters that customize their behavior, though the default parameters work well in most cases. User-space tools can list the modules currently loaded into a running kernel; query all available modules for available parameters and module-specific information; and load or unload (remove) modules dynamically into or from a running kernel. Many of these utilities, which are provided by the module-init-tools package, take module dependencies into account when performing operations so that manual dependency-tracking is rarely necessary.
On modern systems, kernel modules are automatically loaded by various mechanisms when the conditions call for it. However, there are occasions when it is necessary to load and/or unload modules manually, such as when a module provides optional functionality, one module should be preferred over another although either could provide basic functionality, or when a module is misbehaving, among other situations.
This chapter explains how to:
  • use the user-space module-init-tools package to display, query, load and unload kernel modules and their dependencies;
  • set module parameters both dynamically on the command line and permanently so that you can customize the behavior of your kernel modules; and,
  • load modules at boot time.

Note: Installing the module-init-tools package

In order to use the kernel module utilities described in this chapter, first ensure the module-init-tools package is installed on your system by running, as root: 
~]# yum install module-init-tools
For more information on installing packages with Yum, refer to Section 1.2.2, “Installing”.

22.1. Listing Currently-Loaded Modules

You can list all kernel modules that are currently loaded into the kernel by running the lsmod command: 
~]$ lsmod
Module                  Size  Used by
xfs                   803635  1
exportfs                3424  1 xfs
vfat                    8216  1
fat                    43410  1 vfat
tun                    13014  2
fuse                   54749  2
ip6table_filter         2743  0
ip6_tables             16558  1 ip6table_filter
ebtable_nat             1895  0
ebtables               15186  1 ebtable_nat
ipt_MASQUERADE          2208  6
iptable_nat             5420  1
nf_nat                 19059  2 ipt_MASQUERADE,iptable_nat
rfcomm                 65122  4
ipv6                  267017  33
sco                    16204  2
bridge                 45753  0
stp                     1887  1 bridge
llc                     4557  2 bridge,stp
bnep                   15121  2
l2cap                  45185  16 rfcomm,bnep
cpufreq_ondemand        8420  2
acpi_cpufreq            7493  1
freq_table              3851  2 cpufreq_ondemand,acpi_cpufreq
usb_storage            44536  1
sha256_generic         10023  2
aes_x86_64              7654  5
aes_generic            27012  1 aes_x86_64
cbc                     2793  1
dm_crypt               10930  1
kvm_intel              40311  0
kvm                   253162  1 kvm_intel
[output truncated]
Each row of lsmod output specifies:
  • the name of a kernel module currently loaded in memory;
  • the amount of memory it uses; and,
  • the sum total of processes that are using the module and other modules which depend on it, followed by a list of the names of those modules, if there are any. Using this list, you can first unload all the modules depending the module you want to unload. For more information, refer to Section 22.4, “Unloading a Module”.
Finally, note that lsmod output is less verbose and considerably easier to read than the content of the /proc/modules pseudo-file.

22.2. Displaying Information About a Module

You can display detailed information about a kernel module by running the modinfo <module_name> command.

Module names do not end in .ko

When entering the name of a kernel module as an argument to one of the module-init-tools utilities, do not append a .ko extension to the end of the name. Kernel module names do not have extensions: their corresponding files do.
For example, to display information about the e1000e module, which is the Intel PRO/1000 network driver, run:
Example 22.1. Listing information about a kernel module with lsmod
~]# modinfo e1000e
filename:       /lib/modules/2.6.32-71.el6.x86_64/kernel/drivers/net/e1000e/e1000e.ko
version:        1.2.7-k2
license:        GPL
description:    Intel(R) PRO/1000 Network Driver
author:         Intel Corporation, <linux.nics@intel.com>
srcversion:     93CB73D3995B501872B2982
alias:          pci:v00008086d00001503sv*sd*bc*sc*i*
alias:          pci:v00008086d00001502sv*sd*bc*sc*i*
[some alias lines omitted]
alias:          pci:v00008086d0000105Esv*sd*bc*sc*i*
depends:
vermagic:       2.6.32-71.el6.x86_64 SMP mod_unload modversions
parm:           copybreak:Maximum size of packet that is copied to a new buffer on receive (uint)
parm:           TxIntDelay:Transmit Interrupt Delay (array of int)
parm:           TxAbsIntDelay:Transmit Absolute Interrupt Delay (array of int)
parm:           RxIntDelay:Receive Interrupt Delay (array of int)
parm:           RxAbsIntDelay:Receive Absolute Interrupt Delay (array of int)
parm:           InterruptThrottleRate:Interrupt Throttling Rate (array of int)
parm:           IntMode:Interrupt Mode (array of int)
parm:           SmartPowerDownEnable:Enable PHY smart power down (array of int)
parm:           KumeranLockLoss:Enable Kumeran lock loss workaround (array of int)
parm:           WriteProtectNVM:Write-protect NVM [WARNING: disabling this can lead to corrupted NVM] (array of int)
parm:           CrcStripping:Enable CRC Stripping, disable if your BMC needs the CRC (array of int)
parm:           EEE:Enable/disable on parts that support the feature (array of int)

Here are descriptions of a few of the fields in modinfo output:
filename
The absolute path to the .ko kernel object file. You can use modinfo -n as a shorcut command for printing only the filename field.
description
A short description of the module. You can use modinfo -d as a shortcut command for printing only the description field.
alias
The alias field appears as many times as there are aliases for a module, or is omitted entirely if there are none.
depends
This field contains a comma-separated list of all the modules this module depends on.

Note

If a module has no dependencies, the depends field may be omitted from the output.
parm
Each parm field presents one module parameter in the form parameter_name:description, where:
  • parameter_name is the exact syntax you should use when using it as a module parameter on the command line, or in an option line in a .conf file in the /etc/modprobe.d/ directory; and,
  • description is a brief explanation of what the parameter does, along with an expectation for the type of value the parameter accepts (such as int, unit or array of int) in parentheses.
You can list all parameters that the module supports by using the -p option. However, because useful value type information is omitted from modinfo -p output, it is more useful to run: 
~]# modinfo e1000e |grep "^parm" |sort
parm:           copybreak:Maximum size of packet that is copied to a new buffer on receive (uint)
parm:           CrcStripping:Enable CRC Stripping, disable if your BMC needs the CRC (array of int)
parm:           EEE:Enable/disable on parts that support the feature (array of int)
parm:           InterruptThrottleRate:Interrupt Throttling Rate (array of int)
parm:           IntMode:Interrupt Mode (array of int)
parm:           KumeranLockLoss:Enable Kumeran lock loss workaround (array of int)
parm:           RxAbsIntDelay:Receive Absolute Interrupt Delay (array of int)
parm:           RxIntDelay:Receive Interrupt Delay (array of int)
parm:           SmartPowerDownEnable:Enable PHY smart power down (array of int)
parm:           TxAbsIntDelay:Transmit Absolute Interrupt Delay (array of int)
parm:           TxIntDelay:Transmit Interrupt Delay (array of int)
parm:           WriteProtectNVM:Write-protect NVM [WARNING: disabling this can lead to corrupted NVM] (array of int)

22.3. Loading a Module

To load a kernel module, run modprobe <module_name> as root. For example, to load the wacom module, run: 
~]# modprobe wacom
By default, modprobe attempts to load the module from /lib/modules/<kernel_version>/kernel/drivers/. In this directory, each type of module has its own subdirectory, such as net/ and scsi/, for network and SCSI interface drivers respectively.
Some modules have dependencies, which are other kernel modules that must be loaded before the module in question can be loaded. The modprobe command always takes dependencies into account when performing operations. When you ask modprobe to load a specific kernel module, it first examines the dependencies of that module, if there are any, and loads them if they are not already loaded into the kernel. modprobe resolves dependencies recursively: it will load all dependencies of dependencies, and so on, if necessary, thus ensuring that all dependencies are always met.
You can use the -v (i.e. --verbose) option to cause modprobe to display detailed information about what it is doing, which may include loading module dependencies. Here's an example of loading the Fibre Channel over Ethernet module verbosely:
Example 22.2. modprobe -v shows module dependencies as they are loaded
~]# modprobe -v fcoe
insmod /lib/modules/2.6.32-71.el6.x86_64/kernel/drivers/scsi/scsi_tgt.ko
insmod /lib/modules/2.6.32-71.el6.x86_64/kernel/drivers/scsi/scsi_transport_fc.ko
insmod /lib/modules/2.6.32-71.el6.x86_64/kernel/drivers/scsi/libfc/libfc.ko
insmod /lib/modules/2.6.32-71.el6.x86_64/kernel/drivers/scsi/fcoe/libfcoe.ko
insmod /lib/modules/2.6.32-71.el6.x86_64/kernel/drivers/scsi/fcoe/fcoe.ko

Example 22.2, “modprobe -v shows module dependencies as they are loaded” shows that modprobe loaded the scsi_tgt, scsi_transport_fc, libfc and libfcoe modules as dependencies before finally loading fcoe. Also note that modprobe used the more “primitive” insmod command to insert the modules into the running kernel.

Always use modprobe instead of insmod!

Although the insmod command can also be used to load kernel modules, it does not resolve dependencies. Because of this, you should always load modules using modprobe instead.

22.4. Unloading a Module

You can unload a kernel module by running modprobe -r <module_name> as root. For example, assuming that the wacom module is already loaded into the kernel, you can unload it by running: 
~]# modprobe -r wacom
However, this command will fail if a process is using:
  • the wacom module,
  • a module that wacom directly depends on, or,
  • any module that wacom—through the dependency tree—depends on indirectly.
Refer to Section 22.1, “Listing Currently-Loaded Modules” for more information about using lsmod to obtain the names of the modules which are preventing you from unloading a certain module.
For example, if you want to unload the firewire_ohci module because (because you believe there is a bug in it that is affecting system stability, for example), your terminal session might look similar to this: 
~]# modinfo -F depends firewire_ohci
depends:        firewire-core
~]# modinfo -F depends firewire_core
depends:        crc-itu-t
~]# modinfo -F depends crc-itu-t
depends:
You have figured out the dependency tree (which does not branch in this example) for the loaded Firewire modules: firewire_ohci depends on firewire_core, which itself depends on crc-itu-t.
You can unload firewire_ohci using the modprobe -v -r <module_name> command, where -r is short for --remove and -v for --verbose: 
~]# modprobe -r -v firewire_ohci
rmmod /lib/modules/2.6.32-71.el6.x86_64/kernel/drivers/firewire/firewire-ohci.ko
rmmod /lib/modules/2.6.32-71.el6.x86_64/kernel/drivers/firewire/firewire-core.ko
rmmod /lib/modules/2.6.32-71.el6.x86_64/kernel/lib/crc-itu-t.ko
The output shows that modules are unloaded in the reverse order that they are loaded, given that no proceses depend on any of the modules being unloaded.

Do not use rmmod directly!

Although the rmmod command can be used to unload kernel modules, it is recommended to use modprobe -r instead.

22.5. Setting Module Parameters

Like the kernel itself, modules can also take parameters that change their behavior. Most of the time, the default ones work well, but occasionally it is necessary or desirable to set custom parameters for a module. Because parameters cannot be dynamically set for a module that is already loaded into a running kernel, there are two different methods for setting them.
  1. You can unload all dependencies of the module you want to set parameters for, unload the module using modprobe -r, and then load it with modprobe along with a list of customized parameters. This method is often used when the module does not have many dependencies, or to test different combinations of parameters without making them persistent, and is the method covered in this section.
  2. Alternatively, you can list the new parameters in an existing or newly-created file in the /etc/modprobe.d/ directory. This method makes the module parameters persistent by ensuring that they are set each time the module is loaded, such as after every reboot or modprobe command. This method is covered in Section 22.6, “Persistent Module Loading”, though the following information is a prerequisite.
You can use modprobe to load a kernel module with custom parameters using the following command line format:
Example 22.3. Supplying optional parameters when loading a kernel module
~]# modprobe <module_name> [parameter=value]

Here are some things to be aware of when loading a module with custom parameters on the command line:
  • You can enter multiple parameters and values by separating them with spaces.
  • Some module parameters expect a list of comma-separated values as their argument. When entering the list of values, do not insert a space after each comma, or modprobe will incorrectly interpret the values following spaces as additional parameters.
  • The modprobe command silently succeeds with an exit status of 0 if:
    • it successfully loads the module, or
    • the module is already loaded into the kernel.
    Thus, you must ensure that the module is not already loaded before attempting to load it with custom parameters. The modprobe command does not automatically reload the module, or alert you that it is already loaded.
Here are the recommended steps for setting custom parameters and then loading a kernel module. This procedure illustrates the steps using the e1000e module, which is the network driver for Intel PRO/1000 network adapters, as an example:
Procedure 22.1. Loading a Kernel Module with Custom Parameters
  1. First, ensure the module is not already loaded into the kernel: 
    ~]# lsmod |grep e1000e
~]# 
    Output indicates that the module is already loaded into the kernel, in which case you must first unload it before proceeding. Refer to Section 22.4, “Unloading a Module” for instructions on safely unloading it.
  2. Load the module and list all custom parameters after the module name. For example, if you wanted to load the Intel PRO/1000 network driver with the interrupt throttle rate set to 3000 interrupts per second for the first, second and third instances of the driver, and Energy Efficient Ethernet (EEE) turned on[4] , you would run, as root: 
    ~]# modprobe e1000e InterruptThrottleRate=3000,3000,3000 EEE=1
    This example illustrates passing multiple valued to a single parameter by separating them with commas and omitting any spaces between them.

22.6. Persistent Module Loading

As shown in Example 22.1, “Listing information about a kernel module with lsmod”, many kernel modules are loaded automatically at boot time. You can specify additional modules to be loaded by creating a new <file_name>.modules file in the /etc/sysconfig/modules/ directory, where <file_name> is any descriptive name of your choice. Your <file_name>.modules files are treated by the system startup scripts as shell scripts, and as such should begin with an interpreter directive (also called a “bang line”) as their first line:
Example 22.4. First line of a file_name.modules file
#!/bin/sh

Additionally, the <file_name>.modules file should be executable. You can make it executable by running: 
modules]# chmod +x <file_name>.modules
For example, the following bluez-uinput.modules script loads the uinput module:
Example 22.5. /etc/sysconfig/modules/bluez-uinput.modules
#!/bin/sh

if [ ! -c /dev/input/uinput ] ; then
        exec /sbin/modprobe uinput >/dev/null 2>&1
fi
The if-conditional statement on the third line ensures that the /dev/input/uinput file does not already exist (the ! symbol negates the condition), and, if that is the case, loads the uinput module by calling exec /sbin/modprobe uinput. Note that the uinput module creates the /dev/input/uinput file, so testing to see if that file exists serves as verification of whether the uinput module is loaded into the kernel.
The following >/dev/null 2>&1 clause at the end of that line simply redirects any output to /dev/null so that the modprobe command remains quiet.

22.7. Specific Kernel Module Capabilities

This section explains how to enable specific kernel capabilities using various kernel modules.

22.7.1. Using Multiple Ethernet Cards

It is possible to use multiple Ethernet cards on a single machine. For each card there must be an alias and, possibly, options lines for each card in a user-created <module_name>.conf file in the /etc/modprobe.d/ directory.
For additional information about using multiple Ethernet cards, refer to the Linux Ethernet-HOWTO online at http://www.redhat.com/mirrors/LDP/HOWTO/Ethernet-HOWTO.html.

22.7.2. Using Channel Bonding

Red Hat Enterprise Linux allows administrators to bind NICs together into a single channel using the bonding kernel module and a special network interface, called a channel bonding interface. Channel bonding enables two or more network interfaces to act as one, simultaneously increasing the bandwidth and providing redundancy.
To channel bond multiple network interfaces, the administrator must perform the following steps:
  1. As root, create a new file named <bonding>.conf in the /etc/modprobe.d/ directory. Note that you can name this file anything you like as long as it ends with a .conf extension. Insert the following line in this new file: 
    alias bond<N> bonding
    Replace <N> with the interface number, such as 0. For each configured channel bonding interface, there must be a corresponding entry in your new /etc/modprobe.d/<bonding>.conf file.
  2. Configure a channel bonding interface as outlined in Section 4.2.2, “Channel Bonding Interfaces”.
  3. To enhance performance, adjust available module options to ascertain what combination works best. Pay particular attention to the miimon or arp_interval and the arp_ip_target parameters. Refer to Section 22.7.2.1, “Bonding Module Directives” for a list of available options and how to quickly determine the best ones for your bonded interface.

22.7.2.1. Bonding Module Directives

It is a good idea to test which channel bonding module parameters work best for your bonded interfaces before adding them to the BONDING_OPTS="<bonding parameters>" directive in your bonding interface configuration file (ifcfg-bond0 for example). Parameters to bonded interfaces can be configured without unloading (and reloading) the bonding module by manipulating files in the sysfs file system.
sysfs is a virtual file system that represents kernel objects as directories, files and symbolic links. sysfs can be used to query for information about kernel objects, and can also manipulate those objects through the use of normal file system commands. The sysfs virtual file system has a line in /etc/fstab, and is mounted under the /sys/ directory. All bonding interfaces can be configured dynamically by interacting with and manipulating files under the /sys/class/net/ directory.
After you have created a channel bonding interface file such as ifcfg-bond0 and inserted SLAVE=yes and MASTER=bond0 directives in the configuration files for each interface bonded to bond0 following the instructions in Section 4.2.2, “Channel Bonding Interfaces”, you can proceed to testing and determining the best parameters for your bonding interface.
First, bring up the bond you created by running ifconfig bond<N>  up as root: 
~]# ifconfig bond0 up
If you have correctly created the ifcfg-bond0 bonding interface file, you will be able to see bond0 listed in the output of running ifconfig (without any options): 
~]# ifconfig
bond0     Link encap:Ethernet HWaddr 00:00:00:00:00:00
          UP BROADCAST RUNNING MASTER MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
eth0      Link encap:Ethernet  HWaddr 52:54:00:26:9E:F1
          inet addr:192.168.122.251  Bcast:192.168.122.255  Mask:255.255.255.0
          inet6 addr: fe80::5054:ff:fe26:9ef1/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:207 errors:0 dropped:0 overruns:0 frame:0
          TX packets:205 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:70374 (68.7 KiB)  TX bytes:25298 (24.7 KiB)
[output truncated]
To view all existing bonds, even if they are not up, run: 
~]# cat /sys/class/net/bonding_masters
bond0
You can configure each bond individually by manipulating the files located in the /sys/class/net/bond<N>/bonding/ directory. First, the bond you are configuring must be taken down: 
~]# ifconfig bond0 down
As an example, to enable MII monitoring on bond0 with a 1 second interval, you could run (as root): 
~]# echo 1000 > /sys/class/net/bond0/bonding/miimon
To configure bond0 for balance-alb mode, you could run either: 
~]# echo 6 > /sys/class/net/bond0/bonding/mode
...or, using the name of the mode: 
~]# echo balance-alb > /sys/class/net/bond0/bonding/mode
After configuring some options for the bond in question, you can bring it up and test it by running ifconfig bond<N> up . If you decide to change the options, take the interface down, modify its parameters using sysfs, bring it back up, and re-test.
Once you have determined the best set of parameters for your bond, add those parameters as a space-separated list to the BONDING_OPTS= directive of the /etc/sysconfig/network-scripts/ifcfg-bond<N> file for the bonding interface you are configuring. Whenever that bond is brought up (for example, by the system during the boot sequence if the ONBOOT=yes directive is set), the bonding options specified in the BONDING_OPTS will take effect for that bond. For more information on configuring bonding interfaces (and BONDING_OPTS), refer to Section 4.2.2, “Channel Bonding Interfaces”.
The following list provides the names of many of the more common channel bonding parameters, along with a descriptions of what they do. For more information, refer to the brief descriptions for each parm in modinfo bonding output, or the exhaustive descriptions in the bonding.txt file in the kernel-doc package (see Section 22.8, “Additional Resources”).
Bonding Interface Parameters
arp_interval=<time_in_milliseconds>
Specifies (in milliseconds) how often ARP monitoring occurs.

Important

It is essential that both arp_interval and arp_ip_target parameters are specified, or, alternatively, the miimon parameter is specified. Failure to do so can cause degradation of network performance in the event that a link fails.
If using this setting while in mode=0 or mode=1 (the two load-balancing modes), the network switch must be configured to distribute packets evenly across the NICs. For more information on how to accomplish this, refer to /usr/share/doc/kernel-doc-<kernel_version>/Documentation/networking/bonding.txt
The value is set to 0 by default, which disables it.
arp_ip_target=<ip_address>[,<ip_address_2>,…<ip_address_16>]
Specifies the target IP address of ARP requests when the arp_interval parameter is enabled. Up to 16 IP addresses can be specified in a comma separated list.
arp_validate=<value>
Validate source/distribution of ARP probes; default is none. Other valid values are active, backup, and all.
debug=<number>
Enables debug messages. Possible values are:
  • 0 — Debug messages are disabled. This is the default.
  • 1 — Debug messages are enabled.
downdelay=<time_in_milliseconds>
Specifies (in milliseconds) how long to wait after link failure before disabling the link. The value must be a multiple of the value specified in the miimon parameter. The value is set to 0 by default, which disables it.
lacp_rate=<value>
Specifies the rate at which link partners should transmit LACPDU packets in 802.3ad mode. Possible values are:
  • slow or 0 — Default setting. This specifies that partners should transmit LACPDUs every 30 seconds.
  • fast or 1 — Specifies that partners should transmit LACPDUs every 1 second.
miimon=<time_in_milliseconds>
Specifies (in milliseconds) how often MII link monitoring occurs. This is useful if high availability is required because MII is used to verify that the NIC is active. To verify that the driver for a particular NIC supports the MII tool, type the following command as root: 
~]# ethtool <interface_name> | grep "Link detected:"
In this command, replace <interface_name> with the name of the device interface, such as eth0, not the bond interface. If MII is supported, the command returns: 
Link detected: yes
If using a bonded interface for high availability, the module for each NIC must support MII. Setting the value to 0 (the default), turns this feature off. When configuring this setting, a good starting point for this parameter is 100.

Important

It is essential that both arp_interval and arp_ip_target parameters are specified, or, alternatively, the miimon parameter is specified. Failure to do so can cause degradation of network performance in the event that a link fails.
mode=<value>
...where <value> is one of:
  • balance-rr or 0 — Sets a round-robin policy for fault tolerance and load balancing. Transmissions are received and sent out sequentially on each bonded slave interface beginning with the first one available.
  • active-backup or 1 — Sets an active-backup policy for fault tolerance. Transmissions are received and sent out via the first available bonded slave interface. Another bonded slave interface is only used if the active bonded slave interface fails.
  • balance-xor or 2 — Sets an XOR (exclusive-or) policy for fault tolerance and load balancing. Using this method, the interface matches up the incoming request's MAC address with the MAC address for one of the slave NICs. Once this link is established, transmissions are sent out sequentially beginning with the first available interface.
  • broadcast or 3 — Sets a broadcast policy for fault tolerance. All transmissions are sent on all slave interfaces.
  • 802.3ad or 4 — Sets an IEEE 802.3ad dynamic link aggregation policy. Creates aggregation groups that share the same speed and duplex settings. Transmits and receives on all slaves in the active aggregator. Requires a switch that is 802.3ad compliant.
  • balance-tlb or 5 — Sets a Transmit Load Balancing (TLB) policy for fault tolerance and load balancing. The outgoing traffic is distributed according to the current load on each slave interface. Incoming traffic is received by the current slave. If the receiving slave fails, another slave takes over the MAC address of the failed slave.
  • balance-alb or 6 — Sets an Active Load Balancing (ALB) policy for fault tolerance and load balancing. Includes transmit and receive load balancing for IPV4 traffic. Receive load balancing is achieved through ARP negotiation.
num_unsol_na=<number>
Specifies the number of unsolicited IPv6 Neighbor Advertisements to be issued after a failover event. One unsolicited NA is issued immediately after the failover.
The valid range is 0 - 255; the default value is 1. This parameter affects only the active-backup mode.
primary=<interface_name>
Specifies the interface name, such as eth0, of the primary device. The primary device is the first of the bonding interfaces to be used and is not abandoned unless it fails. This setting is particularly useful when one NIC in the bonding interface is faster and, therefore, able to handle a bigger load.
This setting is only valid when the bonding interface is in active-backup mode. Refer to /usr/share/doc/kernel-doc-<kernel-version>/Documentation/networking/bonding.txt for more information.
primary_reselect=<value>
Specifies the reselection policy for the primary slave. This affects how the primary slave is chosen to become the active slave when failure of the active slave or recovery of the primary slave occurs. This parameter is designed to prevent flip-flopping between the primary slave and other slaves. Possible values are:
  • always or 0 (default) — The primary slave becomes the active slave whenever it comes back up.
  • better or 1 — The primary slave becomes the active slave when it comes back up, if the speed and duplex of the primary slave is better than the speed and duplex of the current active slave.
  • failure or 2 — The primary slave becomes the active slave only if the current active slave fails and the primary slave is up.
The primary_reselect setting is ignored in two cases:
  • If no slaves are active, the first slave to recover is made the active slave.
  • When initially enslaved, the primary slave is always made the active slave.
Changing the primary_reselect policy via sysfs will cause an immediate selection of the best active slave according to the new policy. This may or may not result in a change of the active slave, depending upon the circumstances
updelay=<time_in_milliseconds>
Specifies (in milliseconds) how long to wait before enabling a link. The value must be a multiple of the value specified in the miimon parameter. The value is set to 0 by default, which disables it.
use_carrier=<number>
Specifies whether or not miimon should use MII/ETHTOOL ioctls or netif_carrier_ok() to determine the link state. The netif_carrier_ok() function relies on the device driver to maintains its state with netif_carrier_on/off ; most device drivers support this function.
The MII/ETHROOL ioctls tools utilize a deprecated calling sequence within the kernel. However, this is still configurable in case your device driver does not support netif_carrier_on/off .
Valid values are:
  • 1 — Default setting. Enables the use of netif_carrier_ok().
  • 0 — Enables the use of MII/ETHTOOL ioctls.

Tip

If the bonding interface insists that the link is up when it should not be, it is possible that your network device driver does not support netif_carrier_on/off .
xmit_hash_policy=<value>
Selects the transmit hash policy used for slave selection in balance-xor and 802.3ad modes. Possible values are:
  • 0 or layer2 — Default setting. This parameter uses the XOR of hardware MAC addresses to generate the hash. The formula used is: 
    (<source_MAC_address> XOR <destination_MAC>) MODULO <slave_count>
    This algorithhm will place all traffic to a particular network peer on the same slave, and is 802.3ad compliant.
  • 1 or layer3+4 — Uses upper layer protocol information (when available) to generate the hash. This allows for traffic to a particular network peer to span multiple slaves, although a single connection will not span multiple slaves.
    The formula for unfragmented TCP and UDP packets used is: 
    ((<source_port> XOR <dest_port>) XOR
  ((<source_IP> XOR <dest_IP>) AND 0xffff)
    MODULO <slave_count>
    For fragmented TCP or UDP packets and all other IP protocol traffic, the source and destination port information is omitted. For non-IP traffic, the formula is the same as the layer2 transmit hash policy.
    This policy intends to mimic the behavior of certain switches; particularly, Cisco switches with PFC2 as well as some Foundry and IBM products.
    The algorithm used by this policy is not 802.3ad compliant.
  • 2 or layer2+3 — Uses a combination of layer2 and layer3 protocol information to generate the hash.
    Uses XOR of hardware MAC addresses and IP addresses to generate the hash. The formula is: 
    (((<source_IP> XOR <dest_IP>) AND 0xffff) XOR
  ( <source_MAC> XOR <destination_MAC> ))
    MODULO <slave_count>
    This algorithm will place all traffic to a particular network peer on the same slave. For non-IP traffic, the formula is the same as for the layer2 transmit hash policy.
    This policy is intended to provide a more balanced distribution of traffic than layer2 alone, especially in environments where a layer3 gateway device is required to reach most destinations.
    This algorithm is 802.3ad compliant.

22.8. Additional Resources

For more information on kernel modules and their utilities, refer to the following resources.

Manual Page Documentation

  • man lsmod — The lsmod manual page contains usage information and explanation of all options.
  • man modinfo — The modinfo manual page contains usage information and explanation of all options.
  • man modprobe — The modprobe manual page contains usage information and explanation of all options.
  • man rmmod — The rmmod manual page contains usage information and explanation of all options.
  • man ethtool — The ethtool manual page contains usage information and explanation of all options.
  • man mii-tool — The mii-tool manual page contains usage information and explanation of all options.

Installable and External Documentation

  • /usr/share/doc/kernel-doc-<kernel_version>/Documentation/ — This directory, which is provided by the kernel-doc package, contains information on the kernel, kernel modules, and their respective parameters. Before accessing the kernel documentation, you must run the following command as root: 
    ~]# yum install kernel-doc
  • Linux Loadable Kernel Module HOWTO — The Linux Loadable Kernel Module HOWTO from the Linux Documentation Project contains further information on working with kernel modules.

[4] Despite what the example might imply, Energy Efficient Ethernet is turned on by default in the e1000e driver.

Chapter 23. Manually Upgrading the Kernel

23.1. Overview of Kernel Packages
23.2. Preparing to Upgrade
23.3. Downloading the Upgraded Kernel
23.4. Performing the Upgrade
23.5. Verifying the Initial RAM Disk Image
23.6. Verifying the Boot Loader
23.6.1. Configuring the GRUB Boot Loader
23.6.2. Configuring the OS/400® Boot Loader
23.6.3. Configuring the YABOOT Boot Loader
The Red Hat Enterprise Linux kernel is custom-built by the Red Hat Enterprise Linux kernel team to ensure its integrity and compatibility with supported hardware. Before Red Hat releases a kernel, it must first pass a rigorous set of quality assurance tests.
Red Hat Enterprise Linux kernels are packaged in the RPM format so that they are easy to upgrade and verify using the Yum or PackageKit package managers. PackageKit automatically queries the Red Hat Network servers and informs you of packages with available updates, including kernel packages.
This chapter is therefore only useful for users who need to manually update a kernel package using the rpm command instead of yum.

Use Yum to Install Kernels Whenever Possible

Whenever possible, use either the Yum or PackageKit package manager to install a new kernel because they always install a new kernel instead of replacing the current one, which could potentially leave your system unable to boot.

Important

Building a custom kernel is not supported by the Red Hat Global Services Support team, and therefore is not explored in this manual.
For more information on installing kernel packages with Yum, refer to Section 1.1.2, “Updating Packages”.

23.1. Overview of Kernel Packages

Red Hat Enterprise Linux contains the following kernel packages:
  • kernel — Contains the kernel for single, multicore and multiprocessor systems.
  • kernel-debug — Contains a kernel with numerous debugging options enabled for kernel diagnosis, at the expense of reduced performance.
  • kernel-devel — Contains the kernel headers and makefiles sufficient to build modules against the kernel package.
  • kernel-debug-devel — Contains the development version of the kernel with numerous debugging options enabled for kernel diagnosis, at the expense of reduced performance.
  • kernel-doc — Documentation files from the kernel source. Various portions of the Linux kernel and the device drivers shipped with it are documented in these files. Installation of this package provides a reference to the options that can be passed to Linux kernel modules at load time.
    By default, these files are placed in the /usr/share/doc/kernel-doc-<kernel_version>/ directory.
  • kernel-headers — Includes the C header files that specify the interface between the Linux kernel and user-space libraries and programs. The header files define structures and constants that are needed for building most standard programs.
  • kernel-firmware — Contains all of the firmware files that are required by various devices to operate.
  • perf — This package contains supporting scripts and documentation for the perf tool shipped in each kernel image subpackage.

23.2. Preparing to Upgrade

Before upgrading the kernel, it is recommended that you take some precautionary steps.
First, ensure that working boot media exists for the system in case a problem occurs. If the boot loader is not configured properly to boot the new kernel, the system cannot be booted into Red Hat Enterprise Linux without working boot media.
USB media often comes in the form of flash devices sometimes called pen drives, thumb disks, or keys, or as an externally-connected hard disk device. Almost all media of this type is formatted as a VFAT file system. You can create bootable USB media on media formatted as ext2, ext3, or VFAT.
You can transfer a distribution image file or a minimal boot media image file to USB media. Make sure that sufficient free space is available on the device. Around 4 GB is required for a distribution DVD image, around 700 MB for a distribution CD image, or around 10 MB for a minimal boot media image.
You must have a copy of the boot.iso file from a Red Hat Enterprise Linux installation DVD, or installation CD-ROM#1, and you need a USB storage device formatted with the VFAT file system and around 16 MB of free space. The following procedure will not affect existing files on the USB storage device unless they have the same path names as the files that you copy onto it. To create USB boot media, perform the following commands as the root user:
  1. Install the SYSLINUX bootloader on the USB storage device: 
    ~]# syslinux /dev/sdX1
    ...where sdX is the device name.
  2. Create mount points for boot.iso and the USB storage device: 
    ~]# mkdir /mnt/isoboot /mnt/diskboot
  3. Mount boot.iso: 
    ~]# mount -o loop boot.iso /mnt/isoboot
  4. Mount the USB storage device: 
    ~]# mount /dev/<sdX1> /mnt/diskboot
  5. Copy the ISOLINUX files from the boot.iso to the USB storage device: 
    ~]# cp /mnt/isoboot/isolinux/* /mnt/diskboot
  6. Use the isolinux.cfg file from boot.iso as the syslinux.cfg file for the USB device: 
    ~]# grep -v local /mnt/isoboot/isolinux/isolinux.cfg > /mnt/diskboot/syslinux.cfg
  7. Unmount boot.iso and the USB storage device: 
    ~]# umount /mnt/isoboot /mnt/diskboot
  8. You should reboot the machine with the boot media and verify that you are able to boot with it before continuing.
Alternatively, on systems with a floppy drive, you can create a boot diskette by installing the mkbootdisk package and running the mkbootdisk command as root. Refer to man mkbootdisk man page after installing the package for usage information.
To determine which kernel packages are installed, execute the command yum list installed "kernel-*" at a shell prompt. The output will comprise some or all of the following packages, depending on the system's architecture, and the version numbers may differ: 
~]# yum list installed "kernel-*"
kernel.x86_64                   2.6.32-17.el6           installed
kernel-doc.noarch               2.6.32-17.el6           installed
kernel-firmware.noarch          2.6.32-17.el6           installed
kernel-headers.x86_64           2.6.32-17.el6           installed
From the output, determine which packages need to be download for the kernel upgrade. For a single processor system, the only required package is the kernel package. Refer to Section 23.1, “Overview of Kernel Packages” for descriptions of the different packages.

23.3. Downloading the Upgraded Kernel

There are several ways to determine if an updated kernel is available for the system.
  • Security Errata — Refer to http://www.redhat.com/security/updates/ for information on security errata, including kernel upgrades that fix security issues.
  • Via Red Hat Network — Download and install the kernel RPM packages. Red Hat Network can download the latest kernel, upgrade the kernel on the system, create an initial RAM disk image if needed, and configure the boot loader to boot the new kernel. For more information, refer to http://www.redhat.com/docs/manuals/RHNetwork/.
If Red Hat Network was used to download and install the updated kernel, follow the instructions in Section 23.5, “Verifying the Initial RAM Disk Image” and Section 23.6, “Verifying the Boot Loader”, only do not change the kernel to boot by default. Red Hat Network automatically changes the default kernel to the latest version. To install the kernel manually, continue to Section 23.4, “Performing the Upgrade”.

23.4. Performing the Upgrade

After retrieving all of the necessary packages, it is time to upgrade the existing kernel.

Important

It is strongly recommended that you keep the old kernel in case there are problems with the new kernel.
At a shell prompt, change to the directory that contains the kernel RPM packages. Use -i argument with the rpm command to keep the old kernel. Do not use the -U option, since it overwrites the currently installed kernel, which creates boot loader problems. For example: 
~]# rpm -ivh kernel-<kernel_version>.<arch>.rpm
The next step is to verify that the initial RAM disk image has been created. Refer to Section 23.5, “Verifying the Initial RAM Disk Image” for details.

23.5. Verifying the Initial RAM Disk Image

The job of the initial RAM disk image is to preload the block device modules, such as for IDE, SCSI or RAID, so that the root file system, on which those modules normally reside, can then be accessed and mounted. On Red Hat Enterprise Linux 6 systems, whenever a new kernel is installed using either the Yum, PackageKit, or RPM package manager, the Dracut utility is always called by the installation scripts to create an initramfs (initial RAM disk image).
On all architectures other than IBM® eServer™ System i™ (see Section 23.5, “Verifying the Initial RAM Disk Image and Kernel on IBM eServer System i”), you can create an initramfs by running the dracut command. However, you usually don't need to create an initramfs manually: this step is automatically performed if the kernel and its associated packages are installed or upgraded from RPM packages distributed by Red Hat.
You can verify that an initramfs corresponding to your current kernel version exists and is specified correctly in the grub.conf configuration file by following this procedure:
Procedure 23.1. Verifying the Initial RAM Disk Image
  1. As root, list the contents in the /boot/ directory and find the kernel (vmlinuz-<kernel_version> ) and initramfs-<kernel_version> with the latest (most recent) version number:
    Example 23.1. Ensuring that the kernel and initramfs versions match
    ~]# ls /boot/
config-2.6.32-17.el6.x86_64           lost+found
config-2.6.32-19.el6.x86_64           symvers-2.6.32-17.el6.x86_64.gz
config-2.6.32-22.el6.x86_64           symvers-2.6.32-19.el6.x86_64.gz
efi                                   symvers-2.6.32-22.el6.x86_64.gz
grub                                  System.map-2.6.32-17.el6.x86_64
initramfs-2.6.32-17.el6.x86_64.img    System.map-2.6.32-19.el6.x86_64
initramfs-2.6.32-19.el6.x86_64.img    System.map-2.6.32-22.el6.x86_64
initramfs-2.6.32-22.el6.x86_64.img    vmlinuz-2.6.32-17.el6.x86_64
initrd-2.6.32-17.el6.x86_64kdump.img  vmlinuz-2.6.32-19.el6.x86_64
initrd-2.6.32-19.el6.x86_64kdump.img  vmlinuz-2.6.32-22.el6.x86_64
initrd-2.6.32-22.el6.x86_64kdump.img

    Example 23.1, “Ensuring that the kernel and initramfs versions match” shows that:
    • we have three kernels installed (or, more correctly, three kernel files are present in /boot/),
    • the latest kernel is vmlinuz-2.6.32-22.el6.x86_64, and
    • an initramfs file matching our kernel version, initramfs-2.6.32-22.el6.x86_64kdump.img, also exists.

    initrd files in the /boot directory are not the same as initramfs files

    In the /boot/ directory you may find several initrd-<version>kdump.img files. These are special files created by the Kdump mechanism for kernel debugging purposes, are not used to boot the system, and can safely be ignored.
  2. (Optional) If your initramfs-<kernel_version> file does not match the version of the latest kernel in /boot/, or, in certain other situations, you may need to generate an initramfs file with the Dracut utility. Simply invoking dracut as root without options causes it to generate an initramfs file in the /boot/ directory for the latest kernel present in that directory: 
    ~]# dracut
    You must use the --force option if you want dracut to overwrite an existing initramfs (for example, if your initramfs has become corrupt). Otherwise dracut will refuse to overwrite the existing initramfs file: 
    ~]# dracut
Will not override existing initramfs (/boot/initramfs-2.6.32-22.el6.x86_64.img) without --force
    You can create an initramfs in the current directory by calling dracut <initramfs_name> <kernel_version>: 
    ~]# dracut "initramfs-$(uname -r).img" $(uname -r)
    If you need to specify specific kernel modules to be preloaded, add the names of those modules (minus any file name suffixes such as .ko) inside the parentheses of the add_dracutmodules="<module> [<more_modules>]" directive of the /etc/dracut.conf configuration file. You can list the file contents of an initramfs image file created by dracut by using the lsinitrd <initramfs_file> command: 
    ~]# lsinitrd initramfs-2.6.32-22.el6.x86_64.img
initramfs-2.6.32-22.el6.x86_64.img:
========================================================================
dracut-004-17.el6
========================================================================
drwxr-xr-x  23 root     root            0 May  3 22:34 .
drwxr-xr-x   2 root     root            0 May  3 22:33 proc
-rwxr-xr-x   1 root     root         7575 Mar 25 19:53 init
drwxr-xr-x   7 root     root            0 May  3 22:34 etc
drwxr-xr-x   2 root     root            0 May  3 22:34 etc/modprobe.d
[output truncated]
    Refer to man dracut and man dracut.conf for more information on options and usage.
  3. Examine the grub.conf configuration file in the /boot/grub/ directory to ensure that an initrd initramfs-<kernel_version>.img exists for the kernel version you are booting. Refer to Section 23.6, “Verifying the Boot Loader” for more information.

Verifying the Initial RAM Disk Image and Kernel on IBM eServer System i

On IBM eSeries System i machines, the initial RAM disk and kernel files are combined into a single file, which is created with the addRamDisk command. This step is performed automatically if the kernel and its associated packages are installed or upgraded from the RPM packages distributed by Red Hat; thus, it does not need to be executed manually. To verify that it was created, use the command ls -l /boot/ to make sure the /boot/vmlinitrd-<kernel_version> file already exists (the <kernel_version> should match the version of the kernel just installed).

23.6. Verifying the Boot Loader

When you install a kernel using rpm, the kernel package creates an entry in the boot loader configuration file for that new kernel. However, rpm does not configure the new kernel to boot as the default kernel. You must do this manually when installing a new kernel with rpm.
It is always recommended to double-check the boot loader configuration file after installing a new kernel with rpm to ensure that the configuration is correct. Otherwise, the system may not be able to boot into Red Hat Enterprise Linux properly. If this happens, boot the system with the boot media created earlier and re-configure the boot loader.
In the following table, find your system's architecture to determine the boot loader it uses, and then click on the "Refer to" link to jump to the correct instructions for your system.
Table 23.1. Boot Loaders by Architecture
Architecture Boot Loader Refer to
x86 GRUB Section 23.6.1, “Configuring the GRUB Boot Loader”
AMD® AMD64 or Intel 64® GRUB Section 23.6.1, “Configuring the GRUB Boot Loader”
IBM® eServer™ System i™ OS/400® Section 23.6.2, “Configuring the OS/400® Boot Loader”
IBM® eServer™ System p™ YABOOT Section 23.6.3, “Configuring the YABOOT Boot Loader”
IBM® System z® z/IPL

23.6.1. Configuring the GRUB Boot Loader

GRUB's configuration file, /boot/grub/grub.conf, contains a few lines with directives, such as default, timeout, splashimage and hiddenmenu (the last directive has no argument). The remainder of the file contains 4-line stanzas that each refer to an installed kernel. These stanzas always start with a title entry, after which the associated root, kernel and initrd directives should always be indented. Ensure that each stanza starts with a title that contains a version number (in parentheses) that matches the version number in the kernel /vmlinuz-<version_number> line of the same stanza.
Example 23.2. /boot/grub/grub.conf
# grub.conf generated by anaconda
[comments omitted]
default=1
timeout=0
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu

title Red Hat Enterprise Linux (2.6.32-22.el6.x86_64)
        root (hd0,0)
        kernel /vmlinuz-2.6.32-22.el6.x86_64 ro root=/dev/mapper/vg_vm6b-lv_root rd_LVM_LV=vg_vm6b/lv_root rd_NO_LUKS rd_NO_MD rd_NO_DM LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us rhgb quiet crashkernel=auto
        initrd /initramfs-2.6.32-22.el6.x86_64.img

title Red Hat Enterprise Linux (2.6.32-19.el6.x86_64)
        root (hd0,0)
        kernel /vmlinuz-2.6.32-19.el6.x86_64 ro root=/dev/mapper/vg_vm6b-lv_root rd_LVM_LV=vg_vm6b/lv_root rd_NO_LUKS rd_NO_MD rd_NO_DM LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us rhgb quiet crashkernel=auto
        initrd /initramfs-2.6.32-19.el6.x86_64.img

title Red Hat Enterprise Linux 6 (2.6.32-17.el6.x86_64)
        root (hd0,0)
        kernel /vmlinuz-2.6.32-17.el6.x86_64 ro root=/dev/mapper/vg_vm6b-lv_root rd_LVM_LV=vg_vm6b/lv_root rd_NO_LUKS rd_NO_MD rd_NO_DM LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us rhgb quiet
        initrd /initramfs-2.6.32-17.el6.x86_64.img

If a separate /boot/ partition was created, the paths to the kernel and the initramfs image are relative to /boot/. This is the case in Example 23.2, “/boot/grub/grub.conf”, above. Therefore the initrd /initramfs-2.6.32-22.el6.x86_64.img line in the first kernel stanza means that the initramfs image is actually located at /boot/initramfs-2.6.32-22.el6.x86_64.img when the root file system is mounted, and likewise for the kernel path (for example: kernel /vmlinuz-2.6.32-22.el6.x86_64) in each stanza of grub.conf.

The initrd directive in grub.conf refers to an initramfs image

In kernel boot stanzas in grub.conf, the initrd directive must point to the location (relative to the /boot/ directory if it is on a separate partition), of the initramfs file corresponding to the same kernel version. This directive is called initrd because the previous tool which created initial RAM disk images, mkinitrd, created what were known as initrd files. Thus the grub.conf directive remains initrd to maintain compatibility with other tools. The file-naming convention of systems using the dracut utility to create the initial RAM disk image is: initramfs-<kernel_version>.img
Dracut is a new utility available in Red Hat Enterprise Linux 6, and much-improved over mkinitrd. For information on using Dracut, refer to Section 23.5, “Verifying the Initial RAM Disk Image”.
You should ensure that the kernel version number as given on the kernel /vmlinuz-<kernel_version> line matches the version number of the initramfs image given on the initrd /initramfs-<kernel_version>.img line of each stanza. Refer to Procedure 23.1, “Verifying the Initial RAM Disk Image” for more information.
The default= directive tells GRUB which kernel to boot by default. Each title in grub.conf represents a bootable kernel. GRUB counts the titled stanzas representing bootable kernels starting with 0. In Example 23.2, “/boot/grub/grub.conf”, the line default=1 indicates that GRUB will boot, by default, the second kernel entry, i.e. title Red Hat Enterprise Linux (2.6.32-19.el6.x86_64).
In Example 23.2, “/boot/grub/grub.conf” GRUB is therefore configured to boot an older kernel, when we compare by version numbers. In order to boot the newer kernel, which is the first title entry in grub.conf, we would need to change the default value to 0.
After installing a new kernel with rpm, verify that /boot/grub/grub.conf is correct, change the default= value to the new kernel (while remembering to count from 0), and reboot the computer into the new kernel. Ensure your hardware is detected by watching the boot process output.
If GRUB presents an error and is unable to boot into the default kernel, it is often easiest to try to boot into an alternative or older kernel so that you can fix the problem.

Important: Causing the GRUB boot menu to display

If you set the timeout directive in grub.conf to 0, GRUB will not display its list of bootable kernels when the system starts up. In order to display this list when booting, press and hold any alphanumeric key while and immediately after BIOS information is displayed, and GRUB will present you with the GRUB menu.
Alternatively, use the boot media you created earlier to boot the system.

23.6.2. Configuring the OS/400® Boot Loader

The /boot/vmlinitrd-<kernel-version> file is installed when you upgrade the kernel. However, you must use the dd command to configure the system to boot the new kernel.
  1. As root, issue the command cat /proc/iSeries/mf/side to determine the default side (either A, B, or C).
  2. As root, issue the following command, where <kernel-version> is the version of the new kernel and <side> is the side from the previous command: 
    dd if=/boot/vmlinitrd-<kernel-version> of=/proc/iSeries/mf/<side>/vmlinux bs=8k
Begin testing the new kernel by rebooting the computer and watching the messages to ensure that the hardware is detected properly.

23.6.3. Configuring the YABOOT Boot Loader

IBM eServer System p uses YABOOT as its boot loader. YABOOT uses /etc/aboot.conf as its configuration file. Confirm that the file contains an image section with the same version as the kernel package just installed, and likewise for the initramfs image: 
boot=/dev/sda1 init-message=Welcome to Red Hat Enterprise Linux! Hit <TAB> for boot options
partition=2 timeout=30 install=/usr/lib/yaboot/yaboot delay=10 nonvram
image=/vmlinuz-2.6.32-17.EL
	 label=old
	 read-only
	 initrd=/initramfs-2.6.32-17.EL.img
	 append="root=LABEL=/"
image=/vmlinuz-2.6.32-19.EL
	 label=linux
	 read-only
	 initrd=/initramfs-2.6.32-19.EL.img
	 append="root=LABEL=/"
Notice that the default is not set to the new kernel. The kernel in the first image is booted by default. To change the default kernel to boot either move its image stanza so that it is the first one listed or add the directive default and set it to the label of the image stanza that contains the new kernel.
Begin testing the new kernel by rebooting the computer and watching the messages to ensure that the hardware is detected properly.

Chapter 24. The kdump Crash Recovery Service

24.1. Configuring the kdump Service
24.1.1. Configuring the kdump at First Boot
24.1.2. Using the Kernel Dump Configuration Utility
24.1.3. Configuring kdump on the Command Line
24.1.4. Testing the Configuration
24.2. Analyzing the Core Dump
24.2.1. Displaying the Message Buffer
24.2.2. Displaying a Backtrace
24.2.3. Displaying a Process Status
24.2.4. Displaying Virtual Memory Information
24.2.5. Displaying Open Files
24.3. Additional Resources
24.3.1. Installed Documentation
24.3.2. Useful Websites
kdump is an advanced crash dumping mechanism. When enabled, the system is booted from the context of another kernel. This second kernel reserves a small amount of memory, and its only purpose is to capture the core dump image in case the system crashes. Since being able to analyze the core dump helps significantly to determine the exact cause of the system failure, it is strongly recommended to have this feature enabled.
This chapter explains how to configure, test, and use the kdump service in Red Hat Enterprise Linux, and provides a brief overview of how to analyze the resulting core dump using the crash debugging utility.

24.1. Configuring the kdump Service

This section covers three common means of configuring the kdump service: at the first boot, using the Kernel Dump Configuration graphical utility, and doing so manually on the command line. It also describes how to test the configuration to verify that everything works as expected.

Note: Make Sure You Have kexec-tools Installed

To use the kdump service, you must have the kexec-tools package installed. Refer to Section 1.2.2, “Installing” for more information on how to install new packages in Red Hat Enterprise Linux.

24.1.1. Configuring the kdump at First Boot

When the system boots for the first time, the firstboot application is launched to guide a user through the initial configuration of the freshly installed system. To configure kdump, navigate to the Kdump section, and follow the instructions below.

Important: Make Sure the System Has Enough Memory

Unless the system has enough memory, this option will not be available. For the information on minimum memory requirements, refer to the Required minimums section of the Red Hat Enterprise Linux comparison chart. Note that when the kdump crash recovery is enabled, the minimum memory requirements increase by the amount of memory reserved for it. This value is determined by a user, and defaults to 128 MB.

24.1.1.1. Enabling the Service

To start the kdump daemon at boot time, select the Enable kdump? check box. This will enable the service for runlevels 2, 3, 4, and 5, and start it for the current session. Similarly, unselecting the check box will disable it for all runlevels and stop the service immediately.

24.1.1.2. Configuring the Memory Usage

To configure the amount of memory that is reserved for the kdump kernel, click the up and down arrow buttons next to the Kdump Memory field to increase or decrease the value. Notice that the Usable System Memory field changes accordingly showing you the remaining memory that will be available to the system.

24.1.2. Using the Kernel Dump Configuration Utility

To start the Kernel Dump Configuration utility, select System → Administration → Kernel crash dumps from the panel, or type system-config-kdump at a shell prompt (for example, xterm or GNOME Terminal). You will be presented with a window as shown in Figure 24.1, “Basic Settings”.
The utility allows you to configure kdump as well as to enable or disable starting the service at boot time. When you are done, click Apply to save the changes. The system reboot will be requested, and unless you are already authenticated, you will be prompted to enter the superuser password.

Important: Make Sure the System Has Enough Memory

Unless the system has enough memory, the utility will not start, and you will be presented with the following error message:
The “not enough memory” error
For the information on minimum memory requirements, refer to the Required minimums section of the Red Hat Enterprise Linux comparison chart. Note that when the kdump crash recovery is enabled, the minimum memory requirements increase by the amount of memory reserved for it. This value is determined by a user, and defaults to 128 MB.

24.1.2.1. Enabling the Service

To start the kdump daemon at boot time, click the Apply button on the toolbar. This will enable the service for runlevels 2, 3, 4, and 5, and start it for the current session. Similarly, clicking the Disable button will disable it for all runlevels and stop the service immediately.
For more information on runlevels and configuring services in general, refer to Chapter 7, Controlling Access to Services.

24.1.2.2. The Basic Settings Tab

The Basic Settings tab enables you to configure the amount of memory that is reserved for the kdump kernel. To do so, select the Manual kdump memory settings radio button, and click the up and down arrow buttons next to the New kdump Memory field to increase or decrease the value. Notice that the Usable Memory field changes accordingly showing you the remaining memory that will be available to the system.
Basic Settings
Basic Settings
Figure 24.1. Basic Settings

24.1.2.3. The Target Settings Tab

The Target Settings tab enables you to specify the target location for the vmcore dump. It can be either stored as a file in a local file system, written directly to a device, or sent over a network using the NFS (Network File System) or SSH (Secure Shell) protocol.
Target Settings
Target Settings
Figure 24.2. Target Settings

To save the dump to the local file system, select the Local filesystem radio button. Optionally, you can customize the settings by choosing a different partition from the Partition, and a target directory from the Path pulldown lists.
To write the dump directly to a device, select the Raw device radio button, and choose the desired target device from the pulldown list next to it.
To store the dump to a remote machine, select the Network radio button. To use the NFS protocol, select the NFS radio button, and fill the Server name and Path to directory fields. To use the SSH protocol, select the SSH radio button, and fill the Server name, Path to directory, and User name fields with the remote server address, target directory, and a valid remote user name respectively.
Refer to Chapter 9, OpenSSH for information on how to configure an SSH server, and how to set up a key-based authentication.

Important: Using the hpsa Driver for a Storage

Due to known issue with the hpsa driver, kdump is unable to save the dump to a storage that uses this driver for HP Smart Array Controllers. If this applies to your machine, it is advised that you save the dump to a remote system using the NFS or SSH protocol instead.

24.1.2.4. The Filtering Settings Tab

The Filtering Settings tab enables you to select the filtering level for the vmcore dump.
Filtering Settings
Filtering Settings
Figure 24.3. Filtering Settings

To exclude the zero page, cache page, cache private, user data, or free page from the dump, select the check box next to the appropriate label.

24.1.2.5. The Expert Settings Tab

The Expert Settings tab enables you to choose which kernel and initial RAM disk to use, as well as to customize the options that are passed to the kernel and the core collector program.
Expert Settings
Expert Settings
Figure 24.4. Expert Settings

To use a different initial RAM disk, select the Custom initrd radio button, and choose the desired RAM disk from the pulldown list next to it.
To capture a different kernel, select the Custom kernel radio button, and choose the desired kernel image from the pulldown list on the right.
To adjust the list of options that are passed to the kernel at boot time, edit the content of the Edited text field. Note that you can always revert your changes by clicking the Refresh button.
To choose what steps should be taken when the kernel crash is captured, select the appropriate option from the Default action pulldown list. Available options are mount rootfs and run /sbin/init (the default action), reboot (to reboot the system), shell (to present a user with an interactive shell prompt), halt (to halt the system), and poweroff (to power the system off).
To customize the options that are passed to the makedumpfile core collector, edit the Core collector text field; see Section 24.1.3.3, “Configuring the Core Collector” for more information.

24.1.3. Configuring kdump on the Command Line

To perform actions described in this section, you have to be logged in as a superuser: 
~]$ su -
Password:

24.1.3.1. Configuring the Memory Usage

To configure the amount of memory that is reserved for the kdump kernel, open the /boot/grub/grub.conf file in a text editor such as vi or nano, and add the crashkernel=<size>M parameter to the list of kernel options as shown in Example 24.1, “A sample /boot/grub/grub.conf file”.
Example 24.1. A sample /boot/grub/grub.conf file
# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE:  You have a /boot partition.  This means that
#          all kernel and initrd paths are relative to /boot/, eg.
#          root (hd0,0)
#          kernel /vmlinuz-version ro root=/dev/sda3
#          initrd /initrd
#boot=/dev/sda
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Red Hat Enterprise Linux (2.6.32-54.el6.i686)
        root (hd0,0)
        kernel /boot/vmlinuz-2.6.32-54.el6.i686 root=/dev/sda3 ro crashkernel=128M
        initrd /initramfs-2.6.32-54.el6.i686.img

Important: Make Sure the System Has Enough Memory

When the kdump crash recovery is enabled, the minimum memory requirements increase by the amount of memory reserved for it. This value is determined by a user, and defaults to 128 MB, as lower values proved to be unreliable. For more information on minimum memory requirements for Red Hat Enterprise Linux 6, refer to the Required minimums section of the Red Hat Enterprise Linux comparison chart.

24.1.3.2. Configuring the Target Type

When a kernel crash is captured, the core dump can be either stored as a file in a local file system, written directly to a device, or sent over a network using the NFS (Network File System) or SSH (Secure Shell) protocol. Note that only one of these options can be set at the moment. The default option is to store the vmcore file in the /var/crash/ directory of the local file system. To change this, open the /etc/kdump.conf configuration file in a text editor such as vi or nano, and edit the options as described below.
To change the local directory in which the core dump is to be saved, remove the hash sign (“#”) from the beginning of the #path /var/crash line, and replace the value with a desired directory path. Optionally, if you wish to write the file to a different partition, follow the same procedure with the #ext4 /dev/sda3 line as well, and change both the file system type and the device (a device name, a file system label, and UUID are all supported) accordingly. For example: 
ext3 /dev/sda4
path /usr/local/cores
To write the dump directly to a device, remove the hash sign (“#”) from the beginning of the #raw /dev/sda5 line, and replace the value with a desired device name. For example: 
raw /dev/sdb1
To store the dump to a remote machine using the NFS protocol, remove the hash sign (“#”) from the beginning of the #net my.server.com:/export/tmp line, and replace the value with a valid hostname and directory path. For example: 
net penguin.example.com:/export/cores
To store the dump to a remote machine using the SSH protocol, remove the hash sign (“#”) from the beginning of the #net user@my.server.com line, and replace the value with a valid username and hostname. For example: 
net john@penguin.example.com
Refer to Chapter 9, OpenSSH for information on how to configure an SSH server, and how to set up a key-based authentication.

Important: Using the hpsa Driver for a Storage

Due to known issue with the hpsa driver, kdump is unable to save the dump to a storage that uses this driver for HP Smart Array Controllers. If this applies to your machine, it is advised that you save the dump to a remote system using the NFS or SSH protocol instead.

24.1.3.3. Configuring the Core Collector

To reduce the size of the vmcore dump file, kdump allows you to specify an external application (that is, a core collector) to compress the data, and optionally leave out all irrelevant information. Currently, the only fully supported core collector is makedumpfile.
To enable the core collector, open the /etc/kdump.conf configuration file in a text editor such as vi or nano, remove the hash sign (“#”) from the beginning of the #core_collector makedumpfile -c --message-level 1 -d 31 line, and edit the command line options as described below.
To enable the dump file compression, add the -c parameter. For example: 
core_collector makedumpfile -c
To remove certain pages from the dump, add the -d value parameter, where value is a sum of values of pages you want to omit as described in Table 24.1, “Supported filtering levels”. For example, to remove both zero and free pages, use the following: 
core_collector makedumpfile -d 17 -c
Refer to the manual page for makedumpfile for a complete list of available options.
Table 24.1. Supported filtering levels
Option Description
1 Zero pages
2 Cache pages
4 Cache private
8 User pages
16 Free pages

24.1.3.4. Changing the Default Action

By default, when the kernel crash is captured, the root file system is mounted, and /sbin/init is run. To change this behavior, open the /etc/kdump.conf configuration file in a text editor such as vi or nano, remove the hash sign (“#”) from the beginning of the #default shell line, and replace the value with a desired action as described in Table 24.2, “Supported actions”. For example: 
default halt
Table 24.2. Supported actions
Option Description
reboot Reboot the system, losing the core in the process.
halt After attempting to capture a core, halt the system no matter if it succeeded.
poweroff Power off the system.
shell Run the msh session from within the initramfs, allowing a user to record the core manually.

24.1.3.5. Enabling the Service

To start the kdump daemon at boot time, type the following at a shell prompt: 
~]# chkconfig kdump on
This will enable the service for runlevels 2, 3, 4, and 5. Similarly, typing chkconfig kdump off will disable it for all runlevels. To start the service in the current session, use the following command: 
~]# service kdump start
No kdump initial ramdisk found.                            [WARNING]
Rebuilding /boot/initrd-2.6.32-54.el6.i686kdump.img
Starting kdump:                                            [  OK  ]
For more information on runlevels and configuring services in general, refer to Chapter 7, Controlling Access to Services.

24.1.4. Testing the Configuration

Caution: Be Careful When Using These Commands

The commands below will cause the kernel to crash. Use caution when following these steps, and by no means use them on a production machine.
To test the configuration, reboot the system with kdump enabled, and make sure that the service is running (refer to Section 7.3, “Running the Services” for more information on how to run a service in Red Hat Enterprise Linux): 
~]# service kdump status
Kdump is operational
Then type the following commands at a shell prompt: 
~]# echo 1 > /proc/sys/kernel/sysrq
~]# echo c > /proc/sysrq-trigger
This will force the Linux kernel to crash, and the address-YYYY-MM-DD-HH:MM:SS/vmcore file will be copied to the location you have selected in the configuration (that is, to /var/crash/ by default).
Example 24.2. Listing a content of /var/crash/ after a crash
~]# tree --charset=ascii /var/crash
/var/crash
`-- 127.0.0.1-2010-08-25-08:45:02
    `-- vmcore

1 directory, 1 file

24.2. Analyzing the Core Dump

To determine the cause of the system crash, you can use the crash utility. This utility allows you to interactively analyze a running Linux system as well as a core dump created by netdump, diskdump, xendump, or kdump. When started, it presents you with an interactive prompt very similar to the GNU Debugger (GDB).

Note: Make Sure You Have Relevant Packages Installed

To analyze the vmcore dump file, you must have the crash and kernel-debuginfo packages installed. To do so, type the following at a shell prompt: 
~]# yum install --enablerepo=rhel-debuginfo crash kernel-debuginfo
Refer to Section 1.2.2, “Installing” for more information on how to install new packages in Red Hat Enterprise Linux.
To start the utility, type the command in the following form at a shell prompt: 
crash /var/crash/timestamp/vmcore /usr/lib/debug/lib/modules/kernel/vmlinux
Note that the kernel version should be the same that was captured by kdump. To find out which kernel you are currently running, use the uname -r command.
Example 24.3. Running the crash utility
~]# crash /usr/lib/debug/lib/modules/2.6.32-69.el6.i686/vmlinux \
/var/crash/127.0.0.1-2010-08-25-08:45:02/vmcore

crash 5.0.0-23.el6
Copyright (C) 2002-2010  Red Hat, Inc.
Copyright (C) 2004, 2005, 2006  IBM Corporation
Copyright (C) 1999-2006  Hewlett-Packard Co
Copyright (C) 2005, 2006  Fujitsu Limited
Copyright (C) 2006, 2007  VA Linux Systems Japan K.K.
Copyright (C) 2005  NEC Corporation
Copyright (C) 1999, 2002, 2007  Silicon Graphics, Inc.
Copyright (C) 1999, 2000, 2001, 2002  Mission Critical Linux, Inc.
This program is free software, covered by the GNU General Public License,
and you are welcome to change it and/or distribute copies of it under
certain conditions.  Enter "help copying" to see the conditions.
This program has absolutely no warranty.  Enter "help warranty" for details.

GNU gdb (GDB) 7.0
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i686-pc-linux-gnu"...

      KERNEL: /usr/lib/debug/lib/modules/2.6.32-69.el6.i686/vmlinux
    DUMPFILE: /var/crash/127.0.0.1-2010-08-25-08:45:02/vmcore  [PARTIAL DUMP]
        CPUS: 4
        DATE: Wed Aug 25 08:44:47 2010
      UPTIME: 00:09:02
LOAD AVERAGE: 0.00, 0.01, 0.00
       TASKS: 140
    NODENAME: hp-dl320g5-02.lab.bos.redhat.com
     RELEASE: 2.6.32-69.el6.i686
     VERSION: #1 SMP Tue Aug 24 10:31:45 EDT 2010
     MACHINE: i686  (2394 Mhz)
      MEMORY: 8 GB
       PANIC: "Oops: 0002 [#1] SMP " (check log for details)
         PID: 5591
     COMMAND: "bash"
        TASK: f196d560  [THREAD_INFO: ef4da000]
         CPU: 2
       STATE: TASK_RUNNING (PANIC)

crash>

To exit the interactive prompt and terminate crash, type exit.

24.2.1. Displaying the Message Buffer

To display the kernel message buffer, type the log command at the interactive prompt.
Example 24.4. Displaying the kernel message buffer
crash> log
... several lines omitted ...
EIP: 0060:[<c068124f>] EFLAGS: 00010096 CPU: 2
EIP is at sysrq_handle_crash+0xf/0x20
EAX: 00000063 EBX: 00000063 ECX: c09e1c8c EDX: 00000000
ESI: c0a09ca0 EDI: 00000286 EBP: 00000000 ESP: ef4dbf24
 DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
Process bash (pid: 5591, ti=ef4da000 task=f196d560 task.ti=ef4da000)
Stack:
 c068146b c0960891 c0968653 00000003 00000000 00000002 efade5c0 c06814d0
<0> fffffffb c068150f b7776000 f2600c40 c0569ec4 ef4dbf9c 00000002 b7776000
<0> efade5c0 00000002 b7776000 c0569e60 c051de50 ef4dbf9c f196d560 ef4dbfb4
Call Trace:
 [<c068146b>] ? __handle_sysrq+0xfb/0x160
 [<c06814d0>] ? write_sysrq_trigger+0x0/0x50
 [<c068150f>] ? write_sysrq_trigger+0x3f/0x50
 [<c0569ec4>] ? proc_reg_write+0x64/0xa0
 [<c0569e60>] ? proc_reg_write+0x0/0xa0
 [<c051de50>] ? vfs_write+0xa0/0x190
 [<c051e8d1>] ? sys_write+0x41/0x70
 [<c0409adc>] ? syscall_call+0x7/0xb
Code: a0 c0 01 0f b6 41 03 19 d2 f7 d2 83 e2 03 83 e0 cf c1 e2 04 09 d0 88 41 03 f3 c3 90 c7 05 c8 1b 9e c0 01 00 00 00 0f ae f8 89 f6 <c6> 05 00 00 00 00 01 c3 89 f6 8d bc 27 00 00 00 00 8d 50 d0 83
EIP: [<c068124f>] sysrq_handle_crash+0xf/0x20 SS:ESP 0068:ef4dbf24
CR2: 0000000000000000

Type help log for more information on the command usage.

24.2.2. Displaying a Backtrace

To display the kernel stack trace, type the bt command at the interactive prompt. You can use bt pid to display the backtrace of the selected process.
Example 24.5. Displaying the kernel stack trace
crash> bt
PID: 5591   TASK: f196d560  CPU: 2   COMMAND: "bash"
 #0 [ef4dbdcc] crash_kexec at c0494922
 #1 [ef4dbe20] oops_end at c080e402
 #2 [ef4dbe34] no_context at c043089d
 #3 [ef4dbe58] bad_area at c0430b26
 #4 [ef4dbe6c] do_page_fault at c080fb9b
 #5 [ef4dbee4] error_code (via page_fault) at c080d809
    EAX: 00000063  EBX: 00000063  ECX: c09e1c8c  EDX: 00000000  EBP: 00000000
    DS:  007b      ESI: c0a09ca0  ES:  007b      EDI: 00000286  GS:  00e0
    CS:  0060      EIP: c068124f  ERR: ffffffff  EFLAGS: 00010096
 #6 [ef4dbf18] sysrq_handle_crash at c068124f
 #7 [ef4dbf24] __handle_sysrq at c0681469
 #8 [ef4dbf48] write_sysrq_trigger at c068150a
 #9 [ef4dbf54] proc_reg_write at c0569ec2
#10 [ef4dbf74] vfs_write at c051de4e
#11 [ef4dbf94] sys_write at c051e8cc
#12 [ef4dbfb0] system_call at c0409ad5
    EAX: ffffffda  EBX: 00000001  ECX: b7776000  EDX: 00000002
    DS:  007b      ESI: 00000002  ES:  007b      EDI: b7776000
    SS:  007b      ESP: bfcb2088  EBP: bfcb20b4  GS:  0033
    CS:  0073      EIP: 00edc416  ERR: 00000004  EFLAGS: 00000246

Type help bt for more information on the command usage.

24.2.3. Displaying a Process Status

To display status of processes in the system, type the ps command at the interactive prompt. You can use ps pid to display the status of the selected process.
Example 24.6. Displaying status of processes in the system
crash> ps
   PID    PPID  CPU   TASK    ST  %MEM     VSZ    RSS  COMM
>     0      0   0  c09dc560  RU   0.0       0      0  [swapper]
>     0      0   1  f7072030  RU   0.0       0      0  [swapper]
      0      0   2  f70a3a90  RU   0.0       0      0  [swapper]
>     0      0   3  f70ac560  RU   0.0       0      0  [swapper]
      1      0   1  f705ba90  IN   0.0    2828   1424  init
... several lines omitted ...
   5566      1   1  f2592560  IN   0.0   12876    784  auditd
   5567      1   2  ef427560  IN   0.0   12876    784  auditd
   5587   5132   0  f196d030  IN   0.0   11064   3184  sshd
>  5591   5587   2  f196d560  RU   0.0    5084   1648  bash

Type help ps for more information on the command usage.

24.2.4. Displaying Virtual Memory Information

To display basic virtual memory information, type the vm command at the interactive prompt. You can use vm pid to display information on the selected process.
Example 24.7. Displaying virtual memory information of the current context
crash> vm
PID: 5591   TASK: f196d560  CPU: 2   COMMAND: "bash"
   MM       PGD      RSS    TOTAL_VM
f19b5900  ef9c6000  1648k    5084k
  VMA       START      END    FLAGS  FILE
f1bb0310    242000    260000 8000875  /lib/ld-2.12.so
f26af0b8    260000    261000 8100871  /lib/ld-2.12.so
efbc275c    261000    262000 8100873  /lib/ld-2.12.so
efbc2a18    268000    3ed000 8000075  /lib/libc-2.12.so
efbc23d8    3ed000    3ee000 8000070  /lib/libc-2.12.so
efbc2888    3ee000    3f0000 8100071  /lib/libc-2.12.so
efbc2cd4    3f0000    3f1000 8100073  /lib/libc-2.12.so
efbc243c    3f1000    3f4000 100073
efbc28ec    3f6000    3f9000 8000075  /lib/libdl-2.12.so
efbc2568    3f9000    3fa000 8100071  /lib/libdl-2.12.so
efbc2f2c    3fa000    3fb000 8100073  /lib/libdl-2.12.so
f26af888    7e6000    7fc000 8000075  /lib/libtinfo.so.5.7
f26aff2c    7fc000    7ff000 8100073  /lib/libtinfo.so.5.7
efbc211c    d83000    d8f000 8000075  /lib/libnss_files-2.12.so
efbc2504    d8f000    d90000 8100071  /lib/libnss_files-2.12.so
efbc2950    d90000    d91000 8100073  /lib/libnss_files-2.12.so
f26afe00    edc000    edd000 4040075
f1bb0a18   8047000   8118000 8001875  /bin/bash
f1bb01e4   8118000   811d000 8101873  /bin/bash
f1bb0c70   811d000   8122000 100073
f26afae0   9fd9000   9ffa000 100073
... several lines omitted ...

Type help vm for more information on the command usage.

24.2.5. Displaying Open Files

To display information about open files, type the files command at the interactive prompt. You can use files pid to display files opened by the selected process.
Example 24.8. Displaying information about open files of the current context
crash> files
PID: 5591   TASK: f196d560  CPU: 2   COMMAND: "bash"
ROOT: /    CWD: /root
 FD    FILE     DENTRY    INODE    TYPE  PATH
  0  f734f640  eedc2c6c  eecd6048  CHR   /pts/0
  1  efade5c0  eee14090  f00431d4  REG   /proc/sysrq-trigger
  2  f734f640  eedc2c6c  eecd6048  CHR   /pts/0
 10  f734f640  eedc2c6c  eecd6048  CHR   /pts/0
255  f734f640  eedc2c6c  eecd6048  CHR   /pts/0

Type help files for more information on the command usage.

24.3. Additional Resources

24.3.1. Installed Documentation

man kdump.conf
The manual page for the /etc/kdump.conf configuration file containing the full documentation of available options.
man makedumpfile
The manual page for the makedumpfile core collector containing the full documentation on its usage.
man kexec
The manual page for kexec containing the full documentation on its usage.
man crash
The manual page for the crash utility containing the full documentation on its usage.
/usr/share/doc/kexec-tools-version/kexec-kdump-howto.txt
An overview of the kdump and kexec installation and usage.

24.3.2. Useful Websites

https://access.redhat.com/kb/docs/DOC-6039
The Red Hat Knowledgebase article about the kexec and kdump configuration.
http://people.redhat.com/anderson/
The crash utility homepage.

Revision History

Revision History
Revision 2Tue Nov 09 2010Douglas Silas
Red Hat Enterprise Linux 6.0 GA Release of the Deployment Guide.
Revision 1Mon Nov 16 2009Douglas Silas
Initialization of the Red Hat Enterprise Linux 6 Deployment Guide.

Index

Symbols

.fetchmailrc , Fetchmail Configuration Options
server options, Server Options
user options, User Options
.htaccess, Common httpd.conf Directives
(see also Apache HTTP Server)
.htpasswd, Common httpd.conf Directives
(see also Apache HTTP Server)
.procmailrc , Procmail Configuration
/dev/shm , File Systems
/etc/named.conf (see BIND)
/etc/sysconfig/ directory (see sysconfig directory)
/etc/sysconfig/dhcpd , Starting and Stopping the Server
/proc/ directory, Installed Documentation (see proc file system)
/var/spool/anacron , Configuring Anacron Jobs
/var/spool/cron , Configuring Cron Jobs

A

Access Control
configuring in SSSD, Configuring Access Control
in SSSD, rules, The Simple Access Provider
adding
group, Command Line Configuration
user, Command Line Configuration
anacron, Cron and Anacron
anacron configuration file, Configuring Anacron Jobs
user-defined tasks, Configuring Anacron Jobs
anacrontab , Configuring Anacron Jobs
Apache HTTP Server
additional resources
installed documentation, Installed Documentation
useful websites, Useful Websites
checking configuration, Editing the Configuration Files
checking status, Checking the Service Status
directives
<Directory>, Common httpd.conf Directives
<IfDefine>, Common httpd.conf Directives
<IfModule>, Common httpd.conf Directives
<Location>, Common httpd.conf Directives
<Proxy>, Common httpd.conf Directives
<VirtualHost>, Common httpd.conf Directives
AccessFileName, Common httpd.conf Directives
Action, Common httpd.conf Directives
AddDescription, Common httpd.conf Directives
AddEncoding, Common httpd.conf Directives
AddHandler, Common httpd.conf Directives
AddIcon, Common httpd.conf Directives
AddIconByEncoding, Common httpd.conf Directives
AddIconByType, Common httpd.conf Directives
AddLanguage, Common httpd.conf Directives
AddType, Common httpd.conf Directives
Alias, Common httpd.conf Directives
Allow, Common httpd.conf Directives
AllowOverride, Common httpd.conf Directives
BrowserMatch, Common httpd.conf Directives
CacheDefaultExpire, Common httpd.conf Directives
CacheDisable, Common httpd.conf Directives
CacheEnable, Common httpd.conf Directives
CacheLastModifiedFactor, Common httpd.conf Directives
CacheMaxExpire, Common httpd.conf Directives
CacheNegotiatedDocs, Common httpd.conf Directives
CacheRoot, Common httpd.conf Directives
CustomLog, Common httpd.conf Directives
DefaultIcon, Common httpd.conf Directives
DefaultType, Common httpd.conf Directives
Deny, Common httpd.conf Directives
DirectoryIndex, Common httpd.conf Directives
DocumentRoot, Common httpd.conf Directives
ErrorDocument, Common httpd.conf Directives
ErrorLog, Common httpd.conf Directives
ExtendedStatus, Common httpd.conf Directives
Group, Common httpd.conf Directives
HeaderName, Common httpd.conf Directives
HostnameLookups, Common httpd.conf Directives
Include, Common httpd.conf Directives
IndexIgnore, Common httpd.conf Directives
IndexOptions, Common httpd.conf Directives
KeepAlive, Common httpd.conf Directives
KeepAliveTimeout, Common httpd.conf Directives
LanguagePriority, Common httpd.conf Directives
Listen, Common httpd.conf Directives
LoadModule, Common httpd.conf Directives
LogFormat, Common httpd.conf Directives
LogLevel, Common httpd.conf Directives
MaxClients, Common Multi-Processing Module Directives
MaxKeepAliveRequests, Common httpd.conf Directives
MaxSpareServers, Common Multi-Processing Module Directives
MaxSpareThreads, Common Multi-Processing Module Directives
MinSpareServers, Common Multi-Processing Module Directives
MinSpareThreads, Common Multi-Processing Module Directives
NameVirtualHost, Common httpd.conf Directives
Options, Common httpd.conf Directives
Order, Common httpd.conf Directives
PidFile, Common httpd.conf Directives
ProxyRequests, Common httpd.conf Directives
ReadmeName, Common httpd.conf Directives
Redirect, Common httpd.conf Directives
ScriptAlias, Common httpd.conf Directives
ServerAdmin, Common httpd.conf Directives
ServerName, Common httpd.conf Directives
ServerRoot, Common httpd.conf Directives
ServerSignature, Common httpd.conf Directives
ServerTokens, Common httpd.conf Directives
SetEnvIf, Common ssl.conf Directives
StartServers, Common Multi-Processing Module Directives
SuexecUserGroup, Common httpd.conf Directives
ThreadsPerChild, Common Multi-Processing Module Directives
Timeout, Common httpd.conf Directives
TypesConfig, Common httpd.conf Directives
UseCanonicalName, Common httpd.conf Directives
User, Common httpd.conf Directives
UserDir, Common httpd.conf Directives
directories
/etc/httpd/, Common httpd.conf Directives
/etc/httpd/conf.d/, Editing the Configuration Files, Common httpd.conf Directives
/usr/lib/httpd/modules/, Common httpd.conf Directives, Working with Modules
/usr/lib64/httpd/modules/, Common httpd.conf Directives, Working with Modules
/var/cache/mod_proxy/, Common httpd.conf Directives
/var/www/cgi-bin/, Common httpd.conf Directives
/var/www/html/, Common httpd.conf Directives
/var/www/icons/, Common httpd.conf Directives
~/public_html/, Common httpd.conf Directives
files
.htaccess, Common httpd.conf Directives
.htpasswd, Common httpd.conf Directives
/etc/httpd/conf.d/ssl.conf, Common ssl.conf Directives, Enabling the mod_ssl Module
/etc/httpd/conf/httpd.conf, Editing the Configuration Files, Common httpd.conf Directives, Common Multi-Processing Module Directives
/etc/httpd/logs/access_log, Common httpd.conf Directives
/etc/httpd/logs/error_log, Common httpd.conf Directives
/etc/httpd/run/httpd.pid, Common httpd.conf Directives
/etc/mime.types, Common httpd.conf Directives
modules
developing, Writing a Module
loading, Loading a Module
mod_asis, Notable Changes
mod_cache, New Features
mod_cern_meta, Notable Changes
mod_disk_cache, New Features
mod_ext_filter, Notable Changes
mod_proxy_balancer, New Features
mod_rewrite, Common httpd.conf Directives
mod_ssl, Setting Up an SSL Server
mod_userdir, Updating the Configuration
restarting, Restarting the Service
SSL server
certificate, An Overview of Certificates and Security, Using an Existing Key and Certificate, Generating a New Key and Certificate
certificate authority, An Overview of Certificates and Security
private key, An Overview of Certificates and Security, Using an Existing Key and Certificate, Generating a New Key and Certificate
public key, An Overview of Certificates and Security
starting, Starting the Service
stopping, Stopping the Service
version 2.2
changes, Notable Changes
features, New Features
updating from version 2.0, Updating the Configuration
virtual host, Setting Up Virtual Hosts
at , At and Batch
additional resources, Additional Resources
authconfig (see Authentication Configuration Tool )
commands , Command Line Version
authentication
Authentication Configuration Tool , The Authentication Configuration Tool
using fingerprint support , Advanced Options
using smart card authentication , Advanced Options
Authentication Configuration Tool
and Kerberos authentication , Identity & Authentication
and LDAP , Identity & Authentication
and NIS , Identity & Authentication
and NIS authentication , Identity & Authentication
and Winbind , Identity & Authentication
and Winbind authentication , Identity & Authentication
authoritative nameserver (see BIND)
Automated Tasks, Automated Tasks

B

batch , At and Batch
additional resources, Additional Resources
Berkeley Internet Name Domain (see BIND)
BIND
additional resources
installed documentation, Installed Documentation
related books, Related Books
useful websites, Useful Websites
common mistakes, Common Mistakes to Avoid
configuration
acl statement, Common Statement Types
comment tags, Comment Tags
controls statement, Other Statement Types
include statement, Common Statement Types
key statement, Other Statement Types
logging statement, Other Statement Types
options statement, Common Statement Types
server statement, Other Statement Types
trusted-keys statement, Other Statement Types
view statement, Other Statement Types
zone statement, Common Statement Types
directories
/etc/named/, Configuring the named Service
/var/named/, Editing Zone Files
/var/named/data/, Editing Zone Files
/var/named/dynamic/, Editing Zone Files
/var/named/slaves/, Editing Zone Files
features
Automatic Zone Transfer (AXFR), Incremental Zone Transfers (IXFR)
DNS Security Extensions (DNSSEC), DNS Security Extensions (DNSSEC)
Incremental Zone Transfer (IXFR), Incremental Zone Transfers (IXFR)
Internet Protocol version 6 (IPv6), Internet Protocol version 6 (IPv6)
multiple views, Multiple Views
Transaction SIGnature (TSIG), Transaction SIGnatures (TSIG)
files
/etc/named.conf, Configuring the named Service, Configuring the Utility
/etc/rndc.conf, Configuring the Utility
/etc/rndc.key, Configuring the Utility
resource record, Nameserver Zones
types
authoritative nameserver, Nameserver Types
primary (master) nameserver, Nameserver Zones, Nameserver Types
recursive nameserver, Nameserver Types
secondary (slave) nameserver, Nameserver Zones, Nameserver Types
utilities
dig, BIND as a Nameserver, Using the dig Utility, DNS Security Extensions (DNSSEC)
named, BIND as a Nameserver, Configuring the named Service
rndc, BIND as a Nameserver, Using the rndc Utility
zones
$INCLUDE directive, Common Directives
$ORIGIN directive, Common Directives
$TTL directive, Common Directives
A (Address) resource record, Common Resource Records
CNAME (Canonical Name) resource record, Common Resource Records
comment tags, Comment Tags
description, Nameserver Zones
example usage, A Simple Zone File, A Reverse Name Resolution Zone File
MX (Mail Exchange) resource record, Common Resource Records
NS (Nameserver) resource record, Common Resource Records
PTR (Pointer) resource record, Common Resource Records
SOA (Start of Authority) resource record, Common Resource Records
block devices, /proc/devices
(see also /proc/devices )
definition of, /proc/devices
bonding (see channel bonding)
boot loader
verifying, Verifying the Boot Loader
boot media, Preparing to Upgrade

C

ch-email .fetchmailrc
global options, Global Options
chage command
forcing password expiration with, Command Line Configuration
channel bonding
configuration, Using Channel Bonding
description, Using Channel Bonding
interface
configuration of, Channel Bonding Interfaces
parameters to bonded interfaces, Bonding Module Directives
channel bonding interface (see kernel module)
character devices, /proc/devices
(see also /proc/devices )
definition of, /proc/devices
chkconfig (see services configuration)
Configuration File Changes, Preserving Configuration File Changes
crash
analyzing the dump
message buffer, Displaying the Message Buffer
open files, Displaying Open Files
processes, Displaying a Process Status
stack trace, Displaying a Backtrace
virtual memory, Displaying Virtual Memory Information
opening the dump image, Analyzing the Core Dump
system requirements, Analyzing the Core Dump
Cron, Automated Tasks
cron , Cron and Anacron
additional resources, Additional Resources
cron configuration file, Configuring Cron Jobs
user-defined tasks, Configuring Cron Jobs
crontab , Configuring Cron Jobs

D

date (see date configuration)
date configuration
date , Date and Time Setup
system-config-date , Date and Time Properties
deleting cache files
in SSSD, Support for Multiple Domains
Denial of Service attack, /proc/sys/net/
(see also /proc/sys/net/ directory)
definition of, /proc/sys/net/
df , File Systems
DHCP, Dynamic Host Configuration Protocol (DHCP)
additional resources, Additional Resources
client configuration, Configuring a DHCP Client
command line options, Starting and Stopping the Server
connecting to, Configuring a DHCP Client
dhcpd.conf, Configuration File
dhcpd.leases , Starting and Stopping the Server
dhcpd6.conf, DHCP for IPv6 (DHCPv6)
DHCPv6, DHCP for IPv6 (DHCPv6)
dhcrelay , DHCP Relay Agent
global parameters, Configuration File
group, Configuration File
options, Configuration File
reasons for using, Why Use DHCP?
Relay Agent, DHCP Relay Agent
server configuration, Configuring a DHCP Server
shared-network , Configuration File
starting the server, Starting and Stopping the Server
stopping the server, Starting and Stopping the Server
subnet, Configuration File
dhcpd.conf, Configuration File
dhcpd.leases, Starting and Stopping the Server
dhcrelay , DHCP Relay Agent
dig (see BIND)
DNS
definition, The BIND DNS Server
(see also BIND)
documentation
finding installed, Practical and Common Examples of RPM Usage
DoS attack (see Denial of Service attack)
drivers (see kernel module)
DSA keys
generating, Generating Key Pairs
du , File Systems
Dynamic Host Configuration Protocol (see DHCP)

E

email
additional resources, Additional Resources
installed documentation, Installed Documentation
related books, Related Books
useful websites, Useful Websites
Fetchmail, Fetchmail
history of, Email
mail server
Dovecot, Dovecot
Postfix, Postfix
Procmail, Mail Delivery Agents
program classifications, Email Program Classifications
protocols, Email Protocols
IMAP, IMAP
POP, POP
SMTP, SMTP
security, Securing Communication
clients, Secure Email Clients
servers, Securing Email Client Communications
Sendmail, Sendmail
spam
filtering out, Spam Filters
types
Mail Delivery Agent, Mail Delivery Agent
Mail Transport Agent, Mail Transport Agent
Mail User Agent, Mail User Agent
epoch, /proc/stat
(see also /proc/stat )
definition of, /proc/stat
Ethernet (see network)
exec-shield
enabling, /proc/sys/kernel/
introducing, /proc/sys/kernel/
execution domains, /proc/execdomains
(see also /proc/execdomains )
definition of, /proc/execdomains
expiration of password, forcing, Command Line Configuration
extra packages for Enterprise Linux (EPEL)
installable packages, Finding RPM Packages

F

feedback
contact information for this manual, We Need Feedback!
Fetchmail, Fetchmail
additional resources, Additional Resources
command options, Fetchmail Command Options
informational, Informational or Debugging Options
special, Special Options
configuration options, Fetchmail Configuration Options
global options, Global Options
server options, Server Options
user options, User Options
file system
virtual (see proc file system)
file systems, File Systems
files, proc file system
changing, Changing Virtual Files, Using the sysctl Command
viewing, Viewing Virtual Files, Using the sysctl Command
FQDN (see fully qualified domain name)
frame buffer device, /proc/fb
(see also /proc/fb )
free , Memory Usage
fully qualified domain name, Nameserver Zones

G

GNOME System Monitor , System Processes
gnome-system-log (see Log File Viewer )
gnome-system-monitor , System Processes
GnuPG
checking RPM package signatures, Checking a Package's Signature
group confi/sbin/nologinguration
adding groups, Adding a New Group
group configuration
filtering list of groups, User and Group Configuration
groupadd , Command Line Configuration
modify users in groups, Modifying Group Properties
modifying group properties, Modifying Group Properties
viewing list of groups, User and Group Configuration
groups (see group configuration)
additional resources, Additional Resources
installed documentation, Installed Documentation
GID, Users and Groups
introducing, Users and Groups
shared directories, Group Directories
standard, Standard Groups
tools for management of
groupadd , User and Group Management Tools, User Private Groups
system-config-users , User Private Groups
User Manager , User and Group Management Tools
user private, User Private Groups
GRUB boot loader
configuration file, Configuring the GRUB Boot Loader
configuring, Configuring the GRUB Boot Loader

H

hardware
viewing, Hardware
Hardware Browser , Hardware
HTTP server (see Apache HTTP Server)
httpd (see Apache HTTP Server)
hugepages
configuration of, /proc/sys/vm/
hwbrowser , Hardware

I

ifdown , Interface Control Scripts
ifup , Interface Control Scripts
information
about your system, Gathering System Information
initial RAM disk image
verifying, Verifying the Initial RAM Disk Image
IBM eServer System i, Verifying the Initial RAM Disk Image
initial RPM repositories
installable packages, Finding RPM Packages
insmod , Loading a Module
(see also kernel module)
installing package groups
installing package groups with PackageKit, Installing and Removing Package Groups
installing the kernel, Manually Upgrading the Kernel
introduction, Introduction

K

kdump
additional resources
installed documents, Installed Documentation
manual pages, Installed Documentation
websites, Useful Websites
analyzing the dump (see crash)
configuring the service
default action, The Expert Settings Tab, Changing the Default Action
dump image compression, The Expert Settings Tab, Configuring the Core Collector
filtering level, The Filtering Settings Tab, Configuring the Core Collector
initial RAM disk, The Expert Settings Tab, Configuring the Memory Usage
kernel image, The Expert Settings Tab, Configuring the Memory Usage
kernel options, The Expert Settings Tab, Configuring the Memory Usage
memory usage, Configuring the Memory Usage, The Basic Settings Tab, Configuring the Memory Usage
target location, The Target Settings Tab, Configuring the Target Type
enabling the service, Enabling the Service, Enabling the Service, Enabling the Service
known issues
hpsa driver, The Target Settings Tab, Configuring the Target Type
running the service, Enabling the Service
system requirements, Configuring the kdump Service
testing the configuration, Testing the Configuration
kernel
downloading, Downloading the Upgraded Kernel
installing kernel packages, Manually Upgrading the Kernel
kernel packages, Overview of Kernel Packages
package, Manually Upgrading the Kernel
performing kernel upgrade, Performing the Upgrade
RPM package, Manually Upgrading the Kernel
upgrade kernel available, Downloading the Upgraded Kernel
Security Errata, Downloading the Upgraded Kernel
via Red Hat network, Downloading the Upgraded Kernel
upgrading
preparing, Preparing to Upgrade
working boot media, Preparing to Upgrade
upgrading the kernel, Manually Upgrading the Kernel
Kernel Dump Configuration (see kdump)
kernel module
bonding module, Using Channel Bonding
description, Using Channel Bonding
parameters to bonded interfaces, Bonding Module Directives
definition, Working with Kernel Modules
directories
/etc/sysconfig/modules/ , Persistent Module Loading
/lib/modules/<kernel_version>/kernel/drivers/ , Loading a Module
Ethernet module
supporting multiple cards, Using Multiple Ethernet Cards
files
/proc/modules , Listing Currently-Loaded Modules
listing
currently loaded modules, Listing Currently-Loaded Modules
module information, Displaying Information About a Module
loading
at the boot time, Persistent Module Loading
for the current session, Loading a Module
module parameters
bonding module parameters, Bonding Module Directives
supplying, Setting Module Parameters
unloading, Unloading a Module
utilities
insmod , Loading a Module
lsmod , Listing Currently-Loaded Modules
modinfo , Displaying Information About a Module
modprobe , Loading a Module, Unloading a Module
rmmod , Unloading a Module
kernel package
kernel
for single,multicore and multiprocessor systems, Overview of Kernel Packages
kernel-devel
kernel headers and makefiles, Overview of Kernel Packages
kernel-doc
documentation files, Overview of Kernel Packages
kernel-firmware
firmware files, Overview of Kernel Packages
kernel-headers
C header files files, Overview of Kernel Packages
perf
firmware files, Overview of Kernel Packages
kernel upgrading
preparing, Preparing to Upgrade
keyboard configuration, Keyboard Configuration
Keyboard Indicator applet, Adding the Keyboard Layout Indicator
Keyboard Preferences utility, Changing the Keyboard Layout
layout, Changing the Keyboard Layout
typing break, Setting Up a Typing Break
Keyboard Indicator (see keyboard configuration)
Keyboard Preferences (see keyboard configuration)

L

Log File Viewer
filtering, Viewing Log Files
monitoring, Monitoring Log Files
searching, Viewing Log Files
log files, Log Files
(see also Log Viewer )
additional resources
installed documentation, Installed Documentation
useful websites, Useful Websites
description, Log Files
locating, Locating Log Files
monitoring, Monitoring Log Files
rotating, Locating Log Files
rsyslod daemon , Log Files
viewing, Viewing Log Files
Log Viewer
refresh rate, Viewing Log Files
logrotate , Locating Log Files
lsmod , Listing Currently-Loaded Modules
(see also kernel module)
lspci , /proc/bus/pci , Hardware

M

Mail Delivery Agent (see email)
Mail Transport Agent (see email) (see MTA)
Mail Transport Agent Switcher , Mail Transport Agent (MTA) Configuration
Mail User Agent, Mail Transport Agent (MTA) Configuration (see email)
MDA (see Mail Delivery Agent)
memory usage, Memory Usage
modinfo , Displaying Information About a Module
(see also kernel module)
modprobe , Loading a Module, Unloading a Module
(see also kernel module)
module (see kernel module)
module parameters (see kernel module)
MTA (see Mail Transport Agent)
setting default, Mail Transport Agent (MTA) Configuration
switching with Mail Transport Agent Switcher , Mail Transport Agent (MTA) Configuration
MUA, Mail Transport Agent (MTA) Configuration (see Mail User Agent)
Multihomed DHCP
host configuration, Host Configuration
server configuration, Configuring a Multihomed DHCP Server
multiple domains
specifying in SSSD, Support for Multiple Domains

N

named (see BIND)
nameserver (see DNS)
network
additional resources, Additional Resources
commands
/sbin/ifdown , Interface Control Scripts
/sbin/ifup , Interface Control Scripts
/sbin/service network , Interface Control Scripts
configuration, Interface Configuration Files
configuration files, Network Configuration Files
functions, Network Function Files
interface configuration files, Interface Configuration Files
interfaces
alias, Alias and Clone Files
channel bonding, Channel Bonding Interfaces
clone, Alias and Clone Files
dialup, Dialup Interfaces
Ethernet, Ethernet Interfaces
scripts, Network Interfaces
Network Time Protocol (see NTP)
NIC
binding into single channel, Using Channel Bonding
NTP
configuring, Network Time Protocol Properties, Network Time Protocol Setup
ntpd , Network Time Protocol Properties, Network Time Protocol Setup
ntpdate , Network Time Protocol Setup
ntpd (see NTP)
ntpdate (see NTP)
ntsysv (see services configuration)

O

OpenSSH, OpenSSH, Main Features
(see also SSH)
additional resources, Additional Resources
client, OpenSSH Clients
scp , Using the scp Utility
sftp , Using the sftp Utility
ssh , Using the ssh Utility
DSA keys
generating, Generating Key Pairs
RSA keys
generating, Generating Key Pairs
RSA Version 1 keys
generating, Generating Key Pairs
server, Starting an OpenSSH Server
starting, Starting an OpenSSH Server
stopping, Starting an OpenSSH Server
ssh-add , Configuring ssh-agent
ssh-agent , Configuring ssh-agent
ssh-keygen
DSA, Generating Key Pairs
RSA, Generating Key Pairs
RSA Version 1, Generating Key Pairs
using key-based authentication, Using a Key-Based Authentication
OpenSSL
additional resources, Additional Resources
SSL (see SSL)
TLS (see TLS)
OS/400 boot loader
configuration file, Configuring the OS/400® Boot Loader
configuring, Configuring the OS/400® Boot Loader

P

package
kernel RPM, Manually Upgrading the Kernel
PackageKit, PackageKit
adding and removing, Using Add/Remove Software
architecture, PackageKit Architecture
installing and removing package groups, Installing and Removing Package Groups
installing packages , PackageKit
managing packages , PackageKit
PolicyKit
authentication, Updating Packages with Software Update
uninstalling packages , PackageKit
updating packages , PackageKit
viewing packages , PackageKit
viewing transaction log, Viewing the Transaction Log
packages
adding and removing with PackageKit, Using Add/Remove Software
dependencies, Unresolved Dependency
determining file ownership with, Practical and Common Examples of RPM Usage
displaying packages
yum info, Searching, Listing and Displaying Package Information
displaying packages with Yum, Searching, Listing and Displaying Package Information
yum info, Searching, Listing and Displaying Package Information
extra packages for Enterprise Linux (EPEL), Finding RPM Packages
filtering with PackageKit, Finding Packages with Filters
Development, Finding Packages with Filters
Free, Finding Packages with Filters
Graphical, Finding Packages with Filters
hide subpackages, Finding Packages with Filters
installed, Finding Packages with Filters
no filter, Finding Packages with Filters
only available, Finding Packages with Filters
only development, Finding Packages with Filters
only end user files, Finding Packages with Filters
only installed, Finding Packages with Filters
only native packages, Finding Packages with Filters
only newest items, Finding Packages with Filters
filtering with PackageKit for packages, Finding Packages with Filters
finding deleted files from, Practical and Common Examples of RPM Usage
finding RPM packages, Finding RPM Packages
initial RPM repositories, Finding RPM Packages
installing a package group with Yum, Installing
installing and removing package groups, Installing and Removing Package Groups
installing packages with PackageKit, PackageKit, Installing and Removing Packages (and Dependencies)
dependencies, Installing and Removing Packages (and Dependencies)
installing RPM, Installing and Upgrading
installing with Yum, Installing
iRed Hat Enterprise Linux installation media, Finding RPM Packages
kernel
for single,multicore and multiprocessor systems, Overview of Kernel Packages
kernel-devel
kernel headers and makefiles, Overview of Kernel Packages
kernel-doc
documentation files, Overview of Kernel Packages
kernel-firmware
firmware files, Overview of Kernel Packages
kernel-headers
C header files files, Overview of Kernel Packages
listing packages with Yum, Searching, Listing and Displaying Package Information
Glob expressions, Searching, Listing and Displaying Package Information
yum grouplist, Searching, Listing and Displaying Package Information
yum list all, Searching, Listing and Displaying Package Information
yum list available, Searching, Listing and Displaying Package Information
yum list installed, Searching, Listing and Displaying Package Information
yum repolist, Searching, Listing and Displaying Package Information
yum search, Searching, Listing and Displaying Package Information
locating documentation for, Practical and Common Examples of RPM Usage
managing packages with PackageKit, PackageKit
obtaining list of files, Practical and Common Examples of RPM Usage
packages and package groups, Packages and Package Groups
perf
firmware files, Overview of Kernel Packages
querying uninstalled, Practical and Common Examples of RPM Usage
removing, Uninstalling
removing package groups with Yum, Removing
removing packages with PackageKit, Installing and Removing Packages (and Dependencies)
RPM, RPM
already installed, Package Already Installed
configuration file changes, Configuration File Changes
conflict, Conflicting Files
failed dependancies, Unresolved Dependency
freshening, Freshening
prisitne sources, RPM Design Goals
querying, Querying
removing, Uninstalling
source and binary packages, RPM
tips, Practical and Common Examples of RPM Usage
uninstalling, Uninstalling
verifying, Verifying
searching for packages with Yum
yum search, Searching, Listing and Displaying Package Information
searching packages with Yum, Searching, Listing and Displaying Package Information
setting packages with PackageKit
checking interval, Updating Packages with Software Update
uninstalling packages with PackageKit, PackageKit
uninstalling packages with Yum, Removing
yum remove package_name, Removing
updating currently installed packages
available updates, Updating Packages with Software Update
updating packages with PackageKit, PackageKit
PolicyKit, Updating Packages with Software Update
Software Update, Updating Packages with Software Update
upgrading RPM, Installing and Upgrading
viewing packages with PackageKit, PackageKit
viewing transaction log, Viewing the Transaction Log
viewing Yum repositories with PackageKit, Refreshing Software Sources (Yum Repositories)
Yum insead of RPM, RPM
password
aging, Command Line Configuration
expire, Command Line Configuration
passwords
shadow, Shadow Passwords
PCI devices
listing, Hardware
PolicyKit, Updating Packages with Software Update
Postfix, Postfix
default installation, The Default Postfix Installation
postfix, Mail Transport Agent (MTA) Configuration
primary nameserver (see BIND)
proc file system
/proc/buddyinfo , /proc/buddyinfo
/proc/bus/ directory, /proc/bus/
/proc/bus/pci
viewing using lspci , /proc/bus/pci
/proc/cmdline , /proc/cmdline
/proc/cpuinfo , /proc/cpuinfo
/proc/crypto , /proc/crypto
/proc/devices
block devices, /proc/devices
character devices, /proc/devices
/proc/dma , /proc/dma
/proc/driver/ directory, /proc/driver/
/proc/execdomains , /proc/execdomains
/proc/fb , /proc/fb
/proc/filesystems , /proc/filesystems
/proc/fs/ directory, /proc/fs
/proc/interrupts , /proc/interrupts
/proc/iomem , /proc/iomem
/proc/ioports , /proc/ioports
/proc/irq/ directory, /proc/irq/
/proc/kcore , /proc/kcore
/proc/kmsg , /proc/kmsg
/proc/loadavg , /proc/loadavg
/proc/locks , /proc/locks
/proc/mdstat , /proc/mdstat
/proc/meminfo , /proc/meminfo
/proc/misc , /proc/misc
/proc/modules , /proc/modules
/proc/mounts , /proc/mounts
/proc/mtrr , /proc/mtrr
/proc/net/ directory, /proc/net/
/proc/partitions , /proc/partitions
/proc/PID/ directory, /proc/PID/
/proc/scsi/ directory, /proc/scsi/
/proc/self/ directory, /proc/self/
/proc/slabinfo , /proc/slabinfo
/proc/stat , /proc/stat
/proc/swaps , /proc/swaps
/proc/sys/ directory, /proc/sys/ , Using the sysctl Command
(see also sysctl )
/proc/sys/dev/ directory, /proc/sys/dev/
/proc/sys/fs/ directory, /proc/sys/fs/
/proc/sys/kernel/ directory, /proc/sys/kernel/
/proc/sys/kernel/exec-shield , /proc/sys/kernel/
/proc/sys/kernel/sysrq (see system request key)
/proc/sys/net/ directory, /proc/sys/net/
/proc/sys/vm/ directory, /proc/sys/vm/
/proc/sysrq-trigger , /proc/sysrq-trigger
/proc/sysvipc/ directory, /proc/sysvipc/
/proc/tty/ directory, /proc/tty/
/proc/uptime , /proc/uptime
/proc/version , /proc/version
additional resources, References
installed documentation, Installed Documentation
useful websites, Useful Websites
changing files within, Changing Virtual Files, /proc/sys/ , Using the sysctl Command
files within, top-level, Top-level Files within the proc File System
introduced, The proc File System
process directories, Process Directories
subdirectories within, Directories within /proc/
viewing files within, Viewing Virtual Files
processes, System Processes
Procmail, Mail Delivery Agents
additional resources, Additional Resources
configuration, Procmail Configuration
recipes, Procmail Recipes
delivering, Delivering vs. Non-Delivering Recipes
examples, Recipe Examples
flags, Flags
local lockfiles, Specifying a Local Lockfile
non-delivering, Delivering vs. Non-Delivering Recipes
SpamAssassin, Spam Filters
special actions, Special Conditions and Actions
special conditions, Special Conditions and Actions
ps , System Processes

R

RAM, Memory Usage
rcp , Using the scp Utility
recursive nameserver (see BIND)
Red Hat Enterprise Linux installation media
installable packages, Finding RPM Packages
Red Hat RPM Guide , Related Books
removing package groups
removing package groups with PackageKit, Installing and Removing Package Groups
resource record (see BIND)
rmmod , Unloading a Module
(see also kernel module)
rndc (see BIND)
root nameserver (see BIND)
RPM, RPM
additional resources, Additional Resources
already installed, Package Already Installed
basic modes, Using RPM
book about, Related Books
checking package signatures, Checking a Package's Signature
configuration file changes, Configuration File Changes
conf.rpmsave, Configuration File Changes
conflicts, Conflicting Files
dependencies, Unresolved Dependency
design goals, RPM Design Goals
powerful querying, RPM Design Goals
system verification, RPM Design Goals
upgradability, RPM Design Goals
determining file ownership with, Practical and Common Examples of RPM Usage
documentation with, Practical and Common Examples of RPM Usage
failed dependancies, Unresolved Dependency
file conflicts
resolving, Conflicting Files
file name, Installing and Upgrading
finding deleted files with, Practical and Common Examples of RPM Usage
finding RPM packages, Finding RPM Packages
freshening, Freshening
GnuPG, Checking a Package's Signature
installing, Installing and Upgrading
md5sum, Checking a Package's Signature
querying, Querying
querying for file list, Practical and Common Examples of RPM Usage
querying uninstalled packages, Practical and Common Examples of RPM Usage
tips, Practical and Common Examples of RPM Usage
uninstalling, Uninstalling
upgrading, Installing and Upgrading
verifying, Verifying
website, Useful Websites
RPM Package Manager (see RPM)
RSA keys
generating, Generating Key Pairs
RSA Version 1 keys
generating, Generating Key Pairs
rsyslog , Log Files
runlevel (see services configuration)

S

scp (see OpenSSH)
secondary nameserver (see BIND)
security plugin (see Security )
Security-Related Packages
updating security-related packages, Updating Security-Related Packages
Sendmail, Sendmail
additional resources, Additional Resources
aliases, Masquerading
common configuration changes, Common Sendmail Configuration Changes
default installation, The Default Sendmail Installation
LDAP and, Using Sendmail with LDAP
limitations, Purpose and Limitations
masquerading, Masquerading
purpose, Purpose and Limitations
spam, Stopping Spam
with UUCP, Common Sendmail Configuration Changes
sendmail, Mail Transport Agent (MTA) Configuration
service (see services configuration)
services configuration, Controlling Access to Services
chkconfig , Using the chkconfig Utility
ntsysv , Using the ntsysv Utility
runlevel , Configuring the Default Runlevel
service , Using the service Utility
system-config-services , Using the Service Configuration Utility
sftp (see OpenSSH)
shadow passwords
overview of, Shadow Passwords
slab pools (see /proc/slabinfo )
SpamAssassin
using with Procmail, Spam Filters
ssh (see OpenSSH)
SSH protocol
authentication, Authentication
configuration files, Configuration Files
system-wide configuration files, Configuration Files
user-specific configuration files, Configuration Files
connection sequence, Event Sequence of an SSH Connection
features, Main Features
insecure protocols, Requiring SSH for Remote Connections
layers
channels, Channels
transport layer, Transport Layer
port forwarding, Port Forwarding
requiring for remote login, Requiring SSH for Remote Connections
security risks, Why Use SSH?
version 1, Protocol Versions
version 2, Protocol Versions
X11 forwarding, X11 Forwarding
ssh-add , Configuring ssh-agent
ssh-agent , Configuring ssh-agent
SSL, Setting Up an SSL Server
(see also Apache HTTP Server)
SSL server (see Apache HTTP Server)
SSSD
Configuring a Microsoft Active Directory Domain for, Configuring a Microsoft Active Directory Domain
Configuring a proxy domain for, Configuring a Proxy Domain
Configuring an LDAP domain for, Configuring an LDAP Domain
Selecting an LDAP schema for, Configuring an LDAP Domain
Setting Up Kerberos authentication for, Setting Up Kerberos Authentication
Specifying timeout values for, Configuring an LDAP Domain
stunnel , Securing Email Client Communications
sysconfig directory
/etc/sysconfig/apm-scripts/ directory, Directories in the /etc/sysconfig/ Directory
/etc/sysconfig/arpwatch , /etc/sysconfig/arpwatch
/etc/sysconfig/authconfig , /etc/sysconfig/authconfig
/etc/sysconfig/autofs , /etc/sysconfig/autofs
/etc/sysconfig/cbq/ directory, Directories in the /etc/sysconfig/ Directory
/etc/sysconfig/clock , /etc/sysconfig/clock
/etc/sysconfig/dhcpd , /etc/sysconfig/dhcpd
/etc/sysconfig/firstboot , /etc/sysconfig/firstboot
/etc/sysconfig/init , /etc/sysconfig/init
/etc/sysconfig/ip6tables-config , /etc/sysconfig/ip6tables-config
/etc/sysconfig/keyboard , /etc/sysconfig/keyboard
/etc/sysconfig/ldap , /etc/sysconfig/ldap
/etc/sysconfig/named , /etc/sysconfig/named
/etc/sysconfig/network , /etc/sysconfig/network
/etc/sysconfig/network-scripts/ directory, Network Interfaces, Directories in the /etc/sysconfig/ Directory
(see also network)
/etc/sysconfig/networking/ directory, Directories in the /etc/sysconfig/ Directory
/etc/sysconfig/ntpd , /etc/sysconfig/ntpd
/etc/sysconfig/quagga , /etc/sysconfig/quagga
/etc/sysconfig/radvd , /etc/sysconfig/radvd
/etc/sysconfig/rhn/ directory, Directories in the /etc/sysconfig/ Directory
/etc/sysconfig/samba , /etc/sysconfig/samba
/etc/sysconfig/selinux , /etc/sysconfig/selinux
/etc/sysconfig/sendmail , /etc/sysconfig/sendmail
/etc/sysconfig/spamassassin , /etc/sysconfig/spamassassin
/etc/sysconfig/squid , /etc/sysconfig/squid
/etc/sysconfig/system-config-users , /etc/sysconfig/system-config-users
/etc/sysconfig/vncservers , /etc/sysconfig/vncservers
/etc/sysconfig/xinetd , /etc/sysconfig/xinetd
additional information about, The sysconfig Directory
additional resources, Additional Resources
installed documentation, Installed Documentation
directories in, Directories in the /etc/sysconfig/ Directory
files found in, Files in the /etc/sysconfig/ Directory
sysctl
configuring with /etc/sysctl.conf , Using the sysctl Command
controlling /proc/sys/ , Using the sysctl Command
SysRq (see system request key)
system information
file systems, File Systems
/dev/shm , File Systems
gathering, Gathering System Information
hardware, Hardware
memory usage, Memory Usage
processes, System Processes
currently running, System Processes
system request key
enabling, /proc/sys/
System Request Key
definition of, /proc/sys/
setting timing for, /proc/sys/kernel/
system-config-authentication (see Authentication Configuration Tool )
system-config-date (see time configuration, date configuration)
system-config-kdump (see kdump)
system-config-services (see services configuration)
system-config-users (see user configuration and group configuration)

T

time configuration
date , Date and Time Setup
synchronize with NTP server, Network Time Protocol Properties, Network Time Protocol Setup
system-config-date , Date and Time Properties
time zone configuration, Time Zone Properties
TLB cache (see hugepages)
TLS, Setting Up an SSL Server
(see also Apache HTTP Server)
tool
Authentication Configuration Tool , The Authentication Configuration Tool
top , System Processes

U

updating currently installed packages
available updates, Updating Packages with Software Update
updating packages with PackageKit
PolicyKit, Updating Packages with Software Update
user configuration
adding users, Adding a New User
changing full name, Adding a New User
changing home directory, Adding a New User
changing login shell, Adding a New User
changing password, Adding a New User
command line configuration, Command Line Configuration
passwd , Command Line Configuration
useradd , Command Line Configuration
filtering list of users, User and Group Configuration
modify groups for a user, Adding a New User
modifying users, Adding a New User
password
forcing expiration of, Command Line Configuration
viewing list of users, User and Group Configuration
User Manager (see user configuration)
user private groups (see groups)
and shared directories, Group Directories
useradd command
user account creation using, Command Line Configuration
users (see user configuration)
/etc/passwd , Standard Users
additional resources, Additional Resources
installed documentation, Installed Documentation
introducing, Users and Groups
standard, Standard Users
tools for management of
User Manager , User and Group Management Tools
useradd , User and Group Management Tools
UID, Users and Groups

V

virtual file system (see proc file system)
virtual files (see proc file system)
virtual host (see Apache HTTP Server)

W

web server (see Apache HTTP Server)

Y

Yum
Additional Resources, Additional Resources
configuring plugins, Enabling, Configuring and Disabling Yum Plugins
configuring Yum and Yum repositories, Configuring Yum and Yum Repositories
disabling plugins, Enabling, Configuring and Disabling Yum Plugins
displaying packages
yum info, Searching, Listing and Displaying Package Information
displaying packages with Yum, Searching, Listing and Displaying Package Information
yum info, Searching, Listing and Displaying Package Information
enabling plugins, Enabling, Configuring and Disabling Yum Plugins
installing a package group with Yum, Installing
installing with Yum, Installing
listing packages with Yum, Searching, Listing and Displaying Package Information
Glob expressions, Searching, Listing and Displaying Package Information
yum grouplist, Searching, Listing and Displaying Package Information
yum list, Searching, Listing and Displaying Package Information
yum list all, Searching, Listing and Displaying Package Information
yum list available, Searching, Listing and Displaying Package Information
yum list installed, Searching, Listing and Displaying Package Information
yum repolist, Searching, Listing and Displaying Package Information
packages and package groups, Packages and Package Groups
plugins
PackageKit-yum-plugin, Plugin Descriptions
rhnplugin, Plugin Descriptions
yum-plugin-protect-packages, Plugin Descriptions
yum-plugin-security, Plugin Descriptions
yum-presto, Plugin Descriptions
yum-rhn-plugin, Plugin Descriptions
repository, Creating a Yum Repository
searching for packages with Yum
yum search, Searching, Listing and Displaying Package Information
searching packages with Yum, Searching, Listing and Displaying Package Information
setting [main] options, Setting [main] Options
setting [repository] options, Setting [repository] Options
uninstalling package groups with Yum, Removing
uninstalling packages with Yum, Removing
yum remove package_name, Removing
variables, Using Yum Variables
Yum plugins, Yum Plugins
Yum repositories
configuring Yum and Yum repositories, Configuring Yum and Yum Repositories
Yum repositories
viewing Yum repositories with PackageKit, Refreshing Software Sources (Yum Repositories)
Yum Updates
checking for updates, Checking For Updates
updating a single package, Updating Packages
updating all packages and dependencies, Updating Packages
updating packages, Updating Packages
updating security-related packages, Updating Security-Related Packages
Static Wikipedia 2008 (no images)

aa - ab - af - ak - als - am - an - ang - ar - arc - as - ast - av - ay - az - ba - bar - bat_smg - bcl - be - be_x_old - bg - bh - bi - bm - bn - bo - bpy - br - bs - bug - bxr - ca - cbk_zam - cdo - ce - ceb - ch - cho - chr - chy - co - cr - crh - cs - csb - cu - cv - cy - da - de - diq - dsb - dv - dz - ee - el - eml - en - eo - es - et - eu - ext - fa - ff - fi - fiu_vro - fj - fo - fr - frp - fur - fy - ga - gan - gd - gl - glk - gn - got - gu - gv - ha - hak - haw - he - hi - hif - ho - hr - hsb - ht - hu - hy - hz - ia - id - ie - ig - ii - ik - ilo - io - is - it - iu - ja - jbo - jv - ka - kaa - kab - kg - ki - kj - kk - kl - km - kn - ko - kr - ks - ksh - ku - kv - kw - ky - la - lad - lb - lbe - lg - li - lij - lmo - ln - lo - lt - lv - map_bms - mdf - mg - mh - mi - mk - ml - mn - mo - mr - mt - mus - my - myv - mzn - na - nah - nap - nds - nds_nl - ne - new - ng - nl - nn - no - nov - nrm - nv - ny - oc - om - or - os - pa - pag - pam - pap - pdc - pi - pih - pl - pms - ps - pt - qu - quality - rm - rmy - rn - ro - roa_rup - roa_tara - ru - rw - sa - sah - sc - scn - sco - sd - se - sg - sh - si - simple - sk - sl - sm - sn - so - sr - srn - ss - st - stq - su - sv - sw - szl - ta - te - tet - tg - th - ti - tk - tl - tlh - tn - to - tpi - tr - ts - tt - tum - tw - ty - udm - ug - uk - ur - uz - ve - vec - vi - vls - vo - wa - war - wo - wuu - xal - xh - yi - yo - za - zea - zh - zh_classical - zh_min_nan - zh_yue - zu -

Static Wikipedia 2007 (no images)

aa - ab - af - ak - als - am - an - ang - ar - arc - as - ast - av - ay - az - ba - bar - bat_smg - bcl - be - be_x_old - bg - bh - bi - bm - bn - bo - bpy - br - bs - bug - bxr - ca - cbk_zam - cdo - ce - ceb - ch - cho - chr - chy - co - cr - crh - cs - csb - cu - cv - cy - da - de - diq - dsb - dv - dz - ee - el - eml - en - eo - es - et - eu - ext - fa - ff - fi - fiu_vro - fj - fo - fr - frp - fur - fy - ga - gan - gd - gl - glk - gn - got - gu - gv - ha - hak - haw - he - hi - hif - ho - hr - hsb - ht - hu - hy - hz - ia - id - ie - ig - ii - ik - ilo - io - is - it - iu - ja - jbo - jv - ka - kaa - kab - kg - ki - kj - kk - kl - km - kn - ko - kr - ks - ksh - ku - kv - kw - ky - la - lad - lb - lbe - lg - li - lij - lmo - ln - lo - lt - lv - map_bms - mdf - mg - mh - mi - mk - ml - mn - mo - mr - mt - mus - my - myv - mzn - na - nah - nap - nds - nds_nl - ne - new - ng - nl - nn - no - nov - nrm - nv - ny - oc - om - or - os - pa - pag - pam - pap - pdc - pi - pih - pl - pms - ps - pt - qu - quality - rm - rmy - rn - ro - roa_rup - roa_tara - ru - rw - sa - sah - sc - scn - sco - sd - se - sg - sh - si - simple - sk - sl - sm - sn - so - sr - srn - ss - st - stq - su - sv - sw - szl - ta - te - tet - tg - th - ti - tk - tl - tlh - tn - to - tpi - tr - ts - tt - tum - tw - ty - udm - ug - uk - ur - uz - ve - vec - vi - vls - vo - wa - war - wo - wuu - xal - xh - yi - yo - za - zea - zh - zh_classical - zh_min_nan - zh_yue - zu -

Static Wikipedia 2006 (no images)

aa - ab - af - ak - als - am - an - ang - ar - arc - as - ast - av - ay - az - ba - bar - bat_smg - bcl - be - be_x_old - bg - bh - bi - bm - bn - bo - bpy - br - bs - bug - bxr - ca - cbk_zam - cdo - ce - ceb - ch - cho - chr - chy - co - cr - crh - cs - csb - cu - cv - cy - da - de - diq - dsb - dv - dz - ee - el - eml - eo - es - et - eu - ext - fa - ff - fi - fiu_vro - fj - fo - fr - frp - fur - fy - ga - gan - gd - gl - glk - gn - got - gu - gv - ha - hak - haw - he - hi - hif - ho - hr - hsb - ht - hu - hy - hz - ia - id - ie - ig - ii - ik - ilo - io - is - it - iu - ja - jbo - jv - ka - kaa - kab - kg - ki - kj - kk - kl - km - kn - ko - kr - ks - ksh - ku - kv - kw - ky - la - lad - lb - lbe - lg - li - lij - lmo - ln - lo - lt - lv - map_bms - mdf - mg - mh - mi - mk - ml - mn - mo - mr - mt - mus - my - myv - mzn - na - nah - nap - nds - nds_nl - ne - new - ng - nl - nn - no - nov - nrm - nv - ny - oc - om - or - os - pa - pag - pam - pap - pdc - pi - pih - pl - pms - ps - pt - qu - quality - rm - rmy - rn - ro - roa_rup - roa_tara - ru - rw - sa - sah - sc - scn - sco - sd - se - sg - sh - si - simple - sk - sl - sm - sn - so - sr - srn - ss - st - stq - su - sv - sw - szl - ta - te - tet - tg - th - ti - tk - tl - tlh - tn - to - tpi - tr - ts - tt - tum - tw - ty - udm - ug - uk - ur - uz - ve - vec - vi - vls - vo - wa - war - wo - wuu - xal - xh - yi - yo - za - zea - zh - zh_classical - zh_min_nan - zh_yue - zu -

Sub-domains

CDRoms - Magnatune - Librivox - Liber Liber - Encyclopaedia Britannica - Project Gutenberg - Wikipedia 2008 - Wikipedia 2007 - Wikipedia 2006 -

Other Domains

https://www.classicistranieri.it - https://www.ebooksgratis.com - https://www.gutenbergaustralia.com - https://www.englishwikipedia.com - https://www.wikipediazim.com - https://www.wikisourcezim.com - https://www.projectgutenberg.net - https://www.projectgutenberg.es - https://www.radioascolto.com - https://www.debitoformtivo.it - https://www.wikipediaforschools.org - https://www.projectgutenbergzim.com

Static Wikipedia 2008 (March - no images)

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Liber Liber 2023 - Authors

abati - abba - abbate - accademia_degli_intronati - accati - accetto - acerbi - adami - agabiti - agamennone - aganoor - agaraff - agostini - agraives - agresti - agrippa - alamanni - albergati_capacelli - albert - albertazzi - albertelli - alberti - alberti_leandro - alberti_tommaso - albini - albinoni - albori_della_vita_italiana - alcott - aleardi - alfa - alfieri - algarotti - ali - alighieri - alighieri_jacopo - allen - aloysius - amabile - amalteo - amari - amati - ambrogini - amidei - amodeo - andersen - anderson - andrea_da_barberino - andreis - angiolieri - angiolini - anile - anonimo - antiquarie_prospettiche_romane - antoccia - antona_traversi - antonelli - appelius - apuleius - aragona - arbib - archinti - arenskij - aretino - ariosto - aristoteles - armaroli - aroldi - arouet - arrhenius - arrieta - arrighi - arrigoni - arsinov - artom - artusi - atlante - auber - audran - auto_da_fe_in_bologna - avancini - azeglio - bacci - baccini - bacci_peleo - bach - bachi - bachi_riccardo - bachofen - bach_carl_philipp_emanuel - bach_johann_bernhard - bach_johann_ludwig - bach_wilhelm_friedemann - bacigalupo - badia_y_leblich - baffo - bakunin - balakirev - balbo - balbo_italo - baldacci - balsamo - balzac - balzani - banchieri - bandello - bandi - baratono - baratono_adelchi - barbagallo - barbaranelli - barbarani - barbarich - barberini - barbiera - barbieri - barbieri_francisco - barbusse - barella - bargiacchi - baricelli - barla - barni - barrie - barrili - bartok - bartoli - bartoli_daniello - barzini - basile - bassano - bassano_anthony - bastianelli - baudelaire - baunard - bazzero - bazzoni - becattini - beccari - beccaria - beccaria_antonella - beckford - beethoven - belgioioso - belgiojoso - bellacchi - bellani - belli - bellini - belloc_lowndes - bellone - belo - beltrame - beltramelli - bembo - benaglio - benamozegh - benco - benco_delia - benedetti - benelli - beolco - berchet - berchet_guglielmo - berg - berlioz - bernard - bernardino_da_siena - berneri - berneri_camillo - berneri_maria_luisa - berni - bersezio - bertacchi - bertacchi_cosimo - bertelli - berti - bertinetti - bertini - bertola - bertoni - bertoni_brenno - bertoni_luigi - berwald - besana - bestiario_moralizzato - betteloni - betti - bettinelli - bettoni - bevilacqua - beyle - bhagavad_gita - biagi - bianchi - bianchi_giovini - bianco - bianconi - bianconi_giovanni_lodovico - bibbia - bibbiena - biber - biffoli - binazzi - bini - biografie_e_ritratti_d_illustri_siciliani - bisciola - bisi - bizet - bizzarri - bizzozero - blackwood - blake - blanch - blanchard - blaserna - boccaccio - boccalini - boccardi - boccardo - boccherini - bocchi - bodrero - boerio - boghen_conegliani - boiardo - boieldieu - boine - boito - boito_a - bolza - bon - bonacini - bonaparte - bonarelli - bonatelli - bonaventura - bonaventura_enzo - bond - bonfadini - bonghi - bonizzi - bonola - bonomo - bonvesin_de_la_riva - bordenave - borgese - borgese_giuseppe - borghi - borghi_armando - borodin - borri - bortolotti - boschetti_alberti - boscovich - bosio - bossi - botta - bottazzi - bottero - bouchardy - bourcet - bourdet - bouvier - bovio - bovio_libero - bozzano - bozzini - bracco - brahms - brancaccio - brera - bresadola - breton - brocchi - brofferio - broglio - bronte - bronzino - bruch - bruckner - bruna - brunelli - brunetti - bruni - bruni_giuseppe - bruno - brusoni - bufardeci - buia - buonaiuti - buonarroti - buonarroti_il_giovane - buoninsegni - buozzi - burchiello - burckhardt - burke - burnaby - burroughs - burzio - buschi - busetto - busoni - butti - buxtehude - buzzanca - byrne - byron - caccianiga - cacciatore - caccini - cafiero - cagna - cagni - cajkovskij - calandra - calcagno - caldarella - calestani - calvo - calza - camillo - camis - cammarano - camoes - campana - campanella - campolonghi - campra - canestrini - canestrini_alessandro - canina - cannabich - cannizzaro - cantalupo - cantoni - cantoni_giovanni - canto_gregoriano - cantu - capasso - capefigue - capella - capocci - capparoni - capponi - capranica - caprile - capuana - carabellese - caracciolo - caracciolo_enrichetta - carafa_capecelatro - carcano - cardano - cardile - carducci - carlyle - carmina_burana - carnevali - carocci - carpenter - carrera - carroll - carubia - casadei - casanova - casas - cassini - castelli - castelli_david - castelnuovo - castelvetro - casti - castiglione - castiglioni - catalani - caterina_da_siena - cather - cattaneo - cava - cavalcanti - cavallotti - cavara - caversazzi - caviglia - cefali - celesia - cellini - celoria - cena - cenni - cennini - cerlone - cernysevskij - cerro - cervantes - cervesato - cesarotti - cesi - chabrier - chanson_de_roland - chapi - charpentier - chaucer - chausson - chelli - cherubini - cherubini_eugenio - chesterton - cheyney - chiabrera - chiara - chiarelli - chiaretti - chiarini - chiesa - chigi - chiocchetti - chiosso - chiurlo - chopin - christiansen - chueca - ciaceri - ciamician - ciampoli - cian - ciano - cicero - cicogna - cielo - cifra - cimarosa - cinelli - cipriani - cittadella - claps - clarke - clementi - club_alpino_italiano - cocchi - codemo - coffa_caruso - coglitore - colagrossi - colajanni - coleridge - collenuccio - colletta - collins - collodi - colombe - colombo_fernando - colombo_michele - colonna - colonna_vittoria - colorni - columba - cominelli - compagni - compagnia_del_mantellaccio - comparetti - confucius - contessa_lara - conti - coperario - coppi - corano - corbino - cordelia - corelli - coresio - corio - cornaro - cornelius - cornoldi - corradini - cortesi - cosmi - cossa - costa - costa_andrea - coster - couperin - crawford - crawford_morris - cremonese - crispi - croce - crocella - croce_benedetto - croce_enrico - cronica_vita_di_cola_di_rienzo - cucca - cummins - cuneo - cuoco - cuomo - curiel - curti - curti_pier_ambrogio - cusani - cyrano_de_bergerac - dadone - dall_ongaro - dalmasso - dandrieu - danti - darwin - darwin_erasmus - daudet - dauli - da_ponte - da_porto - da_verona - debay - debenedetti - debussy - deledda - delibes - delius - della_casa - della_chiesa - della_porta - della_seta - della_valle - della_valle_pietro - delpino - del_lungo - del_lungo_carlo - dering - desanctis - descalzo - descartes - descuret - despres - devienne - dewey - de_amicis - de_angelis - de_astis - de_blasio - de_boni - de_bosis - de_cesare - de_cleyre - de_filippi - de_foe - de_franchi - de_gamerra - de_giovanni - de_gubernatis - de_marchi - de_maria - de_orestis - de_paoli - de_pellegrini - de_pretto - de_quincey - de_roberto - de_rubris - de_ruggiero - de_sanctis - de_vries - diabelli - diamante - dickens - diderot - difensore_degli_ebrei - dini - dito - dittersdorf - di_blasi - di_genio - di_giacomo - di_giovanni - di_giovanni_alessio - di_grazia - di_monaco - di_san_giusto - dolce - domenichi - donati - donaver - doni - donizetti - dorso - dossi - dostoevskij - douhet - doyle - draeseke - driesch - drigo - drosso - ducati - dukas - dumas - dunant - duparc - durante - du_mage - dvorak - d_albert - d_ambra - d_ancona - d_andrea - d_annunzio - d_arzo - d_emilio - d_india - eco - economisti_del_cinque_e_seicento - eisner - electronic_frontier_foundation - elgar - elia - emanuelli - emerson - emiliani_giudici - emma - emmanuel - engels - enriques - epictetus - epicurus - erasmus_roterodamus - eredia - ermacora - errante - errera - euclides - fabbri - fabiani - fabula_de_etc - faldella - fanciullacci - fanciulli - fanfani - fantazzini - fantoni - farga - fargion - farina - farinelli - farnaby - faure - favaro - fazello - federici - fernandez_caballero - fernandez_guardia - ferrabosco_il_giovane - ferrari - ferrari_carlotta - ferrari_giuseppe - ferrari_giuseppe_1720 - ferrari_paolo - ferrari_pietro - ferrari_pio_vittorio - ferrari_severino - ferrer - ferrero - ferretti - ferri - ferrieri - ferri_dina - ferri_giustino - ferroni - ferruggia - feuerbach - fiacchi - fibich - figner - figuier - filicaia - filippi - fillak - filopanti - finella - fioravanti - fioretti_di_san_francesco - fiore_di_leggende_cantari_antichi_etc - fiorini - firenzuola - flammarion - flaubert - fletcher - flies - florenzi - florio - flotow - fogazzaro - folengo - folgore - fontana - fontanarosa - fontane - fontefrancesco - fontenelle - formichi - fornaciari - forteguerri - fortis - foscolo - fraccacreta - fracchia - france - francesco_d_assisi - franchetti - franck - franco - frari - freud - frezzi - frugoni - fucini - fugassa - funck_brentano - gabetti - gabrieli - gabrieli_giovanni - galassi - galiani - galilei - gallaccini - galleani - galleria_palatina - gallina - gallo - galuppi - gamberi - gandhi - ganot - gargiulo - garibaldi - garrone - gatti - gautier - geminiani - gentile - gentile_iginio - gerard - geremicca - gerli - german - gershwin - gervasoni - gherardi - ghersi - ghislanzoni - ghisleri - giaccani - giacometti - giacosa - giamboni - gianelli - giannone - gibbon - gibellini - gide - gigli - giglioli - gille - gilles - ginzburg - gioberti - giolitti - giordana - giordano - giornale_per_i_bambini - giostra_delle_virtu_e_dei_vizi - giovannetti - giovannitti - giovio - giraud - giraudoux - giretti - giribaldi - giuseppe_da_forio - giusta_idea - giusti - glazunov - glinka - gluck - gobetti - goethe - gogol - goldoni - goldsmith - golgi - goll - gomes - gonin - gori - gori_pietro_1854_1930 - gorkij - gossec - gothein - gounod - gozzano - gozzi - gozzi_gasparo - graf - gramsci - granados - grande - grandi - grassi - grasso - grave - gray - graziani - gregorovius - gretry - grieg - grimaldi - grimm_jakob - grippa - grossi - grossi_vincenzo - groto - guadagnoli - gualandris - gualdo - guardione - guareschi - guarini - guelfi - guerrazzi - guerrini - guglielminetti - guglielmotti - guicciardini - guidetti - guidi - guidiccioni - guidi_michelangelo - guiducci - gulli - guy - haeckel - haendel - hamsun - harding - hasse - hauptmann - hawthorne - haydn - heron - herschel - hewlett - heywood - hichens - historia_di_papa - holborne - holst - homerus - hubay - huch - hugo - hummel - humperdinck - huxley - iacopone_da_todi - iacopo_da_sanseverino - iberti - ibn_gubayr - ibn_miskawayh - ibsen - imbriani - indy - ingrassia - innocentius_papa_12 - intorcetta - invernizio - ippolita_comunita_di_scriventi - ippolitov_ivanov - issel - istoria_critica - italia - jacobsen - james - janacek - jarro - jatta - jeans - jefferson - jenna - jennings - jerome - johansson - johnson - joinville - jolanda - joplin - jovine - joyce - juvalta - kaffka - kahn - kalevala - kalidasa - kant - karr - keynes - kipling - kleist - kollo - komzak - kovalevskaja - kropotkin - labriola - ladenarda - lady_gregory - lafargue - lagerlof - lalande - lalli - lalo - lancillotti - lando - landriani - lanzalone - lao_tzu - lasca - laser - lasso - latini - lattes - lattes_dante - lavater - lawrence - lazzarelli - lazzaretti - lazzeri - la_boetie - la_fontaine - la_lumia - leetherland - leggenda_di_tristano - legouve - lehar - leibniz - leitgeb - lemery - lemonnier - lenti_boero - leonardo - leoncavallo - leoni - leopardi - leroux - lesca - lessig - lessona - lettera_a_diogneto - levati - levi - levi_adolfo - levi_giulio_augusto - lewis - libri_piu_letti - libro_della_cucina - liebig - liesegang - liguria - linati - lipparini - lippi - liszt - littre - lizio_bruno - ljadov - lleo - locatelli - lockyer - lodi - lomazzo - lombardini - lombroso - lombroso_gina - london - longo - longus_sophista - lopez - lorentz - lorenzo - lorenzoni - lori - loria - lortzing - lo_valvo - lucatelli - lucchesini - lucianus - lucini - lucretius - luigini_federico - luini - lully - luna - lupo - lusitania - luther_blissett - luzio - macaulay - maccrie - machiavelli - mackay - maes - maeterlinck - maffei - magalotti - maggi - mahler - maineri - maistre - malamani - malatesta - malinverni - malon - malpassuti - mameli - mamiani - mannarino - manni - manno - mannu - mantegazza - manucci - manzoni - marais - marcelli - marcello - marchand - marchesani - marchesa_colombi - marchetti - marchi - marconi - maresca - mariani - marinelli - marinetti - marino - mario - marrama - marselli - marsili - martello - martineau - martinelli - martinelli_vincenzo - martinetti - martini - martini_ferdinando - martoglio - martucci - marugi - marx - mascagni - masci - masi - massarani - massenet - massimi - mastriani - mastro_titta - mattei - matteucci - mattirolo - maupassant - mazzarino - mazzini - medici - medici_ferdinando_i - medici_lorenzino - mehul - meli - melville - mendelssohn - menghini - mengozzi - merlini - merlino - messa_di_requiem - messina - metastasio - meyer - meyerbeer - meyrink - micanzio - michaelis - michel - michelstaedter - mieli - milani - mill - mille_e_una_notte - milton - mioni - mirbeau - misasi - misefari - moderata_fonte - modigliani - molinari - molnar - mommsen - monchablon - mondaini - moneta - mongai - mongitore - monicelli - monnier - montanelli - montesquieu - montessori - monteverde - monteverdi - monti - monti_achille - montpensier - moore - morandi - morandi_carlo - morando - morasso - more - moresco - moretti - morra - morris - morselli - morselli_ercole - mosca - moscardelli - mosso - mozart - mozzoni - mudge - mulazzi - mule - mule_bertolo - munthe - mura - muratori - muratori_lodovico - murger - murri - musorgskij - mussolini - musumeci - muzzi - nagy - nardini - narrazione_critico_storica_etc - natale - navigazione_di_san_brandano - nazioni_unite - neera - negri - negri_ada - negri_francesco - negri_gaetano - nencioni - nerucci - nettlau - nibby - nibelunghi - niccolini - nicolai - nicolaus_cusanus - nielsen - nieri - nietzsche - nievo - nivers - nobili - nordau - nordhoff - norsa - nota - notari - notturno_napoletano - novacek - novaro - novaro_mario - novatore - novella_del_grasso_legnajuolo - novelle_cinesi - novelle_indo_americane - novelle_italiane_dalle_origini_al_cinquecento - novellino - nucera_abenavoli - nuovi_misteri_del_chiostro_napoletano_etc - offenbach - ojetti - olper_monis - omodeo - onesto - oppenheim - orestano - oriani - orsi - orsini - ortolani - pachelbel - pacini - pacioli - padoa - padula - pagani - paganini - pagliaro - pailleron - paisiello - palazzi - paleologue - palladio - pallavicini - pallavicino - palli_bartolommei - palma - palmeri - palomba - pananti - pani - pannocchieschi - panzacchi - panzini - paolieri - pareto - parini - paris - parlatore - parmeggiani - pascal - pascal_carlo - pascarella - pascoli - pasinetti - pasolini - paterno - pausanias - pavese - peano - pellico - pellizzari - penzig - pepoli - percoto - pergolesi - perlman - perodi - perrault - petrarca - petrocchi - petruccelli_della_gattina - piave - piazza - piazza_antonio - piazzi - pico_della_mirandola - pierantoni_mancini - pieri - pierne - pigafetta - pignata - pinamonti - pinchetti - pindemonte - pino - pintor - pinza - pioda - piola - pirandello - pisacane - piscel - pissilenko - pitre - piva - pizzagalli - pizzigoni - pizzigoni_giuseppina - pizzirani - planche - plato - plinius_caecilius_saecundus - podesta - podrecca - poe - poli - polidori - polidori_francesco - polimanti - poliziano - polo - polybius - pompilj - ponchielli - popper - porati - porta - pov_ray_team - pozzi - pozzi_antonia - praetorius - praga - praga_marco - prati - previati - prevost - prose_e_poesie_giapponesi - proudhon - proust - prunas - puccini - puini - pulci - purcell - purgotti - puskin - puviani - quadrio - quel_libro_nel_cammino_della_mia_vita - quevedo - rabelais - rabizzani - raccolta_di_lettere_ecc - racconti_popolari_dell_ottocento_ligure - rachmaninov - racquet - radcliffe - raffaello_sanzio - raga - ragazzoni - rajberti - rajna - ramazzini - rameau - ramusio - randi - ranieri - rapisardi - rastrelli - ravagli - ravel - razzaguta - reclus - redi - regaldi - regalia - reger - reghini - regina_di_luanto - regnani - regno_d_italia_1805_1814 - reinecke - relazione_dell_atto_della_fede_etc - renan - renier_michiel - rensi - repubblica_romana_1849 - respighi - retif_de_la_bretonne - reuze - reyer - rezzonico - ricchi - ricchieri - ricci - ricci_paterno_castello - ricci_umberto - riccoboni - righetti - righi - rignano - rilke - rimatori_siculo_toscani_del_dugento - rime_dei_memoriali_bolognesi - rimini - rimskij_korsakov - rinaldini - ringhieri - ripa - ripamonti - rizzatti - roberti - robida - rocca - roccatagliata_ceccardi - rocca_enrico - rocco - roggero - rohlfs - rolando - romagnoli - romagnoli_augusto - romani - roma_e_la_opinione_etc - romberg - romussi - roncaglia_gino - rosa - rosadi - rosa_daniele - rose - rosetti - rosi - rosmini - rosselli_carlo - rosselli_nello - rossi - rossini - rossi_emanuele - rossi_giovanni - rostand - rousseau - roussel - rovani - rovetta - rubinstejn - ruffini - ruffini_francesco - russo - russolo - ruzzante - ryner - sabatini - sabatini_rafael - sabbadini - sacchetti - sacchetti_roberto - sacchi - sacheli - sacher_masoch - saffi - saffi_antonio - saint_evremond - saint_saens - salanitro - salfi - salgari - salimbene_da_parma - sallustius - salucci - saluzzo_roero - sangiorgio - sannazaro - santucci - sanudo - sanvittore - sarasate - sardegna_regno - saredo - sarno - sarpi - satta - savarese - savasta - savinio - savio - savioli - savi_lopez - savonarola - scarfoglio - scarlatti - scarpetta - scarpetta_maria - scartabellati - schein - schiaparelli - schiavini - schicchi - schiller - schioppa - schmid - schmidt - schopenhauer - schubert - schumann - schutz - schwarz - scilla - scina - scott - scrofani - scuto - sebastian - secchi - sella - seneca - serafini - serafino_aquilano - serao - sercambi - serena - serge - sergi - serra - servi - settembrini - sfinge - sforza - shakespeare - shaw - shelley - sicilia - siciliani - sidrac - sienkiewicz - sigonio - siliprandi - silva - simpson - sinding - sismondi - skrjabin - slataper - smetana - sobrero - sobrero_mario - socci - soler - solera - solmi - solovev - sommerfeld - sonzogno - sophocles - sorbelli - spampanato - spaventa - spaventa_filippi - sperani - speroni - spinazzola - spinelli - spinoso - spinoza - spohr - spontini - stacpoole - stael - stampa - statius - stefanoni - stein - steiner - stendhal - stenhammar - steno - stephens - sterne - stevenson - stewart - stirner - stoker - storia_dei_paladini_di_francia - storia_di_fra_michele_minorita - stowe - straparola - strauss - strauss_josef - strauss_jr - strauss_richard - strenna_di_ascolti_per_il_natale - stromboli - suk - sullivan - supino - suppe - supplica_degli_stampatori_e_etc - suzzara_verdi - svendsen - svevo - swift - sylos_labini - synge - szanto - szymanowski - tagore - tanini - tanini_alighiero - tarabotti - tarchetti - targioni_tozzetti - tartaglia - tartini - tartufari - tassini - tasso - tassoni - telemann - teloni - tempio - tenca - terentius - tesoro_di_scienze_etc - tessa - testoni - tettoni - theuriet - tholozan - thomas - thoreau - thorpe - thouar - thovez - thucydides - tigri - tilgher - timmermans - timpanaro - tiraboschi - titelouze - tocco - tolstoj - tomei - tommaseo - torelli - torelli_luigi - torricelli - tosco - tosti - tozzi - traina - trebbi - treitschke - trentin - tresca - trilussa - trimmer - troya - tucci - tumiati - turco - turgenev - ubaldini - uccellini - uda - ughetti - ultimi_fatti_di_milano - unesco - unione_europea - untersteiner - urgnani - vailati - valera - valery - vallardi - valles - valletta - valli - valvason - vannicola - vanzetti - varthema - varvaro - vasari - vassallo - vaticano - venerandi - venexiana - veneziani - venier - veniero - venosta - venturi - venturini - venturi_adolfo - verdi - verdinois - verdi_de_suzzara - veresaev - verga - vergilius - verne - veronese - verri_alessandro - verri_pietro - vertua - vettori - viaggi_di_gio_da_mandavilla - viani - vico - vieuxtemps - vigoni - villa - villabianca - villani - villani_matteo - villari - villiers_de_l_isle_adam - vinci - violante - viotti - viriglio - viscnu_sarma - vismara - vitali - vita_delitti - vita_italiana_nel_cinquecento - vita_italiana_nel_rinascimento - vita_italiana_nel_risorgimento - vita_italiana_nel_seicento - vita_italiana_nel_settecento - vita_italiana_nel_trecento - vitruvius - vivaldi - vivante - vivanti - vives - viviani - viviani_raffaele - vogue_melchior_de - volin - volpi - volta - voltaire - volterra - wagenaar - wagner - waldteufel - wallace - wallace_edgar - wallace_lewis - walpole - wassermann - weber - wells - wessely - white_mario - widmann - wieniawski - wilde - wolf - wolf_ferrari - woolf - world_wide_web_consortium - wundt - wu_ming - wu_ming_1 - wu_ming_2 - wu_ming_5 - yambo - yeats - yriarte - zagarrio - zanazzo - zandonai - zanella - zanghi - zanotelli - zavattero - zena - zhuang_zi - zola - zuccoli -