Red Hat Enterprise Linux 6

Deployment Guide

Deployment, Configuration and Administration of Red Hat Enterprise Linux 6

Barbora Ančincová

Red Hat Customer Content Services

Eva Majoršinová

Red Hat Customer Content Services

Jaromír Hradílek

Red Hat Customer Content Services

Douglas Silas

Red Hat Customer Content Services

Martin Prpič

Red Hat Customer Content Services

Stephen Wadeley

Red Hat Customer Content Services

Eva Kopalová

Red Hat Customer Content Services

Peter Ondrejka

Red Hat Customer Content Services

Ella Deon Lackey

Red Hat Customer Content Services

Tomáš Čapek

Red Hat Customer Content Services

Petr Kovář

Red Hat Customer Content Services

Miroslav Svoboda

Red Hat Customer Content Services

Petr Bokoč

Red Hat Customer Content Services

Jiří Herrmann

Red Hat Customer Content Services

Jana Švárová

Red Hat Customer Content Services

Milan Navrátil

Red Hat Customer Content Services

Robert Krátký

Red Hat Customer Content Services

Florian Nadge

Red Hat Customer Content Services

John Ha

Red Hat Customer Content Services

David O'Brien

Red Hat Customer Content Services

Michael Hideo

Red Hat Customer Content Services

Don Domingo

Red Hat Customer Content Services

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Abstract

The Deployment Guide documents relevant information regarding the deployment, configuration and administration of Red Hat Enterprise Linux 6. It is oriented towards system administrators with a basic understanding of the system.
I. Basic System Configuration
1. Keyboard Configuration
1.1. Changing the Keyboard Layout
1.2. Adding the Keyboard Layout Indicator
1.3. Setting Up a Typing Break
2. Date and Time Configuration
2.1. Date/Time Properties Tool
2.1.1. Date and Time Properties
2.1.2. Network Time Protocol Properties
2.1.3. Time Zone Properties
2.2. Command Line Configuration
2.2.1. Date and Time Setup
2.2.2. Network Time Protocol Setup
3. Managing Users and Groups
3.1. What Users and Groups Are
3.2. Managing Users via the User Manager Application
3.2.1. Viewing Users
3.2.2. Adding a New User
3.2.3. Modifying User Properties
3.3. Managing Groups via the User Manager Application
3.3.1. Viewing Groups
3.3.2. Adding a New Group
3.3.3. Modifying Group Properties
3.4. Managing Users via Command-Line Tools
3.4.1. Creating Users
3.4.2. Attaching New Users to Groups
3.4.3. Updating Users' Authentication
3.4.4. Modifying User Settings
3.4.5. Deleting Users
3.4.6. Displaying Comprehensive User Information
3.5. Managing Groups via Command-Line Tools
3.5.1. Creating Groups
3.5.2. Attaching Users to Groups
3.5.3. Updating Group Authentication
3.5.4. Modifying Group Settings
3.5.5. Deleting Groups
3.6. Additional Resources
3.6.1. Installed Documentation
4. Gaining Privileges
4.1. The su Command
4.2. The sudo Command
4.3. Additional Resources
II. Subscription and Support
5. Registering the System and Managing Subscriptions
5.1. Registering the System and Attaching Subscriptions
5.2. Managing Software Repositories
5.3. Removing Subscriptions
5.4. Additional Resources
6. Accessing Support Using the Red Hat Support Tool
6.1. Installing the Red Hat Support Tool
6.2. Registering the Red Hat Support Tool Using the Command Line
6.3. Using the Red Hat Support Tool in Interactive Shell Mode
6.4. Configuring the Red Hat Support Tool
6.4.1. Saving Settings to the Configuration Files
6.5. Opening and Updating Support Cases Using Interactive Mode
6.6. Viewing Support Cases on the Command Line
6.7. Additional Resources
III. Installing and Managing Software
7. Yum
7.1. Checking For and Updating Packages
7.1.1. Checking For Updates
7.1.2. Updating Packages
7.1.3. Preserving Configuration File Changes
7.1.4. Upgrading the System Off-line with ISO and Yum
7.2. Packages and Package Groups
7.2.1. Searching Packages
7.2.2. Listing Packages
7.2.3. Displaying Package Information
7.2.4. Installing Packages
7.2.5. Removing Packages
7.3. Working with Transaction History
7.3.1. Listing Transactions
7.3.2. Examining Transactions
7.3.3. Reverting and Repeating Transactions
7.3.4. Completing Transactions
7.3.5. Starting New Transaction History
7.4. Configuring Yum and Yum Repositories
7.4.1. Setting [main] Options
7.4.2. Setting [repository] Options
7.4.3. Using Yum Variables
7.4.4. Viewing the Current Configuration
7.4.5. Adding, Enabling, and Disabling a Yum Repository
7.4.6. Creating a Yum Repository
7.4.7. Working with Yum Cache
7.4.8. Adding the Optional and Supplementary Repositories
7.5. Yum Plug-ins
7.5.1. Enabling, Configuring, and Disabling Yum Plug-ins
7.5.2. Installing Additional Yum Plug-ins
7.5.3. Plug-in Descriptions
7.6. Additional Resources
8. PackageKit
8.1. Updating Packages with Software Update
8.2. Using Add/Remove Software
8.2.1. Refreshing Software Sources (Yum Repositories)
8.2.2. Finding Packages with Filters
8.2.3. Installing and Removing Packages (and Dependencies)
8.2.4. Installing and Removing Package Groups
8.2.5. Viewing the Transaction Log
8.3. PackageKit Architecture
8.4. Additional Resources
IV. Networking
9. NetworkManager
9.1. The NetworkManager Daemon
9.2. Interacting with NetworkManager
9.2.1. Connecting to a Network
9.2.2. Configuring New and Editing Existing Connections
9.2.3. Connecting to a Network Automatically
9.2.4. User and System Connections
9.3. Establishing Connections
9.3.1. Establishing a Wired (Ethernet) Connection
9.3.2. Establishing a Wireless Connection
9.3.3. Establishing a Mobile Broadband Connection
9.3.4. Establishing a VPN Connection
9.3.5. Establishing a DSL Connection
9.3.6. Establishing a Bond Connection
9.3.7. Establishing a VLAN Connection
9.3.8. Establishing an IP-over-InfiniBand (IPoIB) Connection
9.3.9. Configuring Connection Settings
10. Network Interfaces
10.1. Network Configuration Files
10.2. Interface Configuration Files
10.2.1. Ethernet Interfaces
10.2.2. Specific ifcfg Options for Linux on System z
10.2.3. Required ifcfg Options for Linux on System z
10.2.4. Channel Bonding Interfaces
10.2.5. Configuring a VLAN over a Bond
10.2.6. Network Bridge
10.2.7. Setting Up 802.1Q VLAN Tagging
10.2.8. Alias and Clone Files
10.2.9. Dialup Interfaces
10.2.10. Other Interfaces
10.3. Interface Control Scripts
10.4. Static Routes and the Default Gateway
10.5. Configuring Static Routes in ifcfg files
10.5.1. Static Routes Using the IP Command Arguments Format
10.5.2. Network/Netmask Directives Format
10.6. Configuring IPv6 Tokenized Interface Identifiers
10.7. Network Function Files
10.8. Ethtool
10.9. Additional Resources
V. Infrastructure Services
11. Services and Daemons
11.1. Configuring the Default Runlevel
11.2. Configuring the Services
11.2.1. Using the Service Configuration Utility
11.2.2. Using the ntsysv Utility
11.2.3. Using the chkconfig Utility
11.3. Running Services
11.3.1. Determining the Service Status
11.3.2. Starting a Service
11.3.3. Stopping a Service
11.3.4. Restarting a Service
11.4. Additional Resources
11.4.1. Installed Documentation
11.4.2. Related Books
12. Configuring Authentication
12.1. Configuring System Authentication
12.1.1. Launching the Authentication Configuration Tool UI
12.1.2. Selecting the Identity Store for Authentication
12.1.3. Configuring Alternative Authentication Features
12.1.4. Configuring Authentication from the Command Line
12.1.5. Using Custom Home Directories
12.2. Using and Caching Credentials with SSSD
12.2.1. About SSSD
12.2.2. Setting up the sssd.conf File
12.2.3. Starting and Stopping SSSD
12.2.4. SSSD and System Services
12.2.5. Configuring Services: NSS
12.2.6. Configuring Services: PAM
12.2.7. Configuring Services: autofs
12.2.8. Configuring Services: sudo
12.2.9. Configuring Services: OpenSSH and Cached Keys
12.2.10. SSSD and Identity Providers (Domains)
12.2.11. Creating Domains: LDAP
12.2.12. Creating Domains: Identity Management (IdM)
12.2.13. Creating Domains: Active Directory
12.2.14. Configuring Domains: Active Directory as an LDAP Provider (Alternative)
12.2.15. Domain Options: Setting Username Formats
12.2.16. Domain Options: Enabling Offline Authentication
12.2.17. Domain Options: Setting Password Expirations
12.2.18. Domain Options: Using DNS Service Discovery
12.2.19. Domain Options: Using IP Addresses in Certificate Subject Names (LDAP Only)
12.2.20. Creating Domains: Proxy
12.2.21. Creating Domains: Kerberos Authentication
12.2.22. Creating Domains: Access Control
12.2.23. Creating Domains: Primary Server and Backup Servers
12.2.24. Installing SSSD Utilities
12.2.25. SSSD and UID and GID Numbers
12.2.26. Creating Local System Users
12.2.27. Seeding Users into the SSSD Cache During Kickstart
12.2.28. Managing the SSSD Cache
12.2.29. Downgrading SSSD
12.2.30. Using NSCD with SSSD
12.2.31. Troubleshooting SSSD
13. OpenSSH
13.1. The SSH Protocol
13.1.1. Why Use SSH?
13.1.2. Main Features
13.1.3. Protocol Versions
13.1.4. Event Sequence of an SSH Connection
13.2. Configuring OpenSSH
13.2.1. Configuration Files
13.2.2. Starting an OpenSSH Server
13.2.3. Requiring SSH for Remote Connections
13.2.4. Using Key-Based Authentication
13.3. Using OpenSSH Certificate Authentication
13.3.1. Introduction to SSH Certificates
13.3.2. Support for SSH Certificates
13.3.3. Creating SSH CA Certificate Signing Keys
13.3.4. Distributing and Trusting SSH CA Public Keys
13.3.5. Creating SSH Certificates
13.3.6. Signing an SSH Certificate Using a PKCS#11 Token
13.3.7. Viewing an SSH CA Certificate
13.3.8. Revoking an SSH CA Certificate
13.4. OpenSSH Clients
13.4.1. Using the ssh Utility
13.4.2. Using the scp Utility
13.4.3. Using the sftp Utility
13.5. More Than a Secure Shell
13.5.1. X11 Forwarding
13.5.2. Port Forwarding
13.6. Additional Resources
13.6.1. Installed Documentation
13.6.2. Useful Websites
14. TigerVNC
14.1. VNC Server
14.1.1. Installing VNC Server
14.1.2. Configuring VNC Server
14.1.3. Starting VNC Server
14.1.4. Terminating a VNC Session
14.2. Sharing an Existing Desktop
14.3. Using a VNC Viewer
14.3.1. Installing the VNC Viewer
14.3.2. Connecting to a VNC Server
14.3.3. Connecting to VNC Server Using SSH
14.4. Additional Resources
VI. Servers
15. DHCP Servers
15.1. Why Use DHCP?
15.2. Configuring a DHCP Server
15.2.1. Configuration File
15.2.2. Lease Database
15.2.3. Starting and Stopping the Server
15.2.4. DHCP Relay Agent
15.3. Configuring a DHCP Client
15.4. Configuring a Multihomed DHCP Server
15.4.1. Host Configuration
15.5. DHCP for IPv6 (DHCPv6)
15.6. Additional Resources
15.6.1. Installed Documentation
16. DNS Servers
16.1. Introduction to DNS
16.1.1. Nameserver Zones
16.1.2. Nameserver Types
16.1.3. BIND as a Nameserver
16.2. BIND
16.2.1. Configuring the named Service
16.2.2. Editing Zone Files
16.2.3. Using the rndc Utility
16.2.4. Using the dig Utility
16.2.5. Advanced Features of BIND
16.2.6. Common Mistakes to Avoid
16.2.7. Additional Resources
17. Web Servers
17.1. The Apache HTTP Server
17.1.1. New Features
17.1.2. Notable Changes
17.1.3. Updating the Configuration
17.1.4. Running the httpd Service
17.1.5. Editing the Configuration Files
17.1.6. Working with Modules
17.1.7. Setting Up Virtual Hosts
17.1.8. Setting Up an SSL Server
17.1.9. Enabling the mod_ssl Module
17.1.10. Enabling the mod_nss Module
17.1.11. Using an Existing Key and Certificate
17.1.12. Generating a New Key and Certificate
17.1.13. Configure the Firewall for HTTP and HTTPS Using the Command Line
17.1.14. Additional Resources
18. Mail Servers
18.1. Email Protocols
18.1.1. Mail Transport Protocols
18.1.2. Mail Access Protocols
18.2. Email Program Classifications
18.2.1. Mail Transport Agent
18.2.2. Mail Delivery Agent
18.2.3. Mail User Agent
18.3. Mail Transport Agents
18.3.1. Postfix
18.3.2. Sendmail
18.3.3. Fetchmail
18.3.4. Mail Transport Agent (MTA) Configuration
18.4. Mail Delivery Agents
18.4.1. Procmail Configuration
18.4.2. Procmail Recipes
18.5. Mail User Agents
18.5.1. Securing Communication
18.6. Additional Resources
18.6.1. Installed Documentation
18.6.2. Online Documentation
18.6.3. Related Books
19. Directory Servers
19.1. OpenLDAP
19.1.1. Introduction to LDAP
19.1.2. Installing the OpenLDAP Suite
19.1.3. Configuring an OpenLDAP Server
19.1.4. Running an OpenLDAP Server
19.1.5. Configuring a System to Authenticate Using OpenLDAP
19.1.6. Additional Resources
20. File and Print Servers
20.1. Samba
20.1.1. Introduction to Samba
20.1.2. Samba Daemons and Related Services
20.1.3. Connecting to a Samba Share
20.1.4. Configuring a Samba Server
20.1.5. Starting and Stopping Samba
20.1.6. Samba Server Types and the smb.conf File
20.1.7. Samba Security Modes
20.1.8. Samba Account Information Databases
20.1.9. Samba Network Browsing
20.1.10. Samba with CUPS Printing Support
20.1.11. Samba Distribution Programs
20.1.12. Additional Resources
20.2. FTP
20.2.1. The File Transfer Protocol
20.2.2. The vsftpd Server
20.2.3. Additional Resources
20.3. Printer Configuration
20.3.1. Starting the Printer Configuration Tool
20.3.2. Starting Printer Setup
20.3.3. Adding a Local Printer
20.3.4. Adding an AppSocket/HP JetDirect printer
20.3.5. Adding an IPP Printer
20.3.6. Adding an LPD/LPR Host or Printer
20.3.7. Adding a Samba (SMB) printer
20.3.8. Selecting the Printer Model and Finishing
20.3.9. Printing a Test Page
20.3.10. Modifying Existing Printers
20.3.11. Additional Resources
21. Configuring NTP Using ntpd
21.1. Introduction to NTP
21.2. NTP Strata
21.3. Understanding NTP
21.4. Understanding the Drift File
21.5. UTC, Timezones, and DST
21.6. Authentication Options for NTP
21.7. Managing the Time on Virtual Machines
21.8. Understanding Leap Seconds
21.9. Understanding the ntpd Configuration File
21.10. Understanding the ntpd Sysconfig File
21.11. Checking if the NTP Daemon is Installed
21.12. Installing the NTP Daemon (ntpd)
21.13. Checking the Status of NTP
21.14. Configure the Firewall to Allow Incoming NTP Packets
21.14.1. Configure the Firewall Using the Graphical Tool
21.14.2. Configure the Firewall Using the Command Line
21.15. Configure ntpdate Servers
21.16. Configure NTP
21.16.1. Configure Access Control to an NTP Service
21.16.2. Configure Rate Limiting Access to an NTP Service
21.16.3. Adding a Peer Address
21.16.4. Adding a Server Address
21.16.5. Adding a Broadcast or Multicast Server Address
21.16.6. Adding a Manycast Client Address
21.16.7. Adding a Broadcast Client Address
21.16.8. Adding a Manycast Server Address
21.16.9. Adding a Multicast Client Address
21.16.10. Configuring the Burst Option
21.16.11. Configuring the iburst Option
21.16.12. Configuring Symmetric Authentication Using a Key
21.16.13. Configuring the Poll Interval
21.16.14. Configuring Server Preference
21.16.15. Configuring the Time-to-Live for NTP Packets
21.16.16. Configuring the NTP Version to Use
21.17. Configuring the Hardware Clock Update
21.18. Configuring Clock Sources
21.19. Additional Resources
21.19.1. Installed Documentation
21.19.2. Useful Websites
22. Configuring PTP Using ptp4l
22.1. Introduction to PTP
22.1.1. Understanding PTP
22.1.2. Advantages of PTP
22.2. Using PTP
22.2.1. Checking for Driver and Hardware Support
22.2.2. Installing PTP
22.2.3. Starting ptp4l
22.3. Specifying a Configuration File
22.4. Using the PTP Management Client
22.5. Synchronizing the Clocks
22.6. Verifying Time Synchronization
22.7. Serving PTP Time With NTP
22.8. Serving NTP Time With PTP
22.9. Improving Accuracy
22.10. Additional Resources
22.10.1. Installed Documentation
22.10.2. Useful Websites
VII. Monitoring and Automation
23. System Monitoring Tools
23.1. Viewing System Processes
23.1.1. Using the ps Command
23.1.2. Using the top Command
23.1.3. Using the System Monitor Tool
23.2. Viewing Memory Usage
23.2.1. Using the free Command
23.2.2. Using the System Monitor Tool
23.3. Viewing CPU Usage
23.3.1. Using the System Monitor Tool
23.4. Viewing Block Devices and File Systems
23.4.1. Using the lsblk Command
23.4.2. Using the blkid Command
23.4.3. Using the findmnt Command
23.4.4. Using the df Command
23.4.5. Using the du Command
23.4.6. Using the System Monitor Tool
23.5. Viewing Hardware Information
23.5.1. Using the lspci Command
23.5.2. Using the lsusb Command
23.5.3. Using the lspcmcia Command
23.5.4. Using the lscpu Command
23.6. Monitoring Performance with Net-SNMP
23.6.1. Installing Net-SNMP
23.6.2. Running the Net-SNMP Daemon
23.6.3. Configuring Net-SNMP
23.6.4. Retrieving Performance Data over SNMP
23.6.5. Extending Net-SNMP
23.7. Additional Resources
23.7.1. Installed Documentation
24. Viewing and Managing Log Files
24.1. Installing rsyslog
24.1.1. Upgrading to rsyslog version 7
24.2. Locating Log Files
24.3. Basic Configuration of Rsyslog
24.3.1. Filters
24.3.2. Actions
24.3.3. Templates
24.3.4. Global Directives
24.3.5. Log Rotation
24.4. Using the New Configuration Format
24.4.1. Rulesets
24.4.2. Compatibility with sysklogd
24.5. Working with Queues in Rsyslog
24.5.1. Defining Queues
24.5.2. Creating a New Directory for rsyslog Log Files
24.5.3. Managing Queues
24.5.4. Using the New Syntax for rsyslog queues
24.6. Configuring rsyslog on a Logging Server
24.6.1. Using The New Template Syntax on a Logging Server
24.7. Using Rsyslog Modules
24.7.1. Importing Text Files
24.7.2. Exporting Messages to a Database
24.7.3. Enabling Encrypted Transport
24.8. Debugging Rsyslog
24.9. Managing Log Files in a Graphical Environment
24.9.1. Viewing Log Files
24.9.2. Adding a Log File
24.9.3. Monitoring Log Files
24.10. Additional Resources
25. Automating System Tasks
25.1. Cron and Anacron
25.1.1. Installing Cron and Anacron
25.1.2. Running the Crond Service
25.1.3. Configuring Anacron Jobs
25.1.4. Configuring Cron Jobs
25.1.5. Controlling Access to Cron
25.1.6. Black and White Listing of Cron Jobs
25.2. At and Batch
25.2.1. Installing At and Batch
25.2.2. Running the At Service
25.2.3. Configuring an At Job
25.2.4. Configuring a Batch Job
25.2.5. Viewing Pending Jobs
25.2.6. Additional Command-Line Options
25.2.7. Controlling Access to At and Batch
25.3. Additional Resources
26. Automatic Bug Reporting Tool (ABRT)
26.1. Installing ABRT and Starting its Services
26.2. Using the Graphical User Interface
26.3. Using the Command-Line Interface
26.3.1. Viewing Problems
26.3.2. Reporting Problems
26.3.3. Deleting Problems
26.4. Configuring ABRT
26.4.1. ABRT Events
26.4.2. Standard ABRT Installation Supported Events
26.4.3. Event Configuration in ABRT GUI
26.4.4. ABRT Specific Configuration
26.4.5. Configuring ABRT to Detect a Kernel Panic
26.4.6. Automatic Downloads and Installation of Debuginfo Packages
26.4.7. Configuring Automatic Reporting
26.4.8. Uploading and Reporting Using a Proxy Server
26.5. Configuring Centralized Crash Collection
26.5.1. Configuration Steps Required on a Dedicated System
26.5.2. Configuration Steps Required on a Client System
26.5.3. Saving Package Information
26.5.4. Testing ABRT's Crash Detection
27. OProfile
27.1. Overview of Tools
27.2. Configuring OProfile
27.2.1. Specifying the Kernel
27.2.2. Setting Events to Monitor
27.2.3. Separating Kernel and User-space Profiles
27.3. Starting and Stopping OProfile
27.4. Saving Data
27.5. Analyzing the Data
27.5.1. Using opreport
27.5.2. Using opreport on a Single Executable
27.5.3. Getting more detailed output on the modules
27.5.4. Using opannotate
27.6. Understanding /dev/oprofile/
27.7. Example Usage
27.8. OProfile Support for Java
27.8.1. Profiling Java Code
27.9. Graphical Interface
27.10. OProfile and SystemTap
27.11. Additional Resources
27.11.1. Installed Docs
27.11.2. Useful Websites
VIII. Kernel, Module and Driver Configuration
28. Manually Upgrading the Kernel
28.1. Overview of Kernel Packages
28.2. Preparing to Upgrade
28.3. Downloading the Upgraded Kernel
28.4. Performing the Upgrade
28.5. Verifying the Initial RAM Disk Image
28.6. Verifying the Boot Loader
28.6.1. Configuring the GRUB Boot Loader
28.6.2. Configuring the Loopback Device Limit
28.6.3. Configuring the OS/400 Boot Loader
28.6.4. Configuring the YABOOT Boot Loader
29. Working with Kernel Modules
29.1. Listing Currently-Loaded Modules
29.2. Displaying Information About a Module
29.3. Loading a Module
29.4. Unloading a Module
29.5. Blacklisting a Module
29.6. Setting Module Parameters
29.6.1. Loading a Customized Module - Temporary Changes
29.6.2. Loading a Customized Module - Persistent Changes
29.7. Persistent Module Loading
29.8. Specific Kernel Module Capabilities
29.8.1. Using Channel Bonding
29.9. Additional Resources
30. The kdump Crash Recovery Service
30.1. Installing the kdump Service
30.2. Configuring the kdump Service
30.2.1. Configuring kdump at First Boot
30.2.2. Using the Kernel Dump Configuration Utility
30.2.3. Configuring kdump on the Command Line
30.2.4. Testing the Configuration
30.3. Analyzing the Core Dump
30.3.1. Running the crash Utility
30.3.2. Displaying the Message Buffer
30.3.3. Displaying a Backtrace
30.3.4. Displaying a Process Status
30.3.5. Displaying Virtual Memory Information
30.3.6. Displaying Open Files
30.3.7. Exiting the Utility
30.4. Additional Resources
IX. System Recovery
31. System Recovery
31.1. Rescue Mode
31.2. Single-User Mode
31.3. Emergency Mode
31.4. Resolving Problems in System Recovery Modes
A. Consistent Network Device Naming
A.1. Affected Systems
A.2. System Requirements
A.3. Enabling and Disabling the Feature
A.4. Notes for Administrators
B. RPM
B.1. RPM Design Goals
B.2. Using RPM
B.2.1. Finding RPM Packages
B.2.2. Installing and Upgrading
B.2.3. Configuration File Changes
B.2.4. Uninstalling
B.2.5. Freshening
B.2.6. Querying
B.2.7. Verifying
B.3. Checking a Package's Signature
B.3.1. Importing Keys
B.3.2. Verifying Signature of Packages
B.4. Practical and Common Examples of RPM Usage
B.5. Additional Resources
B.5.1. Installed Documentation
B.5.2. Useful Websites
B.5.3. Related Books
C. The X Window System
C.1. The X Server
C.2. Desktop Environments and Window Managers
C.2.1. Desktop Environments
C.2.2. Window Managers
C.3. X Server Configuration Files
C.3.1. The Structure of the Configuration
C.3.2. The xorg.conf.d Directory
C.3.3. The xorg.conf File
C.4. Fonts
C.4.1. Adding Fonts to Fontconfig
C.5. Runlevels and X
C.5.1. Runlevel 3
C.5.2. Runlevel 5
C.6. Additional Resources
C.6.1. Installed Documentation
C.6.2. Useful Websites
D. The sysconfig Directory
D.1. Files in the /etc/sysconfig/ Directory
D.1.1. /etc/sysconfig/arpwatch
D.1.2. /etc/sysconfig/authconfig
D.1.3. /etc/sysconfig/autofs
D.1.4. /etc/sysconfig/clock
D.1.5. /etc/sysconfig/dhcpd
D.1.6. /etc/sysconfig/firstboot
D.1.7. /etc/sysconfig/i18n
D.1.8. /etc/sysconfig/init
D.1.9. /etc/sysconfig/ip6tables-config
D.1.10. /etc/sysconfig/keyboard
D.1.11. /etc/sysconfig/ldap
D.1.12. /etc/sysconfig/named
D.1.13. /etc/sysconfig/network
D.1.14. /etc/sysconfig/ntpd
D.1.15. /etc/sysconfig/quagga
D.1.16. /etc/sysconfig/radvd
D.1.17. /etc/sysconfig/samba
D.1.18. /etc/sysconfig/saslauthd
D.1.19. /etc/sysconfig/selinux
D.1.20. /etc/sysconfig/sendmail
D.1.21. /etc/sysconfig/spamassassin
D.1.22. /etc/sysconfig/squid
D.1.23. /etc/sysconfig/system-config-users
D.1.24. /etc/sysconfig/vncservers
D.1.25. /etc/sysconfig/xinetd
D.2. Directories in the /etc/sysconfig/ Directory
D.3. Additional Resources
D.3.1. Installed Documentation
E. The proc File System
E.1. A Virtual File System
E.1.1. Viewing Virtual Files
E.1.2. Changing Virtual Files
E.2. Top-level Files within the proc File System
E.2.1. /proc/buddyinfo
E.2.2. /proc/cmdline
E.2.3. /proc/cpuinfo
E.2.4. /proc/crypto
E.2.5. /proc/devices
E.2.6. /proc/dma
E.2.7. /proc/execdomains
E.2.8. /proc/fb
E.2.9. /proc/filesystems
E.2.10. /proc/interrupts
E.2.11. /proc/iomem
E.2.12. /proc/ioports
E.2.13. /proc/kcore
E.2.14. /proc/kmsg
E.2.15. /proc/loadavg
E.2.16. /proc/locks
E.2.17. /proc/mdstat
E.2.18. /proc/meminfo
E.2.19. /proc/misc
E.2.20. /proc/modules
E.2.21. /proc/mounts
E.2.22. /proc/mtrr
E.2.23. /proc/partitions
E.2.24. /proc/slabinfo
E.2.25. /proc/stat
E.2.26. /proc/swaps
E.2.27. /proc/sysrq-trigger
E.2.28. /proc/uptime
E.2.29. /proc/version
E.3. Directories within /proc/
E.3.1. Process Directories
E.3.2. /proc/bus/
E.3.3. /proc/bus/pci
E.3.4. /proc/driver/
E.3.5. /proc/fs
E.3.6. /proc/irq/
E.3.7. /proc/net/
E.3.8. /proc/scsi/
E.3.9. /proc/sys/
E.3.10. /proc/sysvipc/
E.3.11. /proc/tty/
E.3.12. /proc/PID/
E.4. Using the sysctl Command
E.5. Additional Resources
F. Revision History
Index

Part I. Basic System Configuration

Chapter 1. Keyboard Configuration

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.

1.1. Changing the Keyboard Layout

The installation program has 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 SystemPreferencesKeyboard from the panel, and click the Layouts tab.
Keyboard Layout Preferences

Figure 1.1. Keyboard 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 choose which layout you want to add.
Choosing a layout

Figure 1.2. Choosing a layout

Currently, there are two ways how to choose 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 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

Figure 1.3. 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

Figure 1.4. Testing the layout

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 behavior off, clear the Separate layout for each window checkbox.
Doing this has its drawbacks though, as you will no longer be able to choose the default layout by selecting the radio button as shown in Figure 1.3, “Selecting the default layout”. To make the layout the default, drag it to the beginning of the list.

1.2. 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

Figure 1.5. Adding a new applet

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

Figure 1.6. 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

Figure 1.7. The Keyboard Indicator applet

1.3. Setting Up a Typing Break

Typing for a long period of time can be not only tiring, but it can also increase the risk of serious health problems, such as carpal tunnel syndrome. One way of preventing this is to configure the system to enforce typing breaks. To do so, select SystemPreferencesKeyboard from the panel, click the Typing Break tab, and select the Lock screen to enforce typing break checkbox.
Typing Break Properties

Figure 1.8. Typing Break Properties

To increase or decrease the allowed typing time 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 checkbox 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

Figure 1.9. 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 have enabled it, the Postpone Break button will be located at the bottom right corner of the screen.

Chapter 2. Date and Time Configuration

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.

2.1. 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 (see Appendix C, The X Window System for more information on this topic).
To start the tool, select SystemAdministrationDate & 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 2.1. Authentication Query

2.1.1. Date and Time Properties

As shown in Figure 2.2, “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

Figure 2.2. 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.

2.1.2. 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 2.3, “Network Time Protocol Properties”.
Network Time Protocol Properties

Figure 2.3. 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 speed up the initial synchronization of the system clock, or 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.

2.1.3. Time Zone Properties

To configure the system time zone, click the Time Zone tab as shown in Figure 2.4, “Time Zone Properties”.
Time Zone Properties

Figure 2.4. 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.

2.2. 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:

2.2.1. 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 2.1. Displaying the current date and time

~]$ date
Wed Jun  2 11:58:48 CEST 2010

2.2.2. 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 by one 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 2.2.1, “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 11, Services and Daemons.

    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 iburst
    server 1.rhel.pool.ntp.org iburst
    server 2.rhel.pool.ntp.org iburst
    server 3.rhel.pool.ntp.org iburst
    
    The iburst directive at the end of each line is to speed up the initial synchronization. As of Red Hat Enterprise Linux 6.5 it is added by default. If upgrading from a previous minor release, and your /etc/ntp.conf file has been modified, then the upgrade to Red Hat Enterprise Linux 6.5 will create a new file /etc/ntp.conf.rpmnew and will not alter the existing /etc/ntp.conf file.
  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 is started at boot time:
    ~]# chkconfig ntpd on

Chapter 3. Managing Users and Groups

3.1. What Users and Groups Are

The control of users and groups is a core element of Red Hat Enterprise Linux system administration. The user of the system is either a human being or an account used by specific applications identified by a unique numerical identification number called user ID (UID). Users within a group can have read permissions, write permissions, execute permissions or any combination of read/write/execute permissions for files owned by that group.
Red Hat Enterprise Linux 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 this feature, see the Access Control Lists chapter of the Red Hat Enterprise Linux 6 Storage Administration Guide.
A group is an organization unit tying users together for a common purpose, which can be reading permissions, writing permission, or executing permission for files owned by that group. Similar to UID, each group is associated with a group ID (GID).

Note

Red Hat Enterprise Linux reserves user and group IDs below 500 for system users and groups. By default, the User Manager does not display the system users. Reserved user and group IDs are documented in the setup rpm package. To view the documentation, use this command:
cat /usr/share/doc/setup-2.8.14/uidgid
The recommended practice is to assign non-reserved IDs starting at 5,000, as the reserved range can increase in the future.
A user who creates a file is also the owner and primary group owner of that file.

Note

Each member of the system is a member of at least one group, a primary group. A supplementary group is an additional group for accessing files owned by this group. A user can temporarily change what group is his effective primary group with the newgrp command, allowing all files created afterwords (until the effect is undone) to have a specific group ownership
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 root, and access permissions can be changed by both the root user and file owner.
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. Note that only the user who created the file or directory is allowed to make modifications.
Individual users on the system are provided with shadow passwords. Encrypted password hashes are stored in the /etc/shadow file, which is readable only by the root user, and store information about password aging as well. Policies for specific account are stored in /etc/shadow. /etc/login.defs and /etc/default/useradd define default values, which are stored in /etc/shadow when the account is being created. For more information on shadowing, see the pwconv(8) and grpconv(8) manual pages.

Note

Most utilities provided by the shadow-utils package work properly whether or not shadow passwords are enabled, apart from the commands and utilities which create or modify password aging information. These are: chage and gpasswd utilities, the usermod command with the -e or -f options and the useradd command with the -e or -f options. For more information on how to enable password aging, see the Red Hat Enterprise Linux 6 Security Guide.

3.2. Managing Users via the User Manager Application

The User Manager application allows you to view, modify, add, and delete local users and groups in the graphical user interface.

To start the User Manager application:

  • From the toolbar, select SystemAdministrationUsers and Groups.
  • Or, type system-config-users at the shell prompt.

Note

Unless you have superuser privileges, the application will prompt you to authenticate as root.

3.2.1. Viewing Users

In order to display the main window of the User Manager to view users, from the toolbar of User Manager select EditPreferences. If you wish to view all the users, that is including system users, clear the Hide system users and groups checkbox.
The Users tab provides a list of local users along with additional information about their user ID, primary group, home directory, login shell, and full name.
Viewing Users

Figure 3.1. Viewing Users

To find a specific user, type the first few letters of the name in the Search filter field and either press Enter, or click the Apply filter button. You can also sort the items according to any of the available columns by clicking the column header.

3.2.2. Adding a New User

If there is a new user you need to add to the system, follow this procedure:
  1. Click the Add User button.
  2. Enter the user name and full name in the appropriate fields
  3. Type the user's password in the Password and Confirm Password fields. The password must be at least six characters long.

    Note

    For safety reasons, choose a long password not based on a dictionary term; use a combination of letters, numbers, and special characters.
  4. Select a login shell for the user from the Login Shell dropdown list or accept the default value of /bin/bash.
  5. Clear the Create home directory checkbox if you choose not to create the home directory for a new user in /home/username/.
    You can also change this home directory by editing the content of the Home Directory text box. Note that when the home directory is created, default configuration files are copied into it from the /etc/skel/ directory.
  6. Clear the Create a private group for the user checkbox if you do not want a unique group with the same name as the user to be created. User private group (UPG) is a group assigned to a user account to which that user exclusively belongs, which is used for managing file permissions for individual users.
  7. Specify a user ID for the user by selecting Specify user ID manually. If the option is not selected, the next available user ID above 500 is assigned to the new user.
  8. Click the OK button to complete the process.
Look at the sample Add New User dialog box configuration:
To configure more advanced user properties, such as password expiration, modify the user's properties after adding the user.

3.2.3. Modifying User Properties

  1. Select the user from the user list by clicking once on the user name.
  2. Click Properties from the toolbar or choose FileProperties from the dropdown menu.
    User Properties

    Figure 3.2. User Properties

  3. There are four tabs you can update to your preferences. When you have finished, click the OK button to save your changes.

3.3. Managing Groups via the User Manager Application

3.3.1. Viewing Groups

In order to display the main window of User Manager to view groups, from the toolbar select EditPreferences. If you wish to view all the groups, clear the Hide system users and groups checkbox.
The Groups tab provides a list of local groups with information about their group ID and group members as you can see in the picture below.
Viewing Groups

Figure 3.3. Viewing Groups

To find a specific group, type the first few letters of the name in the Search filter field and either press Enter, or click the Apply filter button. You can also sort the items according to any of the available columns by clicking the column header.

3.3.2. Adding a New Group

If there is a new group you need to add to the system, follow this procedure:
  1. Select Add Group from the User Manager toolbar:
    New Group

    Figure 3.4. New Group

  2. Type the name of the new group.
  3. Specify the group ID (GID) for the new group by checking the Specify group ID manually checkbox.
  4. Select the GID. Note that Red Hat Enterprise Linux also reserves group IDs lower than 500 for system groups.
  5. Click OK to create the group. The new group appears in the group list.

3.3.3. Modifying Group Properties

  1. Select the group from the group list by clicking on its name.
  2. Click Properties from the toolbar or choose FileProperties from the dropdown menu.
    Group Properties

    Figure 3.5. Group Properties

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

3.4. Managing Users via Command-Line Tools

When managing users via command line, the following commands are used: useradd, usermod, userdel, or passwd. The files affected include /etc/passwd which stores user accounts information and /etc/shadow, which stores secure user account information.

3.4.1. Creating Users

The useradd utility creates new users and adds them to the system. Following the short procedure below, you will create a default user account with its UID, automatically create a home directory where default user settings will be stored, /home/username/, and set the default shell to /bin/bash.
  1. Run the following command at a shell prompt as root substituting username with the name of your choice:
    useradd username
  2. By setting a password unlock the account to make it accessible. Type the password twice when the program prompts you to.
    passwd

Example 3.1. Creating a User with Default Settings

~]# useradd robert
~]# passwd robert
Changing password for user robert
New password: 
Re-type new password:
passwd: all authentication tokens updated successfully.
Running the useradd robert command creates an account named robert. If you run cat /etc/passwd to view the content of the /etc/passwd file, you can learn more about the new user from the line displayed to you:
robert:x:502:502::/home/robert:/bin/bash
robert has been assigned a UID of 502, which reflects the rule that the default UID values from 0 to 499 are typically reserved for system accounts. GID, group ID of User Private Group, equals to UID. The home directory is set to /home/robert and login shell to /bin/bash. The letter x signals that shadow passwords are used and that the hashed password is stored in /etc/shadow.
If you want to change the basic default setup for the user while creating the account, you can choose from a list of command-line options modifying the behavior of useradd (see the useradd(8) man page for the whole list of options). As you can see from the basic syntax of the command, you can add one or more options:
useradd [option(s)] username
As a system administrator, you can use the -c option to specify, for example, the full name of the user when creating them. Use -c followed by a string, which adds a comment to the user:
useradd -c "string" username

Example 3.2. Specifying a User's Full Name when Creating a User

~]# useradd -c "Robert Smith" robert
~]# cat /etc/passwd
robert:x:502:502:Robert Smith:/home/robert:/bin/bash
A user account has been created with user name robert, sometimes called the login name, and full name Robert Smith.
If you do not want to create the default /home/username/ directory for the user account, set a different one instead of it. Execute the command below:
useradd -d home_directory

Example 3.3. Adding a User with non-default Home Directory

~]# useradd -d /home/dir_1 robert
robert's home directory is now not the default /home/robert but /home/dir_1/.
If you do not want to create the home directory for the user at all, you can do so by running useradd with the -M option. However, when such a user logs into a system that has just booted and their home directory does not exist, their login directory will be the root directory. If such a user logs into a system using the su command, their login directory will be the current directory of the previous user.
useradd -M username
If you need to copy a directory content to the /home directory while creating a new user, make use of the -m and -k options together followed by the path.

Example 3.4. Creating a User while Copying Contents to the Home Directory

The following command copies the contents of a directory named /dir_1 to /home/jane, which is the default home directory of a new user jane:
~]# useradd -m -k /dir_1 jane
As a system administrator, you may need to create a temporary account. Using the useradd command, this means creating an account for a certain amount of time only and disabling it at a certain date. This is a particularly useful setting as there is no security risk resulting from forgetting to delete a certain account. For this, the -e option is used with the specified expire_date in the YYYY-MM-DD format.

Note

Do not confuse account expiration and password expiration. Account expiration is a particular date, after which it is impossible to log in to the account in any way, as the account no longer exists. Password expiration, the maximum password age and date of password creation or last password change, is the date, when it is not possible to log in using the password (but other ways exist, such as loging in by SSH key).
useradd -e YYYY-MM-DD username

Example 3.5. Setting the Account Expiration Date

~]# useradd -e 2015-11-05 emily
The account emily will be created now and automatically disabled on 5 November, 2015.
User's login shell defaults to /bin/bash, but can be changed by the -s option to any other shell different from bash, ksh, csh, tsh, for example.
useradd -s login_shell username

Example 3.6. Adding a User with Non-default Shell

~]# useradd -s /bin/ksh robert
This command creates the user robert which has the /bin/ksh shell.
The -r option creates a system account, which is an account for administrative use that has some, but not all, root privileges. Such accounts have a UID lower than the value of UID_MIN defined in /etc/login.defs, typically 500 and above for ordinary users.
useradd -r username

3.4.2. Attaching New Users to Groups

The useradd command creates a User Private Group (UPG, a group assigned to a user account to which that user exclusively belongs) whenever a new user is added to the system and names the group after the user. For example, when the account robert is created, an UPG named robert is created at the same time, the only member of which is the user robert.
If you do not want to create a User Private Group for a user for whatever reason, execute the useradd command with the following option:
useradd -N username
Instead of automatically creating UPG or not creating it at all, you can specify the user's group membership with -g and -G options. While the -g option specifies the primary group membership, -G refers to supplementary groups into which the user is also included. The group names you specify must already exist on the system.

Example 3.7. Adding a User to a Group

~]# useradd -g "friends" -G "family,schoolmates" emily
The useradd -g "friends" -G "family,schoolmates" emily command creates the user emily but emily's primary group is set to friends as specified by the -g option. emily is also a group member of the supplementary groups family and schoolmates.
Provided the user already exists and you want to add them to certain supplementary group(s), use the usermod command with the -G option and a list of groups divided by commas, no spaces:
usermod -G group_1,group_2,group_3

3.4.3. Updating Users' Authentication

When running the basic useradd username command, the password is automatically set to never expire (see the /etc/shadow file).
If you wish to change this, use passwd, the standard utility for administering the /etc/passwd file. The syntax of the passwd command look as follows:
passwd option(s) username
You can, for example, lock the specified account. The locking is performed by rendering the encrypted password into an invalid string by prefixing the encrypted string with an the exclamation mark (!). If you later find a reason to unlock the account, passwd has a reverse operation for locking. Only root can carry out these two operations.
passwd -l username
passwd -u username

Example 3.8. Unlocking a User Password

~]# passwd -l robert
Locking password for user robert.
passwd: Success
~]# passwd -u robert
passwd: Warning: unlocked password would be empty
passwd: Unsafe operation (use -f to force)
At first, the -l option locks robert's account password successfully. However, running the passwd -u command does not unlock the password because by default passwd refuses to create a passwordless account.
If you wish a password for an account to expire, run passwd with the -e option. The user will be forced to change the password during the next login attempt:
passwd -e username
As far as the password lifetime is concerned, setting the minimum time between password changes is useful for forcing the user to really change the password. The system administrator can set the minimum (the -n option) and the maximum (the -x option) lifetimes. To inform the user about their password expiration, use the -w option. All these options must be accompanied with the number of days and can be run as root only.

Example 3.9. Adjusting Aging Data for User Passwords

~]# passwd -n 10 -x 60 -w 3 jane
The above command has set the minimum password lifetime to 10 days, the maximum password lifetime to 60, and the number of days jane will begin receiving warnings in advance that her password will expire to 3 day.
Later, when you cannot remember the password setting, make use of the -S option which outputs a short information for you to know the status of the password for a given account:
~]# passwd -S jane
jane LK 2014-07-22 10 60 3 -1 (Password locked.)
You can also set the number of days after a password expires with the useradd command, which disables the account permanently. A value of 0 disables the account as soon as the password has expired, and a value of -1 disables the feature, that is, the user will have to change his password when the password expires. The -f option is used to specify the number of days after a password expires until the account is disabled (but may be unblocked by system administrator):
useradd -f number-of-days username
For more information on the passwd command see the passwd(1) man page.

3.4.4. Modifying User Settings

When a user already exists and you need to specify any of the options now, use the usermod command. The logic of using usermod is identical to useradd as well as its syntax:
usermod option(s) username
If you need to change the user's user name, use the -l option with the new user name (or login).

Example 3.10. Changing User's Login

~]# usermod -l "emily-smith" emily
The -l option changes the name of the user from the login emily to the new login, emily-smith. Nothing else is changed. In particular, emily's home directory name (/home/emily) remains the same unless it is changed manually to reflect the new user name.
In the similar way you can change the user's UID or user's home directory. StStudy the example below:

Note

Find all files owned by the specified UID in system and change their owner. Do the same for Access Control List (ACL) referring to the UID. It is recommended to check there are no running processes as they keep running with the old UID.

Example 3.11. Changing User's UID and Home Directory

~]# usermod -a -u 699 -d /home/dir_2 robert
The command with -a -u and -d options changes the settings of user robert. Now, his ID is 699 instead of 501, and his home directory is no longer /home/robert but /home/dir_2.
With the usermod command you can also move the content of the user's home directory to a new location, or lock the account by locking its password.

Example 3.12. Changing User's

~]# usermod -m -d /home/jane -L jane
In this sample command, the -m and -d options used together move the content of jane's home directory to the /home/dir_3 directory. The -L option locks the access to jane's account by locking its password.
For the whole list of options to be used with the usermod command, see the usermod(8) man page or run usermod --help on the command line.

3.4.5. Deleting Users

If you want to remove a user account from the system, use the userdel command on the command line as root.
userdel username
Combining userdel with the -r option removes files in the user's home directory along with the home directory itself and the user's mail spool. Files located in other file systems have to be searched for and deleted manually.
userdel -r username

Note

The -r option is relatively safer, and thus recommended, compared to -f which forces the removal of the user account even if the user is still logged in.

3.4.6. Displaying Comprehensive User Information

When administering users and groups on your system, you need a good tool to monitor their configuration and activity on the system. Red Hat Enterprise Linux 6 provides you with the lslogins command-line utility, which gives you a comprehensive overview of users and groups, not only regarding user or group account configuration but also their activity on the system.
The general syntax of lslogins is the following:
lslogins [OPTIONS]
where OPTIONS can be one or more available options and their related parameters. See the lslogins(1) manual page or the output of the lslogins --help command for the complete list of available options and their usage.
The lslogins utility gives versatile information in a variety of formats based on the chosen options. The following examples introduce the most basic as well as some of the most useful combinations.
Running the lslogins command without any options shows default information about all system and user accounts on the system. Specifically, their UID, user name, and GECOS information, as well as information about the user's last login to the system, and whether their password is locked or login by password disabled.

Example 3.13. Displaying basic information about all accounts on the system

~]# lslogins
  UID USER          PWD-LOCK PWD-DENY  LAST-LOGIN GECOS
    0 root                 0        0             root
    1 bin                  0        1             bin
    2 daemon               0        1             daemon
    3 adm                  0        1             adm
    4 lp                   0        1             lp
    5 sync                 0        1             sync
    6 shutdown             0        1 Jul21/16:20 shutdown
    7 halt                 0        1             halt
    8 mail                 0        1             mail
   10 uucp                 0        1             uucp
   11 operator             0        1             operator
   12 games                0        1             games
   13 gopher               0        1             gopher
   14 ftp                  0        1             FTP User
   29 rpcuser              0        1             RPC Service User
   32 rpc                  0        1             Rpcbind Daemon
   38 ntp                  0        1             
   42 gdm                  0        1             
   48 apache               0        1             Apache
   68 haldaemon            0        1             HAL daemon
   69 vcsa                 0        1             virtual console memory owner
   72 tcpdump              0        1             
   74 sshd                 0        1             Privilege-separated SSH
   81 dbus                 0        1             System message bus
   89 postfix              0        1             
   99 nobody               0        1             Nobody
  113 usbmuxd              0        1             usbmuxd user
  170 avahi-autoipd        0        1             Avahi IPv4LL Stack
  173 abrt                 0        1             
  497 pulse                0        1             PulseAudio System Daemon
  498 saslauth             0        1             Saslauthd user
  499 rtkit                0        1             RealtimeKit
  500 jsmith               0        0    10:56:12 John Smith
  501 jdoe                 0        0    12:13:53 John Doe
  502 esmith               0        0    12:59:05 Emily Smith
  503 jeyre                0        0    12:22:14 Jane Eyre
65534 nfsnobody            0        1             Anonymous NFS User
To display detailed information about a single user, run the lslogins LOGIN command, where LOGIN is either a UID or a user name. The following example displays detailed information about John Doe's account and his activity on the system:

Example 3.14. Displaying detailed information about a single account

~]# lslogins jdoe
Username:                           jdoe                                
UID:                                501                                 
Gecos field:                        John Doe                            
Home directory:                     /home/jdoe                          
Shell:                              /bin/bash                           
No login:                           no                                  
Password is locked:                 no                                  
Password no required:               no                                  
Login by password disabled:         no                                  
Primary group:                      jdoe                                
GID:                                501                                 
Supplementary groups:               users                               
Supplementary group IDs:            100                                 
Last login:                         12:13:53                            
Last terminal:                      pts/3                               
Last hostname:                      192.168.100.1                       
Hushed:                             no                                  
Password expiration warn interval:  7                                   
Password changed:                   Aug01/02:00                            
Maximal change time:                99999                               
Password expiration:                Sep01/02:00                         
Selinux context:                    unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
If you use the --logins=LOGIN option, you can display information about a group of accounts that are specified as a list of UIDs or user names. Specifying the --output=COLUMNS option, where COLUMNS is a list of available output parameters, you can customize the output of the lslogins command. For example, the following command shows login activity of the users root, jsmith, jdoe, and esmith:

Example 3.15. Displaying specific information about a group of users

~]# lslogins --logins=0,500,jdoe,esmith \
> --output=UID,USER,LAST-LOGIN,LAST-TTY,FAILED-LOGIN,FAILED-TTY
UID USER   LAST-LOGIN LAST-TTY FAILED-LOGIN FAILED-TTY
  0 root                                    
500 jsmith   10:56:12 pts/2                 
501 jdoe     12:13:53 pts/3                 
502 esmith   15:46:16 pts/3    15:46:09     ssh:notty
The lslogins utility also distinguishes between system and user accounts. To address system accounts in your query, use the --system-accs option. To address user accounts, use the --user-accs. For example, the following command displays information about supplementary groups and password expirations for all user accounts:

Example 3.16. Displaying information about supplementary groups and password expiration for all user accounts

~]# lslogins --user-accs --supp-groups --acc-expiration
  UID USER        GID GROUP     SUPP-GIDS SUPP-GROUPS PWD-WARN PWD-MIN PWD-MAX PWD-CHANGE
PWD-EXPIR
    0 root          0 root                                   7           99999 Jul21/02:00
  500 jsmith      500 jsmith    1000,100  staff,users        7           99999 Jul21/02:00
  501 jdoe        501 jdoe      100       users              7           99999 Aug01/02:00
Sep01/02:00
  502 esmith      502 esmith    100       users              7           99999 Aug01/02:00
  503 jeyre       503 jeyre     1000,100  staff,users        7           99999 Jul28/02:00
Sep01/02:00
65534 nfsnobody 65534 nfsnobody                                                Jul21/02:00
The ability to format the output of lslogins commands according to the user's needs makes lslogins an ideal tool to use in scripts and for automatic processing. For example, the following command returns a single string that represents the time and date of the last login. This string can be passed as input to another utility for further processing.

Example 3.17. Displaying a single piece of information without the heading

~]# lslogins --logins=jsmith --output=LAST-LOGIN --time-format=iso | tail -1
2014-08-06T10:56:12+0200

3.5. Managing Groups via Command-Line Tools

Groups are a useful tool for permitting co-operation between different users. There is a set of commands for operating with groups such as groupadd, groupmod, groupdel, or gpasswd. The files affected include /etc/group which stores group account information and /etc/gshadow, which stores secure group account information.

3.5.1. Creating Groups

To add a new group to the system with default settings, the groupadd command is run at the shell prompt as root.
groupadd group_name

Example 3.18. Creating a Group with Default Settings

~]# groupadd friends
The groupadd command creates a new group called friends. You can read more information about the group from the newly-created line in the /etc/group file:
classmates:x:30005:
Automatically, the group friends is attached with a unique GID (group ID) of 30005 and is not attached with any users. Optionally, you can set a password for a group by running gpasswd groupname.
Alternatively, you can add command options with specific settings.
groupadd option(s) groupname
If you, for example, want to specify the numerical value of the group's ID (GID) when creating the group, run the groupadd command with the -g option. Remember that this value must be unique (unless the -o option is used) and the value must be non-negative.
groupadd -g GID

Example 3.19. Creating a Group with Specified GID

The command below creates a group named schoolmates and sets GID of 60002 for it:
~]# groupadd -g 60002 schoolmates
When used with -g and GID already exists, groupadd refuses to create another group with existing GID. As a workaround, use the -f option, with which groupadd creates a group, but with a different GID.
groupadd -f GID
You may also create a system group by attaching the -r option to the groupadd command. System groups are used for system purposes, which practically means that GID is allocated from 1 to 499 within the reserved range of 999.
groupadd -r group_name
For more information on groupadd, see the groupadd(8) man pages.

3.5.2. Attaching Users to Groups

If you want to add an existing user to the named group, you can make use of the gpasswd command.
gpasswd -a username which_group_to_edit
To remove a user from the named group, run:
gpasswd -d username which_group_to_edit
To set the list of group members, write the user names after the --members option dividing them with commas and no spaces:
gpasswd --members username_1,username_2 which_group_to_edit

3.5.3. Updating Group Authentication

The gpasswd command administers /etc/group and /etc/gshadow files. Note that this command works only if run by a group administrator.
Who is a group administrator? A group administrator can add and delete users as well as set, change, or remove the group password. A group can have more than one group administrator. The root user can add group administrators with the gpasswd -A users groupname where users is a comma-separated list of existing users you want to be group administrators (without any spaces between commas).
For changing a group's password, run the gpasswd command with the relevant group name. You will be prompted to type the new password of the group.
gpasswd groupname

Example 3.20. Changing a Group Password

~]# gpasswd crowd
Changing password for group crowd
New password:
Re-enter new password:
The password for the group crowd has been changed.
You can also remove the password from the named group by using the -r option.
gpasswd -r schoolmates

3.5.4. Modifying Group Settings

When a group already exists and you need to specify any of the options now, use the groupmod command. The logic of using groupmod is identical to groupadd as well as its syntax:
groupmod option(s) groupname
To change the group ID of a given group, use the groupmod command in the following way:
groupmod -g GID_NEW which_group_to_edit

Note

Find all files owned by the specified GID in system and change their owner. Do the same for Access Control List (ACL) referring to the GID. It is recommended to check there are no running processes as they keep running with the old GID.
To change the name of the group, run the following on the command line. The name of the group will be changed from GROUP_NAME to NEW_GROUP_NAME name.
groupmod -n new_groupname groupname

Example 3.21. Changing a Group's Name

The following command changes the name of the group schoolmates to crowd:
~]# groupmod -n crowd schoolmates

3.5.5. Deleting Groups

The groupdel command modifies the system account files, deleting all entries that see the group. The named group must exist when you execute this command.
groupdel groupname

3.6. Additional Resources

See the following resources for more information about managing users and groups.

3.6.1. Installed Documentation

For information about various utilities for managing users and groups, see the following manual pages:
  • chage(1) — A command to modify password aging policies and account expiration.
  • gpasswd(1) — A command to administer the /etc/group file.
  • groupadd(8) — A command to add groups.
  • grpck(8) — A command to verify the /etc/group file.
  • groupdel(8) — A command to remove groups.
  • groupmod(8) — A command to modify group membership.
  • pwck(8) — A command to verify the /etc/passwd and /etc/shadow files.
  • pwconv(8) — A tool to convert standard passwords to shadow passwords.
  • pwunconv(8) — A tool to convert shadow passwords to standard passwords.
  • useradd(8) — A command to add users.
  • userdel(8) — A command to remove users.
  • usermod(8) — A command to modify users.
For information about related configuration files, see:
  • group(5) — The file containing group information for the system.
  • passwd(5) — The file containing user information for the system.
  • shadow(5) — The file containing passwords and account expiration information for the system.
  • login.defs(5) - The file containing shadow password suite configuration.
  • useradd(8) - For /etc/default/useradd, section “Changing the default values” in manual page.

Chapter 4. Gaining Privileges

System administrators (and in some cases users) will need to perform certain tasks with administrative access. Accessing the system as root is potentially dangerous and can lead to widespread damage to the system and data. This chapter covers ways to gain administrative privileges using setuid programs such as su and sudo. These programs allow specific users to perform tasks which would normally be available only to the root user while maintaining a higher level of control and system security.
See the Red Hat Enterprise Linux 6 Security Guide for more information on administrative controls, potential dangers and ways to prevent data loss resulting from improper use of privileged access.

4.1. The su Command

When a user executes the su command, they are prompted for the root password and, after authentication, are given a root shell prompt.
Once logged in via the su command, the user is the root user and has absolute administrative access to the system[1]. In addition, once a user has become root, it is possible for them to use the su command to change to any other user on the system without being prompted for a password.
Because this program is so powerful, administrators within an organization may wish to limit who has access to the command.
One of the simplest ways to do this is to add users to the special administrative group called wheel. To do this, type the following command as root:
usermod -G wheel <username>
In the previous command, replace <username> with the user name you want to add to the wheel group.
You can also use the User Manager to modify group memberships, as follows. Note: you need Administrator privileges to perform this procedure.
  1. Click the System menu on the Panel, point to Administration and then click Users and Groups to display the User Manager. Alternatively, type the command system-config-users at a shell prompt.
  2. Click the Users tab, and select the required user in the list of users.
  3. Click Properties on the toolbar to display the User Properties dialog box (or choose Properties on the File menu).
  4. Click the Groups tab, select the checkbox for the wheel group, and then click OK.
See Section 3.2, “Managing Users via the User Manager Application” for more information about the User Manager.
After you add the desired users to the wheel group, it is advisable to only allow these specific users to use the su command. To do this, you will need to edit the PAM configuration file for su: /etc/pam.d/su. Open this file in a text editor and remove the comment (#) from the following line:
#auth           required        pam_wheel.so use_uid
This change means that only members of the administrative group wheel can switch to another user using the su command.

Note

The root user is part of the wheel group by default.

4.2. The sudo Command

The sudo command offers another approach to giving users administrative access. When trusted users precede an administrative command with sudo, they are prompted for their own password. Then, when they have been authenticated and assuming that the command is permitted, the administrative command is executed as if they were the root user.
The basic format of the sudo command is as follows:
sudo <command>
In the above example, <command> would be replaced by a command normally reserved for the root user, such as mount.
The sudo command allows for a high degree of flexibility. For instance, only users listed in the /etc/sudoers configuration file are allowed to use the sudo command and the command is executed in the user's shell, not a root shell. This means the root shell can be completely disabled as shown in the Red Hat Enterprise Linux 6 Security Guide.
Each successful authentication using the sudo is logged to the file /var/log/messages and the command issued along with the issuer's user name is logged to the file /var/log/secure. Should you require additional logging, use the pam_tty_audit module to enable TTY auditing for specified users by adding the following line to your /etc/pam.d/system-auth file:
session required pam_tty_audit.so disable=<pattern> enable=<pattern>
where pattern represents a comma-separated listing of users with an optional use of globs. For example, the following configuration will enable TTY auditing for the root user and disable it for all other users:
session required pam_tty_audit.so disable=* enable=root
Another advantage of the sudo command is that an administrator can allow different users access to specific commands based on their needs.
Administrators wanting to edit the sudo configuration file, /etc/sudoers, should use the visudo command.
To give someone full administrative privileges, type visudo and add a line similar to the following in the user privilege specification section:
juan ALL=(ALL) ALL
This example states that the user, juan, can use sudo from any host and execute any command.
The example below illustrates the granularity possible when configuring sudo:
%users localhost=/sbin/shutdown -h now
This example states that any user can issue the command /sbin/shutdown -h now as long as it is issued from the console.
The man page for sudoers has a detailed listing of options for this file.

Important

There are several potential risks to keep in mind when using the sudo command. You can avoid them by editing the /etc/sudoers configuration file using visudo as described above. Leaving the /etc/sudoers file in its default state gives every user in the wheel group unlimited root access.
  • By default, sudo stores the sudoer's password for a five minute timeout period. Any subsequent uses of the command during this period will not prompt the user for a password. This could be exploited by an attacker if the user leaves his workstation unattended and unlocked while still being logged in. This behavior can be changed by adding the following line to the /etc/sudoers file:
    Defaults    timestamp_timeout=<value>
    where <value> is the desired timeout length in minutes. Setting the <value> to 0 causes sudo to require a password every time.
  • If a sudoer's account is compromised, an attacker can use sudo to open a new shell with administrative privileges:
    sudo /bin/bash
    Opening a new shell as root in this or similar fashion gives the attacker administrative access for a theoretically unlimited amount of time, bypassing the timeout period specified in the /etc/sudoers file and never requiring the attacker to input a password for sudo again until the newly opened session is closed.

4.3. Additional Resources

While programs allowing users to gain administrative privileges are a potential security risk, security itself is beyond the scope of this particular book. You should therefore see sources listed below for more information regarding security and privileged access.

Installed Documentation

  • su(1) - the manual page for su provides information regarding the options available with this command.
  • sudo(8) - the manual page for sudo includes a detailed description of this command as well as a list of options available for customizing sudo's behavior.
  • pam(8) - the manual page describing the use of Pluggable Authentication Modules for Linux.

Online Documentation



[1] This access is still subject to the restrictions imposed by SELinux, if it is enabled.

Part II. Subscription and Support

To receive updates to the software on a Red Hat Enterprise Linux system it must be subscribed to the Red Hat Content Delivery Network (CDN) and the appropriate repositories enabled. This part describes how to subscribe a system to the Red Hat Content Delivery Network.
Red Hat provides support via the Customer Portal, and you can access this support directly from the command line using the Red Hat Support Tool. This part describes the use of this command-line tool.

Chapter 5. Registering the System and Managing Subscriptions

The subscription service provides a mechanism to handle Red Hat software inventory and allows you to install additional software or update already installed programs to newer versions using the yum or PackageKit package managers. In Red Hat Enterprise Linux 6 the recommended way to register your system and attach subscriptions is to use Red Hat Subscription Management.

Note

It is also possible to register the system and attach subscriptions after installation during the firstboot process. For detailed information about firstboot see the Firstboot chapter in the Installation Guide for Red Hat Enterprise Linux 6. Note that firstboot is only available on systems after a graphical installation or after a kickstart installation where a desktop and the X window system were installed and graphical login was enabled.

5.1. Registering the System and Attaching Subscriptions

Complete the following steps to register your system and attach one or more subscriptions using Red Hat Subscription Management. Note that all subscription-manager commands are supposed to be run as root.
  1. Run the following command to register your system. You will be prompted to enter your user name and password. Note that the user name and password are the same as your login credentials for Red Hat Customer Portal.
    subscription-manager register
  2. Determine the pool ID of a subscription that you requires. To do so, type the following at a shell prompt to display a list of all subscriptions that are available for your system:
    subscription-manager list --available
    For each available subscription, this command displays its name, unique identifier, expiration date, and other details related to your subscription. The pool ID is listed on a line beginning with Pool ID.
  3. Attach the appropriate subscription to your system by entering a command as follows:
    subscription-manager attach --pool=pool_id
    Replace pool_id with the pool ID you determined in the previous step. To verify the list of subscriptions your system has currently attached, at any time, run:
    subscription-manager list --consumed

Note

The auto-attach option automatically attaches compatible subscriptions to the system so that you can register the system and attach subscriptions in one step by executing the following command:
subscription-manager register --auto-attach
For more information on how to register your system using Red Hat Subscription Management and associate it with subscriptions, see the Red Hat Subscription Management collection of guides.

5.2. Managing Software Repositories

When a system is subscribed to the Red Hat Content Delivery Network, a repository file is created in the /etc/yum.repos.d/ directory. To verify that, use yum to list all enabled repositories:
yum repolist
Red Hat Subscription Management also allows you to manually enable or disable software repositories provided by Red Hat. To list all available repositories, use the following command:
subscription-manager repos --list
The repository names depend on the specific version of Red Hat Enterprise Linux you are using and are in the following format:
rhel-variant-rhscl-version-rpms
rhel-variant-rhscl-version-debug-rpms
rhel-variant-rhscl-version-source-rpms
Where variant is the Red Hat Enterprise Linux system variant (server or workstation), and version is the Red Hat Enterprise Linux system version (6 or 7), for example:
rhel-server-rhscl-6-eus-rpms
rhel-server-rhscl-6-eus-source-rpms
rhel-server-rhscl-6-eus-debug-rpms
To enable a repository, enter a command as follows:
subscription-manager repos --enable repository
Replace repository with a name of the repository to enable.
Similarly, to disable a repository, use the following command:
subscription-manager repos --disable repository
Section 7.4, “Configuring Yum and Yum Repositories” provides detailed information about managing software repositories using yum.

5.3. Removing Subscriptions

To remove a particular subscription, complete the following steps.
  1. Determine the serial number of the subscription you want to remove by listing information about already attached subscriptions:
    subscription-manager list --consumed
    The serial number is the number listed as serial. For instance, 744993814251016831 in the example below:
    SKU:               ES0113909
    Contract:          01234567
    Account:           1234567
    Serial:            744993814251016831
    Pool ID:           8a85f9894bba16dc014bccdd905a5e23
    Active:            False
    Quantity Used:     1
    Service Level:     SELF-SUPPORT
    Service Type:      L1-L3
    Status Details:    
    Subscription Type: Standard
    Starts:            02/27/2015
    Ends:              02/27/2016
    System Type:       Virtual
  2. Enter a command as follows to remove the selected subscription:
    subscription-manager remove --serial=serial_number
    Replace serial_number with the serial number you determined in the previous step.
To remove all subscriptions attached to the system, run the following command:
subscription-manager remove --all

5.4. Additional Resources

For more information on how to register your system using Red Hat Subscription Management and associate it with subscriptions, see the resources listed below.

Installed Documentation

  • subscription-manager(8) — the manual page for Red Hat Subscription Management provides a complete list of supported options and commands.

Related Books

Online Resources

See Also

  • Chapter 4, Gaining Privileges documents how to gain administrative privileges by using the su and sudo commands.
  • Chapter 7, Yum provides information about using the yum packages manager to install and update software.
  • Chapter 8, PackageKit provides information about using the PackageKit package manager to install and update software.

Chapter 6. Accessing Support Using the Red Hat Support Tool

The Red Hat Support Tool, in the redhat-support-tool package, can function as both an interactive shell and as a single-execution program. It can be run over SSH or from any terminal. It enables, for example, searching the Red Hat Knowledgebase from the command line, copying solutions directly on the command line, opening and updating support cases, and sending files to Red Hat for analysis.

6.1. Installing the Red Hat Support Tool

The Red Hat Support Tool is installed by default on Red Hat Enterprise Linux. If required, to ensure that it is, enter the following command as root:
~]# yum install redhat-support-tool

6.2. Registering the Red Hat Support Tool Using the Command Line

To register the Red Hat Support Tool to the customer portal using the command line, proceed as follows:
  1. ~]# redhat-support-tool config user username
    Where username is the user name of the Red Hat Customer Portal account.
  2. ~]# redhat-support-tool config password
    Please enter the password for username:

6.3. Using the Red Hat Support Tool in Interactive Shell Mode

To start the tool in interactive mode, enter the following command:
~]$ redhat-support-tool
Welcome to the Red Hat Support Tool.
Command (? for help):
The tool can be run as an unprivileged user, with a consequently reduced set of commands, or as root.
The commands can be listed by entering the ? character. The program or menu selection can be exited by entering the q or e character. You will be prompted for your Red Hat Customer Portal user name and password when you first search the Knowledgebase or support cases. Alternately, set the user name and password for your Red Hat Customer Portal account using interactive mode, and optionally save it to the configuration file.

6.4. Configuring the Red Hat Support Tool

When in interactive mode, the configuration options can be listed by entering the command config --help:
~]# redhat-support-tool
Welcome to the Red Hat Support Tool.
Command (? for help): config --help

Usage: config [options] config.option <new option value>

Use the 'config' command to set or get configuration file values.
Options:
  -h, --help    show this help message and exit
  -g, --global  Save configuration option in /etc/redhat-support-tool.conf.
  -u, --unset   Unset configuration option.

The configuration file options which can be set are:
 user      : The Red Hat Customer Portal user.
 password  : The Red Hat Customer Portal password.
 debug     : CRITICAL, ERROR, WARNING, INFO, or DEBUG
 url       : The support services URL.  Default=https://api.access.redhat.com
 proxy_url : A proxy server URL.
 proxy_user: A proxy server user.
 proxy_password: A password for the proxy server user.
 ssl_ca    : Path to certificate authorities to trust during communication.
 kern_debug_dir: Path to the directory where kernel debug symbols should be downloaded and cached. Default=/var/lib/redhat-support-tool/debugkernels

Examples:
- config user
- config user my-rhn-username
- config --unset user

Procedure 6.1. Registering the Red Hat Support Tool Using Interactive Mode

To register the Red Hat Support Tool to the customer portal using interactive mode, proceed as follows:
  1. Start the tool by entering the following command:
    ~]# redhat-support-tool
  2. Enter your Red Hat Customer Portal user name:
    Command (? for help): config user username
    To save your user name to the global configuration file, add the -g option.
  3. Enter your Red Hat Customer Portal password:
    Command (? for help): config password
    Please enter the password for username:

6.4.1. Saving Settings to the Configuration Files

The Red Hat Support Tool, unless otherwise directed, stores values and options locally in the home directory of the current user, using the ~/.redhat-support-tool/redhat-support-tool.conf configuration file. If required, it is recommended to save passwords to this file because it is only readable by that particular user. When the tool starts, it will read values from the global configuration file /etc/redhat-support-tool.conf and from the local configuration file. Locally stored values and options take precedence over globally stored settings.

Warning

It is recommended not to save passwords in the global /etc/redhat-support-tool.conf configuration file because the password is just base64 encoded and can easily be decoded. In addition, the file is world readable.
To save a value or option to the global configuration file, add the -g, --global option as follows:
Command (? for help): config setting -g value

Note

In order to be able to save settings globally, using the -g, --global option, the Red Hat Support Tool must be run as root because normal users do not have the permissions required to write to /etc/redhat-support-tool.conf.
To remove a value or option from the local configuration file, add the -u, --unset option as follows:
Command (? for help): config setting -u value
This will clear, unset, the parameter from the tool and fall back to the equivalent setting in the global configuration file, if available.

Note

When running as an unprivileged user, values stored in the global configuration file cannot be removed using the -u, --unset option, but they can be cleared, unset, from the current running instance of the tool by using the -g, --global option simultaneously with the -u, --unset option. If running as root, values and options can be removed from the global configuration file using -g, --global simultaneously with the -u, --unset option.

6.5. Opening and Updating Support Cases Using Interactive Mode

Procedure 6.2. Opening a New Support Case Using Interactive Mode

To open a new support case using interactive mode, proceed as follows:
  1. Start the tool by entering the following command:
    ~]# redhat-support-tool
  2. Enter the opencase command:
    Command (? for help): opencase
  3. Follow the on screen prompts to select a product and then a version.
  4. Enter a summary of the case.
  5. Enter a description of the case and press Ctrl+D on an empty line when complete.
  6. Select a severity of the case.
  7. Optionally chose to see if there is a solution to this problem before opening a support case.
  8. Confirm you would still like to open the support case.
    Support case 0123456789 has successfully been opened
  9. Optionally chose to attach an SOS report.
  10. Optionally chose to attach a file.

Procedure 6.3. Viewing and Updating an Existing Support Case Using Interactive Mode

To view and update an existing support case using interactive mode, proceed as follows:
  1. Start the tool by entering the following command:
    ~]# redhat-support-tool
  2. Enter the getcase command:
    Command (? for help): getcase case-number
    Where case-number is the number of the case you want to view and update.
  3. Follow the on screen prompts to view the case, modify or add comments, and get or add attachments.

Procedure 6.4. Modifying an Existing Support Case Using Interactive Mode

To modify the attributes of an existing support case using interactive mode, proceed as follows:
  1. Start the tool by entering the following command:
    ~]# redhat-support-tool
  2. Enter the modifycase command:
    Command (? for help): modifycase case-number
    Where case-number is the number of the case you want to view and update.
  3. The modify selection list appears:
    Type the number of the attribute to modify or 'e' to return to the previous menu.
     1 Modify Type
     2 Modify Severity
     3 Modify Status
     4 Modify Alternative-ID
     5 Modify Product
     6 Modify Version
    End of options.
    Follow the on screen prompts to modify one or more of the options.
  4. For example, to modify the status, enter 3:
    Selection: 3
     1   Waiting on Customer                                                        
     2   Waiting on Red Hat                                                         
     3   Closed                                                                     
    Please select a status (or 'q' to exit):

6.6. Viewing Support Cases on the Command Line

Viewing the contents of a case on the command line provides a quick and easy way to apply solutions from the command line.
To view an existing support case on the command line, enter a command as follows:
~]# redhat-support-tool getcase case-number
Where case-number is the number of the case you want to download.

6.7. Additional Resources

The Red Hat Knowledgebase article Red Hat Support Tool has additional information, examples, and video tutorials.

Part III. Installing and Managing Software

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

Chapter 7. Yum

Yum is the Red Hat package manager that is able to query for information about available packages, fetch packages from repositories, install and uninstall them, and update an entire system to the latest available version. 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 plug-ins 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. See Section 7.4, “Configuring Yum and Yum Repositories” for details on enabling signature-checking with Yum, or Section B.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. See Chapter 8, PackageKit for details on using PackageKit.

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.

7.1. Checking For and Updating Packages

7.1.1. Checking For Updates

To see which installed packages on your system have updates available, use the following command:
yum check-update
For example:
~]# yum check-update
Loaded plugins: product-id, refresh-packagekit, subscription-manager
Updating Red Hat repositories.
INFO:rhsm-app.repolib:repos updated: 0
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
The packages in the above output are listed as having updates available. The first package in the list is PackageKit, the graphical package manager. The line in the example 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.

7.1.2. 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.

Updating a Single Package

To update a single package, run the following command as root:
yum update package_name
For example, to update the udev package, type:
~]# yum update udev
Loaded plugins: product-id, refresh-packagekit, subscription-manager
Updating Red Hat repositories.
INFO:rhsm-app.repolib:repos updated: 0
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: product-id, refresh-packagekit, subscription-manageryum always informs you which Yum plug-ins are installed and enabled. See Section 7.5, “Yum Plug-ins” for general information on Yum plug-ins, or to Section 7.5.3, “Plug-in Descriptions” for descriptions of specific plug-ins.
  2. udev.x86_64 — you can download and install new udev package.
  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 the yum command plans to perform, you can use the -y option to automatically answer yes to any questions that yum asks (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 transaction history by using the yum history command as described in Section 7.3, “Working with Transaction History”.

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). See Section B.2.2, “Installing and Upgrading” for more information on installing/upgrading kernels with RPM.

Updating All Packages and Their Dependencies

To update all packages and their dependencies, enter yum update (without any arguments):
yum update

Updating Security-Related Packages

Discovering which packages have security updates available and then updating those packages quickly and easily is important. Yum provides the plug-in for this purpose. The security plug-in extends the yum command with a set of highly-useful security-centric commands, subcommands and options. See Section 7.5.3, “Plug-in Descriptions” for specific information.

Updating Packages Automatically

It is also possible to set up periodical automatic updates for your packages. For this purpose, Red Hat Enterprise Linux 6 uses the yum-cron package. It provides a Yum interface for the cron daemon and downloads metadata from your package repositories. With the yum-cron service enabled, the user can schedule an automated daily Yum update as a cron job.

Note

The yum-cron package is provided by the Optional subscription channel. See Section 7.4.8, “Adding the Optional and Supplementary Repositories” for more information on Red Hat additional channels.
To install yum-cron issue the following command:
~]# yum install yum-cron
By default, the yum-cron service is disabled and needs to be activated and started manually:
~]# chkconfig yum-cron on
~]# service yum-cron start
To verify the status of the service, run the following command:
~]# service yum-cron status
The script included in the yum-cron package can be configured to change the extent and frequency of the updates, as well as to send notifications to e-mail. To customize yum-cron, edit the /etc/sysconfig/yum-cron file.
Additional details and instructions for yum-cron can be found in the comments within /etc/sysconfig/yum-cron and at the yum-cron(8) manual page.

7.1.3. 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. See Section B.2.2, “Installing and Upgrading” for details on how to manage changes to configuration files across package upgrades.

7.1.4. Upgrading the System Off-line with ISO and Yum

For systems that are disconnected from the Internet or Red Hat Network, using the yum update command with the Red Hat Enterprise Linux installation ISO image is an easy and quick way to upgrade systems to the latest minor version. The following steps illustrate the upgrading process:
  1. Create a target directory to mount your ISO image. This directory is not automatically created when mounting, so create it before proceeding to the next step. As root, type:
    mkdir mount_dir
    Replace mount_dir with a path to the mount directory. Typically, users create it as a subdirectory in the /media/ directory.
  2. Mount the Red Hat Enterprise Linux 6 installation ISO image to the previously created target directory. As root, type:
    mount -o loop iso_name mount_dir
    Replace iso_name with a path to your ISO image and mount_dir with a path to the target directory. Here, the -o loop option is required to mount the file as a block device.
  3. Copy the media.repo file from the mount directory to the /etc/yum.repos.d/ directory. Note that configuration files in this directory must have the .repo extension to function properly.
    cp mount_dir/media.repo /etc/yum.repos.d/new.repo
    This creates a configuration file for the yum repository. Replace new.repo with the filename, for example rhel6.repo.
  4. Edit the new configuration file so that it points to the Red Hat Enterprise Linux installation ISO. Add the following line into the /etc/yum.repos.d/new.repo file:
    baseurl=file://mount_dir
    Replace mount_dir with a path to the mount point.
  5. Update all yum repositories including /etc/yum.repos.d/new.repo created in previous steps. As root, type:
    yum update
    This upgrades your system to the version provided by the mounted ISO image.
  6. After successful upgrade, you can unmount the ISO image. As root, type:
    umount mount_dir
    where mount_dir is a path to your mount directory. Also, you can remove the mount directory created in the first step. As root, type:
    rmdir mount_dir
  7. If you will not use the previously created configuration file for another installation or update, you can remove it. As root, type:
    rm /etc/yum.repos.d/new.repo

Example 7.1. Upgrading from Red Hat Enterprise Linux 6.3 to 6.4

Imagine you need to upgrade your system without access to the Internet. To do so, you want to use an ISO image with the newer version of the system, called for instance RHEL6.4-Server-20130130.0-x86_64-DVD1.iso. A target directory created for mounting is /media/rhel6/. As root, change into the directory with your ISO image and type:
~]# mount -o loop RHEL6.4-Server-20130130.0-x86_64-DVD1.iso /media/rhel6/
Then set up a yum repository for your image by copying the media.repo file from the mount directory:
~]# cp /media/rhel6/media.repo /etc/yum.repos.d/rhel6.repo
To make yum recognize the mount point as a repository, add the following line into the /etc/yum.repos.d/rhel6.repo copied in the previous step:
baseurl=file:///media/rhel6/
Now, updating the yum repository will upgrade your system to a version provided by RHEL6.4-Server-20130130.0-x86_64-DVD1.iso. As root, execute:
~]# yum update
When your system is successfully upgraded, you can unmount the image, remove the target directory and the configuration file:
~]# umount /media/rhel6/
~]# rmdir /media/rhel6/
~]# rm /etc/yum.repos.d/rhel6.repo

7.2. Packages and Package Groups

7.2.1. Searching Packages

You can search all RPM package names, descriptions and summaries by using the following command:
yum search term
This command displays the list of matches for each term. For example, to list all packages that match meld or kompare, type:
~]# yum search meld kompare
Loaded plugins: product-id, refresh-packagekit, subscription-manager
Updating Red Hat repositories.
INFO:rhsm-app.repolib:repos updated: 0
============================ Matched: kompare =============================
kdesdk.x86_64 : The KDE Software Development Kit (SDK)
Warning: No matches found for: meld
The yum search command is useful for searching for packages you do not know the name of, but for which you know a related term.

7.2.2. Listing Packages

yum list and related commands provide information about packages, package groups, and repositories.
All of Yum's 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).

Filtering results with glob expressions

Be careful to escape the glob expressions when passing them as arguments to a yum command, otherwise the Bash shell will interpret these expressions as pathname expansions, and potentially pass all files in the current directory that match the globs to yum. To make sure the glob expressions are passed to yum as intended, either:
  • escape the wildcard characters by preceding them with a backslash character
  • double-quote or single-quote the entire glob expression.
yum list glob_expression
Lists information on installed and available packages matching all glob expressions.

Example 7.2. Listing all ABRT addons and plug-ins using glob expressions

Packages with various ABRT addons and plug-ins either begin with abrt-addon-, or abrt-plugin-. To list these packages, type the following at a shell prompt:
~]# yum list abrt-addon\* abrt-plugin\*
Loaded plugins: product-id, refresh-packagekit, subscription-manager
Updating Red Hat repositories.
INFO:rhsm-app.repolib:repos updated: 0
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
Lists all installed and available packages.
yum list installed
Lists all packages installed on your system. The rightmost column in the output lists the repository from which the package was retrieved.

Example 7.3. Listing installed packages using a double-quoted glob expression

To list all installed packages that begin with krb followed by exactly one character and a hyphen, type:
~]# yum list installed "krb?-*"
Loaded plugins: product-id, refresh-packagekit, subscription-manager
Updating Red Hat repositories.
INFO:rhsm-app.repolib:repos updated: 0
Installed Packages
krb5-libs.x86_64                         1.8.1-3.el6                  @rhel
krb5-workstation.x86_64                  1.8.1-3.el6                  @rhel
yum list available
Lists all available packages in all enabled repositories.

Example 7.4. Listing available packages using a single glob expression with escaped wildcard characters

To list all available packages with names that contain gstreamer and then plugin, run the following command:
~]# yum list available gstreamer\*plugin\*
Loaded plugins: product-id, refresh-packagekit, subscription-manager
Updating Red Hat repositories.
INFO:rhsm-app.repolib:repos updated: 0
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
yum grouplist
Lists all package groups.
yum repolist
Lists the repository ID, name, and number of packages it provides for each enabled repository.

7.2.3. Displaying Package Information

To display information about one or more packages (glob expressions are valid here as well), use the following command:
yum info package_name
For example, to display information about the abrt package, type:
~]# yum info abrt
Loaded plugins: product-id, refresh-packagekit, subscription-manager
Updating Red Hat repositories.
INFO:rhsm-app.repolib:repos updated: 0
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.
The yum info package_name command 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).
You can also query the Yum database for alternative and useful information about a package by using the following command:
yumdb info package_name
This command provides additional 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). For example, to display additional information about the yum package, type:
~]# yumdb info yum
Loaded plugins: product-id, refresh-packagekit, subscription-manager
yum-3.2.27-4.el6.noarch
     checksum_data = 23d337ed51a9757bbfbdceb82c4eaca9808ff1009b51e9626d540f44fe95f771
     checksum_type = sha256
     from_repo = rhel
     from_repo_revision = 1298613159
     from_repo_timestamp = 1298614288
     installed_by = 4294967295
     reason = user
     releasever = 6.1
For more information on the yumdb command, see the yumdb(8) manual page.

Listing Files Contained in a Package

repoquery is a program for querying information from yum repositories similarly to rpm queries. You can query both package groups and individual packages. To list all files contained in a specific package, type:
repoquery --list package_name
Replace package_name with a name of the package you want to inspect. For more information on the repoquery command, see the repoquery manual page.
To find out which package provides a specific file, you can use the yum provides command, described in Finding which package owns a file

7.2.4. Installing Packages

Yum allows you to install both a single package and multiple packages, as well as a package group of your choice.

Installing Individual Packages

To install a single package and all of its non-installed dependencies, enter a command in the following form:
yum install package_name
You can also install multiple packages simultaneously by appending their names as arguments:
yum install package_name package_name
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 is available in an enabled repository) by appending .arch to the package name. For example, to install the sqlite package for i686, type:
~]# yum install sqlite.i686
You can use glob expressions to quickly install multiple similarly-named packages:
~]# yum install perl-Crypt-\*
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.

Finding which package owns a file

If you know you want to install the package that contains the named binary, but you do not know in which bin or sbin directory is the file installed, use the yum provides command with a glob expression:
~]# yum provides "*bin/named"
Loaded plugins: product-id, refresh-packagekit, subscription-manager
Updating Red Hat repositories.
INFO:rhsm-app.repolib:repos updated: 0
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 provides "*/file_name" is a common and useful trick to 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 in the following example:
~]# yum -v grouplist kde\*
Loading "product-id" plugin
Loading "refresh-packagekit" plugin
Loading "subscription-manager" plugin
Updating Red Hat repositories.
INFO:rhsm-app.repolib:repos updated: 0
Config time: 0.123
Yum Version: 3.2.29
Setting up Group Process
Looking for repo options for [rhel]
rpmdb time: 0.001
group time: 1.291
Available Groups:
   KDE Desktop (kde-desktop)
Done
You can install a package group by passing its full group name (without the groupid part) to groupinstall:
yum groupinstall group_name
You can also install by groupid:
yum groupinstall groupid
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 @group
For example, the following are alternative but equivalent ways of installing the KDE Desktop group:
~]# yum groupinstall "KDE Desktop"
~]# yum groupinstall kde-desktop
~]# yum install @kde-desktop

7.2.5. Removing Packages

Similarly to package installation, Yum allows you to uninstall (remove in RPM and Yum terminology) both individual packages and a package group.

Removing Individual Packages

To uninstall a particular package, as well as any packages that depend on it, run the following command as root:
yum remove package_name
As when you install multiple packages, you can remove several at once by adding more package names to the command. For example, to remove totem, rhythmbox, and sound-juicer, type the following at a shell prompt:
~]# yum remove totem rhythmbox sound-juicer
Similar to install, remove can take these arguments:
  • package names
  • glob expressions
  • file lists
  • package provides

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, see Section B.2.4, “Uninstalling” in the RPM chapter.

Removing a Package Group

You can remove a package group using syntax congruent with the install syntax:
yum groupremove group
yum remove @group
The following are alternative but equivalent ways of removing the KDE Desktop group:
~]# yum groupremove "KDE Desktop"
~]# yum groupremove kde-desktop
~]# yum remove @kde-desktop

Intelligent 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, see Section 7.4.1, “Setting [main] Options”.

7.3. Working with Transaction History

The yum history command allows users to review information about a timeline of Yum transactions, the dates and times they occurred, the number of packages affected, whether transactions succeeded or were aborted, and if the RPM database was changed between transactions. Additionally, this command can be used to undo or redo certain transactions.

7.3.1. Listing Transactions

To display a list of twenty most recent transactions, as root, either run yum history with no additional arguments, or type the following at a shell prompt:
yum history list
To display all transactions, add the all keyword:
yum history list all
To display only transactions in a given range, use the command in the following form:
yum history list start_id..end_id
You can also list only transactions regarding a particular package or packages. To do so, use the command with a package name or a glob expression:
yum history list glob_expression
For example, the list of the first five transactions looks as follows:
~]# yum history list 1..5
Loaded plugins: product-id, refresh-packagekit, subscription-manager
ID     | Login user               | Date and time    | Action(s)      | Altered
-------------------------------------------------------------------------------
     5 | Jaromir ... <jhradilek>  | 2011-07-29 15:33 | Install        |    1
     4 | Jaromir ... <jhradilek>  | 2011-07-21 15:10 | Install        |    1
     3 | Jaromir ... <jhradilek>  | 2011-07-16 15:27 | I, U           |   73
     2 | System <unset>           | 2011-07-16 15:19 | Update         |    1
     1 | System <unset>           | 2011-07-16 14:38 | Install        | 1106
history list
All forms of the yum history list command produce tabular output with each row consisting of the following columns:
  • ID — an integer value that identifies a particular transaction.
  • Login user — the name of the user whose login session was used to initiate a transaction. This information is typically presented in the Full Name <username> form. For transactions that were not issued by a user (such as an automatic system update), System <unset> is used instead.
  • Date and time — the date and time when a transaction was issued.
  • Action(s) — a list of actions that were performed during a transaction as described in Table 7.1, “Possible values of the Action(s) field”.
  • Altered — the number of packages that were affected by a transaction, possibly followed by additional information as described in Table 7.2, “Possible values of the Altered field”.

Table 7.1. Possible values of the Action(s) field

Action Abbreviation Description
Downgrade D At least one package has been downgraded to an older version.
Erase E At least one package has been removed.
Install I At least one new package has been installed.
Obsoleting O At least one package has been marked as obsolete.
Reinstall R At least one package has been reinstalled.
Update U At least one package has been updated to a newer version.

Table 7.2. Possible values of the Altered field

Symbol Description
< Before the transaction finished, the rpmdb database was changed outside Yum.
> After the transaction finished, the rpmdb database was changed outside Yum.
* The transaction failed to finish.
# The transaction finished successfully, but yum returned a non-zero exit code.
E The transaction finished successfully, but an error or a warning was displayed.
P The transaction finished successfully, but problems already existed in the rpmdb database.
s The transaction finished successfully, but the --skip-broken command-line option was used and certain packages were skipped.
Yum also allows you to display a summary of all past transactions. To do so, run the command in the following form as root:
yum history summary
To display only transactions in a given range, type:
yum history summary start_id..end_id
Similarly to the yum history list command, you can also display a summary of transactions regarding a certain package or packages by supplying a package name or a glob expression:
yum history summary glob_expression
For instance, a summary of the transaction history displayed above would look like the following:
~]# yum history summary 1..5
Loaded plugins: product-id, refresh-packagekit, subscription-manager
Login user                 | Time                | Action(s)        | Altered
-------------------------------------------------------------------------------
Jaromir ... <jhradilek>    | Last day            | Install          |        1
Jaromir ... <jhradilek>    | Last week           | Install          |        1
Jaromir ... <jhradilek>    | Last 2 weeks        | I, U             |       73
System <unset>             | Last 2 weeks        | I, U             |     1107
history summary
All forms of the yum history summary command produce simplified tabular output similar to the output of yum history list.
As shown above, both yum history list and yum history summary are oriented towards transactions, and although they allow you to display only transactions related to a given package or packages, they lack important details, such as package versions. To list transactions from the perspective of a package, run the following command as root:
yum history package-list glob_expression
For example, to trace the history of subscription-manager and related packages, type the following at a shell prompt:
~]# yum history package-list subscription-manager\*
Loaded plugins: product-id, refresh-packagekit, subscription-manager
ID     | Action(s)      | Package
-------------------------------------------------------------------------------
     3 | Updated        | subscription-manager-0.95.11-1.el6.x86_64
     3 | Update         |                      0.95.17-1.el6_1.x86_64
     3 | Updated        | subscription-manager-firstboot-0.95.11-1.el6.x86_64
     3 | Update         |                                0.95.17-1.el6_1.x86_64
     3 | Updated        | subscription-manager-gnome-0.95.11-1.el6.x86_64
     3 | Update         |                            0.95.17-1.el6_1.x86_64
     1 | Install        | subscription-manager-0.95.11-1.el6.x86_64
     1 | Install        | subscription-manager-firstboot-0.95.11-1.el6.x86_64
     1 | Install        | subscription-manager-gnome-0.95.11-1.el6.x86_64
history package-list
In this example, three packages were installed during the initial system installation: subscription-manager, subscription-manager-firstboot, and subscription-manager-gnome. In the third transaction, all these packages were updated from version 0.95.11 to version 0.95.17.

7.3.2. Examining Transactions

To display the summary of a single transaction, as root, use the yum history summary command in the following form:
yum history summary id
To examine a particular transaction or transactions in more detail, run the following command as root:
yum history info id
The id argument is optional and when you omit it, yum automatically uses the last transaction. Note that when specifying more than one transaction, you can also use a range:
yum history info start_id..end_id
The following is sample output for two transactions, each installing one new package:
~]# yum history info 4..5
Loaded plugins: product-id, refresh-packagekit, subscription-manager
Transaction ID : 4..5
Begin time     : Thu Jul 21 15:10:46 2011
Begin rpmdb    : 1107:0c67c32219c199f92ed8da7572b4c6df64eacd3a
End time       :            15:33:15 2011 (22 minutes)
End rpmdb      : 1109:1171025bd9b6b5f8db30d063598f590f1c1f3242
User           : Jaromir Hradilek <jhradilek>
Return-Code    : Success
Command Line   : install screen
Command Line   : install yum-plugin-security
Transaction performed with:
    Installed     rpm-4.8.0-16.el6.x86_64
    Installed     yum-3.2.29-17.el6.noarch
    Installed     yum-metadata-parser-1.1.2-16.el6.x86_64
Packages Altered:
    Install screen-4.0.3-16.el6.x86_64
    Install yum-plugin-security-1.1.30-17.el6.noarch
history info
You can also view additional information, such as what configuration options were used at the time of the transaction, or from what repository and why were certain packages installed. To determine what additional information is available for a certain transaction, type the following at a shell prompt as root:
yum history addon-info id
Similarly to yum history info, when no id is provided, yum automatically uses the latest transaction. Another way to see the latest transaction is to use the last keyword:
yum history addon-info last
For instance, for the first transaction in the previous example, the yum history addon-info command would provide the following output:
~]# yum history addon-info 4
Loaded plugins: product-id, refresh-packagekit, subscription-manager
Transaction ID: 4
Available additional history information:
  config-main
  config-repos
  saved_tx

history addon-info
In this example, three types of information are available:
  • config-main — global Yum options that were in use during the transaction. See Section 7.4.1, “Setting [main] Options” for information on how to change global options.
  • config-repos — options for individual Yum repositories. See Section 7.4.2, “Setting [repository] Options” for information on how to change options for individual repositories.
  • saved_tx — the data that can be used by the yum load-transaction command in order to repeat the transaction on another machine (see below).
To display selected type of additional information, run the following command as root:
yum history addon-info id information

7.3.3. Reverting and Repeating Transactions

Apart from reviewing the transaction history, the yum history command provides means to revert or repeat a selected transaction. To revert a transaction, type the following at a shell prompt as root:
yum history undo id
To repeat a particular transaction, as root, run the following command:
yum history redo id
Both commands also accept the last keyword to undo or repeat the latest transaction.
Note that both yum history undo and yum history redo commands only revert or repeat the steps that were performed during a transaction. If the transaction installed a new package, the yum history undo command will uninstall it, and if the transaction uninstalled a package the command will again install it. This command also attempts to downgrade all updated packages to their previous version, if these older packages are still available.
When managing several identical systems, Yum also allows you to perform a transaction on one of them, store the transaction details in a file, and after a period of testing, repeat the same transaction on the remaining systems as well. To store the transaction details to a file, type the following at a shell prompt as root:
yum -q history addon-info id saved_tx > file_name
Once you copy this file to the target system, you can repeat the transaction by using the following command as root:
yum load-transaction file_name
Note, however that the rpmdb version stored in the file must be identical to the version on the target system. You can verify the rpmdb version by using the yum version nogroups command.

7.3.4. Completing Transactions

An unexpected situation, such as power loss or system crash, can prevent you from completing your yum transaction. When such event occurs in the middle of your transaction, you can try to resume it later with the following command as root:
yum-complete-transaction
The yum-complete-transaction tool searches for incomplete or aborted yum transactions on a system and attempts to complete them. By default, these transactions are listed in the /var/lib/yum/transaction-all and /var/lib/yum/transaction-done files. If there are more unfinished transactions, yum-complete-transaction attempts to complete the most recent one first.
To clean transaction journal files without attempting to resume the aborted transactions, use the --cleanup-only option:
yum-complete-transaction --cleanup-only

7.3.5. Starting New Transaction History

Yum stores the transaction history in a single SQLite database file. To start new transaction history, run the following command as root:
yum history new
This will create a new, empty database file in the /var/lib/yum/history/ directory. The old transaction history will be kept, but will not be accessible as long as a newer database file is present in the directory.

7.4. Configuring Yum and Yum Repositories

The configuration file for yum and related utilities is located at /etc/yum.conf. This file contains one mandatory [main] section, which allows you to set Yum options that have global effect, and can also contain one or more [repository] sections, which allow you to set repository-specific options. However, it is recommended to define individual repositories in new or existing .repo files in the /etc/yum.repos.d/directory. The values you define in the [main] section of the /etc/yum.conf file can override values set in individual [repository] sections.
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 the /etc/yum.repos.d/ directory so that dynamic version and architecture values are handled correctly;
  • add, enable, and disable Yum repositories on the command line; and,
  • set up your own custom Yum repository.

7.4.1. Setting [main] Options

The /etc/yum.conf configuration file contains exactly one [main] section, and while some of the key-value pairs in this section affect how yum operates, others affect how Yum treats repositories. You can add many additional options under the [main] section heading in /etc/yum.conf.
A sample /etc/yum.conf configuration file can look like this:
[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
The following are the most commonly-used options in the [main] section:
assumeyes=value
…where value is one of:
0yum 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=directory
…where directory is an absolute path to 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 7.4.3, “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; that is, you can enable GPG-checking on one repository while disabling it on another. Setting gpgcheck=value for an individual repository in its corresponding .repo file overrides the default if it is present in /etc/yum.conf.
For more information on GPG signature-checking, see Section B.3, “Checking a Package's Signature”.
groupremove_leaf_only=value
…where value is one of:
0yum 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.
1yum should check the dependencies of each package when removing a package group, and remove only those packages which are not required by any other package or group.
For more information on removing packages, see Intelligent 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. See the yum.conf(5) manual page 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 yum.conf(5). 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.
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=file_name
…where file_name is an absolute path to the file in which yum should write 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 i686 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 plug-ins globally.

Disabling all plug-ins is not advised

Disabling all plug-ins is not advised because certain plug-ins provide important Yum services. In particular, rhnplugin provides support for RHN Classic, and product-id and subscription-manager plug-ins provide support for the certificate-based Content Delivery Network (CDN). Disabling plug-ins globally is provided as a convenience option, and is generally only recommended when diagnosing a potential problem with Yum.
1 — Enable all Yum plug-ins globally. With plugins=1, you can still disable a specific Yum plug-in by setting enabled=0 in that plug-in's configuration file.
For more information about various Yum plug-ins, see Section 7.5, “Yum Plug-ins”. For further information on controlling plug-ins, see Section 7.5.1, “Enabling, Configuring, and Disabling Yum Plug-ins”.
reposdir=directory
…where directory is an absolute path to the directory where .repo files are located. All .repo files contain repository information (similar to the [repository] sections 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. 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.
For a complete list of available [main] options, see the [main] OPTIONS section of the yum.conf(5) manual page.

7.4.2. Setting [repository] Options

The [repository] sections, where repository is a unique repository ID such as my_personal_repo (spaces are not permitted), allow you to define individual Yum repositories. To avoid conflicts, custom repositories should not use names used by Red Hat repositories.
The following is a bare-minimum example of the form a [repository] section takes:
[repository]
name=repository_name
baseurl=repository_url
Every [repository] section must contain the following directives:
name=repository_name
…where repository_name is a human-readable string describing the repository.
baseurl=repository_url
…where repository_url is a URL to the directory where the repodata directory of a repository is located:
  • If the repository is available over HTTP, use: http://path/to/repo
  • 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 user name and password by prepending it to the URL as username:password@link. For example, if a repository on http://www.example.com/repo/ requires a user name of user and a password of password, then the baseurl link could be specified as http://user:password@www.example.com/repo/.
Usually this URL is an HTTP link, such as:
baseurl=http://path/to/repo/releases/$releasever/server/$basearch/os/
Note that Yum always expands the $releasever, $arch, and $basearch variables in URLs. For more information about Yum variables, see Section 7.4.3, “Using Yum Variables”.
Another useful [repository] directive is the following:
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 by passing either the --enablerepo=repo_name or --disablerepo=repo_name option to yum, or through the Add/Remove Software window of the PackageKit utility.
Many more [repository] options exist. For a complete list, see the [repository] OPTIONS section of the yum.conf(5) manual page.

Example 7.5. A sample /etc/yum.repos.d/redhat.repo file

The following is a sample /etc/yum.repos.d/redhat.repo file:
#
# Red Hat Repositories
# Managed by (rhsm) subscription-manager
#

[red-hat-enterprise-linux-scalable-file-system-for-rhel-6-entitlement-rpms]
name = Red Hat Enterprise Linux Scalable File System (for RHEL 6 Entitlement) (RPMs)
baseurl = https://cdn.redhat.com/content/dist/rhel/entitlement-6/releases/$releasever/$basearch/scalablefilesystem/os
enabled = 1
gpgcheck = 1
gpgkey = file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release
sslverify = 1
sslcacert = /etc/rhsm/ca/redhat-uep.pem
sslclientkey = /etc/pki/entitlement/key.pem
sslclientcert = /etc/pki/entitlement/11300387955690106.pem

[red-hat-enterprise-linux-scalable-file-system-for-rhel-6-entitlement-source-rpms]
name = Red Hat Enterprise Linux Scalable File System (for RHEL 6 Entitlement) (Source RPMs)
baseurl = https://cdn.redhat.com/content/dist/rhel/entitlement-6/releases/$releasever/$basearch/scalablefilesystem/source/SRPMS
enabled = 0
gpgcheck = 1
gpgkey = file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release
sslverify = 1
sslcacert = /etc/rhsm/ca/redhat-uep.pem
sslclientkey = /etc/pki/entitlement/key.pem
sslclientcert = /etc/pki/entitlement/11300387955690106.pem

[red-hat-enterprise-linux-scalable-file-system-for-rhel-6-entitlement-debug-rpms]
name = Red Hat Enterprise Linux Scalable File System (for RHEL 6 Entitlement) (Debug RPMs)
baseurl = https://cdn.redhat.com/content/dist/rhel/entitlement-6/releases/$releasever/$basearch/scalablefilesystem/debug
enabled = 0
gpgcheck = 1
gpgkey = file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release
sslverify = 1
sslcacert = /etc/rhsm/ca/redhat-uep.pem
sslclientkey = /etc/pki/entitlement/key.pem
sslclientcert = /etc/pki/entitlement/11300387955690106.pem

7.4.3. Using Yum Variables

You can use and reference the following built-in variables in yum commands and in all Yum configuration files (that is, /etc/yum.conf and all .repo files in the /etc/yum.repos.d/ directory):
$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. The value of $releasever typically consists of the major release number and the variant of Red Hat Enterprise Linux, for example 6Client, or 6Server.
$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 i686 and x86_64.
$basearch
You can use $basearch to reference the base architecture of the system. For example, i686 machines 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.
To define a custom variable or to override the value of an existing one, create a file with the same name as the variable (without the $ sign) in the /etc/yum/vars/ directory, and add the desired value on its first line.
For example, repository descriptions often include the operating system name. To define a new variable called $osname, create a new file with Red Hat Enterprise Linux on the first line and save it as /etc/yum/vars/osname:
~]# echo "Red Hat Enterprise Linux" > /etc/yum/vars/osname
Instead of Red Hat Enterprise Linux 6, you can now use the following in the .repo files:
name=$osname $releasever

7.4.4. Viewing the Current Configuration

To display the current values of global Yum options (that is, the options specified in the [main] section of the /etc/yum.conf file), run the yum-config-manager with no command-line options:
yum-config-manager
To list the content of a different configuration section or sections, use the command in the following form:
yum-config-manager section
You can also use a glob expression to display the configuration of all matching sections:
yum-config-manager glob_expression
For example, to list all configuration options and their corresponding values, type the following at a shell prompt:
~]$ yum-config-manager main \*
Loaded plugins: product-id, refresh-packagekit, subscription-manager
================================== main ===================================
[main]
alwaysprompt = True
assumeyes = False
bandwith = 0
bugtracker_url = https://bugzilla.redhat.com/enter_bug.cgi?product=Red%20Hat%20Enterprise%20Linux%206&component=yum
cache = 0
[output truncated]

7.4.5. Adding, Enabling, and Disabling a Yum Repository

Section 7.4.2, “Setting [repository] Options” described various options you can use to define a Yum repository. This section explains how to add, enable, and disable a repository by using the yum-config-manager command.

The /etc/yum.repos.d/redhat.repo file

When the system is registered with the certificate-based Red Hat Network, the Red Hat Subscription Manager tools are used to manage repositories in the /etc/yum.repos.d/redhat.repo file. See Chapter 5, Registering the System and Managing Subscriptions for more information how to register a system with Red Hat Network and use the Red Hat Subscription Manager tools to manage subscriptions.

Adding a Yum Repository

To define a new repository, you can either add a [repository] section to the /etc/yum.conf file, or to a .repo file in the /etc/yum.repos.d/ directory. All files with the .repo file extension in this directory are read by yum, and it is recommended to define your repositories here instead of in /etc/yum.conf.

Be careful when using untrusted software sources

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, and maintainability issues.
Yum repositories commonly provide their own .repo file. To add such a repository to your system and enable it, run the following command as root:
yum-config-manager --add-repo repository_url
…where repository_url is a link to the .repo file. For example, to add a repository located at http://www.example.com/example.repo, type the following at a shell prompt:
~]# yum-config-manager --add-repo http://www.example.com/example.repo
Loaded plugins: product-id, refresh-packagekit, subscription-manager
adding repo from: http://www.example.com/example.repo
grabbing file http://www.example.com/example.repo to /etc/yum.repos.d/example.repo
example.repo                                             |  413 B     00:00
repo saved to /etc/yum.repos.d/example.repo

Enabling a Yum Repository

To enable a particular repository or repositories, type the following at a shell prompt as root:
yum-config-manager --enable repository
…where repository is the unique repository ID (use yum repolist all to list available repository IDs). Alternatively, you can use a glob expression to enable all matching repositories:
yum-config-manager --enable glob_expression
For example, to enable repositories defined in the [example], [example-debuginfo], and [example-source]sections, type:
~]# yum-config-manager --enable example\*
Loaded plugins: product-id, refresh-packagekit, subscription-manager
============================== repo: example ==============================
[example]
bandwidth = 0
base_persistdir = /var/lib/yum/repos/x86_64/6Server
baseurl = http://www.example.com/repo/6Server/x86_64/
cache = 0
cachedir = /var/cache/yum/x86_64/6Server/example
[output truncated]
When successful, the yum-config-manager --enable command displays the current repository configuration.

Disabling a Yum Repository

To disable a Yum repository, run the following command as root:
yum-config-manager --disable repository
…where repository is the unique repository ID (use yum repolist all to list available repository IDs). Similarly to yum-config-manager --enable, you can use a glob expression to disable all matching repositories at the same time:
yum-config-manager --disable glob_expression
When successful, the yum-config-manager --disable command displays the current configuration.

7.4.6. Creating a Yum Repository

To set up a Yum repository, follow these steps:
  1. Install the createrepo package. To do so, type the following at a shell prompt as root:
    yum install createrepo
  2. Copy all packages that you want to have in your repository into one directory, such as /mnt/local_repo/.
  3. Change to this directory and run the following command:
    createrepo --database /mnt/local_repo
    This creates the necessary metadata for your Yum repository, as well as the sqlite database for speeding up yum operations.

    Using the createrepo command on Red Hat Enterprise Linux 5

    Compared to Red Hat Enterprise Linux 5, RPM packages for Red Hat Enterprise Linux 6 are compressed with the XZ lossless data compression format and can be signed with newer hash algorithms like SHA-256. Consequently, it is not recommended to use the createrepo command on Red Hat Enterprise Linux 5 to create the package metadata for Red Hat Enterprise Linux 6.

7.4.7. Working with Yum Cache

By default, yum deletes downloaded data files when they are no longer needed after a successful operation. This minimizes the amount of storage space that yum uses. However, you can enable caching, so that the package files downloaded by yum stay in cache directories. By using cached data, you can carry out certain operations without a network connection, you can also copy packages stored in the caches and reuse them elsewhere.
Yum stores temporary files in the /var/cache/yum/$basearch/$releasever/ directory, where $basearch and $releasever are Yum variables referring to base architecture of the system and the release version of Red Hat Enterprise Linux. Each configured repository has one subdirectory. For example, the directory /var/cache/yum/$basearch/$releasever/development/packages/ holds packages downloaded from the development repository. You can find the values for the $basearch and $releasever variables in the output of the yum version command.
To change the default cache location, modify the cachedir option in the [main] section of the /etc/yum.conf configuration file. See Section 7.4, “Configuring Yum and Yum Repositories” for more information on configuring yum.

Enabling the Caches

To retain the cache of packages after a successful installation, add the following text to the [main] section of /etc/yum.conf.
keepcache = 1
Once you enabled caching, every yum operation may download package data from the configured repositories.
To download and make usable all the metadata for the currently enabled yum repositories, type:
yum makecache
This is useful if you want to make sure that the cache is fully up to date with all metadata. To set the time after which the metadata will expire, use the metadata-expire setting in /etc/yum.conf.

Using yum in Cache-only Mode

To carry out a yum command without a network connection, add the -C or --cacheonly command-line option. With this option, yum proceeds without checking any network repositories, and uses only cached files. In this mode, yum may only install packages that have been downloaded and cached by a previous operation.
For instance, to list packages that use the currently cached data with names that contain “gstreamer”, enter the following command:
yum -C list gstreamer*

Clearing the yum Caches

It is often useful to remove entries accumulated in the /var/cache/yum/ directory. If you remove a package from the cache, you do not affect the copy of the software installed on your system. To remove all entries for currently enabled repositories from the cache, type the following as a root:
yum clean all
There are various ways to invoke yum in clean mode depending on the type of cached data you want to remove. See Table 7.3, “Available yum clean options” for a complete list of available configuration options.

Table 7.3. Available yum clean options

OptionDescription
expire-cacheeliminates time records of the metadata and mirrorlists download for each repository. This forces yum to revalidate the cache for each repository the next time it is used.
packageseliminates any cached packages from the system
headerseliminates all header files that previous versions of yum used for dependency resolution
metadataeliminates all files that yum uses to determine the remote availability of packages. These metadata are downloaded again the next time yum is run.
dbcacheeliminates the sqlite cache used for faster access to metadata. Using this option will force yum to download the sqlite metadata the next time it is run. This does not apply for repositories that contain only .xml data, in that case, sqlite data are deleted but without subsequent download
rpmdbeliminates any cached data from the local rpmdb
pluginsenabled plugins are forced to eliminate their cached data
allremoves all of the above
The expire-cache option is most preferred from the above list. In many cases, it is a sufficient and much faster replacement for clean all.

7.4.8. Adding the Optional and Supplementary Repositories

Optional and Supplementary subscription channels provide additional software packages for Red Hat Enterprise Linux that cover open source licensed software (in the Optional channel) and proprietary licensed software (in the Supplementary channel).
Before subscribing to the Optional and Supplementary channels see the Scope of Coverage Details. If you decide to install packages from these channels, follow the steps documented in the article called How to access Optional and Supplementary channels, and -devel packages using Red Hat Subscription Manager (RHSM)? on the Red Hat Customer Portal.

7.5. Yum Plug-ins

Yum provides plug-ins that extend and enhance its operations. Certain plug-ins are installed by default. Yum always informs you which plug-ins, if any, are loaded and active whenever you call any yum command. For example:
~]# yum info yum
Loaded plugins: product-id, refresh-packagekit, subscription-manager
[output truncated]
Note that the plug-in names which follow Loaded plugins are the names you can provide to the --disableplugins=plugin_name option.

7.5.1. Enabling, Configuring, and Disabling Yum Plug-ins

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

Disabling all plug-ins is not advised

Disabling all plug-ins is not advised because certain plug-ins provide important Yum services. In particular, rhnplugin provides support for RHN Classic, and product-id and subscription-manager plug-ins provide support for the certificate-based Content Delivery Network (CDN). Disabling plug-ins globally is provided as a convenience option, and is generally only recommended when diagnosing a potential problem with Yum.
Every installed plug-in has its own configuration file in the /etc/yum/pluginconf.d/ directory. You can set plug-in specific options in these files. For example, here is the refresh-packagekit plug-in's refresh-packagekit.conf configuration file:
[main]
enabled=1
Plug-in 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 plug-in is enabled when you run yum commands.
If you disable all plug-ins by setting enabled=0 in /etc/yum.conf, then all plug-ins are disabled regardless of whether they are enabled in their individual configuration files.
If you merely want to disable all Yum plug-ins for a single yum command, use the --noplugins option.
If you want to disable one or more Yum plug-ins for a single yum command, add the --disableplugin=plugin_name option to the command. For example, to disable the presto plug-in while updating a system, type:
~]# yum update --disableplugin=presto
The plug-in 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 plug-ins by separating their names with commas. In addition, you can match multiple plug-in names or shorten long ones by using glob expressions:
~]# yum update --disableplugin=presto,refresh-pack*

7.5.2. Installing Additional Yum Plug-ins

Yum plug-ins usually adhere to the yum-plugin-plugin_name package-naming convention, but not always: the package which provides the presto plug-in is named yum-presto, for example. You can install a Yum plug-in in the same way you install other packages. For instance, to install the security plug-in, type the following at a shell prompt:
~]# yum install yum-plugin-security

7.5.3. Plug-in Descriptions

The following list provides descriptions of a few useful Yum plug-ins:
kabi (kabi-yum-plugins)
The kabi plug-in checks whether a driver update package conforms with official Red Hat kernel Application Binary Interface (kABI). With this plug-in enabled, when a user attempts to install a package that uses kernel symbols which are not on a whitelist, a warning message is written to the system log. Additionally, configuring the plug-in to run in enforcing mode prevents such packages from being installed at all.
To configure the kabi plug-in, edit the configuration file located in /etc/yum/pluginconf.d/kabi.conf. See Table 7.4, “Supported kabi.conf directives” for a list of directives that can be used in the [main] section.

Table 7.4. Supported kabi.conf directives

Directive Description
enabled=value Allows you to enable or disable the plug-in. The value must be either 1 (enabled), or 0 (disabled). When installed, the plug-in is enabled by default.
whitelists=directory Allows you to specify the directory in which the files with supported kernel symbols are located. By default, the kabi plug-in uses files provided by the kernel-abi-whitelists package (that is, the /lib/modules/kabi/ directory).
enforce=value Allows you to enable or disable enforcing mode. The value must be either 1 (enabled), or 0 (disabled). By default, this option is commented out and the kabi plug-in only displays a warning message.
presto (yum-presto)
The presto plug-in 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 to apply the difference to the currently-installed package and thus create the full, updated package. This process takes CPU time on the installing machine. Using delta RPMs is therefore a compromise between time-to-download, which depends on the network connection, and time-to-rebuild, which is CPU-bound. Using the presto plug-in is recommended for fast machines and systems with slower network connections, while slower machines on very fast connections benefit more from downloading normal RPM packages, that is, by disabling presto.
product-id (subscription-manager)
The product-id plug-in manages product identity certificates for products installed from the Content Delivery Network. The product-id plug-in is installed by default.
refresh-packagekit (PackageKit-yum-plugin)
The refresh-packagekit plug-in updates metadata for PackageKit whenever yum is run. The refresh-packagekit plug-in is installed by default.
rhnplugin (yum-rhn-plugin)
The rhnplugin provides support for connecting to RHN Classic. This allows systems registered with RHN Classic to update and install packages from this system. Note that RHN Classic is only provided for older Red Hat Enterprise Linux systems (that is, Red Hat Enterprise Linux 4.x, Red Hat Enterprise Linux 5.x, and Satellite 5.x) in order to migrate them over to Red Hat Enterprise Linux 6. The rhnplugin is installed by default.
See the rhnplugin(8) manual page for more information about the plug-in.
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 plug-in, which extends yum with a set of highly-useful security-related commands, subcommands and options.
You can check for security-related updates as follows:
~]# yum check-update --security
Loaded plugins: product-id, refresh-packagekit, security, subscription-manager
Updating Red Hat repositories.
INFO:rhsm-app.repolib:repos updated: 0
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 advisory 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 probably want to use update-minimal to reduce the risk incurred by updating packages as much as possible.
See the yum-security(8) manual page for usage details and further explanation of the enhancements the security plug-in adds to yum.
subscription-manager (subscription-manager)
The subscription-manager plug-in provides support for connecting to Red Hat Network. This allows systems registered with Red Hat Network to update and install packages from the certificate-based Content Delivery Network. The subscription-manager plug-in is installed by default.
See Chapter 5, Registering the System and Managing Subscriptions for more information how to manage product subscriptions and entitlements.
yum-downloadonly (yum-plugin-downloadonly)
The yum-downloadonly plug-in provides the --downloadonly command-line option which can be used to download packages from Red Hat Network or a configured Yum repository without installing the packages.
To install the package, follow the instructions in Section 7.5.2, “Installing Additional Yum Plug-ins”. After the installation, see the contents of the /etc/yum/pluginconf.d/downloadonly.conf file to ensure that the plug-in is enabled:
~]$ cat /etc/yum/pluginconf.d/downloadonly.conf
[main]
enabled=1
In the following example, the yum install --downloadonly command is run to download the latest version of the httpd package, without installing it:
~]# yum install httpd --downloadonly
Loaded plugins: downloadonly, product-id, refresh-packagekit, rhnplugin,
              : subscription-manager
Updating Red Hat repositories.
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package httpd.x86_64 0:2.2.15-9.el6_1.2 will be updated
---> Package httpd.x86_64 0:2.2.15-15.el6_2.1 will be an update
--> Processing Dependency: httpd-tools = 2.2.15-15.el6_2.1 for package: httpd-2.2.15-15.el6_2.1.x86_64
--> Running transaction check
---> Package httpd-tools.x86_64 0:2.2.15-9.el6_1.2 will be updated
---> Package httpd-tools.x86_64 0:2.2.15-15.el6_2.1 will be an update
--> Finished Dependency Resolution

Dependencies Resolved

================================================================================
 Package        Arch      Version                 Repository               Size
================================================================================
Updating:
 httpd          x86_64    2.2.15-15.el6_2.1       rhel-x86_64-server-6    812 k
Updating for dependencies:
 httpd-tools    x86_64    2.2.15-15.el6_2.1       rhel-x86_64-server-6     70 k

Transaction Summary
================================================================================
Upgrade       2 Package(s)

Total download size: 882 k
Is this ok [y/N]: y
Downloading Packages:
(1/2): httpd-2.2.15-15.el6_2.1.x86_64.rpm                | 812 kB     00:00
(2/2): httpd-tools-2.2.15-15.el6_2.1.x86_64.rpm          |  70 kB     00:00
--------------------------------------------------------------------------------
Total                                           301 kB/s | 882 kB     00:02


exiting because --downloadonly specified
By default, packages downloaded using the --downloadonly option are saved in one of the subdirectories of the /var/cache/yum directory, depending on the Red Hat Enterprise Linux variant and architecture.
If you want to specify an alternate directory to save the packages, pass the --downloaddir option along with --downloadonly:
~]# yum install --downloadonly --downloaddir=/path/to/directory httpd

Note

As an alternative to the yum-downloadonly plugin — to download packages without installing them — you can use the yumdownloader utility that is provided by the yum-utils package.

7.6. Additional Resources

For more information on how to manage software packages on Red Hat Enterprise Linux, see the resources listed below.

Installed Documentation

  • yum(8) — The manual page for the yum command-line utility provides a complete list of supported options and commands.
  • yumdb(8) — The manual page for the yumdb command-line utility documents how to use this tool to query and, if necessary, alter the yum database.
  • yum.conf(5) — The manual page named yum.conf documents available yum configuration options.
  • yum-utils(1) — The manual page named yum-utils lists and briefly describes additional utilities for managing yum configuration, manipulating repositories, and working with yum database.

Online Resources

  • Yum Guides — The Yum Guides page on the project home page provides links to further documentation.
  • Red Hat Access Labs — The Red Hat Access Labs includes a Yum Repository Configuration Helper.

See Also

  • Chapter 4, Gaining Privileges documents how to gain administrative privileges by using the su and sudo commands.
  • Appendix B, RPM describes the RPM Package Manager (RPM), the packaging system used by Red Hat Enterprise Linux.

Chapter 8. PackageKit

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, see Section 8.3, “PackageKit Architecture”.

8.1. Updating Packages with Software Update

PackageKit displays a starburst icon in the Notification Area whenever updates are available to be installed on your system.
PackageKit's icon in the Notification Area

Figure 8.1. PackageKit's icon in the Notification Area

Clicking on the notification icon opens the Software Update window. Alternatively, you can open Software Updates by clicking SystemAdministrationSoftware 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

Figure 8.2. 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.
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. 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

Figure 8.3. Setting PackageKit's update-checking interval

8.2. Using Add/Remove Software

To find and install a new package, on the GNOME panel click on SystemAdministrationAdd/Remove Software, or run the gpk-application command at the shell prompt.
PackageKit's Add/Remove Software window

Figure 8.4. PackageKit's Add/Remove Software window

8.2.1. 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 SystemSoftware 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). You can enable or disable any of the listed Yum repositories by selecting or clearing the checkbox. Note that doing so causes PolicyKit to prompt you for superuser authentication.
The Enabled column corresponds to the enabled=<1 or 0> field in [repository] sections. When you click the checkbox, PackageKit 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.
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 default.
After making a change to the available Yum repositories, click on SystemRefresh package lists to make sure your package list is up-to-date.

8.2.2. 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 FiltersInstalled and select the Only available radio button.
Filtering out already-installed packages

Figure 8.5. Filtering out already-installed packages

Also, unless you require development files such as C header files, click FiltersDevelopment and select the Only end user files radio button. This filters out all of the <package_name>-devel packages we are not interested in.
Filtering out development packages from the list of Find results

Figure 8.6. 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 (Only graphical) or those that do not. 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. See the Fedora Licensing List for details on approved licenses.
The remaining filters can be enabled by selecting the checkboxes next to them:
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 packages
Checking Only newest packages filters out all older versions of the same package from the list of results, which is generally what we want. Note that 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.

8.2.3. Installing and Removing Packages (and Dependencies)

With the two filters selected, Only available and Only end user files, search for the screen window manager for the command line 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; 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

Figure 8.7. 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.
Select screen and click the Apply button. You will then be prompted for the superuser password; enter it, and PackageKit will install screen. After finishing the installation, PackageKit sometimes presents you with a list of your newly-installed applications and offers 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 screen, a screen manager that allows you to have multiple logins on one terminal, by typing screen at a shell prompt.
screen is a very useful utility, but we decide that we do not need it 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 FiltersInstalled, we search for screen 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.

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 behave erratically and/or crash.
Removing a package with PackageKit's Add/Remove Software window

Figure 8.8. Removing a package with PackageKit's Add/Remove Software window

8.2.4. 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

Figure 8.9. Installing the Czech Support package group

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

8.2.5. 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 SystemSoftware log, or run the gpk-log command at the shell prompt.
The Software Log Viewer shows the following information:
  • Date — the date on which the transaction was performed.
  • Action — the action that was performed during the transaction, for example Updated packages or Installed packages.
  • Details — the transaction type such as Updated, Installed, or Removed, followed by a list of affected packages.
  • Username — the name of the user who performed the action.
  • Application — the front end application that was used to perform the action, for example Update System.
Typing the name of a package in the top text entry field filters the list of transactions to those which affected that package.
Viewing the log of package management transactions with the Software Log Viewer

Figure 8.10. Viewing the log of package management transactions with the Software Log Viewer

8.3. 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 8.1, “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 8.1. 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: SystemAdministrationAdd/Remove Software
gpk-application
Software Update Perform package updates
From the GNOME panel: SystemAdministrationSoftware Update
gpk-update-viewer
Software Sources Enable and disable Yum repositories
From Add/Remove Software: SystemSoftware Sources
gpk-repo
Software Log Viewer View the transaction log
From Add/Remove Software: SystemSoftware Log
gpk-log
Software Update Preferences Set PackageKit preferences gpk-prefs
(Notification Area Alert) Alerts you when updates are available
From the GNOME panel: SystemPreferencesStartup Applications, the 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 system. On Linux systems other than Red Hat Enterprise Linux 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.
Finally, PackageKit also comes with a console-based front end called pkcon.

8.4. Additional Resources

For more information about PackageKit, see the resources listed below.

Installed Documentation

  • gpk-application(1) — The manual page containing information about the gpk-application command.
  • gpk-backend-status(1) — The manual page containing information about the gpk-backend-status command.
  • gpk-install-local-file(1) — The manual page containing information about the gpk-install-local-file command.
  • gpk-install-mime-type(1) — The manual page containing information about the gpk-install-mime-type command.
  • gpk-install-package-name(1) — The manual page containing information about the qpk-install-package-name command.
  • gpk-install-package-name(1) — The manual page containing information about the gpk-install-package-name command.
  • gpk-prefs(1) — The manual page containing information about the gpk-prefs command.
  • gpk-repo(1) — The manual page containing information about the gpk-repo command.
  • gpk-update-icon(1) — The manual page containing information about the gpk-update-icon command.
  • gpk-update-viewer(1) — The manual page containing information about the gpk-update-viewer command.
  • pkcon(1) and pkmon(1) — The manual pages containing information about the PackageKit console client.
  • pkgenpack(1) — The manual page containing information about the PackageKit Pack Generator.

Online Documentation

  • PackageKit home page — The PackageKit home page listing detailed information about the PackageKit software suite.
  • PackageKit FAQ — An informative list of Frequently Asked Questions for the PackageKit software suite.

See Also



[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 off commands. They can typically be recognized by a d appended to their name, such as the packagekitd daemon. See Chapter 11, Services and Daemons for information about system services.

Part IV. Networking

This part describes how to configure the network on Red Hat Enterprise Linux.

Chapter 9. NetworkManager

NetworkManager is a dynamic network control and configuration system that attempts to keep network devices and connections up and active when they are available. NetworkManager consists of a core daemon, a GNOME Notification Area applet that provides network status information, and graphical configuration tools that can create, edit and remove connections and interfaces. NetworkManager can be used to configure the following types of connections: Ethernet, wireless, mobile broadband (such as cellular 3G), and DSL and PPPoE (Point-to-Point over Ethernet). In addition, NetworkManager allows for the configuration of network aliases, static routes, DNS information and VPN connections, as well as many connection-specific parameters. Finally, NetworkManager provides a rich API via D-Bus which allows applications to query and control network configuration and state.
Previous versions of Red Hat Enterprise Linux included the Network Administration Tool, which was commonly known as system-config-network after its command-line invocation. In Red Hat Enterprise Linux 6, NetworkManager replaces the former Network Administration Tool while providing enhanced functionality, such as user-specific and mobile broadband configuration. It is also possible to configure the network in Red Hat Enterprise Linux 6 by editing interface configuration files; see Chapter 10, Network Interfaces for more information.
NetworkManager may be installed by default on your version of Red Hat Enterprise Linux. To ensure that it is, run the following command as root:
~]# yum install NetworkManager

9.1. The NetworkManager Daemon

The NetworkManager daemon runs with root privileges and is usually configured to start up at boot time. You can determine whether the NetworkManager daemon is running by entering this command as root:
~]# service NetworkManager status
    NetworkManager (pid  1527) is running...
The service command will report NetworkManager is stopped if the NetworkManager service is not running. To start it for the current session:
~]# service NetworkManager start
Run the chkconfig command to ensure that NetworkManager starts up every time the system boots:
~]# chkconfig NetworkManager on
For more information on starting, stopping and managing services and runlevels, see Chapter 11, Services and Daemons.

9.2. Interacting with NetworkManager

Users do not interact with the NetworkManager system service directly. Instead, you can perform network configuration tasks via NetworkManager's Notification Area applet. The applet has multiple states that serve as visual indicators for the type of connection you are currently using. Hover the pointer over the applet icon for tooltip information on the current connection state.

Figure 9.1. NetworkManager applet states

If you do not see the NetworkManager applet in the GNOME panel, and assuming that the NetworkManager package is installed on your system, you can start the applet by running the following command as a normal user (not root):
~]$ nm-applet &
After running this command, the applet appears in your Notification Area. You can ensure that the applet runs each time you log in by clicking SystemPreferencesStartup Applications to open the Startup Applications Preferences window. Then, select the Startup Programs tab and check the box next to NetworkManager.

9.2.1. Connecting to a Network

When you left-click on the applet icon, you are presented with:
  • a list of categorized networks you are currently connected to (such as Wired and Wireless);
  • a list of all Available Networks that NetworkManager has detected;
  • options for connecting to any configured Virtual Private Networks (VPNs); and,
  • options for connecting to hidden or new wireless networks.
If you are connected to a network, its name is presented in bold typeface under its network type, such as Wired or Wireless. When many networks are available, such as wireless access points, the More networks expandable menu entry appears.

Figure 9.2. The NetworkManager applet's left-click menu, showing all available and connected-to networks

9.2.2. Configuring New and Editing Existing Connections

Next, right-click on the NetworkManager applet to open its context menu, which is the main point of entry for interacting with NetworkManager to configure connections.

Figure 9.3. The NetworkManager applet's context menu

Ensure that the Enable Networking box is checked. If the system has detected a wireless card, then you will also see an Enable Wireless menu option. Check the Enable Wireless checkbox as well. NetworkManager notifies you of network connection status changes if you check the Enable Notifications box. Clicking the Connection Information entry presents an informative Connection Information window that lists the connection type and interface, your IP address and routing details, and so on.
Finally, clicking on Edit Connections opens the Network Connections window, from where you can perform most of your network configuration tasks. Note that this window can also be opened by running, as a normal user:
~]$ nm-connection-editor &

Figure 9.4. Configure networks using the Network Connections window

There is an arrow head symbol to the left which can be clicked to hide and reveal entries as needed. To create a new connection, click the Add button to view the selection list, select the connection type and click the Create button. Alternatively, to edit an existing connection select the interface name from the list and click the Edit button.
Then, to configure:

9.2.3. Connecting to a Network Automatically

For any connection type you add or configure, you can choose whether you want NetworkManager to try to connect to that network automatically when it is available.

Procedure 9.1. Configuring NetworkManager to Connect to a Network Automatically When Detected

  1. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  2. Click the arrow head if necessary to reveal the list of connections.
  3. Select the specific connection that you want to configure and click Edit.
  4. Check Connect automatically to cause NetworkManager to auto-connect to the connection whenever NetworkManager detects that it is available. Uncheck the checkbox if you do not want NetworkManager to connect automatically. If the box is unchecked, you will have to select that connection manually in the NetworkManager applet's left-click menu to cause it to connect.

9.2.4. User and System Connections

NetworkManager connections are always either user connections or system connections. Depending on the system-specific policy that the administrator has configured, users may need root privileges to create and modify system connections. NetworkManager's default policy enables users to create and modify user connections, but requires them to have root privileges to add, modify or delete system connections.
User connections are so-called because they are specific to the user who creates them. In contrast to system connections, whose configurations are stored under the /etc/sysconfig/network-scripts/ directory (mainly in ifcfg-<network_type> interface configuration files), user connection settings are stored in the GConf configuration database and the GNOME keyring, and are only available during login sessions for the user who created them. Thus, logging out of the desktop session causes user-specific connections to become unavailable.

Increase security by making VPN connections user-specific

Because NetworkManager uses the GConf and GNOME keyring applications to store user connection settings, and because these settings are specific to your desktop session, it is highly recommended to configure your personal VPN connections as user connections. If you do so, other Non-root users on the system cannot view or access these connections in any way.
System connections, on the other hand, become available at boot time and can be used by other users on the system without first logging in to a desktop session.
NetworkManager can quickly and conveniently convert user to system connections and vice versa. Converting a user connection to a system connection causes NetworkManager to create the relevant interface configuration files under the /etc/sysconfig/network-scripts/ directory, and to delete the GConf settings from the user's session. Conversely, converting a system to a user-specific connection causes NetworkManager to remove the system-wide configuration files and create the corresponding GConf/GNOME keyring settings.

Figure 9.5. The Available to all users checkbox controls whether connections are user-specific or system-wide

Procedure 9.2. Changing a Connection to be User-Specific instead of System-Wide, or Vice-Versa

Root privileges may be required

Depending on the system's policy, you may need root privileges on the system in order to change whether a connection is user-specific or system-wide.
  1. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  2. If needed, select the arrow head (on the left hand side) to hide and reveal the types of available network connections.
  3. Select the specific connection that you want to configure and click Edit.
  4. Check the Available to all users checkbox to ask NetworkManager to make the connection a system-wide connection. Depending on system policy, you may then be prompted for the root password by the PolicyKit application. If so, enter the root password to finalize the change.
    Conversely, uncheck the Available to all users checkbox to make the connection user-specific.

9.3. Establishing Connections

9.3.1. Establishing a Wired (Ethernet) Connection

To establish a wired network connection, Right-click on the NetworkManager applet to open its context menu, ensure that the Enable Networking box is checked, then click on Edit Connections. This opens the Network Connections window. Note that this window can also be opened by running, as a normal user:
~]$ nm-connection-editor &
You can click on the arrow head to reveal and hide the list of connections as needed.

Figure 9.6. The Network Connections window showing the newly created System eth0 connection

The system startup scripts create and configure a single wired connection called System eth0 by default on all systems. Although you can edit System eth0, creating a new wired connection for your custom settings is recommended. You can create a new wired connection by clicking the Add button, selecting the Wired entry from the list that appears and then clicking the Create button.

Figure 9.7. Selecting a new connection type from the "Choose a Connection Type" list

The dialog for adding and editing connections is the same

When you add a new connection by clicking the Add button, a list of connection types appears. Once you have made a selection and clicked on the Create button, NetworkManager creates a new configuration file for that connection and then opens the same dialog that is used for editing an existing connection. There is no difference between these dialogs. In effect, you are always editing a connection; the difference only lies in whether that connection previously existed or was just created by NetworkManager when you clicked Create.

Figure 9.8.  Editing the newly created Wired connection System eth0

Configuring the Connection Name, Auto-Connect Behavior, and Availability Settings

Three settings in the Editing dialog are common to all connection types:
  • Connection name — Enter a descriptive name for your network connection. This name will be used to list this connection in the Wired section of the Network Connections window.
  • Connect automatically — Check this box if you want NetworkManager to auto-connect to this connection when it is available. See Section 9.2.3, “Connecting to a Network Automatically” for more information.
  • Available to all users — Check this box to create a connection available to all users on the system. Changing this setting may require root privileges. See Section 9.2.4, “User and System Connections” for details.

Configuring the Wired Tab

The final three configurable settings are located within the Wired tab itself: the first is a text-entry field where you can specify a MAC (Media Access Control) address, and the second allows you to specify a cloned MAC address, and third allows you to specify the MTU (Maximum Transmission Unit) value. Normally, you can leave the MAC address field blank and the MTU set to automatic. These defaults will suffice unless you are associating a wired connection with a second or specific NIC, or performing advanced networking. In such cases, see the following descriptions:
MAC Address
Network hardware such as a Network Interface Card (NIC) has a unique MAC address (Media Access Control; also known as a hardware address) that identifies it to the system. Running the ip addr command will show the MAC address associated with each interface. For example, in the following ip addr output, the MAC address for the eth0 interface (which is 52:54:00:26:9e:f1) immediately follows the link/ether keyword:
~]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
    link/ether 52:54:00:26:9e:f1 brd ff:ff:ff:ff:ff:ff
    inet 192.168.122.251/24 brd 192.168.122.255 scope global eth0
    inet6 fe80::5054:ff:fe26:9ef1/64 scope link
       valid_lft forever preferred_lft forever
A single system can have one or more NICs installed on it. The MAC address field therefore allows you to associate a specific NIC with a specific connection (or connections). As mentioned, you can determine the MAC address using the ip addr command, and then copy and paste that value into the MAC address text-entry field.
The cloned MAC address field is mostly for use in such situations were a network service has been restricted to a specific MAC address and you need to emulate that MAC address.
MTU
The MTU (Maximum Transmission Unit) value represents the size in bytes of the largest packet that the connection will use to transmit. This value defaults to 1500 when using IPv4, or a variable number 1280 or higher for IPv6, and does not generally need to be specified or changed.

Saving Your New (or Modified) Connection and Making Further Configurations

Once you have finished editing your wired connection, click the Apply button and NetworkManager will immediately save your customized configuration. Given a correct configuration, you can connect to your new or customized connection by selecting it from the NetworkManager Notification Area applet. See Section 9.2.1, “Connecting to a Network” for information on using your new or altered connection.
You can further configure an existing connection by selecting it in the Network Connections window and clicking Edit to return to the Editing dialog.
Then, to configure:

9.3.2. Establishing a Wireless Connection

This section explains how to use NetworkManager to configure a wireless (also known as Wi-Fi or 802.11a/b/g/n) connection to an Access Point.
To configure a mobile broadband (such as 3G) connection, see Section 9.3.3, “Establishing a Mobile Broadband Connection”.

Quickly Connecting to an Available Access Point

The easiest way to connect to an available access point is to left-click on the NetworkManager applet, locate the Service Set Identifier (SSID) of the access point in the list of Available networks, and click on it. If the access point is secured, a dialog prompts you for authentication.

Figure 9.9. Authenticating to a wireless access point

NetworkManager tries to auto-detect the type of security used by the access point. If there are multiple possibilities, NetworkManager guesses the security type and presents it in the Wireless security dropdown menu. To see if there are multiple choices, click the Wireless security dropdown menu and select the type of security the access point is using. If you are unsure, try connecting to each type in turn. Finally, enter the key or passphrase in the Password field. Certain password types, such as a 40-bit WEP or 128-bit WPA key, are invalid unless they are of a requisite length. The Connect button will remain inactive until you enter a key of the length required for the selected security type. To learn more about wireless security, see Section 9.3.9.2, “Configuring Wireless Security”.

Prevent Roaming On The Same Access Point

In the case of WPA and WPA2 (Personal and Enterprise), an option to select between Auto, WPA and WPA2 has been added. This option is intended for use with an access point that is offering both WPA and WPA2. Select one of the protocols if you would like to prevent roaming between the two protocols. Roaming between WPA and WPA2 on the same access point can cause loss of service.
If NetworkManager connects to the access point successfully, its applet icon will change into a graphical indicator of the wireless connection's signal strength.

Figure 9.10. Applet icon indicating a wireless connection signal strength of 75%

You can also edit the settings for one of these auto-created access point connections just as if you had added it yourself. The Wireless tab of the Network Connections window lists all of the connections you have ever tried to connect to: NetworkManager names each of them Auto <SSID>, where SSID is the Service Set identifier of the access point.

Figure 9.11. An example of access points that have previously been connected to

Connecting to a Hidden Wireless Network

All access points have a Service Set Identifier (SSID) to identify them. However, an access point may be configured not to broadcast its SSID, in which case it is hidden, and will not show up in NetworkManager's list of Available networks. You can still connect to a wireless access point that is hiding its SSID as long as you know its SSID, authentication method, and secrets.
To connect to a hidden wireless network, left-click NetworkManager's applet icon and select Connect to Hidden Wireless Network to cause a dialog to appear. If you have connected to the hidden network before, use the Connection dropdown to select it, and click Connect. If you have not, leave the Connection dropdown as New, enter the SSID of the hidden network, select its Wireless security method, enter the correct authentication secrets, and click Connect.
For more information on wireless security settings, see Section 9.3.9.2, “Configuring Wireless Security”.

Editing a Connection, or Creating a Completely New One

You can edit an existing connection that you have tried or succeeded in connecting to in the past by opening the Wireless tab of the Network Connections, selecting the connection by name (words which follow Auto refer to the SSID of an access point), and clicking Edit.
You can create a new connection by opening the Network Connections window, clicking the Add button, selecting Wireless, and clicking the Create button.
  1. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  2. Click the Add button.
  3. Select the Wireless entry from the list.
  4. Click the Create button.

Figure 9.12. Editing the newly created Wireless connection 1

Configuring the Connection Name, Auto-Connect Behavior, and Availability Settings

Three settings in the Editing dialog are common to all connection types:
  • Connection name — Enter a descriptive name for your network connection. This name will be used to list this connection in the Wireless section of the Network Connections window. By default, wireless connections are named the same as the SSID of the wireless access point. You can rename the wireless connection without affecting its ability to connect, but it is recommended to retain the SSID name.
  • Connect automatically — Check this box if you want NetworkManager to auto-connect to this connection when it is available. See Section 9.2.3, “Connecting to a Network Automatically” for more information.
  • Available to all users — Check this box to create a connection available to all users on the system. Changing this setting may require root privileges. See Section 9.2.4, “User and System Connections” for details.

Configuring the Wireless Tab

SSID
All access points have a Service Set identifier to identify them. However, an access point may be configured not to broadcast its SSID, in which case it is hidden, and will not show up in NetworkManager's list of Available networks. You can still connect to a wireless access point that is hiding its SSID as long as you know its SSID (and authentication secrets).
For information on connecting to a hidden wireless network, see Section 9.3.2, “Connecting to a Hidden Wireless Network”.
Mode
Infrastructure — Set Mode to Infrastructure if you are connecting to a dedicated wireless access point or one built into a network device such as a router or a switch.
Ad-hoc — Set Mode to Ad-hoc if you are creating a peer-to-peer network for two or more mobile devices to communicate directly with each other. If you use Ad-hoc mode, referred to as Independent Basic Service Set (IBSS) in the 802.11 standard, you must ensure that the same SSID is set for all participating wireless devices, and that they are all communicating over the same channel.
BSSID
The Basic Service Set Identifier (BSSID) is the MAC address of the specific wireless access point you are connecting to when in Infrastructure mode. This field is blank by default, and you are able to connect to a wireless access point by SSID without having to specify its BSSID. If the BSSID is specified, it will force the system to associate to a specific access point only.
For ad-hoc networks, the BSSID is generated randomly by the mac80211 subsystem when the ad-hoc network is created. It is not displayed by NetworkManager
MAC address
Like an Ethernet Network Interface Card (NIC), a wireless adapter has a unique MAC address (Media Access Control; also known as a hardware address) that identifies it to the system. Running the ip addr command will show the MAC address associated with each interface. For example, in the following ip addr output, the MAC address for the wlan0 interface (which is 00:1c:bf:02:f8:70) immediately follows the link/ether keyword:
~]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
    link/ether 52:54:00:26:9e:f1 brd ff:ff:ff:ff:ff:ff
    inet 192.168.122.251/24 brd 192.168.122.255 scope global eth0
    inet6 fe80::5054:ff:fe26:9ef1/64 scope link
       valid_lft forever preferred_lft forever
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000
    link/ether 00:1c:bf:02:f8:70 brd ff:ff:ff:ff:ff:ff
    inet 10.200.130.67/24 brd 10.200.130.255 scope global wlan0
    inet6 fe80::21c:bfff:fe02:f870/64 scope link
       valid_lft forever preferred_lft forever
A single system could have one or more wireless network adapters connected to it. The MAC address field therefore allows you to associate a specific wireless adapter with a specific connection (or connections). As mentioned, you can determine the MAC address using the ip addr command, and then copy and paste that value into the MAC address text-entry field.
MTU
The MTU (Maximum Transmission Unit) value represents the size in bytes of the largest packet that the connection will use to transmit. If set to a non-zero number, only packets of the specified size or smaller will be transmitted. Larger packets are broken up into multiple Ethernet frames. It is recommended to leave this setting on automatic.

Saving Your New (or Modified) Connection and Making Further Configurations

Once you have finished editing the wireless connection, click the Apply button and NetworkManager will immediately save your customized configuration. Given a correct configuration, you can successfully connect to your the modified connection by selecting it from the NetworkManager Notification Area applet. See Section 9.2.1, “Connecting to a Network” for details on selecting and connecting to a network.
You can further configure an existing connection by selecting it in the Network Connections window and clicking Edit to return to the Editing dialog.
Then, to configure:

9.3.3. Establishing a Mobile Broadband Connection

You can use NetworkManager's mobile broadband connection abilities to connect to the following 2G and 3G services:
  • 2G — GPRS (General Packet Radio Service) or EDGE (Enhanced Data Rates for GSM Evolution)
  • 3G — UMTS (Universal Mobile Telecommunications System) or HSPA (High Speed Packet Access)
Your computer must have a mobile broadband device (modem), which the system has discovered and recognized, in order to create the connection. Such a device may be built into your computer (as is the case on many notebooks and netbooks), or may be provided separately as internal or external hardware. Examples include PC card, USB Modem or Dongle, mobile or cellular telephone capable of acting as a modem.

Procedure 9.3. Adding a New Mobile Broadband Connection

You can configure a mobile broadband connection by opening the Network Connections window, clicking Add, and selecting Mobile Broadband from the list.
  1. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  2. Click the Add button to open the selection list. Select Mobile Broadband and then click Create. The Set up a Mobile Broadband Connection assistant appears.
  3. Under Create a connection for this mobile broadband device, choose the 2G- or 3G-capable device you want to use with the connection. If the dropdown menu is inactive, this indicates that the system was unable to detect a device capable of mobile broadband. In this case, click Cancel, ensure that you do have a mobile broadband-capable device attached and recognized by the computer and then retry this procedure. Click the Forward button.
  4. Select the country where your service provider is located from the list and click the Forward button.
  5. Select your provider from the list or enter it manually. Click the Forward button.
  6. Select your payment plan from the dropdown menu and confirm the Access Point Name (APN) is correct. Click the Forward button.
  7. Review and confirm the settings and then click the Apply button.
  8. Edit the mobile broadband-specific settings by referring to the Configuring the Mobile Broadband Tab description below .

Procedure 9.4. Editing an Existing Mobile Broadband Connection

Follow these steps to edit an existing mobile broadband connection.
  1. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  2. Select the connection you wish to edit and click the Edit button.
  3. Select the Mobile Broadband tab.
  4. Configure the connection name, auto-connect behavior, and availability settings.
    Three settings in the Editing dialog are common to all connection types:
    • Connection name — Enter a descriptive name for your network connection. This name will be used to list this connection in the Mobile Broadband section of the Network Connections window.
    • Connect automatically — Check this box if you want NetworkManager to auto-connect to this connection when it is available. See Section 9.2.3, “Connecting to a Network Automatically” for more information.
    • Available to all users — Check this box to create a connection available to all users on the system. Changing this setting may require root privileges. See Section 9.2.4, “User and System Connections” for details.
  5. Edit the mobile broadband-specific settings by referring to the Configuring the Mobile Broadband Tab description below .

Saving Your New (or Modified) Connection and Making Further Configurations

Once you have finished editing your mobile broadband connection, click the Apply button and NetworkManager will immediately save your customized configuration. Given a correct configuration, you can connect to your new or customized connection by selecting it from the NetworkManager Notification Area applet. See Section 9.2.1, “Connecting to a Network” for information on using your new or altered connection.
You can further configure an existing connection by selecting it in the Network Connections window and clicking Edit to return to the Editing dialog.
Then, to configure:

Configuring the Mobile Broadband Tab

If you have already added a new mobile broadband connection using the assistant (see Procedure 9.3, “Adding a New Mobile Broadband Connection” for instructions), you can edit the Mobile Broadband tab to disable roaming if home network is not available, assign a network ID, or instruct NetworkManager to prefer a certain technology (such as 3G or 2G) when using the connection.
Number
The number that is dialed to establish a PPP connection with the GSM-based mobile broadband network. This field may be automatically populated during the initial installation of the broadband device. You can usually leave this field blank and enter the APN instead.
Username
Enter the user name used to authenticate with the network. Some providers do not provide a user name, or accept any user name when connecting to the network.
Password
Enter the password used to authenticate with the network. Some providers do not provide a password, or accept any password.
APN
Enter the Access Point Name (APN) used to establish a connection with the GSM-based network. Entering the correct APN for a connection is important because it often determines:
  • how the user is billed for their network usage; and/or
  • whether the user has access to the Internet, an intranet, or a subnetwork.
Network ID
Entering a Network ID causes NetworkManager to force the device to register only to a specific network. This can be used to ensure the connection does not roam when it is not possible to control roaming directly.
Type
Any — The default value of Any leaves the modem to select the fastest network.
3G (UMTS/HSPA) — Force the connection to use only 3G network technologies.
2G (GPRS/EDGE) — Force the connection to use only 2G network technologies.
Prefer 3G (UMTS/HSPA) — First attempt to connect using a 3G technology such as HSPA or UMTS, and fall back to GPRS or EDGE only upon failure.
Prefer 2G (GPRS/EDGE) — First attempt to connect using a 2G technology such as GPRS or EDGE, and fall back to HSPA or UMTS only upon failure.
Allow roaming if home network is not available
Uncheck this box if you want NetworkManager to terminate the connection rather than transition from the home network to a roaming one, thereby avoiding possible roaming charges. If the box is checked, NetworkManager will attempt to maintain a good connection by transitioning from the home network to a roaming one, and vice versa.
PIN
If your device's SIM (Subscriber Identity Module) is locked with a PIN (Personal Identification Number), enter the PIN so that NetworkManager can unlock the device. NetworkManager must unlock the SIM if a PIN is required in order to use the device for any purpose.

9.3.4. Establishing a VPN Connection

Establishing an encrypted Virtual Private Network (VPN) enables you to communicate securely between your Local Area Network (LAN), and another, remote LAN. After successfully establishing a VPN connection, a VPN router or gateway performs the following actions upon the packets you transmit:
  1. it adds an Authentication Header for routing and authentication purposes;
  2. it encrypts the packet data; and,
  3. it encloses the data with an Encapsulating Security Payload (ESP), which constitutes the decryption and handling instructions.
The receiving VPN router strips the header information, decrypts the data, and routes it to its intended destination (either a workstation or other node on a network). Using a network-to-network connection, the receiving node on the local network receives the packets already decrypted and ready for processing. The encryption/decryption process in a network-to-network VPN connection is therefore transparent to clients.
Because they employ several layers of authentication and encryption, VPNs are a secure and effective means of connecting multiple remote nodes to act as a unified intranet.

Procedure 9.5. Adding a New VPN Connection

  1. You can configure a new VPN connection by opening the Network Connections window, clicking the Add button and selecting a type of VPN from the VPN section of the new connection list.
  2. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  3. Click the Add button.
  4. The Choose a Connection Type list appears.
  5. A VPN plug-in is required

    The appropriate NetworkManager VPN plug-in for the VPN type you want to configure must be installed (see Section 7.2.4, “Installing Packages” for more information on how to install new packages in Red Hat Enterprise Linux 6).
    The VPN section in the Choose a Connection Type list will not appear if you do not have a suitable plug-in installed.
  6. Select the VPN protocol for the gateway you are connecting to from the Choose a Connection Type list. The VPN protocols available for selection in the list correspond to the NetworkManager VPN plug-ins installed. For example, if the NetworkManager VPN plug-in for openswan, NetworkManager-openswan, is installed then the IPsec based VPN will be selectable from the Choose a Connection Type list.
    After selecting the correct one, press the Create button.
  7. The Editing VPN Connection 1 window then appears. This window presents settings customized for the type of VPN connection you selected in Step 6.

Procedure 9.6. Editing an Existing VPN Connection

You can configure an existing VPN connection by opening the Network Connections window and selecting the name of the connection from the list. Then click the Edit button.
  1. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  2. Select the connection you wish to edit and click the Edit button.

Figure 9.13. Editing the newly created IPsec VPN connection 1

Configuring the Connection Name, Auto-Connect Behavior, and Availability Settings

Three settings in the Editing dialog are common to all connection types:
  • Connection name — Enter a descriptive name for your network connection. This name will be used to list this connection in the VPN section of the Network Connections window.
  • Connect automatically — Check this box if you want NetworkManager to auto-connect to this connection when it is available. See Section 9.2.3, “Connecting to a Network Automatically” for more information.
  • Available to all users — Check this box to create a connection available to all users on the system. Changing this setting may require root privileges. See Section 9.2.4, “User and System Connections” for details.

Configuring the VPN Tab

Gateway
The name or IP address of the remote VPN gateway.
Group name
The name of a VPN group configured on the remote gateway.
User password
If required, enter the password used to authenticate with the VPN.
Group password
If required, enter the password used to authenticate with the VPN.
User name
If required, enter the user name used to authenticate with the VPN.
Phase1 Algorithms
If required, enter the algorithms to be used to authenticate and set up an encrypted channel.
Phase2 Algorithms
If required, enter the algorithms to be used for the IPsec negotiations.
Domain
If required, enter the Domain Name.
NAT traversal
Cisco UDP (default) — IPsec over UDP.
NAT-T — ESP encapsulation and IKE extensions are used to handle NAT Traversal.
Disabled — No special NAT measures required.
Disable Dead Peer Detection — Disable the sending of probes to the remote gateway or endpoint.

Saving Your New (or Modified) Connection and Making Further Configurations

Once you have finished editing your new VPN connection, click the Apply button and NetworkManager will immediately save your customized configuration. Given a correct configuration, you can connect to your new or customized connection by selecting it from the NetworkManager Notification Area applet. See Section 9.2.1, “Connecting to a Network” for information on using your new or altered connection.
You can further configure an existing connection by selecting it in the Network Connections window and clicking Edit to return to the Editing dialog.
Then, to configure:

9.3.5. Establishing a DSL Connection

This section is intended for those installations which have a DSL card fitted within a host rather than the external combined DSL modem router combinations typical of private consumer or SOHO installations.

Procedure 9.7. Adding a New DSL Connection

You can configure a new DSL connection by opening the Network Connections window, clicking the Add button and selecting DSL from the Hardware section of the new connection list.
  1. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  2. Click the Add button.
  3. The Choose a Connection Type list appears.
  4. Select DSL and press the Create button.
  5. The Editing DSL Connection 1 window appears.

Procedure 9.8. Editing an Existing DSL Connection

You can configure an existing DSL connection by opening the Network Connections window and selecting the name of the connection from the list. Then click the Edit button.
  1. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  2. Select the connection you wish to edit and click the Edit button.

Configuring the Connection Name, Auto-Connect Behavior, and Availability Settings

Three settings in the Editing dialog are common to all connection types:
  • Connection name — Enter a descriptive name for your network connection. This name will be used to list this connection in the DSL section of the Network Connections window.
  • Connect automatically — Check this box if you want NetworkManager to auto-connect to this connection when it is available. See Section 9.2.3, “Connecting to a Network Automatically” for more information.
  • Available to all users — Check this box to create a connection available to all users on the system. Changing this setting may require root privileges. See Section 9.2.4, “User and System Connections” for details.

Configuring the DSL Tab

Username
Enter the user name used to authenticate with the service provider.
Service
Leave blank unless otherwise directed.
Password
Enter the password supplied by the service provider.

Saving Your New (or Modified) Connection and Making Further Configurations

Once you have finished editing your DSL connection, click the Apply button and NetworkManager will immediately save your customized configuration. Given a correct configuration, you can connect to your new or customized connection by selecting it from the NetworkManager Notification Area applet. See Section 9.2.1, “Connecting to a Network” for information on using your new or altered connection.
You can further configure an existing connection by selecting it in the Network Connections window and clicking Edit to return to the Editing dialog.
Then, to configure:

9.3.6. Establishing a Bond Connection

You can use NetworkManager to create a Bond from two or more Wired or Infiniband connections. It is not necessary to create the connections to be bonded first. They can be configured as part of the process to configure the bond. You must have the MAC addresses of the interfaces available in order to complete the configuration process.

Note

NetworkManager support for bonding must be enabled by means of the NM_BOND_VLAN_ENABLED directive and then NetworkManager must be restarted. See Section 10.2.1, “Ethernet Interfaces” for an explanation of NM_CONTROLLED and the NM_BOND_VLAN_ENABLED directive. See Section 11.3.4, “Restarting a Service” for an explantion of restarting a service such as NetworkManager from the command line. Alternatively, for a graphical tool see Section 11.2.1, “Using the Service Configuration Utility”.

Procedure 9.9. Adding a New Bond Connection

You can configure a Bond connection by opening the Network Connections window, clicking Add, and selecting Bond from the list.
  1. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  2. Click the Add button to open the selection list. Select Bond and then click Create. The Editing Bond connection 1 window appears.
  3. On the Bond tab, click Add and select the type of interface you want to use with the bond connection. Click the Create button. Note that the dialog to select the slave type only comes up when you create the first slave; after that, it will automatically use that same type for all further slaves.
  4. The Editing bond0 slave 1 window appears. Fill in the MAC address of the first interface to be bonded. The first slave's MAC address will be used as the MAC address for the bond interface. If required, enter a clone MAC address to be used as the bond's MAC address. Click the Apply button.
  5. The Authenticate window appears. Enter the root password to continue. Click the Authenticate button.
  6. The name of the bonded slave appears in the Bonded Connections window. Click the Add button to add further slave connections.
  7. Review and confirm the settings and then click the Apply button.
  8. Edit the bond-specific settings by referring to Section 9.3.6, “Configuring the Bond Tab” below.

Figure 9.14. Editing the newly created Bond connection 1

Procedure 9.10. Editing an Existing Bond Connection

Follow these steps to edit an existing bond connection.
  1. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  2. Select the connection you want to edit and click the Edit button.
  3. Select the Bond tab.
  4. Configure the connection name, auto-connect behavior, and availability settings.
    Three settings in the Editing dialog are common to all connection types:
    • Connection name — Enter a descriptive name for your network connection. This name will be used to list this connection in the Bond section of the Network Connections window.
    • Connect automatically — Select this box if you want NetworkManager to auto-connect to this connection when it is available. See Section 9.2.3, “Connecting to a Network Automatically” for more information.
    • Available to all users — Select this box to create a connection available to all users on the system. Changing this setting may require root privileges. See Section 9.2.4, “User and System Connections” for details.
  5. Edit the bond-specific settings by referring to Section 9.3.6, “Configuring the Bond Tab” below.

Saving Your New (or Modified) Connection and Making Further Configurations

Once you have finished editing your bond connection, click the Apply button to save your customized configuration. Given a correct configuration, you can connect to your new or customized connection by selecting it from the NetworkManager Notification Area applet. See Section 9.2.1, “Connecting to a Network” for information on using your new or altered connection.
You can further configure an existing connection by selecting it in the Network Connections window and clicking Edit to return to the Editing dialog.
Then, to configure:

Configuring the Bond Tab

If you have already added a new bond connection (see Procedure 9.9, “Adding a New Bond Connection” for instructions), you can edit the Bond tab to set the load sharing mode and the type of link monitoring to use to detect failures of a slave connection.
Mode
The mode that is used to share traffic over the slave connections which make up the bond. The default is Round-robin. Other load sharing modes, such as 802.3ad, can be selected by means of the drop-down list.
Link Monitoring
The method of monitoring the slaves ability to carry network traffic.
The following modes of load sharing are selectable from the Mode drop-down list:
Round-robin
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. This mode might not work behind a bridge with virtual machines without additional switch configuration.
Active backup
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. Note that this is the only mode available for bonds of InfiniBand devices.
XOR
Sets an XOR (exclusive-or) policy. Transmissions are based on the selected hash policy. The default is to derive a hash by XOR of the source and destination MAC addresses multiplied by the modulo of the number of slave interfaces. In this mode traffic destined for specific peers will always be sent over the same interface. As the destination is determined by the MAC addresses this method works best for traffic to peers on the same link or local network. If traffic has to pass through a single router then this mode of traffic balancing will be suboptimal.
Broadcast
Sets a broadcast policy for fault tolerance. All transmissions are sent on all slave interfaces. This mode might not work behind a bridge with virtual machines without additional switch configuration.
802.3ad
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 network switch that is 802.3ad compliant.
Adaptive transmit load balancing
Sets an adaptive 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. This mode is only suitable for local addresses known to the kernel bonding module and therefore cannot be used behind a bridge with virtual machines.
Adaptive load balancing
Sets an Adaptive 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. This mode is only suitable for local addresses known to the kernel bonding module and therefore cannot be used behind a bridge with virtual machines.
The following types of link monitoring can be selected from the Link Monitoring drop-down list. It is a good idea to test which channel bonding module parameters work best for your bonded interfaces.
MII (Media Independent Interface)
The state of the carrier wave of the interface is monitored. This can be done by querying the driver, by querying MII registers directly, or by using ethtool to query the device. Three options are available:
Monitoring Frequency
The time interval, in milliseconds, between querying the driver or MII registers.
Link up delay
The time in milliseconds to wait before attempting to use a link that has been reported as up. This delay can be used if some gratuitous ARP requests are lost in the period immediately following the link being reported as up. This can happen during switch initialization for example.
Link down delay
The time in milliseconds to wait before changing to another link when a previously active link has been reported as down. This delay can be used if an attached switch takes a relatively long time to change to backup mode.
ARP
The address resolution protocol (ARP) is used to probe one or more peers to determine how well the link-layer connections are working. It is dependent on the device driver providing the transmit start time and the last receive time.
Two options are available:
Monitoring Frequency
The time interval, in milliseconds, between sending ARP requests.
ARP targets
A comma separated list of IP addresses to send ARP requests to.

9.3.7. Establishing a VLAN Connection

You can use NetworkManager to create a VLAN using an existing interface. Currently, at time of writing, you can only make VLANs on Ethernet devices.

Procedure 9.11. Adding a New VLAN Connection

You can configure a VLAN connection by opening the Network Connections window, clicking Add, and selecting VLAN from the list.
  1. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  2. Click the Add button to open the selection list. Select VLAN and then click Create. The Editing VLAN Connection 1 window appears.
  3. On the VLAN tab, select the parent interface from the drop-down list you want to use for the VLAN connection.
  4. Enter the VLAN ID
  5. Enter a VLAN interface name. This is the name of the VLAN interface that will be created. For example, "eth0.1" or "vlan2". (Normally this is either the parent interface name plus "." and the VLAN ID, or "vlan" plus the VLAN ID.)
  6. Review and confirm the settings and then click the Apply button.
  7. Edit the VLAN-specific settings by referring to the Configuring the VLAN Tab description below .

Procedure 9.12. Editing an Existing VLAN Connection

Follow these steps to edit an existing VLAN connection.
  1. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  2. Select the connection you wish to edit and click the Edit button.
  3. Select the VLAN tab.
  4. Configure the connection name, auto-connect behavior, and availability settings.
    Three settings in the Editing dialog are common to all connection types:
    • Connection name — Enter a descriptive name for your network connection. This name will be used to list this connection in the VLAN section of the Network Connections window.
    • Connect automatically — Check this box if you want NetworkManager to auto-connect to this connection when it is available. See Section 9.2.3, “Connecting to a Network Automatically” for more information.
    • Available to all users — Check this box to create a connection available to all users on the system. Changing this setting may require root privileges. See Section 9.2.4, “User and System Connections” for details.
  5. Edit the VLAN-specific settings by referring to the Configuring the VLAN Tab description below .

Saving Your New (or Modified) Connection and Making Further Configurations

Once you have finished editing your VLAN connection, click the Apply button and NetworkManager will immediately save your customized configuration. Given a correct configuration, you can connect to your new or customized connection by selecting it from the NetworkManager Notification Area applet. See Section 9.2.1, “Connecting to a Network” for information on using your new or altered connection.
You can further configure an existing connection by selecting it in the Network Connections window and clicking Edit to return to the Editing dialog.
Then, to configure:

Configuring the VLAN Tab

If you have already added a new VLAN connection (see Procedure 9.11, “Adding a New VLAN Connection” for instructions), you can edit the VLAN tab to set the parent interface and the VLAN ID.
Parent Interface
A previously configured interface can be selected in the drop-down list.
VLAN ID
The identification number to be used to tag the VLAN network traffic.
VLAN interface name
The name of the VLAN interface that will be created. For example, "eth0.1" or "vlan2".
Cloned MAC address
Optionally sets an alternate MAC address to use for identifying the VLAN interface. This can be used to change the source MAC address for packets sent on this VLAN.
MTU
Optionally sets a Maximum Transmission Unit (MTU) size to be used for packets to be sent over the VLAN connection.

9.3.8. Establishing an IP-over-InfiniBand (IPoIB) Connection

You can use NetworkManager to create an InfiniBand connection.

Procedure 9.13. Adding a New InfiniBand Connection

You can configure an InfiniBand connection by opening the Network Connections window, clicking Add, and selecting InfiniBand from the list.
  1. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  2. Click the Add button to open the selection list. Select InfiniBand and then click Create. The Editing InfiniBand Connection 1 window appears.
  3. On the InfiniBand tab, select the transport mode from the drop-down list you want to use for the InfiniBand connection.
  4. Enter the InfiniBand MAC address.
  5. Review and confirm the settings and then click the Apply button.
  6. Edit the InfiniBand-specific settings by referring to the Configuring the InfiniBand Tab description below .

Figure 9.15. Editing the newly created InfiniBand connection 1

Procedure 9.14. Editing an Existing InfiniBand Connection

Follow these steps to edit an existing InfiniBand connection.
  1. Right-click on the NetworkManager applet icon in the Notification Area and click Edit Connections. The Network Connections window appears.
  2. Select the connection you wish to edit and click the Edit button.
  3. Select the InfiniBand tab.
  4. Configure the connection name, auto-connect behavior, and availability settings.
    Three settings in the Editing dialog are common to all connection types:
    • Connection name — Enter a descriptive name for your network connection. This name will be used to list this connection in the InfiniBand section of the Network Connections window.
    • Connect automatically — Check this box if you want NetworkManager to auto-connect to this connection when it is available. See Section 9.2.3, “Connecting to a Network Automatically” for more information.
    • Available to all users — Check this box to create a connection available to all users on the system. Changing this setting may require root privileges. See Section 9.2.4, “User and System Connections” for details.
  5. Edit the InfiniBand-specific settings by referring to the Configuring the InfiniBand Tab description below .

Saving Your New (or Modified) Connection and Making Further Configurations

Once you have finished editing your InfiniBand connection, click the Apply button and NetworkManager will immediately save your customized configuration. Given a correct configuration, you can connect to your new or customized connection by selecting it from the NetworkManager Notification Area applet. See Section 9.2.1, “Connecting to a Network” for information on using your new or altered connection.
You can further configure an existing connection by selecting it in the Network Connections window and clicking Edit to return to the Editing dialog.
Then, to configure:

Configuring the InfiniBand Tab

If you have already added a new InfiniBand connection (see Procedure 9.13, “Adding a New InfiniBand Connection” for instructions), you can edit the InfiniBand tab to set the parent interface and the InfiniBand ID.
Transport mode
Datagram or Connected mode can be selected from the drop-down list. Select the same mode the rest of your IPoIB network is using.
Device MAC address
The MAC address of the InfiniBand capable device to be used for the InfiniBand network traffic.This hardware address field will be pre-filled if you have InfiniBand hardware installed.
MTU
Optionally sets a Maximum Transmission Unit (MTU) size to be used for packets to be sent over the InfiniBand connection.

9.3.9. Configuring Connection Settings

9.3.9.1. Configuring 802.1X Security

802.1X security is the name of the IEEE standard for port-based Network Access Control (PNAC). Simply put, 802.1X security is a way of defining a logical network out of a physical one. All clients who want to join the logical network must authenticate with the server (a router, for example) using the correct 802.1X authentication method.
802.1X security is most often associated with securing wireless networks (WLANs), but can also be used to prevent intruders with physical access to the network (LAN) from gaining entry. In the past, DHCP servers were configured not to lease IP addresses to unauthorized users, but for various reasons this practice is both impractical and insecure, and thus is no longer recommended. Instead, 802.1X security is used to ensure a logically-secure network through port-based authentication.
802.1X provides a framework for WLAN and LAN access control and serves as an envelope for carrying one of the Extensible Authentication Protocol (EAP) types. An EAP type is a protocol that defines how WLAN security is achieved on the network.
You can configure 802.1X security for a wired or wireless connection type by opening the Network Connections window (see Section 9.2.2, “Configuring New and Editing Existing Connections”) and following the applicable procedure:

Procedure 9.15. For a wired connection...

  1. Either click Add, select a new network connection for which you want to configure 802.1X security and then click Create, or select an existing connection and click Edit.
  2. Then select the 802.1X Security tab and check the Use 802.1X security for this connection checkbox to enable settings configuration.

Procedure 9.16. For a wireless connection...

  1. Either click on Add, select a new network connection for which you want to configure 802.1X security and then click Create, or select an existing connection and click Edit.
  2. Select the Wireless Security tab.
  3. Then click the Security dropdown and choose one of the following security methods: LEAP, Dynamic WEP (802.1X), or WPA & WPA2 Enterprise.
  4. See Section 9.3.9.1.1, “Configuring TLS (Transport Layer Security) Settings” for descriptions of which EAP types correspond to your selection in the Security dropdown.
9.3.9.1.1. Configuring TLS (Transport Layer Security) Settings
With Transport Layer Security, the client and server mutually authenticate using the TLS protocol. The server demonstrates that it holds a digital certificate, the client proves its own identity using its client-side certificate, and key information is exchanged. Once authentication is complete, the TLS tunnel is no longer used. Instead, the client and server use the exchanged keys to encrypt data using AES, TKIP or WEP.
The fact that certificates must be distributed to all clients who want to authenticate means that the EAP-TLS authentication method is very strong, but also more complicated to set up. Using TLS security requires the overhead of a public key infrastructure (PKI) to manage certificates. The benefit of using TLS security is that a compromised password does not allow access to the (W)LAN: an intruder must also have access to the authenticating client's private key.
NetworkManager does not determine the version of TLS supported. NetworkManager gathers the parameters entered by the user and passes them to the daemon, wpa_supplicant, that handles the procedure. It in turn uses OpenSSL to establish the TLS tunnel. OpenSSL itself negotiates the SSL/TLS protocol version. It uses the highest version both ends support.
Identity
Identity string for EAP authentication methods, such as a user name or login name.
User certificate
Click to browse for, and select, a user's certificate.
CA certificate
Click to browse for, and select, a Certificate Authority's certificate.
Private key
Click to browse for, and select, a user's private key file. Note that the key must be password protected.
Private key password
Enter the user password corresponding to the user's private key.
9.3.9.1.2. Configuring Tunneled TLS Settings
Anonymous identity
This value is used as the unencrypted identity.
CA certificate
Click to browse for, and select, a Certificate Authority's certificate.
Inner authentication
PAP — Password Authentication Protocol.
MSCHAP — Challenge Handshake Authentication Protocol.
MSCHAPv2 — Microsoft Challenge Handshake Authentication Protocol version 2.
CHAP — Challenge Handshake Authentication Protocol.
Username
Enter the user name to be used in the authentication process.
Password
Enter the password to be used in the authentication process.
9.3.9.1.3. Configuring Protected EAP (PEAP) Settings
Anonymous Identity
This value is used as the unencrypted identity.
CA certificate
Click to browse for, and select, a Certificate Authority's certificate.
PEAP version
The version of Protected EAP to use. Automatic, 0 or 1.
Inner authentication
MSCHAPv2 — Microsoft Challenge Handshake Authentication Protocol version 2.
MD5 — Message Digest 5, a cryptographic hash function.
GTC — Generic Token Card.
Username
Enter the user name to be used in the authentication process.
Password
Enter the password to be used in the authentication process.

9.3.9.2. Configuring Wireless Security

Security
None — Do not encrypt the Wi-Fi connection.
WEP 40/128-bit Key — Wired Equivalent Privacy (WEP), from the IEEE 802.11 standard. Uses a single pre-shared key (PSK).
WEP 128-bit Passphrase — An MD5 hash of the passphrase will be used to derive a WEP key.
LEAP — Lightweight Extensible Authentication Protocol, from Cisco Systems.
Dynamic WEP (802.1X) — WEP keys are changed dynamically.
WPA & WPA2 Personal — Wi-Fi Protected Access (WPA), from the draft IEEE 802.11i standard. A replacement for WEP. Wi-Fi Protected Access II (WPA2), from the 802.11i-2004 standard. Personal mode uses a pre-shared key (WPA-PSK).
WPA & WPA2 Enterprise — WPA for use with a RADIUS authentication server to provide IEEE 802.1X network access control.
Password
Enter the password to be used in the authentication process.

Prevent Roaming On The Same Access Point

In the case of WPA and WPA2 (Personal and Enterprise), an option to select between Auto, WPA and WPA2 has been added. This option is intended for use with an access point that is offering both WPA and WPA2. Select one of the protocols if you would like to prevent roaming between the two protocols. Roaming between WPA and WPA2 on the same access point can cause loss of service.

Figure 9.16. Editing the Wireless Security tab and selecting the WPA protocol

9.3.9.3. Configuring PPP (Point-to-Point) Settings

Configure Methods
Use point-to-point encryption (MPPE)
Microsoft Point-To-Point Encryption protocol (RFC 3078).
Allow BSD data compression
PPP BSD Compression Protocol (RFC 1977).
Allow Deflate data compression
PPP Deflate Protocol (RFC 1979).
Use TCP header compression
Compressing TCP/IP Headers for Low-Speed Serial Links (RFC 1144).
Send PPP echo packets
LCP Echo-Request and Echo-Reply Codes for loopback tests (RFC 1661).

9.3.9.4. Configuring IPv4 Settings

Figure 9.17. Editing the IPv4 Settings Tab

The IPv4 Settings tab allows you to configure the method by which you connect to the Internet and enter IP address, route, and DNS information as required. The IPv4 Settings tab is available when you create and modify one of the following connection types: wired, wireless, mobile broadband, VPN or DSL.
If you are using DHCP to obtain a dynamic IP address from a DHCP server, you can set Method to Automatic (DHCP).
Setting the Method

Available IPv4 Methods by Connection Type

When you click the Method dropdown menu, depending on the type of connection you are configuring, you are able to select one of the following IPv4 connection methods. All of the methods are listed here according to which connection type or types they are associated with.
Method
Automatic (DHCP) — Choose this option if the network you are connecting to uses a DHCP server to assign IP addresses. You do not need to fill in the DHCP client ID field.
Automatic (DHCP) addresses only — Choose this option if the network you are connecting to uses a DHCP server to assign IP addresses but you want to assign DNS servers manually.
Link-Local Only — Choose this option if the network you are connecting to does not have a DHCP server and you do not want to assign IP addresses manually. Random addresses will be selected as per RFC 3927.
Shared to other computers — Choose this option if the interface you are configuring is for sharing an Internet or WAN connection.
Wired, Wireless and DSL Connection Methods
Manual — Choose this option if the network you are connecting to does not have a DHCP server and you want to assign IP addresses manually.
Mobile Broadband Connection Methods
Automatic (PPP) — Choose this option if the network you are connecting to uses a DHCP server to assign IP addresses.
Automatic (PPP) addresses only — Choose this option if the network you are connecting to uses a DHCP server to assign IP addresses but you want to assign DNS servers manually.
VPN Connection Methods
Automatic (VPN) — Choose this option if the network you are connecting to uses a DHCP server to assign IP addresses.
Automatic (VPN) addresses only — Choose this option if the network you are connecting to uses a DHCP server to assign IP addresses but you want to assign DNS servers manually.
DSL Connection Methods
Automatic (PPPoE) — Choose this option if the network you are connecting to uses a DHCP server to assign IP addresses.
Automatic (PPPoE) addresses only — Choose this option if the network you are connecting to uses a DHCP server to assign IP addresses but you want to assign DNS servers manually.
PPPoE Specific Configuration Steps
If more than one NIC is installed, and PPPoE will only be run over one NIC but not the other, then for correct PPPoE operation it is also necessary to lock the connection to the specific Ethernet device PPPoE is supposed to be run over. To lock the connection to one specific NIC, do one of the following:
  • Enter the MAC address in nm-connection-editor for that connection. Optionally select Connect automatically and Available to all users to make the connection come up without requiring user login after system start.
  • Set the hardware-address in the [802-3-ethernet] section in the appropriate file for that connection in /etc/NetworkManager/system-connections/ as follows:
    [802-3-ethernet]
    mac-address=00:11:22:33:44:55
    Mere presence of the file in /etc/NetworkManager/system-connections/ means that it is available to all users. Ensure that autoconnect=true appears in the [connection] section for the connection to be brought up without requiring user login after system start.
For information on configuring static routes for the network connection, go to Section 9.3.9.6, “Configuring Routes”.

9.3.9.5. Configuring IPv6 Settings

Method
Ignore — Choose this option if you want to disable IPv6 settings.
Automatic — Choose this option if the network you are connecting to uses a DHCP server to assign IP addresses.
Automatic, addresses only — Choose this option if the network you are connecting to uses a DHCP server to assign IP addresses but you want to assign DNS servers manually.
Manual — Choose this option if the network you are connecting to does not have a DHCP server and you want to assign IP addresses manually.
Link-Local Only — Choose this option if the network you are connecting to does not have a DHCP server and you do not want to assign IP addresses manually. Random addresses will be selected as per RFC 4862.
Shared to other computers — Choose this option if the interface you are configuring is for sharing an Internet or WAN connection.
Addresses
DNS servers — Enter a comma separated list of DNS servers.
Search domains — Enter a comma separated list of domain controllers.
For information on configuring static routes for the network connection, go to Section 9.3.9.6, “Configuring Routes”.

9.3.9.6. Configuring Routes

A host's routing table will be automatically populated with routes to directly connected networks. The routes are learned by observing the network interfaces when they are up. This section is for entering static routes to networks or hosts which can be reached by traversing an intermediate network or connection, such as a VPN or leased line.

Figure 9.18. Configuring static network routes

Addresses
Address — The IP address of a network, sub-net or host.
Netmask — The netmask or prefix length of the IP address just entered.
Gateway — The IP address of the gateway leading to the network, sub-net or host.
Metric — A network cost, that is to say a preference value to give to this route. Lower values will be preferred over higher values.
Ignore automatically obtained routes
Select this checkbox to only use manually entered routes for this connection.
Use this connection only for resources on its network
Select this checkbox to prevent the connection from becoming the default route. Typical examples are where a connection is a VPN or a leased line to a head office and you do not want any Internet bound traffic to pass over the connection. Selecting this option means that only traffic specifically destined for routes learned automatically over the connection or entered here manually will be routed over the connection.

Chapter 10. Network Interfaces

Under Red Hat Enterprise Linux, all network communications occur between configured software interfaces and physical networking devices connected to the system.
The configuration files for network interfaces are located in the /etc/sysconfig/network-scripts/ directory. The scripts used to activate and deactivate these network interfaces are also located here. Although the number and type of interface files can differ from system to system, there are three categories of files that exist in this directory:
  1. Interface configuration files
  2. Interface control scripts
  3. Network function files
The files in each of these categories work together to enable various network devices.
This chapter explores the relationship between these files and how they are used.

10.1. Network Configuration Files

Before delving into the interface configuration files, let us first itemize the primary configuration files used in network configuration. Understanding the role these files play in setting up the network stack can be helpful when customizing a Red Hat Enterprise Linux system.
The primary network configuration files are as follows:
/etc/hosts
The main purpose of this file is to resolve host names that cannot be resolved any other way. It can also be used to resolve host names on small networks with no DNS server. Regardless of the type of network the computer is on, this file should contain a line specifying the IP address of the loopback device (127.0.0.1) as localhost.localdomain. For more information, see the hosts(5) manual page.
/etc/resolv.conf
This file specifies the IP addresses of DNS servers and the search domain. Unless configured to do otherwise, the network initialization scripts populate this file. For more information about this file, see the resolv.conf(5) manual page.
/etc/sysconfig/network
This file specifies routing and host information for all network interfaces. It is used to contain directives which are to have global effect and not to be interface specific. For more information about this file and the directives it accepts, see Section D.1.13, “/etc/sysconfig/network”.
/etc/sysconfig/network-scripts/ifcfg-interface-name
For each network interface, there is a corresponding interface configuration script. Each of these files provide information specific to a particular network interface. See Section 10.2, “Interface Configuration Files” for more information on this type of file and the directives it accepts.

Network interface names

Network interface names may be different on different hardware types. See Appendix A, Consistent Network Device Naming for more information.

The /etc/sysconfig/networking/ directory

The /etc/sysconfig/networking/ directory is used by the now deprecated Network Administration Tool (system-config-network). Its contents should not be edited manually. Using only one method for network configuration is strongly encouraged, due to the risk of configuration deletion. For more information about configuring network interfaces using graphical configuration tools, see Chapter 9, NetworkManager.

10.2. Interface Configuration Files

Interface configuration files control the software interfaces for individual network devices. As the system boots, it uses these files to determine what interfaces to bring up and how to configure them. These files are usually named ifcfg-name, where name refers to the name of the device that the configuration file controls.

10.2.1. Ethernet Interfaces

One of the most common interface files is /etc/sysconfig/network-scripts/ifcfg-eth0, which controls the first Ethernet network interface card or NIC in the system. In a system with multiple NICs, there are multiple ifcfg-ethX files (where X is a unique number corresponding to a specific interface). Because each device has its own configuration file, an administrator can control how each interface functions individually.
The following is a sample ifcfg-eth0 file for a system using a fixed IP address:
DEVICE=eth0
BOOTPROTO=none
ONBOOT=yes
NETMASK=255.255.255.0
IPADDR=10.0.1.27
USERCTL=no
The values required in an interface configuration file can change based on other values. For example, the ifcfg-eth0 file for an interface using DHCP looks different because IP information is provided by the DHCP server:
DEVICE=eth0
BOOTPROTO=dhcp
ONBOOT=yes
NetworkManager is graphical configuration tool which provides an easy way to make changes to the various network interface configuration files (see Chapter 9, NetworkManager for detailed instructions on using this tool).
However, it is also possible to manually edit the configuration files for a given network interface.
Below is a listing of the configurable parameters in an Ethernet interface configuration file:
BONDING_OPTS=parameters
sets the configuration parameters for the bonding device, and is used in /etc/sysconfig/network-scripts/ifcfg-bondN (see Section 10.2.4, “Channel Bonding Interfaces”). These parameters are identical to those used for bonding devices in /sys/class/net/bonding_device/bonding, and the module parameters for the bonding driver as described in bonding Module Directives.
This configuration method is used so that multiple bonding devices can have different configurations. In Red Hat Enterprise Linux 6, place all interface-specific bonding options after the BONDING_OPTS directive in ifcfg-name files. See Where to specify bonding module parameters for more information.
BOOTPROTO=protocol
where protocol is one of the following:
  • none — No boot-time protocol should be used.
  • bootp — The BOOTP protocol should be used.
  • dhcp — The DHCP protocol should be used.
BROADCAST=address
where address is the broadcast address. This directive is deprecated, as the value is calculated automatically with ipcalc.
DEVICE=name
where name is the name of the physical device (except for dynamically-allocated PPP devices where it is the logical name).
DHCP_HOSTNAME=name
where name is a short host name to be sent to the DHCP server. Use this option only if the DHCP server requires the client to specify a host name before receiving an IP address.
DHCPV6C=answer
where answer is one of the following:
  • yes — Use DHCP to obtain an IPv6 address for this interface.
  • no — Do not use DHCP to obtain an IPv6 address for this interface. This is the default value.
An IPv6 link-local address will still be assigned by default. The link-local address is based on the MAC address of the interface as per RFC 4862.
DHCPV6C_OPTIONS=answer
where answer is one of the following:
  • -P — Enable IPv6 prefix delegation.
  • -S — Use DHCP to obtain stateless configuration only, not addresses, for this interface.
  • -N — Restore normal operation after using the -T or -P options.
  • -T — Use DHCP to obtain a temporary IPv6 address for this interface.
  • -D — Override the default when selecting the type of DHCP Unique Identifier (DUID) to use.
    By default, the DHCP client (dhclient) creates a DHCP Unique Identifier (DUID) based on the link-layer address (DUID-LL) if it is running in stateless mode (with the -S option, to not request an address), or it creates an identifier based on the link-layer address plus a timestamp (DUID-LLT) if it is running in stateful mode (without -S, requesting an address). The -D option overrides this default, with a value of either LL or LLT.
DNS{1,2}=address
where address is a name server address to be placed in /etc/resolv.conf provided that the PEERDNS directive is not set to no.
ETHTOOL_OPTS=options
where options are any device-specific options supported by ethtool. For example, if you wanted to force 100Mb, full duplex:
ETHTOOL_OPTS="autoneg off speed 100 duplex full"
Instead of a custom initscript, use ETHTOOL_OPTS to set the interface speed and duplex settings. Custom initscripts run outside of the network init script lead to unpredictable results during a post-boot network service restart.

Set autoneg off before changing speed or duplex settings

Changing speed or duplex settings almost always requires disabling auto-negotiation with the autoneg off option. This option needs to be stated first, as the option entries are order-dependent.
See Section 10.8, “Ethtool” for more ethtool options.
HOTPLUG=answer
where answer is one of the following:
  • yes — This device should be activated when it is hot-plugged (this is the default option).
  • no — This device should not be activated when it is hot-plugged.
The HOTPLUG=no option can be used to prevent a channel bonding interface from being activated when a bonding kernel module is loaded.
See Section 10.2.4, “Channel Bonding Interfaces” for more information about channel bonding interfaces.
HWADDR=MAC-address
where MAC-address is the hardware address of the Ethernet device in the form AA:BB:CC:DD:EE:FF. This directive must be used in machines containing more than one NIC to ensure that the interfaces are assigned the correct device names regardless of the configured load order for each NIC's module. This directive should not be used in conjunction with MACADDR.

Note

  • Persistent device names are now handled by /etc/udev/rules.d/70-persistent-net.rules.
  • HWADDR must not be used with System z network devices.
  • See Section 25.3.3, "Mapping subchannels and network device names", in the Red Hat Enterprise Linux 6 Installation Guide.
IPADDR=address
where address is the IPv4 address.
IPV6ADDR=address
where address is the first static, or primary, IPv6 address on an interface.
The format is Address/Prefix-length. If no prefix length is specified, /64 is assumed. Note that this setting depends on IPV6INIT being enabled.
IPV6ADDR_SECONDARIES=address
where address is one or more, space separated, additional IPv6 addresses.
The format is Address/Prefix-length. If no prefix length is specified, /64 is assumed. Note that this setting depends on IPV6INIT being enabled.
IPV6INIT=answer
where answer is one of the following:
  • yes — Initialize this interface for IPv6 addressing.
  • no — Do not initialize this interface for IPv6 addressing. This is the default value.
    This setting is required for IPv6 static and DHCP assignment of IPv6 addresses. It does not affect IPv6 Stateless Address Autoconfiguration (SLAAC) as per RFC 4862.
    See Section D.1.13, “/etc/sysconfig/network” for information on disabling IPv6.
IPV6_AUTOCONF=answer
where answer is one of the following:
  • yes — Enable IPv6 autoconf configuration for this interface.
  • no — Disable IPv6 autoconf configuration for this interface.
If enabled, an IPv6 address will be requested using Neighbor Discovery (ND) from a router running the radvd daemon.
Note that the default value of IPV6_AUTOCONF depends on IPV6FORWARDING as follows:
  • If IPV6FORWARDING=yes, then IPV6_AUTOCONF will default to no.
  • If IPV6FORWARDING=no, then IPV6_AUTOCONF will default to yes and IPV6_ROUTER has no effect.
IPV6_MTU=value
where value is an optional dedicated MTU for this interface.
IPV6_PRIVACY=rfc3041
where rfc3041 optionally sets this interface to support RFC 3041 Privacy Extensions for Stateless Address Autoconfiguration in IPv6. Note that this setting depends on IPV6INIT option being enabled.
The default is for RFC 3041 support to be disabled. Stateless Autoconfiguration will derive addresses based on the MAC address, when available, using the modified EUI-64 method. The address is appended to a prefix but as the address is normally derived from the MAC address it is globally unique even when the prefix changes. In the case of a link-local address the prefix is fe80::/64 as per RFC 2462 IPv6 Stateless Address Autoconfiguration.
LINKDELAY=time
where time is the number of seconds to wait for link negotiation before configuring the device. The default is 5 secs. Delays in link negotiation, caused by STP for example, can be overcome by increasing this value.
MACADDR=MAC-address
where MAC-address is the hardware address of the Ethernet device in the form AA:BB:CC:DD:EE:FF.
This directive is used to assign a MAC address to an interface, overriding the one assigned to the physical NIC. This directive should not be used in conjunction with the HWADDR directive.
MASTER=bond-interface
where bond-interface is the channel bonding interface to which the Ethernet interface is linked.
This directive is used in conjunction with the SLAVE directive.
See Section 10.2.4, “Channel Bonding Interfaces” for more information about channel bonding interfaces.
NETMASK=mask
where mask is the netmask value.
NETWORK=address
where address is the network address. This directive is deprecated, as the value is calculated automatically with ipcalc.
NM_CONTROLLED=answer
where answer is one of the following:
  • yesNetworkManager is permitted to configure this device. This is the default behavior and can be omitted.
  • noNetworkManager is not permitted to configure this device.

Note

The NM_CONTROLLED directive is now, as of Red Hat Enterprise Linux 6.3, dependent on the NM_BOND_VLAN_ENABLED directive in /etc/sysconfig/network. If and only if that directive is present and is one of yes, y, or true, will NetworkManager detect and manage bonding and VLAN interfaces.
ONBOOT=answer
where answer is one of the following:
  • yes — This device should be activated at boot-time.
  • no — This device should not be activated at boot-time.
PEERDNS=answer
where answer is one of the following:
  • yes — Modify /etc/resolv.conf if the DNS directive is set, if using DHCP, or if using Microsoft's RFC 1877 IPCP extensions with PPP. In all cases yes is the default.
  • no — Do not modify /etc/resolv.conf.
SLAVE=answer
where answer is one of the following:
  • yes — This device is controlled by the channel bonding interface specified in the MASTER directive.
  • no — This device is not controlled by the channel bonding interface specified in the MASTER directive.
This directive is used in conjunction with the MASTER directive.
See Section 10.2.4, “Channel Bonding Interfaces” for more about channel bonding interfaces.
SRCADDR=address
where address is the specified source IP address for outgoing packets.
USERCTL=answer
where answer is one of the following:
  • yes — Non-root users are allowed to control this device.
  • no — Non-root users are not allowed to control this device.

10.2.2. Specific ifcfg Options for Linux on System z

SUBCHANNELS=<read_device_bus_id>, <write_device_bus_id>, <data_device_bus_id>
where <read_device_bus_id>, <write_device_bus_id>, and <data_device_bus_id> are the three device bus IDs representing a network device.
PORTNAME=myname;
where myname is the Open Systems Adapter (OSA) portname or LAN Channel Station (LCS) portnumber.
CTCPROT=answer
where answer is one of the following:
  • 0 — Compatibility mode, TCP/IP for Virtual Machines (used with non-Linux peers other than IBM S/390 and IBM System z operating systems). This is the default mode.
  • 1 — Extended mode, used for Linux-to-Linux Peers.
  • 3 — Compatibility mode for S/390 and IBM System z operating systems.
This directive is used in conjunction with the NETTYPE directive. It specifies the CTC protocol for NETTYPE='ctc'. The default is 0.
OPTION='answer'
where 'answer' is a quoted string of any valid sysfs attributes and their value. The Red Hat Enterprise Linux installer currently uses this to configure the layer mode, (layer2), and the relative port number, (portno), of QETH devices. For example:
OPTIONS='layer2=1 portno=0'

10.2.3. Required ifcfg Options for Linux on System z

NETTYPE=answer
where answer is one of the following:
  • ctc — Channel-to-Channel communication. For point-to-point TCP/IP or TTY.
  • lcs — LAN Channel Station (LCS).
  • qeth — QETH (QDIO Ethernet). This is the default network interface. It is the preferred installation method for supporting real or virtual OSA cards and HiperSockets devices.

10.2.4. Channel Bonding Interfaces

Red Hat Enterprise Linux allows administrators to bind multiple network interfaces 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.

Warning

The use of direct cable connections without network switches is not supported for bonding. The failover mechanisms described here will not work as expected without the presence of network switches. See the Red Hat Knowledgebase article Why is bonding in not supported with direct connection using crossover cables? for more information.

Note

The active-backup, balance-tlb and balance-alb modes do not require any specific configuration of the switch. Other bonding modes require configuring the switch to aggregate the links. For example, a Cisco switch requires EtherChannel for Modes 0, 2, and 3, but for Mode 4 LACP and EtherChannel are required. See the documentation supplied with your switch and the bonding.txt file in the kernel-doc package (see Section 29.9, “Additional Resources”).

10.2.4.1. Check if Bonding Kernel Module is Installed

In Red Hat Enterprise Linux 6, the bonding module is not loaded by default. You can load the module by issuing the following command as root:
~]# modprobe --first-time bonding
No visual output indicates the module was not running and has now been loaded. This activation will not persist across system restarts. See Section 29.7, “Persistent Module Loading” for an explanation of persistent module loading. Note that given a correct configuration file using the BONDING_OPTS directive, the bonding module will be loaded as required and therefore does not need to be loaded separately.
To display information about the module, issue the following command:
~]$ modinfo bonding
See the modprobe(8) man page for more command options and see Chapter 29, Working with Kernel Modules for information on loading and unloading modules.

10.2.4.2. Create a Channel Bonding Interface

To create a channel bonding interface, create a file in the /etc/sysconfig/network-scripts/ directory called ifcfg-bondN, replacing N with the number for the interface, such as 0.
The contents of the file can be identical to whatever type of interface is getting bonded, such as an Ethernet interface. The only difference is that the DEVICE directive is bondN, replacing N with the number for the interface. The NM_CONTROLLED directive can be added to prevent NetworkManager from configuring this device.

Example 10.1. Example ifcfg-bond0 interface configuration file

The following is an example of a channel bonding interface configuration file:
DEVICE=bond0
IPADDR=192.168.1.1
NETMASK=255.255.255.0
ONBOOT=yes
BOOTPROTO=none
USERCTL=no
NM_CONTROLLED=no
BONDING_OPTS="bonding parameters separated by spaces"
The MAC address of the bond will be taken from the first interface to be enslaved. It can also be specified using the HWADDR directive if required. If you want NetworkManager to control this interface, remove the NM_CONTROLLED=no directive, or set it to yes, and add TYPE=Bond and BONDING_MASTER=yes.
After the channel bonding interface is created, the network interfaces to be bound together must be configured by adding the MASTER and SLAVE directives to their configuration files. The configuration files for each of the channel-bonded interfaces can be nearly identical.

Example 10.2. Example ifcfg-ethX bonded interface configuration file

If two Ethernet interfaces are being channel bonded, both eth0 and eth1 can be as follows:
DEVICE=ethX
BOOTPROTO=none
ONBOOT=yes
MASTER=bond0
SLAVE=yes
USERCTL=no
NM_CONTROLLED=no
In this example, replace X with the numerical value for the interface.
Once the interfaces have been configured, restart the network service to bring the bond up. As root, issue the following command:
~]# service network restart
To view the status of a bond, view the /proc/ file by issuing a command in the following format:
 cat /proc/net/bonding/bondN
For example:
~]$ cat /proc/net/bonding/bond0
Ethernet Channel Bonding Driver: v3.6.0 (September 26, 2009)

Bonding Mode: load balancing (round-robin)
MII Status: down
MII Polling Interval (ms): 0
Up Delay (ms): 0
Down Delay (ms): 0
For further instructions and advice on configuring the bonding module and to view the list of bonding parameters, see Section 29.8.1, “Using Channel Bonding”.
Support for bonding was added to NetworkManager in Red Hat Enterprise Linux 6.3. See Section 10.2.1, “Ethernet Interfaces” for an explanation of NM_CONTROLLED and the NM_BOND_VLAN_ENABLED directive.

Where to specify bonding module parameters

In Red Hat Enterprise Linux 6, interface-specific parameters for the bonding kernel module must be specified as a space-separated list in the BONDING_OPTS="bonding parameters" directive in the ifcfg-bondN interface file. Do not specify options specific to a bond in /etc/modprobe.d/bonding.conf, or in the deprecated /etc/modprobe.conf file.
The max_bonds parameter is not interface specific and therefore, if required, should be specified in /etc/modprobe.d/bonding.conf as follows:
options bonding max_bonds=1
However, the max_bonds parameter should not be set when using ifcfg-bondN files with the BONDING_OPTS directive as this directive will cause the network scripts to create the bond interfaces as required.
Note that any changes to /etc/modprobe.d/bonding.conf will not take effect until the module is next loaded. A running module must first be unloaded. See Chapter 29, Working with Kernel Modules for more information on loading and unloading modules.
10.2.4.2.1. Creating Multiple Bonds
In Red Hat Enterprise Linux 6, for each bond a channel bonding interface is created including the BONDING_OPTS directive. This configuration method is used so that multiple bonding devices can have different configurations. To create multiple channel bonding interfaces, proceed as follows:
  • Create multiple ifcfg-bondN files with the BONDING_OPTS directive; this directive will cause the network scripts to create the bond interfaces as required.
  • Create, or edit existing, interface configuration files to be bonded and include the SLAVE directive.
  • Assign the interfaces to be bonded, the slave interfaces, to the channel bonding interfaces by means of the MASTER directive.

Example 10.3. Example multiple ifcfg-bondN interface configuration files

The following is an example of a channel bonding interface configuration file:
DEVICE=bondN
IPADDR=192.168.1.1
NETMASK=255.255.255.0
ONBOOT=yes
BOOTPROTO=none
USERCTL=no
NM_CONTROLLED=no
BONDING_OPTS="bonding parameters separated by spaces"
In this example, replace N with the number for the bond interface. For example, to create two bonds create two configuration files, ifcfg-bond0 and ifcfg-bond1.
Create the interfaces to be bonded as per Example 10.2, “Example ifcfg-ethX bonded interface configuration file” and assign them to the bond interfaces as required using the MASTER=bondN directive. For example, continuing on from the example above, if two interfaces per bond are required, then for two bonds create four interface configuration files and assign the first two using MASTER=bond0 and the next two using MASTER=bond1.

10.2.5. Configuring a VLAN over a Bond

This section will show configuring a VLAN over a bond consisting of two Ethernet links between a server and an Ethernet switch. The switch has a second bond to another server. Only the configuration for the first server will be shown as the other is essentially the same apart from the IP addresses.

Warning

The use of direct cable connections without network switches is not supported for bonding. The failover mechanisms described here will not work as expected without the presence of network switches. See the Red Hat Knowledgebase article Why is bonding in not supported with direct connection using crossover cables? for more information.

Note

The active-backup, balance-tlb and balance-alb modes do not require any specific configuration of the switch. Other bonding modes require configuring the switch to aggregate the links. For example, a Cisco switch requires EtherChannel for Modes 0, 2, and 3, but for Mode 4 LACP and EtherChannel are required. See the documentation supplied with your switch and the bonding.txt file in the kernel-doc package (see Section 29.9, “Additional Resources”).
Check the available interfaces on the server:
~]$ ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN qlen 1000
    link/ether 52:54:00:19:28:fe brd ff:ff:ff:ff:ff:ff
3: eth1: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN qlen 1000
    link/ether 52:54:00:f6:63:9a brd ff:ff:ff:ff:ff:ff

Procedure 10.1. Configuring the Interfaces on the Server

  1. Configure a slave interface using eth0:
    ~]# vi /etc/sysconfig/network-scripts/ifcfg-eth0
    NAME=bond0-slave0
    DEVICE=eth0 
    TYPE=Ethernet
    BOOTPROTO=none
    ONBOOT=yes
    MASTER=bond0
    SLAVE=yes
    NM_CONTROLLED=no
    The use of the NAME directive is optional. It is for display by a GUI interface, such as nm-connection-editor and nm-applet.
  2. Configure a slave interface using eth1:
    ~]# vi /etc/sysconfig/network-scripts/ifcfg-eth1
    NAME=bond0-slave1
    DEVICE=eth1
    TYPE=Ethernet
    BOOTPROTO=none
    ONBOOT=yes
    MASTER=bond0
    SLAVE=yes
    NM_CONTROLLED=no
    The use of the NAME directive is optional. It is for display by a GUI interface, such as nm-connection-editor and nm-applet.
  3. Configure a channel bonding interface ifcfg-bond0:
    ~]# vi /etc/sysconfig/network-scripts/ifcfg-bond0
    NAME=bond0
    DEVICE=bond0
    BONDING_MASTER=yes
    TYPE=Bond
    IPADDR=192.168.100.100
    NETMASK=255.255.255.0
    ONBOOT=yes
    BOOTPROTO=none
    BONDING_OPTS="mode=active-backup miimon=100"
    NM_CONTROLLED=no
    The use of the NAME directive is optional. It is for display by a GUI interface, such as nm-connection-editor and nm-applet. In this example MII is used for link monitoring, see the Section 29.8.1.1, “Bonding Module Directives” section for more information on link monitoring.
  4. Check the status of the interfaces on the server:
    ~]$ ip addr
    1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
        link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
        inet 127.0.0.1/8 scope host lo
        inet6 ::1/128 scope host 
           valid_lft forever preferred_lft forever
    2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
        link/ether 52:54:00:19:28:fe brd ff:ff:ff:ff:ff:ff
        inet6 fe80::5054:ff:fe19:28fe/64 scope link 
           valid_lft forever preferred_lft forever
    3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
        link/ether 52:54:00:f6:63:9a brd ff:ff:ff:ff:ff:ff
        inet6 fe80::5054:ff:fef6:639a/64 scope link
           valid_lft forever preferred_lft forever

Procedure 10.2. Resolving Conflicts with Interfaces

The interfaces configured as slaves should not have IP addresses assigned to them apart from the IPv6 link-local addresses (starting fe80). If you have an unexpected IP address, then there may be another configuration file with ONBOOT set to yes.
  1. If this occurs, issue the following command to list all ifcfg files that may be causing a conflict:
    ~]$ grep -r "ONBOOT=yes" /etc/sysconfig/network-scripts/ | cut -f1 -d":" | xargs grep -E "IPADDR|SLAVE"
    /etc/sysconfig/network-scripts/ifcfg-lo:IPADDR=127.0.0.1
    The above shows the expected result on a new installation. Any file having both the ONBOOT directive as well as the IPADDR or SLAVE directive will be displayed. For example, if the ifcfg-eth1 file was incorrectly configured, the display might look similar to the following:
    ~]# grep -r "ONBOOT=yes" /etc/sysconfig/network-scripts/ | cut -f1 -d":" | xargs grep -E "IPADDR|SLAVE"
    /etc/sysconfig/network-scripts/ifcfg-lo:IPADDR=127.0.0.1
    /etc/sysconfig/network-scripts/ifcfg-eth1:SLAVE=yes
    /etc/sysconfig/network-scripts/ifcfg-eth1:IPADDR=192.168.55.55
  2. Any other configuration files found should be moved to a different directory for backup, or assigned to a different interface by means of the HWADDR directive. After resolving any conflict set the interfaces down and up again or restart the network service as root:
    ~]# service network restart
    Shutting down interface bond0:                             [  OK  ]
    Shutting down loopback interface:                          [  OK  ]
    Bringing up loopback interface:                            [  OK  ]
    Bringing up interface bond0:  Determining if ip address 192.168.100.100 is already in use for device bond0...
                                                               [  OK  ]
    If you are using NetworkManager, you might need to restart it at this point to make it forget the unwanted IP address. As root:
    ~]# service NetworkManager restart

Procedure 10.3. Checking the bond on the Server

  1. Bring up the bond on the server as root:
    ~]# ifup /etc/sysconfig/network-scripts/ifcfg-bond0
    Determining if ip address 192.168.100.100 is already in use for device bond0...
  2. Check the status of the interfaces on the server:
    ~]$ ip addr
    1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN 
        link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
        inet 127.0.0.1/8 scope host lo
        inet6 ::1/128 scope host 
           valid_lft forever preferred_lft forever
    2: eth0: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP qlen 1000
        link/ether 52:54:00:19:28:fe brd ff:ff:ff:ff:ff:ff
    3: eth1: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP qlen 1000
        link/ether 52:54:00:f6:63:9a brd ff:ff:ff:ff:ff:ff
    4: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP 
        link/ether 52:54:00:19:28:fe brd ff:ff:ff:ff:ff:ff
        inet 192.168.100.100/24 brd 192.168.100.255 scope global bond0
        inet6 fe80::5054:ff:fe19:28fe/64 scope link 
           valid_lft forever preferred_lft forever
    Notice that eth0 and eth1 have master bond0 state UP and bond0 has status of MASTER,UP.
  3. View the bond configuration details:
    ~]$ cat /proc/net/bonding/bond0
    Ethernet Channel Bonding Driver: v3.6.0 (September 26, 2009)
    
    Bonding Mode: transmit load balancing
    Primary Slave: None
    Currently Active Slave: eth0
    MII Status: up
    MII Polling Interval (ms): 100
    Up Delay (ms): 0
    Down Delay (ms): 0
    
    Slave Interface: eth0
    MII Status: up
    Speed: 100 Mbps
    Duplex: full
    Link Failure Count: 0
    Permanent HW addr: 52:54:00:19:28:fe
    Slave queue ID: 0
    
    Slave Interface: eth1
    MII Status: up
    Speed: 100 Mbps
    Duplex: full
    Link Failure Count: 0
    Permanent HW addr: 52:54:00:f6:63:9a
    Slave queue ID: 0
  4. Check the routes on the server:
    ~]$ ip route
    192.168.100.0/24 dev bond0  proto kernel  scope link  src 192.168.100.100
    169.254.0.0/16 dev bond0  scope link  metric 1004

Procedure 10.4. Configuring the VLAN on the Server

Important

At the time of writing, it is important that the bond has slaves and that they are up before bringing up the VLAN interface. At the time of writing, adding a VLAN interface to a bond without slaves does not work. In Red Hat Enterprise Linux 6, setting the ONPARENT directive to yes is important to ensure that the VLAN interface does not attempt to come up before the bond is up. This is because a VLAN virtual device takes the MAC address of its parent, and when a NIC is enslaved, the bond changes its MAC address to that NIC's MAC address.

Note

A VLAN slave cannot be configured on a bond with the fail_over_mac=follow option, because the VLAN virtual device cannot change its MAC address to match the parent's new MAC address. In such a case, traffic would still be sent with the now incorrect source MAC address.
Some older network interface cards, loopback interfaces, Wimax cards, and some Infiniband devices, are said to be VLAN challenged, meaning they cannot support VLANs. This is usually because the devices cannot cope with VLAN headers and the larger MTU size associated with VLANs.
  1. Create a VLAN interface file bond0.192:
    ~]# vi /etc/sysconfig/network-scripts/ifcfg-bond0.192
    DEVICE=bond0.192
    NAME=bond0.192
    BOOTPROTO=none
    ONPARENT=yes
    IPADDR=192.168.10.1
    NETMASK=255.255.255.0
    VLAN=yes
    NM_CONTROLLED=no
  2. Bring up the VLAN interface as root:
    ~]# ifup /etc/sysconfig/network-scripts/ifcfg-bond0.192
    Determining if ip address 192.168.10.1 is already in use for device bond0.192...
  3. Enabling VLAN tagging on the network switch. Consult the documentation for the switch to see what configuration is required.
  4. Check the status of the interfaces on the server:
    ~]# ip addr
    1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
        link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
        inet 127.0.0.1/8 scope host lo
        inet6 ::1/128 scope host 
           valid_lft forever preferred_lft forever
    2: eth0: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP qlen 1000
        link/ether 52:54:00:19:28:fe brd ff:ff:ff:ff:ff:ff
    3: eth1: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP qlen 1000
        link/ether 52:54:00:f6:63:9a brd ff:ff:ff:ff:ff:ff
    4: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP 
        link/ether 52:54:00:19:28:fe brd ff:ff:ff:ff:ff:ff
        inet 192.168.100.100/24 brd 192.168.100.255 scope global bond0
        inet6 fe80::5054:ff:fe19:28fe/64 scope link 
           valid_lft forever preferred_lft forever
    5: bond0.192@bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP
        link/ether 52:54:00:19:28:fe brd ff:ff:ff:ff:ff:ff
        inet 192.168.10.1/24 brd 192.168.10.255 scope global bond0.192
        inet6 fe80::5054:ff:fe19:28fe/64 scope link
           valid_lft forever preferred_lft forever
    Notice there is now bond0.192@bond0 in the list of interfaces and the status is MASTER,UP.
  5. Check the route on the server:
    ~]$ ip route
    192.168.100.0/24 dev bond0  proto kernel  scope link  src 192.168.100.100
    192.168.10.0/24 dev bond0.192  proto kernel  scope link  src 192.168.10.1
    169.254.0.0/16 dev bond0  scope link  metric 1004 
    169.254.0.0/16 dev bond0.192  scope link  metric 1005
    Notice there is now a route for the 192.168.10.0/24 network pointing to the VLAN interface bond0.192.

Configuring the Second Server

Repeat the configuration steps for the second server, using different IP addresses but from the same subnets respectively.
Test the bond is up and the network switch is working as expected:
~]$ ping -c4 192.168.100.100
PING 192.168.100.100 (192.168.100.100) 56(84) bytes of data.
64 bytes from 192.168.100.100: icmp_seq=1 ttl=64 time=1.35 ms
64 bytes from 192.168.100.100: icmp_seq=2 ttl=64 time=0.214 ms
64 bytes from 192.168.100.100: icmp_seq=3 ttl=64 time=0.383 ms
64 bytes from 192.168.100.100: icmp_seq=4 ttl=64 time=0.396 ms

--- 192.168.100.100 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3002ms
rtt min/avg/max/mdev = 0.214/0.586/1.353/0.448 ms

Testing the VLAN

To test that the network switch is configured for the VLAN, try to ping the first servers' VLAN interface:
~]# ping -c2 192.168.10.1
PING 192.168.10.1 (192.168.10.1) 56(84) bytes of data.
64 bytes from 192.168.10.1: icmp_seq=1 ttl=64 time=0.781 ms
64 bytes from 192.168.10.1: icmp_seq=2 ttl=64 time=0.977 ms
--- 192.168.10.1 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 0.781/0.879/0.977/0.098 ms
No packet loss suggests everything is configured correctly and that the VLAN and underlying interfaces are up.

Optional Steps

  • If required, perform further tests by removing and replacing network cables one at a time to verify that failover works as expected. Make use of the ethtool utility to verify which interface is connected to which cable. For example:
    ethtool --identify ifname integer
    Where integer is the number of times to flash the LED on the network interface.
  • The bonding module does not support STP, therefore consider disabling the sending of BPDU packets from the network switch.
  • If the system is not linked to the network except over the connection just configured, consider enabling the switch port to transition directly to sending and receiving. For example on a Cisco switch, by means of the portfast command.

10.2.6. Network Bridge

A network bridge is a Link Layer device which forwards traffic between networks based on MAC addresses and is therefore also referred to as a Layer 2 device. It makes forwarding decisions based on tables of MAC addresses which it builds by learning what hosts are connected to each network. A software bridge can be used within a Linux host in order to emulate a hardware bridge, for example in virtualization applications for sharing a NIC with one or more virtual NICs. This case will be illustrated here as an example.
To create a network bridge, create a file in the /etc/sysconfig/network-scripts/ directory called ifcfg-brN, replacing N with the number for the interface, such as 0.
The contents of the file is similar to whatever type of interface is getting bridged to, such as an Ethernet interface. The differences in this example are as follows:
  • The DEVICE directive is given an interface name as its argument in the format brN, where N is replaced with the number of the interface.
  • The TYPE directive is given an argument Bridge. This directive determines the device type and the argument is case sensitive.
  • The bridge interface configuration file now has the IP address and the physical interface has only a MAC address.
  • An extra directive, DELAY=0, is added to prevent the bridge from waiting while it monitors traffic, learns where hosts are located, and builds a table of MAC addresses on which to base its filtering decisions. The default delay of 15 seconds is not needed if no routing loops are possible.
  • The NM_CONTROLLED=no should be added to the Ethernet interface to prevent NetworkManager from altering the file. It can also be added to the bridge configuration file in case future versions of NetworkManager support bridge configuration.
The following is a sample bridge interface configuration file using a static IP address:

Example 10.4. Sample ifcfg-br0 interface configuration file

DEVICE=br0
TYPE=Bridge
IPADDR=192.168.1.1
NETMASK=255.255.255.0
ONBOOT=yes
BOOTPROTO=none
NM_CONTROLLED=no
DELAY=0
To complete the bridge another interface is created, or an existing interface is modified, and pointed to the bridge interface. The following is a sample Ethernet interface configuration file pointing to a bridge interface. Configure your physical interface in /etc/sysconfig/network-scripts/ifcfg-ethX, where X is a unique number corresponding to a specific interface, as follows:

Example 10.5. Sample ifcfg-ethX interface configuration file

DEVICE=ethX
TYPE=Ethernet
HWADDR=AA:BB:CC:DD:EE:FF
BOOTPROTO=none
ONBOOT=yes
NM_CONTROLLED=no
BRIDGE=br0

Note

For the DEVICE directive, almost any interface name could be used as it does not determine the device type. Other commonly used names include tap, dummy and bond for example. TYPE=Ethernet is not strictly required. If the TYPE directive is not set, the device is treated as an Ethernet device (unless its name explicitly matches a different interface configuration file.)
You can see Section 10.2, “Interface Configuration Files” for a review of the directives and options used in network interface config files.

Warning

If you are configuring bridging on a remote host, and you are connected to that host over the physical NIC you are configuring, please consider the implications of losing connectivity before proceeding. You will lose connectivity when restarting the service and may not be able to regain connectivity if any errors have been made. Console, or out-of-band access is advised.
Restart the networking service, in order for the changes to take effect, as follows:
 service network restart 

10.2.6.1. Network Bridge with Bond

An example of a network bridge formed from two or more bonded Ethernet interfaces will now be given as this is another common application in a virtualization environment. If you are not very familiar with the configuration files for bonded interfaces then please see Section 10.2.4, “Channel Bonding Interfaces”
Create or edit two or more Ethernet interface configuration files, which are to be bonded, as follows:
DEVICE=ethX
TYPE=Ethernet
USERCTL=no
SLAVE=yes
MASTER=bond0
BOOTPROTO=none
HWADDR=AA:BB:CC:DD:EE:FF
NM_CONTROLLED=no

Note

Using ethX as the interface name is common practice but almost any name could be used. Names such as tap, dummy and bond are commonly used.
Create or edit one interface configuration file, /etc/sysconfig/network-scripts/ifcfg-bond0, as follows:
DEVICE=bond0
ONBOOT=yes
BONDING_OPTS='mode=1 miimon=100'
BRIDGE=br0
NM_CONTROLLED=no
For further instructions and advice on configuring the bonding module and to view the list of bonding parameters, see Section 29.8.1, “Using Channel Bonding”.
Create or edit one interface configuration file, /etc/sysconfig/network-scripts/ifcfg-br0, as follows:
DEVICE=br0
ONBOOT=yes
TYPE=Bridge
IPADDR=192.168.1.1
NETMASK=255.255.255.0
NM_CONTROLLED=no

Figure 10.1. A network bridge consisting of two bonded Ethernet interfaces.

We now have two or more interface configuration files with the MASTER=bond0 directive. These point to the configuration file named /etc/sysconfig/network-scripts/ifcfg-bond0, which contains the DEVICE=bond0 directive. This ifcfg-bond0 in turn points to the /etc/sysconfig/network-scripts/ifcfg-br0 configuration file, which contains the IP address, and acts as an interface to the virtual networks inside the host.
To bring up the new or recently configured interfaces, issue a command as root in the following format:
ifup device
Alternatively, restart the networking service, in order for the changes to take effect, as follows:
~]# service network restart

10.2.6.2. Network Bridge with Bonded VLAN

Virtualization servers that intend to have distinct subnets for its guests while still ensuring availability in the event of a NIC failure will often combine bonds, VLANs, and bridges. An example of this configuration will now be given. By creating a bridge on the VLAN instead of the underlying device we allow VLAN tagging to be handled entirely through the host with no need to configure the guests' interfaces.
  1. Ensure the bond and VLAN have been configured as outlined in Section 10.2.5, “Configuring a VLAN over a Bond”.
  2. Create the bridge's configuration file, ifcfg-br0:
    ~]# vi /etc/sysconfig/network-scripts/ifcfg-br0
    DEVICE=br0
    ONBOOT=yes
    TYPE=Bridge
    IPADDR=192.168.10.1
    NETMASK=255.255.255.0
    NM_CONTROLLED=no
  3. Adjust the VLAN's configuration file, ifcfg-bond0.192 from the earlier example, to use the newly created br0 as its master:
    ~]# vi /etc/sysconfig/network-scripts/ifcfg-bond0.192
    DEVICE=bond0.192
    BOOTPROTO=none
    ONPARENT=yes
    #IPADDR=192.168.10.1
    #NETMASK=255.255.255.0
    VLAN=yes
    NM_CONTROLLED=no
    BRIDGE=br0
  4. To bring up the new or recently configured interfaces, issue a command as root in the following format:
    ifup device
    Alternatively, restart the networking service, in order for the changes to take effect, as follows:
    ~]# service network restart

10.2.7. Setting Up 802.1Q VLAN Tagging

  1. If required, start the VLAN 8021q module by issuing the following command as root:
    ~]# modprobe --first-time 8021q
    No visual output indicates the module was not running and has now been loaded. Note that given a correct configuration file, the VLAN 8021q module will be loaded as required and therefore does not need to be loaded separately.
  2. Configure your physical interface in /etc/sysconfig/network-scripts/ifcfg-ethX, where X is a unique number corresponding to a specific interface, as follows:
    DEVICE=ethX
    TYPE=Ethernet
    BOOTPROTO=none
    ONBOOT=yes
  3. Configure the VLAN interface configuration in /etc/sysconfig/network-scripts. The configuration filename should be the physical interface plus a . character plus the VLAN ID number. For example, if the VLAN ID is 192, and the physical interface is eth0, then the configuration filename should be ifcfg-eth0.192:
    DEVICE=ethX.192
    BOOTPROTO=none
    ONBOOT=yes
    IPADDR=192.168.1.1
    NETMASK=255.255.255.0
    USERCTL=no
    NETWORK=192.168.1.0
    VLAN=yes
    If there is a need to configure a second VLAN, with for example, VLAN ID 193, on the same interface, eth0 , add a new file with the name eth0.193 with the VLAN configuration details.
  4. Restart the networking service, in order for the changes to take effect. Issue the following command as root:
    ~]# service network restart

10.2.8. Alias and Clone Files

Two lesser-used types of interface configuration files are alias and clone files. As the ip utility now supports assigning multiple addresses to the same interface it is no longer necessary to use this method of binding multiple addresses to the same interface. The ip command to assign an address can be repeated multiple times in order to assign multiple address. For example:
~]# ip address add 192.168.2.223/24 dev eth1
~]# ip address add 192.168.4.223/24 dev eth1
~]# ip addr
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 52:54:00:fb:77:9e brd ff:ff:ff:ff:ff:ff
    inet 192.168.2.223/24 scope global eth1
    inet 192.168.4.223/24 scope global eth1
The commands for the ip utility, sometimes referred to as iproute2 after the upstream package name, are documented in the man ip(8) page. The package name in Red Hat Enterprise Linux 6 is iproute.

Note

In Red Hat Enterprise Linux 6, NetworkManager now reads ifcfg alias files and assigns the addresses in them to their master interface, using the alias name as the address label. For example, if ifcfg-eth0 and ifcfg-eth0:1 files are present, NetworkManager reads the alias file's DEVICE line and stores this as an address label. The use of secondary addresses rather than alias is still preferred.
For new installations, users should select the Manual method on the IPv4 or IPv6 tab in NetworkManager to assign multiple IP address to the same interface. For more information on using this tool, see Chapter 9, NetworkManager.
Alias interface configuration files, which are used to bind multiple addresses to a single interface, use the ifcfg-if-name:alias-value naming scheme.
For example, an ifcfg-eth0:0 file could be configured to specify DEVICE=eth0:0 and a static IP address of 10.0.0.2, serving as an alias of an Ethernet interface already configured to receive its IP information via DHCP in ifcfg-eth0. Under this configuration, eth0 is bound to a dynamic IP address, but the same physical network card can receive requests via the fixed, 10.0.0.2 IP address.

Warning

Alias interfaces do not support DHCP.
A clone interface configuration file should use the following naming convention: ifcfg-if-name-clone-name. While an alias file allows multiple addresses for an existing interface, a clone file is used to specify additional options for an interface. For example, a standard DHCP Ethernet interface called eth0, may look similar to this:
DEVICE=eth0
ONBOOT=yes
BOOTPROTO=dhcp
Since the default value for the USERCTL directive is no if it is not specified, users cannot bring this interface up and down. To give users the ability to control the interface, create a clone by copying ifcfg-eth0 to ifcfg-eth0-user and add the following line to ifcfg-eth0-user:
USERCTL=yes
This way a user can bring up the eth0 interface using the /sbin/ifup eth0-user command because the configuration options from ifcfg-eth0 and ifcfg-eth0-user are combined. While this is a very basic example, this method can be used with a variety of options and interfaces.
It is no longer possible to create alias and clone interface configuration files using a graphical tool. However, as explained at the beginning of this section, it is no longer necessary to use this method as it is now possible to directly assign multiple IP address to the same interface. For new installations, users should select the Manual method on the IPv4 or IPv6 tab in NetworkManager to assign multiple IP address to the same interface. For more information on using this tool, see Chapter 9, NetworkManager.

10.2.9. Dialup Interfaces

If you are connecting to the Internet via a dialup connection, a configuration file is necessary for the interface.
PPP interface files are named using the following format:
ifcfg-pppX
where X is a unique number corresponding to a specific interface.
The PPP interface configuration file is created automatically when wvdial, or Kppp is used to create a dialup account. It is also possible to create and edit this file manually.
The following is a typical /etc/sysconfig/network-scripts/ifcfg-ppp0 file:
DEVICE=ppp0
NAME=test
WVDIALSECT=test
MODEMPORT=/dev/modem
LINESPEED=115200
PAPNAME=test
USERCTL=true
ONBOOT=no
PERSIST=no
DEFROUTE=yes
PEERDNS=yes
DEMAND=no
IDLETIMEOUT=600
Serial Line Internet Protocol (SLIP) is another dialup interface, although it is used less frequently. SLIP files have interface configuration file names such as ifcfg-sl0.
Other options that may be used in these files include:
DEFROUTE=answer
where answer is one of the following:
  • yes — Set this interface as the default route.
  • no — Do not set this interface as the default route.
DEMAND=answer
where answer is one of the following:
  • yes — This interface allows pppd to initiate a connection when someone attempts to use it.
  • no — A connection must be manually established for this interface.
IDLETIMEOUT=value
where value is the number of seconds of idle activity before the interface disconnects itself.
INITSTRING=string
where string is the initialization string passed to the modem device. This option is primarily used in conjunction with SLIP interfaces.
LINESPEED=value
where value is the baud rate of the device. Possible standard values include 57600, 38400, 19200, and 9600.
MODEMPORT=device
where device is the name of the serial device that is used to establish the connection for the interface.
MTU=value
where value is the Maximum Transfer Unit (MTU) setting for the interface. The MTU refers to the largest number of bytes of data a frame can carry, not counting its header information. In some dialup situations, setting this to a value of 576 results in fewer packets dropped and a slight improvement to the throughput for a connection.
NAME=name
where name is the reference to the title given to a collection of dialup connection configurations.
PAPNAME=name
where name is the user name given during the Password Authentication Protocol (PAP) exchange that occurs to allow connections to a remote system.
PERSIST=answer
where answer is one of the following:
  • yes — This interface should be kept active at all times, even if deactivated after a modem hang up.
  • no — This interface should not be kept active at all times.
REMIP=address
where address is the IP address of the remote system. This is usually left unspecified.
WVDIALSECT=name
where name associates this interface with a dialer configuration in /etc/wvdial.conf. This file contains the phone number to be dialed and other important information for the interface.

10.2.10. Other Interfaces

Other common interface configuration files include the following:
ifcfg-lo
A local loopback interface is often used in testing, as well as being used in a variety of applications that require an IP address pointing back to the same system. Any data sent to the loopback device is immediately returned to the host's network layer.

Do not manually edit the ifcfg-lo script

The loopback interface script, /etc/sysconfig/network-scripts/ifcfg-lo, should never be edited manually. Doing so can prevent the system from operating correctly.
ifcfg-irlan0
An infrared interface allows information between devices, such as a laptop and a printer, to flow over an infrared link. This works in a similar way to an Ethernet device except that it commonly occurs over a peer-to-peer connection.
ifcfg-plip0
A Parallel Line Interface Protocol (PLIP) connection works much the same way as an Ethernet device, except that it utilizes a parallel port.
Interface configuration files for Linux on System z include the following:
ifcfg-hsiN
A HiperSockets interface is an interface for high-speed TCP/IP communication within and across z/VM guest virtual machines and logical partitions (LPARs) on an IBM System z mainframe.

10.3. Interface Control Scripts

The interface control scripts activate and deactivate system interfaces. There are two primary interface control scripts that call on control scripts located in the /etc/sysconfig/network-scripts/ directory: /sbin/ifdown and /sbin/ifup.
The ifup and ifdown interface scripts are symbolic links to scripts in the /sbin/ directory. When either of these scripts are called, they require the value of the interface to be specified, such as:
ifup eth0

Use the ifup and ifdown interface scripts

The ifup and ifdown interface scripts are the only scripts that the user should use to bring up and take down network interfaces.
The following scripts are described for reference purposes only.
Two files used to perform a variety of network initialization tasks during the process of bringing up a network interface are /etc/rc.d/init.d/functions and /etc/sysconfig/network-scripts/network-functions. See Section 10.7, “Network Function Files” for more information.
After verifying that an interface has been specified and that the user executing the request is allowed to control the interface, the correct script brings the interface up or down. The following are common interface control scripts found within the /etc/sysconfig/network-scripts/ directory:
ifup-aliases
Configures IP aliases from interface configuration files when more than one IP address is associated with an interface.
ifup-ippp and ifdown-ippp
Brings ISDN interfaces up and down.
ifup-ipv6 and ifdown-ipv6
Brings IPv6 interfaces up and down.
ifup-plip
Brings up a PLIP interface.
ifup-plusb
Brings up a USB interface for network connections.
ifup-post and ifdown-post
Contains commands to be executed after an interface is brought up or down.
ifup-ppp and ifdown-ppp
Brings a PPP interface up or down.
ifup-routes
Adds static routes for a device as its interface is brought up.
ifdown-sit and ifup-sit
Contains function calls related to bringing up and down an IPv6 tunnel within an IPv4 connection.
ifup-wireless
Brings up a wireless interface.

Be careful when removing or modifying network scripts!

Removing or modifying any scripts in the /etc/sysconfig/network-scripts/ directory can cause interface connections to act irregularly or fail. Only advanced users should modify scripts related to a network interface.
The easiest way to manipulate all network scripts simultaneously is to use the /sbin/service command on the network service (/etc/rc.d/init.d/network), as illustrated by the following command:
/sbin/service network action
Here, action can be either start, stop, or restart.
To view a list of configured devices and currently active network interfaces, use the following command:
/sbin/service network status

10.4. Static Routes and the Default Gateway

Static routes are for traffic that must not, or should not, go through the default gateway. Routing is often handled by devices on the network dedicated to routing (although any device can be configured to perform routing). Therefore, it is often not necessary to configure static routes on Red Hat Enterprise Linux servers or clients. Exceptions include traffic that must pass through an encrypted VPN tunnel or traffic that should take a specific route for reasons of cost or security. The default gateway is for any and all traffic which is not destined for the local network and for which no preferred route is specified in the routing table. The default gateway is traditionally a dedicated network router.

Configuring Static Routes Using the Command Line

If static routes are required, they can be added to the routing table by means of the ip route add command and removed using the ip route del command. The more frequently used ip route commands take the following form:
ip route [ add | del | change | append | replace ] destination-address
See the ip-route(8) man page for more details on the options and formats.
Use the ip route command without options to display the IP routing table. For example:
~]$ ip route
default via 192.168.122.1 dev eth0  proto static  metric 1024
192.168.122.0/24 dev ens9  proto kernel  scope link  src 192.168.122.107
192.168.122.0/24 dev eth0  proto kernel  scope link  src 192.168.122.126
To add a static route to a host address, in other words to a single IP address, issue a command as root:
~]# ip route add 192.0.2.1 via 10.0.0.1 [dev ifname]
Where 192.0.2.1 is the IP address of the host in dotted decimal notation, 10.0.0.1 is the next hop address and ifname is the exit interface leading to the next hop.
To add a static route to a network, in other words to an IP address representing a range of IP addresses, issue the following command as root:
~]# ip route add 192.0.2.0/24 via 10.0.0.1 [dev ifname]
where 192.0.2.0 is the IP address of the destination network in dotted decimal notation and /24 is the network prefix. The network prefix is the number of enabled bits in the subnet mask. This format of network address slash network prefix length is sometimes referred to as classless inter-domain routing (CIDR) notation.
Static route configuration can be stored per-interface in a /etc/sysconfig/network-scripts/route-interface file. For example, static routes for the eth0 interface would be stored in the /etc/sysconfig/network-scripts/route-eth0 file. The route-interface file has two formats: ip command arguments and network/netmask directives. These are described below.
See the ip-route(8) man page for more information on the ip route command.

Configuring The Default Gateway

The default gateway is determined by the network scripts which parse the /etc/sysconfig/network file first and then the network interface ifcfg files for interfaces that are up. The ifcfg files are parsed in numerically ascending order, and the last GATEWAY directive to be read is used to compose a default route in the routing table.
The default route can thus be indicated by means of the GATEWAY directive and can be specified either globally or in interface-specific configuration files. Specifying the gateway globally has certain advantages in static networking environments, especially if more than one network interface is present. It can make fault finding simpler if applied consistently. There is also the GATEWAYDEV directive, which is a global option. If multiple devices specify GATEWAY, and one interface uses the GATEWAYDEV directive, that directive will take precedence. This option is not recommend as it can have unexpected consequences if an interface goes down and it can complicate fault finding.
In dynamic network environments, where mobile hosts are managed by NetworkManager, gateway information is likely to be interface specific and is best left to be assigned by DHCP. In special cases where it is necessary to influence NetworkManager's selection of the exit interface to be used to reach a gateway, make use of the DEFROUTE=no command in the ifcfg files for those interfaces which do not lead to the default gateway.
Global default gateway configuration is stored in the /etc/sysconfig/network file. This file specifies gateway and host information for all network interfaces. For more information about this file and the directives it accepts, see Section D.1.13, “/etc/sysconfig/network”.

10.5. Configuring Static Routes in ifcfg files

Static routes set using ip commands at the command prompt will be lost if the system is shutdown or restarted. To configure static routes to be persistent after a system restart, they must be placed in per-interface configuration files in the /etc/sysconfig/network-scripts/ directory. The file name should be of the format route-ifname. There are two types of commands to use in the configuration files; ip commands as explained in Section 10.5.1, “Static Routes Using the IP Command Arguments Format” and the Network/Netmask format as explained in Section 10.5.2, “Network/Netmask Directives Format”.

10.5.1. Static Routes Using the IP Command Arguments Format

If required in a per-interface configuration file, for example /etc/sysconfig/network-scripts/route-eth0, define a route to a default gateway on the first line. This is only required if the gateway is not set via DHCP and is not set globally in the /etc/sysconfig/network file:
default via 192.168.1.1 dev interface
where 192.168.1.1 is the IP address of the default gateway. The interface is the interface that is connected to, or can reach, the default gateway. The dev option can be omitted, it is optional. Note that this setting takes precedence over a setting in the /etc/sysconfig/network file.
If a route to a remote network is required, a static route can be specified as follows. Each line is parsed as an individual route:
10.10.10.0/24 via 192.168.1.1 [dev interface]
where 10.10.10.0/24 is the network address and prefix length of the remote or destination network. The address 192.168.1.1 is the IP address leading to the remote network. It is preferably the next hop address but the address of the exit interface will work. The next hop means the remote end of a link, for example a gateway or router. The dev option can be used to specify the exit interface interface but it is not required. Add as many static routes as required.
The following is an example of a route-interface file using the ip command arguments format. The default gateway is 192.168.0.1, interface eth0 and a leased line or WAN connection is available at 192.168.0.10. The two static routes are for reaching the 10.10.10.0/24 network and the 172.16.1.10/32 host:
default via 192.168.0.1 dev eth0
10.10.10.0/24 via 192.168.0.10 dev eth0
172.16.1.10/32 via 192.168.0.10 dev eth0
In the above example, packets going to the local 192.168.0.0/24 network will be directed out the interface attached to that network. Packets going to the 10.10.10.0/24 network and 172.16.1.10/32 host will be directed to 192.168.0.10. Packets to unknown, remote, networks will use the default gateway therefore static routes should only be configured for remote networks or hosts if the default route is not suitable. Remote in this context means any networks or hosts that are not directly attached to the system.
Specifying an exit interface is optional. It can be useful if you want to force traffic out of a specific interface. For example, in the case of a VPN, you can force traffic to a remote network to pass through a tun0 interface even when the interface is in a different subnet to the destination network.

Duplicate default gateways

If the default gateway is already assigned from DHCP, the IP command arguments format can cause one of two errors during start-up, or when bringing up an interface from the down state using the ifup command: "RTNETLINK answers: File exists" or 'Error: either "to" is a duplicate, or "X.X.X.X" is a garbage.', where X.X.X.X is the gateway, or a different IP address. These errors can also occur if you have another route to another network using the default gateway. Both of these errors are safe to ignore.

10.5.2. Network/Netmask Directives Format

You can also use the network/netmask directives format for route-interface files. The following is a template for the network/netmask format, with instructions following afterwards:
ADDRESS0=10.10.10.0
NETMASK0=255.255.255.0
GATEWAY0=192.168.1.1
  • ADDRESS0=10.10.10.0 is the network address of the remote network or host to be reached.
  • NETMASK0=255.255.255.0 is the netmask for the network address defined with ADDRESS0=10.10.10.0.
  • GATEWAY0=192.168.1.1 is the default gateway, or an IP address that can be used to reach ADDRESS0=10.10.10.0
The following is an example of a route-interface file using the network/netmask directives format. The default gateway is 192.168.0.1 but a leased line or WAN connection is available at 192.168.0.10. The two static routes are for reaching the 10.10.10.0/24 and 172.16.1.0/24 networks:
ADDRESS0=10.10.10.0
NETMASK0=255.255.255.0
GATEWAY0=192.168.0.10
ADDRESS1=172.16.1.10
NETMASK1=255.255.255.0
GATEWAY1=192.168.0.10
Subsequent static routes must be numbered sequentially, and must not skip any values. For example, ADDRESS0, ADDRESS1, ADDRESS2, and so on.

10.6. Configuring IPv6 Tokenized Interface Identifiers

In a network, servers are generally given static addresses and these are usually configured manually to avoid relying on a DHCP server which may fail or run out of addresses. The IPv6 protocol introduced Stateless Address Autoconfiguration (SLAAC) which enables clients to assign themselves an address without relying on a DHCPv6 server. SLAAC derives the IPv6 address based on the interface hardware, therefore it should not be used for servers in case the hardware is changed and the associated SLAAC generated address changes with it. In an IPv6 environment, if the network prefix is changed, or the system is moved to a new location, any manually configured static addresses would have to be edited due to the changed prefix.
To address these problems, the IETF draft Tokenised IPv6 Identifiers has been implemented in the kernel together with corresponding additions to the ip utility. This enables the lower 64 bit interface identifier part of the IPv6 address to be based on a token, supplied by the administrator, leaving the network prefix, the higher 64 bits, to be obtained from router advertisements (RA). This means that if the network interface hardware is changed, the lower 64 bits of the address will not change, and if the system is moved to another network, the network prefix will be obtained from router advertisements automatically, thus no manual editing is required.
To configure an interface to use a tokenized IPv6 identifier, issue a command in the following format as root user:
~]# ip token set ::1a:2b:3c:4d/64 dev eth4
Where ::1a:2b:3c:4d/64 is the token to be used. This setting is not persistent. To make it persistent, add the command to an init script. See Section 10.3, “Interface Control Scripts”.
Using a memorable token is possible, but is limited to the range of valid hexadecimal digits. For example, for a DNS server, which traditionally uses port 53, a token of ::53/64 could be used.
To view all the configured IPv6 tokens, issue the following command:
~]$ ip token
     token :: dev eth0 
     token :: dev eth1 
     token :: dev eth2 
     token :: dev eth3 
     token ::1a:2b:3c:4d dev eth4
To view the configured IPv6 token for a specific interface, issue the following command:
~]$ ip token get dev eth4
     token ::1a:2b:3c:4d dev eth4
Note that adding a token to an interface will replace a previously allocated token, and in turn invalidate the address derived from it. Supplying a new token causes a new address to be generated and applied, but this process will leave any other addresses unchanged. In other words, a new tokenized identifier only replaces a previously existing tokenized identifier, not any other IP address.

Note

Take care not to add the same token to more than one system or interface as the duplicate address detection (DAD) mechanism will not be able to resolve the problem. Once a token is set, it cannot be cleared or reset, except by rebooting the machine.

10.7. Network Function Files

Red Hat Enterprise Linux makes use of several files that contain important common functions used to bring interfaces up and down. Rather than forcing each interface control file to contain these functions, they are grouped together in a few files that are called upon when necessary.
The /etc/sysconfig/network-scripts/network-functions file contains the most commonly used IPv4 functions, which are useful to many interface control scripts. These functions include contacting running programs that have requested information about changes in the status of an interface, setting host names, finding a gateway device, verifying whether or not a particular device is down, and adding a default route.
As the functions required for IPv6 interfaces are different from IPv4 interfaces, a /etc/sysconfig/network-scripts/network-functions-ipv6 file exists specifically to hold this information. The functions in this file configure and delete static IPv6 routes, create and remove tunnels, add and remove IPv6 addresses to an interface, and test for the existence of an IPv6 address on an interface.

10.8. Ethtool

Ethtool is a utility for configuration of Network Interface Cards (NICs). This utility allows querying and changing settings such as speed, port, auto-negotiation, PCI locations and checksum offload on many network devices, especially Ethernet devices.
We present here a short selection of often used ethtool commands together with some useful commands that are not well known. For a full list of commands type ethtool -h or see the man page, ethtool(8), for a more comprehensive list and explanation. The first two examples are information queries and show the use of the different formats of the command.
But first, the command structure:
ethtool [option...] devname
where option is none or more options, and devname is your Network Interface Card (NIC). For example eth0 or em1.
ethtool
The ethtool command with only a device name as an option is used to print the current settings of the specified device. It takes the following form:
ethtool devname
where devname is your NIC. For example eth0 or em1.
Some values can only be obtained when the command is run as root. Here is an example of the output when the command is run as root:
~]# ethtool em1
Settings for em1:
	Supported ports: [ TP ]
	Supported link modes:   10baseT/Half 10baseT/Full
	                        100baseT/Half 100baseT/Full
	                        1000baseT/Full
	Supported pause frame use: No
	Supports auto-negotiation: Yes
	Advertised link modes:  10baseT/Half 10baseT/Full
	                        100baseT/Half 100baseT/Full
	                        1000baseT/Full
	Advertised pause frame use: No
	Advertised auto-negotiation: Yes
	Speed: 1000Mb/s
	Duplex: Full
	Port: Twisted Pair
	PHYAD: 2
	Transceiver: internal
	Auto-negotiation: on
	MDI-X: on
	Supports Wake-on: pumbg
	Wake-on: g
	Current message level: 0x00000007 (7)
			       drv probe link
	Link detected: yes
Issue the following command, using the short or long form of the argument, to query the specified network device for associated driver information:
ethtool -i, --driver devname
where devname is your Network Interface Card (NIC). For example eth0 or em1.
Here is an example of the output:
~]$ ethtool -i em1
driver: e1000e
version: 2.0.0-k
firmware-version: 0.13-3
bus-info: 0000:00:19.0
supports-statistics: yes
supports-test: yes
supports-eeprom-access: yes
supports-register-dump: yes
Here follows a list of command options to query, identify or reset the device. They are in the usual -short and --long form:
--statistics
The --statistics or -S queries the specified network device for NIC and driver statistics. It takes the following form:
-S, --statistics devname
where devname is your NIC.
--identify
The --identify or -p option initiates adapter-specific action intended to enable an operator to easily identify the adapter by sight. Typically this involves blinking one or more LEDs on the specified network port. It takes the following form:
-p, --identify devname integer
where integer is length of time in seconds to perform the action,
and devname is your NIC.
--show-time-stamping
The --show-time-stamping or -T option queries the specified network device for time stamping parameters. It takes the following form:
-T, --show-time-stamping devname
where devname is your NIC.
--show-offload
The --show-features, or --show-offload, or -k option queries the specified network device for the state of protocol offload and other features. It takes the following form:
-k, --show-features, --show-offload devname
where devname is your NIC.
--test
The --test or -t option is used to perform tests on a Network Interface Card. It takes the following form:
-t, --test devname word
where word is one of the following:
  • offline — Perform a comprehensive set of tests. Service will be interrupted.
  • online — Perform a reduced set of tests. Service should not be interrupted.
  • external_lb — Perform full set of tests including loopback tests while fitted with a loopback cable.
and devname is your NIC.
Changing some or all settings of the specified network device requires the -s or --change option. All the following options are only applied if the -s or --change option is also specified. For the sake of clarity we will omit it here.
To make these settings permanent you can make use of the ETHTOOL_OPTS directive. It can be used in interface configuration files to set the desired options when the network interface is brought up. See Section 10.2.1, “Ethernet Interfaces” for more details on how to use this directive.
--offload
The --features, or --offload, or -K option changes the offload parameters and other features of the specified network device. It takes the following form:
-K, --features, --offload devname feature boolean
where feature is a built-in or kernel supplied feature,
boolean is one of ON or OFF,
and devname is your NIC.
The ethtool(8) man page lists most features. As the feature set is dependent on the NIC driver, you should consult the driver documentation for features not listed in the man page.
--speed
The --speed option is used to set the speed in megabits per second (Mb/s). Omitting the speed value will show the supported device speeds. It takes the following form:
--speed number devname
where number is the speed in megabits per second (Mb/s),
and devname is your NIC.
--duplex
The --duplex option is used to set the transmit and receive mode of operation. It takes the following form:
 --duplex word devname
where word is one of the following:
  • half — Sets half-duplex mode. Usually used when connected to a hub.
  • full — Sets full-duplex mode. Usually used when connected to a switch or another host.
and devname is your NIC.
--port
The --port option is used to select the device port . It takes the following form:
--port value devname
where value is one of the following:
  • tp — An Ethernet interface using Twisted-Pair cable as the medium.
  • aui — Attachment Unit Interface (AUI). Normally used with hubs.
  • bnc — An Ethernet interface using BNC connectors and co-axial cable.
  • mii — An Ethernet interface using a Media Independent Interface (MII).
  • fibre — An Ethernet interface using Optical Fibre as the medium.
and devname is your NIC.
--autoneg
The --autoneg option is used to control auto-negotiation of network speed and mode of operation (full-duplex or half-duplex mode). If auto-negotiation is enabled you can initiate re-negotiation of network speeds and mode of operation by using the -r, --negotiate option. You can display the auto-negotiation state using the --a, --show-pause option.
It takes the following form:
--autoneg value devname
where value is one of the following:
  • yes — Allow auto-negotiating of network speed and mode of operation.
  • no — Do not allow auto-negotiating of network speed and mode of operation.
and devname is your NIC.
--advertise
The --advertise option is used to set what speeds and modes of operation (duplex mode) are advertised for auto-negotiation. The argument is one or more hexadecimal values from Table 10.1, “Ethtool advertise options: speed and mode of operation”.
It takes the following form:
--advertise option devname
where option is one or more of the hexadecimal values from the table below and devname is your NIC.

Table 10.1. Ethtool advertise options: speed and mode of operation

Hex Value Speed Duplex Mode IEEE standard?
0x001 10
Half
Yes
0x002 10
Full
Yes
0x004 100
Half
Yes
0x008 100
Full
Yes
0x010 1000 Half No
0x020 1000
Full
Yes
0x8000 2500 Full Yes
0x1000 10000 Full Yes
0x20000 20000MLD2 Full No
0x20000 20000MLD2 Full No
0x40000 20000KR2 Full No
--phyad
The --phyad option is used to change the physical address. Often referred to as the MAC or hardware address but in this context referred to as the physical address.
It takes the following form:
--phyad physical_address devname
where physical_address is the physical address in hexadecimal format and devname is your NIC.
--xcvr
The --xcvr option is used to select the transceiver type. Currently only internal and external can be specified. In the future other types might be added.
It takes the following form:
--xcvr word devname
where word is one of the following:
  • internal — Use internal transceiver.
  • external — Use external transceiver.
and devname is your NIC.
--wol
The --wol option is used to set Wake-on-LAN options. Not all devices support this. The argument to this option is a string of characters specifying which options to enable.
It takes the following form:
--wol value devname
where value is one or more of the following:
  • p — Wake on PHY activity.
  • u — Wake on unicast messages.
  • m — Wake on multicast messages.
  • b — Wake on broadcast messages.
  • g — Wake-on-Lan; wake on receipt of a "magic packet".
  • s — Enable security function using password for Wake-on-Lan.
  • d — Disable Wake-on-Lan and clear all settings.
and devname is your NIC.
--sopass
The --sopass option is used to set the SecureOn password. The argument to this option must be 6 bytes in Ethernet MAC hexadecimal format (xx:yy:zz:aa:bb:cc).
It takes the following form:
--sopass xx:yy:zz:aa:bb:cc devname
where xx:yy:zz:aa:bb:cc is the password in the same format as a MAC address and devname is your NIC.
--msglvl
The --msglvl option is used to set the driver message-type flags by name or number. The precise meanings of these type flags differ between drivers.
It takes the following form:
--msglvl message_type devname
where message_type is one of:
  • message type name in plain text.
  • hexadecimal number indicating the message type.
and devname is your NIC.
The defined message type names and numbers are shown in the table below:

Table 10.2. Driver message type

Message Type Hex Value Description
drv 0x0001
General driver status
probe 0x0002
Hardware probing
link 0x0004
Link state
timer 0x0008
Periodic status check
ifdown 0x0010 Interface being brought down
ifup 0x0020
Interface being brought up
rx_err 0x0040 Receive error
tx_err 0x0080 Transmit error
intr 0x0200 Interrupt handling
tx_done 0x0400 Transmit completion
rx_status 0x0800 Receive completion
pktdata 0x1000 Packet contents
hw 0x2000 Hardware status
wol 0x4000 Wake-on-LAN status

10.9. Additional Resources

The following are resources which explain more about network interfaces.

Installed Documentation

  • /usr/share/doc/initscripts-version/sysconfig.txt — A guide to available options for network configuration files, including IPv6 options not covered in this chapter.

Online Resources

  • http://linux-ip.net/gl/ip-cref/ — This document contains a wealth of information about the ip command, which can be used to manipulate routing tables, among other things.
  • Red Hat Access Labs — The Red Hat Access Labs includes a Network Bonding Helper.

See Also

  • Appendix E, The proc File System — Describes the sysctl utility and the virtual files within the /proc/ directory, which contain networking parameters and statistics among other things.

Part V. Infrastructure Services

This part provides information how to configure services and daemons, configure authentication, and enable remote logins.

Table of Contents

11. Services and Daemons
11.1. Configuring the Default Runlevel
11.2. Configuring the Services
11.2.1. Using the Service Configuration Utility
11.2.2. Using the ntsysv Utility
11.2.3. Using the chkconfig Utility
11.3. Running Services
11.3.1. Determining the Service Status
11.3.2. Starting a Service
11.3.3. Stopping a Service
11.3.4. Restarting a Service
11.4. Additional Resources
11.4.1. Installed Documentation
11.4.2. Related Books
12. Configuring Authentication
12.1. Configuring System Authentication
12.1.1. Launching the Authentication Configuration Tool UI
12.1.2. Selecting the Identity Store for Authentication
12.1.3. Configuring Alternative Authentication Features
12.1.4. Configuring Authentication from the Command Line
12.1.5. Using Custom Home Directories
12.2. Using and Caching Credentials with SSSD
12.2.1. About SSSD
12.2.2. Setting up the sssd.conf File
12.2.3. Starting and Stopping SSSD
12.2.4. SSSD and System Services
12.2.5. Configuring Services: NSS
12.2.6. Configuring Services: PAM
12.2.7. Configuring Services: autofs
12.2.8. Configuring Services: sudo
12.2.9. Configuring Services: OpenSSH and Cached Keys
12.2.10. SSSD and Identity Providers (Domains)
12.2.11. Creating Domains: LDAP
12.2.12. Creating Domains: Identity Management (IdM)
12.2.13. Creating Domains: Active Directory
12.2.14. Configuring Domains: Active Directory as an LDAP Provider (Alternative)
12.2.15. Domain Options: Setting Username Formats
12.2.16. Domain Options: Enabling Offline Authentication
12.2.17. Domain Options: Setting Password Expirations
12.2.18. Domain Options: Using DNS Service Discovery
12.2.19. Domain Options: Using IP Addresses in Certificate Subject Names (LDAP Only)
12.2.20. Creating Domains: Proxy
12.2.21. Creating Domains: Kerberos Authentication
12.2.22. Creating Domains: Access Control
12.2.23. Creating Domains: Primary Server and Backup Servers
12.2.24. Installing SSSD Utilities
12.2.25. SSSD and UID and GID Numbers
12.2.26. Creating Local System Users
12.2.27. Seeding Users into the SSSD Cache During Kickstart
12.2.28. Managing the SSSD Cache
12.2.29. Downgrading SSSD
12.2.30. Using NSCD with SSSD
12.2.31. Troubleshooting SSSD
13. OpenSSH
13.1. The SSH Protocol
13.1.1. Why Use SSH?
13.1.2. Main Features
13.1.3. Protocol Versions
13.1.4. Event Sequence of an SSH Connection
13.2. Configuring OpenSSH
13.2.1. Configuration Files
13.2.2. Starting an OpenSSH Server
13.2.3. Requiring SSH for Remote Connections
13.2.4. Using Key-Based Authentication
13.3. Using OpenSSH Certificate Authentication
13.3.1. Introduction to SSH Certificates
13.3.2. Support for SSH Certificates
13.3.3. Creating SSH CA Certificate Signing Keys
13.3.4. Distributing and Trusting SSH CA Public Keys
13.3.5. Creating SSH Certificates
13.3.6. Signing an SSH Certificate Using a PKCS#11 Token
13.3.7. Viewing an SSH CA Certificate
13.3.8. Revoking an SSH CA Certificate
13.4. OpenSSH Clients
13.4.1. Using the ssh Utility
13.4.2. Using the scp Utility
13.4.3. Using the sftp Utility
13.5. More Than a Secure Shell
13.5.1. X11 Forwarding
13.5.2. Port Forwarding
13.6. Additional Resources
13.6.1. Installed Documentation
13.6.2. Useful Websites
14. TigerVNC
14.1. VNC Server
14.1.1. Installing VNC Server
14.1.2. Configuring VNC Server
14.1.3. Starting VNC Server
14.1.4. Terminating a VNC Session
14.2. Sharing an Existing Desktop
14.3. Using a VNC Viewer
14.3.1. Installing the VNC Viewer
14.3.2. Connecting to a VNC Server
14.3.3. Connecting to VNC Server Using SSH
14.4. Additional Resources

Chapter 11. Services and Daemons

Maintaining security on your system is extremely important, and one approach for this task is to manage access to system services carefully. Your system may need to provide open access to particular services (for example, httpd if you are running a web server). However, if you do not need to provide a service, you should turn it off to minimize your exposure to possible bug exploits.
This chapter explains the concept of runlevels, and describes how to set the default one. It also covers the setup of the services to be run in each of these runlevels, and provides information on how to start, stop, and restart the services on the command line using the service command.

Keep the system secure

When you allow access for new services, always remember that both the firewall and SELinux need to be configured as well. One of the most common mistakes committed when configuring a new service is neglecting to implement the necessary firewall configuration and SELinux policies to allow access for it. For more information, see the Red Hat Enterprise Linux 6 Security Guide.

11.1. Configuring the Default Runlevel

A runlevel is a state, or mode, defined by services that are meant to be run when this runlevel is selected. Seven numbered runlevels exist (indexed from 0):

Table 11.1. Runlevels in Red Hat Enterprise Linux

RunlevelDescription
0 Used to halt the system. This runlevel is reserved and cannot be changed.
1 Used to run in a single-user mode. This runlevel is reserved and cannot be changed.
2 Not used by default. You are free to define it yourself.
3 Used to run in a full multi-user mode with a command-line user interface.
4 Not used by default. You are free to define it yourself.
5 Used to run in a full multi-user mode with a graphical user interface.
6 Used to reboot the system. This runlevel is reserved and cannot be changed.
To check in which runlevel you are operating, type the following:
~]$ runlevel
N 5
The runlevel command displays previous and current runlevel. In this case it is number 5, which means the system is running in a full multi-user mode with a graphical user interface.
The default runlevel can be changed by modifying the /etc/inittab file, which contains a line near the end of the file similar to the following:
id:5:initdefault:
To do so, edit this file as root and change the number on this line to the desired value. The change will take effect the next time you reboot the system.

11.2. Configuring the Services

To allow you to configure which services are started at boot time, Red Hat Enterprise Linux is shipped with the following utilities: the Service Configuration graphical application, the ntsysv text user interface, and the chkconfig command-line tool.

Enabling the irqbalance service

To ensure optimal performance on POWER architecture, it is recommended that the irqbalance service is enabled. In most cases, this service is installed and configured to run during the Red Hat Enterprise Linux 6 installation. To verify that irqbalance is running, as root, type the following at a shell prompt:
~]# service irqbalance status
irqbalance (pid  1234) is running...
For information on how to enable and run a service using a graphical user interface, see Section 11.2.1, “Using the Service Configuration Utility”. For instructions on how to perform these task on the command line, see Section 11.2.3, “Using the chkconfig Utility” and Section 11.3, “Running Services” respectively.

11.2.1. Using the Service Configuration Utility

The Service Configuration utility is a graphical application developed by Red Hat to configure which services are started in a particular runlevel, as well as to start, stop, and restart them from the menu. To start the utility, select SystemAdministrationServices from the panel, or type the command system-config-services at a shell prompt.

Note

The system-config-services utility is provided by the system-config-services package, which may not be installed by default on your version of Red Hat Enterprise Linux. To ensure that, first run the following command:
~]$ rpm -q system-config-services
If the package is not installed by default, install it manually by running the following command as root:
~]# yum install system-config-services
The Service Configuration utility

Figure 11.1. The Service Configuration utility

The utility displays the list of all available services (services from the /etc/rc.d/init.d/ directory, as well as services controlled by xinetd) along with their description and the current status. For a complete list of used icons and an explanation of their meaning, see Table 11.2, “Possible service states”.
Note that unless you are already authenticated, you will be prompted to enter the superuser password the first time you make a change.

Table 11.2. Possible service states

IconDescription
The service is enabled.
The service is disabled.
The service is enabled for selected runlevels only.
The service is running.
The service is stopped.
There is something wrong with the service.
The status of the service is unknown.

11.2.1.1. Enabling and Disabling a Service

To enable a service, select it from the list and either click the Enable button on the toolbar, or choose ServiceEnable from the main menu.
To disable a service, select it from the list and either click the Disable button on the toolbar, or choose ServiceDisable from the main menu.

11.2.1.2. Starting, Restarting, and Stopping a Service

To start a service, select it from the list and either click the Start button on the toolbar, or choose ServiceStart from the main menu. Note that this option is not available for services controlled by xinetd, as they are started by it on demand.
To restart a running service, select it from the list and either click the Restart button on the toolbar, or choose ServiceRestart from the main menu. Note that this option is not available for services controlled by xinetd, as they are started and stopped by it automatically.
To stop a service, select it from the list and either click the Stop button on the toolbar, or choose ServiceStop from the main menu. Note that this option is not available for services controlled by xinetd, as they are stopped by it when their job is finished.

11.2.1.3. Selecting Runlevels

To enable the service for certain runlevels only, select it from the list and either click the Customize button on the toolbar, or choose ServiceCustomize from the main menu. Then select the checkbox beside each runlevel in which you want the service to run. Note that this option is not available for services controlled by xinetd.

11.2.2. Using the ntsysv Utility

The ntsysv utility is a command-line application with a simple text user interface to configure which services are to be started in selected runlevels. To start the utility, type ntsysv at a shell prompt as root.
The ntsysv utility

Figure 11.2. The ntsysv utility

The utility displays the list of available services (the services from the /etc/rc.d/init.d/ directory) along with their current status and a description obtainable by pressing F1. For a list of used symbols and an explanation of their meaning, see Table 11.3, “Possible service states”.

Table 11.3. Possible service states

SymbolDescription
[*] The service is enabled.
[ ] The service is disabled.

11.2.2.1. Enabling and Disabling a Service

To enable a service, navigate through the list using the Up and Down arrows keys, and select it with the Spacebar. An asterisk (*) appears in the brackets.
To disable a service, navigate through the list using the Up and Down arrows keys, and toggle its status with the Spacebar. An asterisk (*) in the brackets disappears.
Once you are done, use the Tab key to navigate to the Ok button, and confirm the changes by pressing Enter. Keep in mind that ntsysv does not actually start or stop the service. If you need to start or stop the service immediately, use the service command as described in Section 11.3.2, “Starting a Service”.

11.2.2.2. Selecting Runlevels

By default, the ntsysv utility only affects the current runlevel. To enable or disable services for other runlevels, as root, run the command with the additional --level option followed by numbers from 0 to 6 representing each runlevel you want to configure:
ntsysv --level runlevels
For example, to configure runlevels 3 and 5, type:
~]# ntsysv --level 35

11.2.3. Using the chkconfig Utility

The chkconfig utility is a command-line tool that allows you to specify in which runlevel to start a selected service, as well as to list all available services along with their current setting. Note that with the exception of listing, you must have superuser privileges to use this command.

11.2.3.1. Listing the Services

To display a list of system services (services from the /etc/rc.d/init.d/ directory, as well as the services controlled by xinetd), either type chkconfig --list, or use chkconfig with no additional arguments. You will be presented with an output similar to the following:
~]# chkconfig --list
NetworkManager  0:off   1:off   2:on    3:on    4:on    5:on    6:off
abrtd           0:off   1:off   2:off   3:on    4:off   5:on    6:off
acpid           0:off   1:off   2:on    3:on    4:on    5:on    6:off
anamon          0:off   1:off   2:off   3:off   4:off   5:off   6:off
atd             0:off   1:off   2:off   3:on    4:on    5:on    6:off
auditd          0:off   1:off   2:on    3:on    4:on    5:on    6:off
avahi-daemon    0:off   1:off   2:off   3:on    4:on    5:on    6:off
... several lines omitted ...
wpa_supplicant  0:off   1:off   2:off   3:off   4:off   5:off   6:off

xinetd based services:
        chargen-dgram:  off
        chargen-stream: off
        cvs:            off
        daytime-dgram:  off
        daytime-stream: off
        discard-dgram:  off
... several lines omitted ...
        time-stream:    off
Each line consists of the name of the service followed by its status (on or off) for each of the seven numbered runlevels. For example, in the listing above, NetworkManager is enabled in runlevel 2, 3, 4, and 5, while abrtd runs in runlevel 3 and 5. The xinetd based services are listed at the end, being either on, or off.
To display the current settings for a selected service only, use chkconfig --list followed by the name of the service:
chkconfig --list service_name
For example, to display the current settings for the sshd service, type:
~]# chkconfig --list sshd
sshd            0:off   1:off   2:on    3:on    4:on    5:on    6:off
You can also use this command to display the status of a service that is managed by xinetd. In that case, the output will only contain the information whether the service is enabled or disabled:
~]# chkconfig --list rsync
rsync           off

11.2.3.2. Enabling a Service

To enable a service in runlevels 2, 3, 4, and 5, type the following at a shell prompt as root:
chkconfig service_name on
For example, to enable the httpd service in these four runlevels, type:
~]# chkconfig httpd on
To enable a service in certain runlevels only, add the --level option followed by numbers from 0 to 6 representing each runlevel in which you want the service to run:
chkconfig service_name on --level runlevels
For instance, to enable the abrtd service in runlevels 3 and 5, type:
~]# chkconfig abrtd on --level 35
The service will be started the next time you enter one of these runlevels. If you need to start the service immediately, use the service command as described in Section 11.3.2, “Starting a Service”.
Do not use the --level option when working with a service that is managed by xinetd, as it is not supported. For example, to enable the rsync service, type:
~]# chkconfig rsync on
If the xinetd daemon is running, the service is immediately enabled without having to manually restart the daemon.

11.2.3.3. Disabling a Service

To disable a service in runlevels 2, 3, 4, and 5, type the following at a shell prompt as root:
chkconfig service_name off
For instance, to disable the httpd service in these four runlevels, type:
~]# chkconfig httpd off
To disable a service in certain runlevels only, add the --level option followed by numbers from 0 to 6 representing each runlevel in which you do not want the service to run:
chkconfig service_name off --level runlevels
For instance, to disable the abrtd in runlevels 2 and 4, type:
~]# chkconfig abrtd off --level 24
The service will be stopped the next time you enter one of these runlevels. If you need to stop the service immediately, use the service command as described in Section 11.3.3, “Stopping a Service”.
Do not use the --level option when working with a service that is managed by xinetd, as it is not supported. For example, to disable the rsync service, type:
~]# chkconfig rsync off
If the xinetd daemon is running, the service is immediately disabled without having to manually restart the daemon.

11.3. Running Services

The service utility allows you to start, stop, or restart the services from the /etc/init.d/ directory.

11.3.1. Determining the Service Status

To determine the current status of a service, type the following at a shell prompt:
service service_name status
For example, to determine the status of the httpd service, type:
~]# service httpd status
httpd (pid  7474) is running...
To display the status of all available services at once, run the service command with the --status-all option:
~]# service --status-all
abrt (pid  1492) is running...
acpid (pid  1305) is running...
atd (pid  1540) is running...
auditd (pid  1103) is running...
automount (pid 1315) is running...
Avahi daemon is running
cpuspeed is stopped
... several lines omitted ...
wpa_supplicant (pid  1227) is running...
Note that you can also use the Service Configuration utility as described in Section 11.2.1, “Using the Service Configuration Utility”.

11.3.2. Starting a Service

To start a service, type the following at a shell prompt as root:
service service_name start
For example, to start the httpd service, type:
~]# service httpd start
Starting httpd:                                            [  OK  ]

11.3.3. Stopping a Service

To stop a running service, type the following at a shell prompt as root:
service service_name stop
For example, to stop the httpd service, type:
~]# service httpd stop
Stopping httpd:                                            [  OK  ]

11.3.4. Restarting a Service

To restart the service, type the following at a shell prompt as root:
service service_name restart
For example, to restart the httpd service, type:
~]# service httpd restart
Stopping httpd:                                            [  OK  ]
Starting httpd:                                            [  OK  ]

11.4. Additional Resources

11.4.1. Installed Documentation

  • chkconfig(8) — a manual page for the chkconfig utility.
  • ntsysv(8) — a manual page for the ntsysv utility.
  • service(8) — a manual page for the service utility.
  • system-config-services(8) — a manual page for the system-config-services utility.

11.4.2. Related Books

Red Hat Enterprise Linux 6 Security Guide
A guide to securing Red Hat Enterprise Linux 6. It contains valuable information on how to set up the firewall, as well as the configuration of SELinux.

Chapter 12. Configuring Authentication

12.1. Configuring System Authentication
12.1.1. Launching the Authentication Configuration Tool UI
12.1.2. Selecting the Identity Store for Authentication
12.1.3. Configuring Alternative Authentication Features
12.1.4. Configuring Authentication from the Command Line
12.1.5. Using Custom Home Directories
12.2. Using and Caching Credentials with SSSD
12.2.1. About SSSD
12.2.2. Setting up the sssd.conf File
12.2.3. Starting and Stopping SSSD
12.2.4. SSSD and System Services
12.2.5. Configuring Services: NSS
12.2.6. Configuring Services: PAM
12.2.7. Configuring Services: autofs
12.2.8. Configuring Services: sudo
12.2.9. Configuring Services: OpenSSH and Cached Keys
12.2.10. SSSD and Identity Providers (Domains)
12.2.11. Creating Domains: LDAP
12.2.12. Creating Domains: Identity Management (IdM)
12.2.13. Creating Domains: Active Directory
12.2.14. Configuring Domains: Active Directory as an LDAP Provider (Alternative)
12.2.15. Domain Options: Setting Username Formats
12.2.16. Domain Options: Enabling Offline Authentication
12.2.17. Domain Options: Setting Password Expirations
12.2.18. Domain Options: Using DNS Service Discovery
12.2.19. Domain Options: Using IP Addresses in Certificate Subject Names (LDAP Only)
12.2.20. Creating Domains: Proxy
12.2.21. Creating Domains: Kerberos Authentication
12.2.22. Creating Domains: Access Control
12.2.23. Creating Domains: Primary Server and Backup Servers
12.2.24. Installing SSSD Utilities
12.2.25. SSSD and UID and GID Numbers
12.2.26. Creating Local System Users
12.2.27. Seeding Users into the SSSD Cache During Kickstart
12.2.28. Managing the SSSD Cache
12.2.29. Downgrading SSSD
12.2.30. Using NSCD with SSSD
12.2.31. Troubleshooting SSSD
Authentication is the way that a user is identified and verified to a system. The authentication process requires presenting some sort of identity and credentials, like a user name and password. The credentials are then compared to information stored in some data store on the system. In Red Hat Enterprise Linux, the Authentication Configuration Tool helps configure what kind of data store to use for user credentials, such as LDAP.
For convenience and potentially part of single sign-on, Red Hat Enterprise Linux can use a central daemon to store user credentials for a number of different data stores. The System Security Services Daemon (SSSD) can interact with LDAP, Kerberos, and external applications to verify user credentials. The Authentication Configuration Tool can configure SSSD along with NIS, Winbind, and LDAP, so that authentication processing and caching can be combined.

12.1. Configuring System Authentication

When a user logs into a Red Hat Enterprise Linux system, that user presents some sort of credential to establish the user identity. The system then checks those credentials against the configured authentication service. If the credentials match and the user account is active, then the user is authenticated. (Once a user is authenticated, then the information is passed to the access control service to determine what the user is permitted to do. Those are the resources the user is authorized to access.)
The information to verify the user can be located on the local system or the local system can reference a user database on a remote system, such as LDAP or Kerberos.
The system must have a configured list of valid account databases for it to check for user authentication. On Red Hat Enterprise Linux, the Authentication Configuration Tool has both GUI and command-line options to configure any user data stores.
A local system can use a variety of different data stores for user information, including Lightweight Directory Access Protocol (LDAP), Network Information Service (NIS), and Winbind. Additionally, both LDAP and NIS data stores can use Kerberos to authenticate users.

Important

If a medium or high security level is set during installation or with the Security Level Configuration Tool, then the firewall prevents NIS authentication. For more information about firewalls, see the "Firewalls" section of the Security Guide.

12.1.1. Launching the Authentication Configuration Tool UI

  1. Log into the system as root.
  2. Open the System.
  3. Select the Administration menu.
  4. Select the Authentication item.
Alternatively, run the system-config-authentication command.

Important

Any changes take effect immediately when the Authentication Configuration Tool UI is closed.
There are two configuration tabs in the Authentication dialog box:
  • Identity & Authentication, which configures the resource used as the identity store (the data repository where the user IDs and corresponding credentials are stored).
  • Advanced Options, which allows authentication methods other than passwords or certificates, like smart cards and fingerprint.

12.1.2. Selecting the Identity Store for Authentication

The Identity & Authentication tab sets how users should be authenticated. The default is to use local system authentication, meaning the users and their passwords are checked against local system accounts. A Red Hat Enterprise Linux machine can also use external resources which contain the users and credentials, including LDAP, NIS, and Winbind.
Local Authentication

Figure 12.1. Local Authentication

12.1.2.1. Configuring LDAP Authentication

Either the openldap-clients package or the sssd package is used to configure an LDAP server for the user database. Both packages are installed by default.
  1. Open the Authentication Configuration Tool, as in Section 12.1.1, “Launching the Authentication Configuration Tool UI”.
  2. Select LDAP in the User Account Database drop-down menu.
  3. Set the information that is required to connect to the LDAP server.
    • LDAP Search Base DN gives the root suffix or distinguished name (DN) for the user directory. All of the user entries used for identity/authentication will exist below this parent entry. For example, ou=people,dc=example,dc=com.
      This field is optional. If it is not specified, then the System Security Services Daemon (SSSD) attempts to detect the search base using the namingContexts and defaultNamingContext attributes in the LDAP server's configuration entry.
    • LDAP Server gives the URL of the LDAP server. This usually requires both the host name and port number of the LDAP server, such as ldap://ldap.example.com:389.
      Entering the secure protocol in the URL, ldaps://, enables the Download CA Certificate button.
    • Use TLS to encrypt connections sets whether to use Start TLS to encrypt the connections to the LDAP server. This enables a secure connection over a standard port.
      Selecting TLS enables the Download CA Certificate button, which retrieves the issuing CA certificate for the LDAP server from whatever certificate authority issued it. The CA certificate must be in the privacy enhanced mail (PEM) format.

      Important

      Do not select Use TLS to encrypt connections if the server URL uses a secure protocol (ldaps). This option uses Start TLS, which initiates a secure connection over a standard port; if a secure port is specified, then a protocol like SSL must be used instead of Start TLS.
  4. Select the authentication method. LDAP allows simple password authentication or Kerberos authentication.
    The LDAP password option uses PAM applications to use LDAP authentication. This option requires either a secure (ldaps://) URL or the TLS option to connect to the LDAP server.

12.1.2.2. Configuring NIS Authentication

  1. Install the ypbind package. This is required for NIS services, but is not installed by default.
    ~]# yum install ypbind
    When the ypbind service is installed, the portmap and ypbind services are started and enabled to start at boot time.
  2. Open the Authentication Configuration Tool, as in Section 12.1.1, “Launching the Authentication Configuration Tool UI”.
  3. Select NIS in the User Account Database drop-down menu.
  4. Set the information to connect to the NIS server, meaning the NIS domain name and the server host name. If the NIS server is not specified, the authconfig daemon scans for the NIS server.
  5. Select the authentication method. NIS allows simple password authentication or Kerberos authentication.
For more information about NIS, see the "Securing NIS" section of the Security Guide.

12.1.2.3. Configuring Winbind Authentication

  1. Install the samba-winbind package. This is required for Windows integration features in Samba services, but is not installed by default.
    ~]# yum install samba-winbind
  2. Open the Authentication Configuration Tool, as in Section 12.1.1, “Launching the Authentication Configuration Tool UI”.
  3. Select Winbind in the User Account Database drop-down menu.
  4. Set the information that is required to connect to the Microsoft Active Directory domain controller.
    • Winbind Domain gives the Windows domain to connect to.
      This should be in the Windows 2000 format, such as DOMAIN.
    • Security Model sets the security model to use for Samba clients. authconfig supports four types of security models:
      • ads configures Samba to act as a domain member in an Active Directory Server realm. To operate in this mode, the krb5-server package must be installed and Kerberos must be configured properly. Also, when joining to the Active Directory Server using the command line, the following command must be used:
        net ads join
      • domain has Samba validate the user name/password by authenticating it through a Windows primary or backup domain controller, much like a Windows server.
      • server has a local Samba server validate the user name/password by authenticating it through another server, such as a Windows server. If the server authentication attempt fails, the system then attempts to authenticate using user mode.
      • user requires a client to log in with a valid user name and password. This mode does support encrypted passwords.
        The user name format must be domain\user, such as EXAMPLE\jsmith.

        Note

        When verifying that a given user exists in the Windows domain, always use Windows 2000-style formats and escape the backslash (\) character. For example:
        ~]# getent passwd domain\\user DOMAIN\user:*:16777216:16777216:Name Surname:/home/DOMAIN/user:/bin/bash
        This is the default option.
    • Winbind ADS Realm gives the Active Directory realm that the Samba server will join. This is only used with the ads security model.
    • Winbind Domain Controllers gives the domain controller to use. For more information about domain controllers, see Section 20.1.6.3, “Domain Controller”.
    • Template Shell sets which login shell to use for Windows user account settings.
    • Allow offline login allows authentication information to be stored in a local cache. The cache is referenced when a user attempts to authenticate to system resources while the system is offline.
For more information about the Winbind service, see Section 20.1.2, “Samba Daemons and Related Services”.
For additional information about configuring Winbind and troubleshooting tips, see the Knowledgebase on the Red Hat Customer Portal.
Also, the Red Hat Access Labs page includes the Winbind Mapper utility that generates a part of the smb.conf file to help you connect a Red Hat Enterprise Linux to an Active Directory.

12.1.2.4. Using Kerberos with LDAP or NIS Authentication

Both LDAP and NIS authentication stores support Kerberos authentication methods. Using Kerberos has a couple of benefits:
  • It uses a security layer for communication while still allowing connections over standard ports.
  • It automatically uses credentials caching with SSSD, which allows offline logins.
Using Kerberos authentication requires the krb5-libs and krb5-workstation packages.
The Kerberos password option from the Authentication Method drop-down menu automatically opens the fields required to connect to the Kerberos realm.
Kerberos Fields

Figure 12.2. Kerberos Fields

  • Realm gives the name for the realm for the Kerberos server. The realm is the network that uses Kerberos, composed of one or more key distribution centers (KDC) and a potentially large number of clients.
  • KDCs gives a comma-separated list of servers that issue Kerberos tickets.
  • Admin Servers gives a list of administration servers running the kadmind process in the realm.
  • Optionally, use DNS to resolve server host name and to find additional KDCs within the realm.
For more information about Kerberos, see section "Using Kerberos" of the Red Hat Enterprise Linux 6 Managing Single Sign-On and Smart Cards guide.

12.1.3. Configuring Alternative Authentication Features

The Authentication Configuration Tool also configures settings related to authentication behavior, apart from the identity store. This includes entirely different authentication methods (fingerprint scans and smart cards) or local authentication rules. These alternative authentication options are configured in the Advanced Options tab.
Advanced Options

Figure 12.3. Advanced Options

12.1.3.1. Using Fingerprint Authentication

When there is appropriate hardware available, the Enable fingerprint reader support option allows fingerprint scans to be used to authenticate local users in addition to other credentials.

12.1.3.2. Setting Local Authentication Parameters

There are two options in the Local Authentication Options area which define authentication behavior on the local system:
  • Enable local access control instructs the /etc/security/access.conf file to check for local user authorization rules.
  • Password Hashing Algorithm sets the hashing algorithm to use to encrypt locally-stored passwords.

12.1.3.3. Enabling Smart Card Authentication

When there are appropriate smart card readers available, a system can accept smart cards (or tokens) instead of other user credentials to authenticate.
Once the Enable smart card support option is selected, then the behaviors of smart card authentication can be defined:
  • Card Removal Action tells the system how to respond when the card is removed from the card reader during an active session. A system can either ignore the removal and allow the user to access resources as normal, or a system can immediately lock until the smart card is supplied.
  • Require smart card login sets whether a smart card is required for logins or allowed for logins. When this option is selected, all other methods of authentication are immediately blocked.

    Warning

    Do not select this option until you have successfully authenticated to the system using a smart card.
Using smart cards requires the pam_pkcs11 package.

12.1.3.4. Creating User Home Directories

There is an option (Create home directories on the first login) to create a home directory automatically the first time that a user logs in.
This option is beneficial with accounts that are managed centrally, such as with LDAP. However, this option should not be selected if a system like automount is used to manage user home directories.

12.1.4. Configuring Authentication from the Command Line

The authconfig command-line tool updates all of the configuration files and services required for system authentication, according to the settings passed to the script. Along with allowing all of the identity and authentication configuration options that can be set through the UI, the authconfig tool can also be used to create backup and kickstart files.
For a complete list of authconfig options, check the help output and the man page.

12.1.4.1. Tips for Using authconfig

There are some things to remember when running authconfig:
  • With every command, use either the --update or --test option. One of those options is required for the command to run successfully. Using --update writes the configuration changes. --test prints the changes to stdout but does not apply the changes to the configuration.
  • Each enable option has a corresponding disable option.

12.1.4.2. Configuring LDAP User Stores

To use an LDAP identity store, use the --enableldap. To use LDAP as the authentication source, use --enableldapauth and then the requisite connection information, like the LDAP server name, base DN for the user suffix, and (optionally) whether to use TLS. The authconfig command also has options to enable or disable RFC 2307bis schema for user entries, which is not possible through the Authentication Configuration UI.
Be sure to use the full LDAP URL, including the protocol (ldap or ldaps) and the port number. Do not use a secure LDAP URL (ldaps) with the --enableldaptls option.
authconfig --enableldap --enableldapauth --ldapserver=ldap://ldap.example.com:389,ldap://ldap2.example.com:389 --ldapbasedn="ou=people,dc=example,dc=com" --enableldaptls --ldaploadcacert=https://ca.server.example.com/caCert.crt --update
Instead of using --ldapauth for LDAP password authentication, it is possible to use Kerberos with the LDAP user store. These options are described in Section 12.1.4.5, “Configuring Kerberos Authentication”.

12.1.4.3. Configuring NIS User Stores

To use a NIS identity store, use the --enablenis. This automatically uses NIS authentication, unless the Kerberos parameters are explicitly set, so it uses Kerberos authentication (Section 12.1.4.5, “Configuring Kerberos Authentication”). The only parameters are to identify the NIS server and NIS domain; if these are not used, then the authconfig service scans the network for NIS servers.
authconfig --enablenis --nisdomain=EXAMPLE --nisserver=nis.example.com --update

12.1.4.4. Configuring Winbind User Stores

Windows domains have several different security models, and the security model used in the domain determines the authentication configuration for the local system.
For user and server security models, the Winbind configuration requires only the domain (or workgroup) name and the domain controller host names.
authconfig --enablewinbind --enablewinbindauth --smbsecurity=user|server  --enablewinbindoffline --smbservers=ad.example.com --smbworkgroup=EXAMPLE --update

Note

The user name format must be domain\user, such as EXAMPLE\jsmith.
When verifying that a given user exists in the Windows domain, always use Windows 2000-style formats and escape the backslash (\) character. For example:
~]# getent passwd domain\\user DOMAIN\user:*:16777216:16777216:Name Surname:/home/DOMAIN/user:/bin/bash
For ads and domain security models, the Winbind configuration allows additional configuration for the template shell and realm (ads only). For example:
authconfig --enablewinbind --enablewinbindauth --smbsecurity ads  --enablewinbindoffline --smbservers=ad.example.com --smbworkgroup=EXAMPLE --smbrealm EXAMPLE.COM --winbindtemplateshell=/bin/sh --update
There are a lot of other options for configuring Windows-based authentication and the information for Windows user accounts, such as name formats, whether to require the domain name with the user name, and UID ranges. These options are listed in the authconfig help.

12.1.4.5. Configuring Kerberos Authentication

Both LDAP and NIS allow Kerberos authentication to be used in place of their native authentication mechanisms. At a minimum, using Kerberos authentication requires specifying the realm, the KDC, and the administrative server. There are also options to use DNS to resolve client names and to find additional admin servers.
authconfig NIS or LDAP options --enablekrb5 --krb5realm EXAMPLE --krb5kdc kdc.example.com:88,server.example.com:88 --krb5adminserver server.example.com:749 --enablekrb5kdcdns --enablekrb5realmdns --update

12.1.4.6. Configuring Local Authentication Settings

The Authentication Configuration Tool can also control some user settings that relate to security, such as creating home directories, setting password hash algorithms, and authorization. These settings are done independently of identity/user store settings.
For example, to create user home directories:
authconfig --enablemkhomedir --update
To set or change the hash algorithm used to encrypt user passwords:
authconfig --passalgo=sha512 --update

12.1.4.7. Configuring Fingerprint Authentication

There is one option to enable support for fingerprint readers. This option can be used alone or in conjunction with other authconfig settings, like LDAP user stores.
~]# authconfig --enablefingerprint --update

12.1.4.8. Configuring Smart Card Authentication

All that is required to use smart cards with a system is to set the --enablesmartcard option:
~]# authconfig --enablesmartcard --update
There are other configuration options for smart cards, such as changing the default smart card module, setting the behavior of the system when the smart card is removed, and requiring smart cards for login.
For example, this command instructs the system to lock out a user immediately if the smart card is removed (a setting of 1 ignores it if the smart card is removed):
~]# authconfig --enablesmartcard --smartcardaction=0 --update
Once smart card authentication has been successfully configured and tested, then the system can be configured to require smart card authentication for users rather than simple password-based authentication.
~]# authconfig --enablerequiresmartcard --update

Warning

Do not use the --enablerequiresmartcard option until you have successfully authenticated to the system using a smart card. Otherwise, users may be unable to log into the system.

12.1.4.9. Managing Kickstart and Configuration Files

The --update option updates all of the configuration files with the configuration changes. There are a couple of alternative options with slightly different behavior:
  • --kickstart writes the updated configuration to a kickstart file.
  • --test prints the full configuration, with changes, to stdout but does not edit any configuration files.
Additionally, authconfig can be used to back up and restore previous configurations. All archives are saved to a unique subdirectory in the /var/lib/authconfig/ directory. For example, the --savebackup option gives the backup directory as 2011-07-01:
~]# authconfig --savebackup=2011-07-01
This backs up all of the authentication configuration files beneath the /var/lib/authconfig/backup-2011-07-01 directory.
Any of the saved backups can be used to restore the configuration using the --restorebackup option, giving the name of the manually-saved configuration:
~]# authconfig --restorebackup=2011-07-01
Additionally, authconfig automatically makes a backup of the configuration before it applies any changes (with the --update option). The configuration can be restored from the most recent automatic backup, without having to specify the exact backup, using the --restorelastbackup option.

12.1.5. Using Custom Home Directories

If LDAP users have home directories that are not in /home and the system is configured to create home directories the first time users log in, then these directories are created with the wrong permissions.
  1. Apply the correct SELinux context and permissions from the /home directory to the home directory that is created on the local system. For example:
    ~]# semanage fcontext -a -e /home /home/locale
  2. Install the oddjob-mkhomedir package on the system.
    This package provides the pam_oddjob_mkhomedir.so library, which the Authentication Configuration Tool uses to create home directories. The pam_oddjob_mkhomedir.so library, unlike the default pam_mkhomedir.so library, can create SELinux labels.
    The Authentication Configuration Tool automatically uses the pam_oddjob_mkhomedir.so library if it is available. Otherwise, it will default to using pam_mkhomedir.so.
  3. Make sure the oddjobd service is running.
  4. Re-run the Authentication Configuration Tool and enable home directories, as in Section 12.1.3, “Configuring Alternative Authentication Features”.
If home directories were created before the home directory configuration was changed, then correct the permissions and SELinux contexts. For example:
~]# semanage fcontext -a -e /home /home/locale
# restorecon -R -v /home/locale

12.2. Using and Caching Credentials with SSSD

The System Security Services Daemon (SSSD) provides access to different identity and authentication providers.

12.2.1. About SSSD

Most system authentication is configured locally, which means that services must check with a local user store to determine users and credentials. What SSSD does is allow a local service to check with a local cache in SSSD, but that cache may be taken from any variety of remote identity providers — an LDAP directory, an Identity Management domain, Active Directory, possibly even a Kerberos realm.
SSSD also caches those users and credentials, so if the local system or the identity provider go offline, the user credentials are still available to services to verify.
SSSD is an intermediary between local clients and any configured data store. This relationship brings a number of benefits for administrators:
  • Reducing the load on identification/authentication servers. Rather than having every client service attempt to contact the identification server directly, all of the local clients can contact SSSD which can connect to the identification server or check its cache.
  • Permitting offline authentication. SSSD can optionally keep a cache of user identities and credentials that it retrieves from remote services. This allows users to authenticate to resources successfully, even if the remote identification server is offline or the local machine is offline.
  • Using a single user account. Remote users frequently have two (or even more) user accounts, such as one for their local system and one for the organizational system. This is necessary to connect to a virtual private network (VPN). Because SSSD supports caching and offline authentication, remote users can connect to network resources by authenticating to their local machine and then SSSD maintains their network credentials.
Additional Resources
While this chapter covers the basics of configuring services and domains in SSSD, this is not a comprehensive resource. Many other configuration options are available for each functional area in SSSD; check out the man page for the specific functional area to get a complete list of options.
Some of the common man pages are listed in Table 12.1, “A Sampling of SSSD Man Pages”. There is also a complete list of SSSD man pages in the "See Also" section of the sssd(8) man page.

Table 12.1. A Sampling of SSSD Man Pages

Functional Area Man Page
General Configuration sssd.conf(8)
sudo Services sssd-sudo
LDAP Domains sssd-ldap
Active Directory Domains
sssd-ad
sssd-ldap
Identity Management (IdM or IPA) Domains
sssd-ipa
sssd-ldap
Kerberos Authentication for Domains sssd-krb5
OpenSSH Keys
sss_ssh_authorizedkeys
sss_ssh_knownhostsproxy
Cache Maintenance
sss_cache (cleanup)
sss_useradd, sss_usermod, sss_userdel, sss_seed (user cache entry management)

12.2.2. Setting up the sssd.conf File

SSSD services and domains are configured in a .conf file. By default, this is /etc/sssd/sssd.conf — although that file must be created and configured manually, since SSSD is not configured after installation.

12.2.2.1. Creating the sssd.conf File

There are three parts of the SSSD configuration file:
  • [sssd], for general SSSD process and operational configuration; this basically lists the configured services, domains, and configuration parameters for each
  • [service_name], for configuration options for each supported system service, as described in Section 12.2.4, “SSSD and System Services”
  • [domain_type/DOMAIN_NAME], for configuration options for each configured identity provider

    Important

    While services are optional, at least one identity provider domain must be configured before the SSSD service can be started.

Example 12.1. Simple sssd.conf File

[sssd]
domains = LOCAL
services = nss
config_file_version = 2

[nss]
filter_groups = root
filter_users = root

[domain/LOCAL]
id_provider = local
auth_provider = local
access_provider = permit
The [sssd] section has three important parameters:
  • domains lists all of the domains, configured in the sssd.conf, which SSSD uses as identity providers. If a domain is not listed in the domains key, it is not used by SSSD, even if it has a configuration section.
  • services lists all of the system services, configured in the sssd.conf, which use SSSD; when SSSD starts, the corresponding SSSD service is started for each configured system service. If a service is not listed in the services key, it is not used by SSSD, even if it has a configuration section.
  • config_file_version sets the version of the configuration file to set file format expectations. This is version 2, for all recent SSSD versions.

Note

Even if a service or domain is configured in the sssd.conf file, SSSD does not interact with that service or domain unless it is listed in the services or domains parameters, respectively, in the [sssd] section.
Other configuration parameters are listed in the sssd.conf man page.
Each service and domain parameter is described in its respective configuration section in this chapter and in their man pages.

12.2.2.2. Using a Custom Configuration File

By default, the sssd process assumes that the configuration file is /etc/sssd/sssd.conf.
An alternative file can be passed to SSSD by using the -c option with the sssd command:
~]# sssd -c /etc/sssd/customfile.conf --daemon

12.2.3. Starting and Stopping SSSD

Important

Configure at least one domain before starting SSSD for the first time. See Section 12.2.10, “SSSD and Identity Providers (Domains)”.
Either the service command or the /etc/init.d/sssd script can start SSSD. For example:
~]# service sssd start
By default, SSSD is not configured to start automatically. There are two ways to change this behavior:
  • Enabling SSSD through the authconfig command:
    ~]# authconfig --enablesssd --enablesssdauth --update
  • Adding the SSSD process to the start list using the chkconfig command:
    ~]# chkconfig sssd on

12.2.4. SSSD and System Services

SSSD and its associated services are configured in the sssd.conf file. The [sssd] section also lists the services that are active and should be started when sssd starts within the services directive.
SSSD can provide credentials caches for several system services:

12.2.5. Configuring Services: NSS

SSSD provides an NSS module, sssd_nss, which instructs the system to use SSSD to retrieve user information. The NSS configuration must include a reference to the SSSD module, and then the SSSD configuration sets how SSSD interacts with NSS.

About NSS Service Maps and SSSD

The Name Service Switch (NSS) provides a central configuration for services to look up a number of configuration and name resolution services. NSS provides one method of mapping system identities and services with configuration sources.
SSSD works with NSS as a provider services for several types of NSS maps:
  • Passwords (passwd)
  • User groups (shadow)
  • Groups (groups)
  • Netgroups (netgroups)
  • Services (services)

Procedure 12.1. Configuring NSS Services to Use SSSD

NSS can use multiple identity and configuration providers for any and all of its service maps. The default is to use system files for services; for SSSD to be included, the nss_sss module has to be included for the desired service type.
  1. Use the Authentication Configuration tool to enable SSSD. This automatically configured the nsswitch.conf file to use SSSD as a provider.
    ~]# authconfig --enablesssd --update
    This automatically configures the password, shadow, group, and netgroups services maps to use the SSSD module:
    passwd:     files sss
    shadow:     files sss
    group:      files sss
    
    netgroup:   files sss
  2. The services map is not enabled by default when SSSD is enabled with authconfig. To include that map, open the nsswitch.conf file and add the sss module to the services map:
    ~]# vim /etc/nsswitch.conf
    
    ...
    services: file sss
    ...

Procedure 12.2. Configuring SSSD to Work with NSS

The options and configuration that SSSD uses to service NSS requests are configured in the SSSD configuration file, in the [nss] services section.
  1. Open the sssd.conf file.
    ~]# vim /etc/sssd/sssd.conf
  2. Make sure that NSS is listed as one of the services that works with SSSD.
    [sssd]
    config_file_version = 2
    reconnection_retries = 3
    sbus_timeout = 30
    services = nss, pam
  3. In the [nss] section, change any of the NSS parameters. These are listed in Table 12.2, “SSSD [nss] Configuration Parameters”.
    [nss]
    filter_groups = root
    filter_users = root
    reconnection_retries = 3
    entry_cache_timeout = 300
    entry_cache_nowait_percentage = 75
  4. Restart SSSD.
    ~]# service sssd restart

Table 12.2. SSSD [nss] Configuration Parameters

Parameter Value Format Description
entry_cache_nowait_percentage integer Specifies how long sssd_nss should return cached entries before refreshing the cache. Setting this to zero (0) disables the entry cache refresh.
This configures the entry cache to update entries in the background automatically if they are requested if the time before the next update is a certain percentage of the next interval. For example, if the interval is 300 seconds and the cache percentage is 75, then the entry cache will begin refreshing when a request comes in at 225 seconds — 75% of the interval.
The allowed values for this option are 0 to 99, which sets the percentage based on the entry_cache_timeout value. The default value is 50%.
entry_negative_timeout integer Specifies how long, in seconds, sssd_nss should cache negative cache hits. A negative cache hit is a query for an invalid database entries, including non-existent entries.
filter_users, filter_groups string Tells SSSD to exclude certain users from being fetched from the NSS database. This is particularly useful for system accounts such as root.
filter_users_in_groups Boolean Sets whether users listed in the filter_users list appear in group memberships when performing group lookups. If set to FALSE, group lookups return all users that are members of that group. If not specified, this value defaults to true, which filters the group member lists.
debug_level integer, 0 - 9 Sets a debug logging level.

NSS Compatibility Mode

NSS compatibility (compat) mode provides the support for additional entries in the /etc/passwd file to ensure that users or members of netgroups have access to the system.
To enable NSS compatibility mode to work with SSSD, add the following entries to the /etc/nsswitch.conf file:
passwd: compat
passwd_compat: sss
Once NSS compatibility mode is enabled, the following passwd entries are supported:
  • +user -user
    Include (+) or exclude (-) a specified user from the Network Information System (NIS) map.
  • +@netgroup -@netgroup
    Include (+) or exclude (-) all users in the given netgroup from the NIS map.
  • +
    Exclude all users, except previously excluded ones from the NIS map.
For more information about NSS compatibility mode, see the nsswitch.conf(5) manual page.

12.2.6. Configuring Services: PAM

Warning

A mistake in the PAM configuration file can lock users out of the system completely. Always back up the configuration files before performing any changes, and keep a session open so that any changes can be reverted.
SSSD provides a PAM module, sssd_pam, which instructs the system to use SSSD to retrieve user information. The PAM configuration must include a reference to the SSSD module, and then the SSSD configuration sets how SSSD interacts with PAM.

Procedure 12.3. Configuring PAM

  1. Use authconfig to enable SSSD for system authentication.
    # authconfig --update --enablesssd --enablesssdauth
    This automatically updates the PAM configuration to reference all of the SSSD modules:
    #%PAM-1.0
    # This file is auto-generated.
    # User changes will be destroyed the next time authconfig is run.
    auth        required      pam_env.so
    auth        sufficient    pam_unix.so nullok try_first_pass
    auth        requisite     pam_succeed_if.so uid >= 500 quiet
    auth sufficient pam_sss.so use_first_pass
    auth        required      pam_deny.so
    
    account     required      pam_unix.so 
    account     sufficient    pam_localuser.so
    account     sufficient    pam_succeed_if.so uid < 500 quiet
    account [default=bad success=ok user_unknown=ignore] pam_sss.so
    account     required      pam_permit.so
    
    password    requisite     pam_cracklib.so try_first_pass retry=3
    password    sufficient    pam_unix.so sha512 shadow nullok try_first_pass use_authtok
    password sufficient pam_sss.so use_authtok
    password    required      pam_deny.so
    
    session     optional      pam_keyinit.so revoke
    session     required      pam_limits.so
    session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
    session sufficient pam_sss.so
    session     required      pam_unix.so
    These modules can be set to include statements, as necessary.
  2. Open the sssd.conf file.
    # vim /etc/sssd/sssd.conf
  3. Make sure that PAM is listed as one of the services that works with SSSD.
    [sssd]
    config_file_version = 2
    reconnection_retries = 3
    sbus_timeout = 30
    services = nss, pam
  4. In the [pam] section, change any of the PAM parameters. These are listed in Table 12.3, “SSSD [pam] Configuration Parameters”.
    [pam]
    reconnection_retries = 3
    offline_credentials_expiration = 2
    offline_failed_login_attempts = 3
    offline_failed_login_delay = 5
  5. Restart SSSD.
    ~]# service sssd restart

Table 12.3. SSSD [pam] Configuration Parameters

Parameter Value Format Description
offline_credentials_expiration integer Sets how long, in days, to allow cached logins if the authentication provider is offline. This value is measured from the last successful online login. If not specified, this defaults to zero (0), which is unlimited.
offline_failed_login_attempts integer Sets how many failed login attempts are allowed if the authentication provider is offline. If not specified, this defaults to zero (0), which is unlimited.
offline_failed_login_delay integer Sets how long to prevent login attempts if a user hits the failed login attempt limit. If set to zero (0), the user cannot authenticate while the provider is offline once he hits the failed attempt limit. Only a successful online authentication can re-enable offline authentication. If not specified, this defaults to five (5).

12.2.7. Configuring Services: autofs

About Automount, LDAP, and SSSD

Automount maps are commonly flat files, which define a relationship between a map, a mount directory, and a fileserver. (Automount is described in the Storage Administration Guide.)
For example, let's say that there is a fileserver called nfs.example.com which hosts the directory pub, and automount is configured to mount directories in the /shares/ directory. So, the mount location is /shares/pub. All of the mounts are listed in the auto.master file, which identifies the different mount directories and the files which configure them. The auto.shares file then identifies each file server and mount directory which goes into the /shares/ directory. The relationships could be viewed like this:
        auto.master
   _________|__________
   |                 |
   |                 |
/shares/        auto.shares
                     |
		     |
		     |
            nfs.example.com:pub
Every mount point, then, is defined in two different files (at a minimum): the auto.master and auto.whatever file, and those files have to be available to each local automount process.
One way for administrators to manage that for large environments is to store the automount configuration in a central LDAP directory, and just configure each local system to point to that LDAP directory. That means that updates only need to be made in a single location, and any new maps are automatically recognized by local systems.
For automount-LDAP configuration, the automount files are stored as LDAP entries, which are then translated into the requisite automount files. Each element is then translated into an LDAP attribute.
The LDAP entries look like this:
# container entry
dn: cn=automount,dc=example,dc=com
objectClass: nsContainer
objectClass: top
cn: automount

# master map entry
dn: automountMapName=auto.master,cn=automount,dc=example,dc=com
objectClass: automountMap
objectClass: top
automountMapName: auto.master

# shares map entry
dn: automountMapName=auto.shares,cn=automount,dc=example,dc=com
objectClass: automountMap
objectClass: top
automountMapName: auto.shares

# shares mount point
dn: automountKey=/shares,automountMapName=auto.master,cn=automount,dc=example,dc=com
objectClass: automount
objectClass: top
automountKey: /shares
automountInformation: auto.shares

# pub mount point
dn: automountKey=pub,automountMapName=auto.shares,cn=automount,dc=example,dc=com
objectClass: automount
objectClass: top
automountKey: pub
automountInformation: filer.example.com:/pub
description: pub
The schema elements, then, match up to the structure like this (with the RFC 2307 schema):
	              auto.master
                      objectclass: automountMap
                      filename attribute: automountMapName
   _______________________|_________________________
   |                                               |
   |                                               |
/shares/                                       auto.shares
objectclass: automount                         objectclass: automountMap
mount point name attribute: automountKey       filename attribute: automountMapName
map name attribute: automountInformation           |
		                                   |
                                                   |
                                          nfs.example.com:pub
                                          objectclass: automount
                                          mount point name attribute: automountKey
                                          fileserver attribute: automountInformation
autofs uses those schema elements to derive the automount configuration. The /etc/sysconfig/autofs file identifies the LDAP server, directory location, and schema elements used for automount entities:
LDAP_URI=ldap://ldap.example.com
SEARCH_BASE="cn=automount,dc=example,dc=com"
MAP_OBJECT_CLASS="automountMap"
ENTRY_OBJECT_CLASS="automount"
MAP_ATTRIBUTE="automountMapName"
ENTRY_ATTRIBUTE="automountKey"
VALUE_ATTRIBUTE="automountInformation"
Rather than pointing the automount configuration to the LDAP directory, it can be configured to point to SSSD. SSSD, then, stores all of the information that automount needs, and as a user attempts to mount a directory, that information is cached into SSSD. This offers several advantages for configuration — such as failover, service discovery, and timeouts — as well as performance improvements by reducing the number of connections to the LDAP server. Most important, using SSSD allows all mount information to be cached, so that clients can still successfully mount directories even if the LDAP server goes offline.

Procedure 12.4. Configuring autofs Services in SSSD

  1. Make sure that the autofs and sssd-common packages are installed.
  2. Open the sssd.conf file.
    ~]# vim /etc/sssd/sssd.conf
  3. Add the autofs service to the list of services that SSSD manages.
    [sssd]
    services = nss,pam,autofs
    ....
  4. Create a new [autofs] service configuration section. This section can be left blank; there is only one configurable option, for timeouts for negative cache hits.
    This section is required, however, for SSSD to recognize the autofs service and supply the default configuration.
    [autofs]
    
    
    
  5. The automount information is read from a configured LDAP domain in the SSSD configuration, so an LDAP domain must be available. If no additional settings are made, then the configuration defaults to the RFC 2307 schema and the LDAP search base (ldap_search_base) for the automount information. This can be customized:
    • The directory type, autofs_provider; this defaults to the id_provider value; a value of none explicitly disables autofs for the domain.
    • The search base, ldap_autofs_search_base.
    • The object class to use to recognize map entries, ldap_autofs_map_object_class
    • The attribute to use to recognize map names, ldap_autofs_map_name
    • The object class to use to recognize mount point entries, ldap_autofs_entry_object_class
    • The attribute to use to recognize mount point names, ldap_autofs_entry_key
    • The attribute to use for additional configuration information for the mount point, ldap_autofs_entry_value
    For example:
    [domain/LDAP]
    ...
    autofs_provider=ldap
    ldap_autofs_search_base=cn=automount,dc=example,dc=com
    ldap_autofs_map_object_class=automountMap
    ldap_autofs_entry_object_class=automount
    ldap_autofs_map_name=automountMapName
    ldap_autofs_entry_key=automountKey
    ldap_autofs_entry_value=automountInformation
  6. Save and close the sssd.conf file.
  7. Configure autofs to look for the automount map information in SSSD by editing the nsswitch.conf file and changing the location from ldap to sss:
    # vim /etc/nsswitch.conf
    
    automount: files sss
  8. Restart SSSD.
    # service sssd restart

12.2.8. Configuring Services: sudo

About sudo, LDAP, and SSSD

sudo rules are defined in the sudoers file, which must be distributed separately to every machine to maintain consistency.
One way for administrators to manage that for large environments is to store the sudo configuration in a central LDAP directory, and just configure each local system to point to that LDAP directory. That means that updates only need to be made in a single location, and any new rules are automatically recognized by local systems.
For sudo-LDAP configuration, each sudo rule is stored as an LDAP entry, with each component of the sudo rule defined in an LDAP attribute.
The sudoers rule looks like this:
Defaults    env_keep+=SSH_AUTH_SOCK
...
%wheel        ALL=(ALL)       ALL
The LDAP entry looks like this:
# sudo defaults
dn: cn=defaults,ou=SUDOers,dc=example,dc=com
objectClass: top
objectClass: sudoRole
cn: defaults
description: Default sudoOptions go here
sudoOption: env_keep+=SSH_AUTH_SOCK

# sudo rule
dn: cn=%wheel,ou=SUDOers,dc=example,dc=com
objectClass: top
objectClass: sudoRole
cn: %wheel
sudoUser: %wheel
sudoHost: ALL
sudoCommand: ALL

Note

SSSD only caches sudo rules which apply to the local system, depending on the value of the sudoHost attribute. This can mean that the sudoHost value is set to ALL, uses a regular expression that matches the host name, matches the systems netgroup, or matches the systems host name, fully-qualified domain name, or IP address.
The sudo service can be configured to point to an LDAP server and to pull its rule configuration from those LDAP entries. Rather than pointing the sudo configuration to the LDAP directory, it can be configured to point to SSSD. SSSD, then, stores all of the information that sudo needs, and every time a user attempts a sudo-related operation, the latest sudo configuration can be pulled from the LDAP directory (through SSSD). SSSD, however, also caches all of the sudo riles, so that users can perform tasks, using that centralized LDAP configuration, even if the LDAP server goes offline.

Procedure 12.5. Configuring sudo with SSSD

All of the SSSD sudo configuration options are listed in the sssd-ldap(5) man page.
  1. Make sure that the sssd-common package is installed.
    ~]$ rpm -q sssd-common
  2. Open the sssd.conf file.
    ~]# vim /etc/sssd/sssd.conf
  3. Add the sudo service to the list of services that SSSD manages.
    [sssd]
    services = nss,pam,sudo
    ....
  4. Create a new [sudo] service configuration section. This section can be left blank; there is only one configurable option, for evaluating the sudo not before/after period.
    This section is required, however, for SSSD to recognize the sudo service and supply the default configuration.
    [sudo]
  5. The sudo information is read from a configured LDAP domain in the SSSD configuration, so an LDAP domain must be available. For an LDAP provider, these parameters are required:
    • The directory type, sudo_provider; this is always ldap.
    • The search base, ldap_sudo_search_base.
    • The URI for the LDAP server, ldap_uri.
    For example:
    [domain/LDAP]
    id_provider = ldap
    
    sudo_provider = ldap
    ldap_uri = ldap://example.com
    ldap_sudo_search_base = ou=sudoers,dc=example,dc=com
    For an Identity Management (IdM or IPA) provider, there are additional parameters required to perform Kerberos authentication when connecting to the server.
    [domain/IDM]
    id_provider = ipa
    ipa_domain = example.com
    ipa_server = ipa.example.com
    ldap_tls_cacert = /etc/ipa/ca.crt
    
    sudo_provider = ldap
    ldap_uri = ldap://ipa.example.com
    ldap_sudo_search_base = ou=sudoers,dc=example,dc=com
    ldap_sasl_mech = GSSAPI
    ldap_sasl_authid = host/hostname.example.com
    ldap_sasl_realm = EXAMPLE.COM
    krb5_server = ipa.example.com

    Note

    The sudo_provider type for an Identity Management provider is still ldap.
  6. Set the intervals to use to refresh the sudo rule cache.
    The cache for a specific system user is always checked and updated whenever that user performs a task. However, SSSD caches all rules which relate to the local system. That complete cache is updated in two ways:
    • Incrementally, meaning only changes to rules since the last full update (ldap_sudo_smart_refresh_interval, the time in seconds); the default is 15 minutes,
    • Fully, which dumps the entire caches and pulls in all of the current rules on the LDAP server(ldap_sudo_full_refresh_interval, the time in seconds); the default is six hours.
    These two refresh intervals are set separately. For example:
    [domain/LDAP]
    ...
    ldap_sudo_full_refresh_interval=86400
    ldap_sudo_smart_refresh_interval=3600

    Note

    SSSD only caches sudo rules which apply to the local system. This can mean that the sudoHost value is set to ALL, uses a regular expression that matches the host name, matches the systems netgroup, or matches the systems host name, fully-qualified domain name, or IP address.
  7. Optionally, set any values to change the schema used for sudo rules.
    Schema elements are set in the ldap_sudorule_* attributes. By default, all of the schema elements use the schema defined in sudoers.ldap; these defaults will be used in almost all deployments.
  8. Save and close the sssd.conf file.
  9. Configure sudo to look for rules configuration in SSSD by editing the nsswitch.conf file and adding the sss location:
    ~]# vim /etc/nsswitch.conf
    
    sudoers: files sss
  10. Restart SSSD.
    ~]# service sssd restart

12.2.9. Configuring Services: OpenSSH and Cached Keys

OpenSSH creates secure, encrypted connections between two systems. One machine authenticates to another machine to allow access; the authentication can be of the machine itself for server connections or of a user on that machine. OpenSSH is described in more detail in Chapter 13, OpenSSH.
This authentication is performed through public-private key pairs that identify the authenticating user or machine. The remote machine or user attempting to access the machine presents a key pair. The local machine then elects whether to trust that remote entity; if it is trusted, the public key for that remote machine is stored in the known_hosts file or for the remote user in authorized_keys. Whenever that remote machine or user attempts to authenticate again, the local system checks the known_hosts or authorized_keys file first to see if that remote entity is recognized and trusted. If it is, then access is granted.
The first problem comes in verifying those identities reliably.
The known_hosts file is a triplet of the machine name, its IP address, and its public key:
server.example.com,255.255.255.255 ssh-rsa AbcdEfg1234ZYX098776/AbcdEfg1234ZYX098776/AbcdEfg1234ZYX098776=
The known_hosts file can quickly become outdated for a number of different reasons: systems using DHCP cycle through IP addresses, new keys can be re-issued periodically, or virtual machines or services can be brought online and removed. This changes the host name, IP address, and key triplet.
Administrators have to clean and maintain a current known_hosts file to maintain security. (Or system users get in the habit of accepting any machine and key presented, which negates the security benefits of key-based security.)
Additionally, a problem for both machines and users is distributing keys in a scalable way. Machines can send their keys as part of establishing an encrypted session, but users have to supply their keys in advance. Simply propagating and then updating keys consistently is a difficult administrative task.
Lastly, SSH key and machine information are only maintained locally. There may be machines or users on the network which are recognized and trusted by some systems and not by others because the known_hosts file has not been updated uniformly.
The goal of SSSD is to server as a credentials cache. This includes working as a credentials cache for SSH public keys for machines and users. OpenSSH is configured to reference SSSD to check for cached keys; SSSD uses Red Hat Linux's Identity Management (IPA) domain as an identity, and Identity Management actually stores the public keys and host information.

Note

Only Linux machines enrolled, or joined, in the Identity Management domain can use SSSD as a key cache for OpenSSH. Other Unix machines and Windows machines must use the regular authentication mechanisms with the known_hosts file.

Configuring OpenSSH to Use SSSD for Host Keys

OpenSSH is configured in either a user-specific configuration file (~/.ssh/config) or a system-wide configuration file (/etc/ssh/ssh_config). The user file has precedence over the system settings and the first obtained value for a parameter is used. The formatting and conventions for this file are covered in Chapter 13, OpenSSH.
In order to manage host keys, SSSD has a tool, sss_ssh_knownhostsproxy, which performs two operations:
  1. Asks SSSD to retrieve the public host key from the Identity Management server and store it in the /var/lib/sss/pubconf/known_hosts file.
  2. Establishes a connection with the host machine, using either a socket (the default) or a proxy command.
This tool has the format:
sss_ssh_knownhostsproxy [-d sssd_domain] [-p ssh_port] HOST [PROXY_COMMAND]

Table 12.4. sss_ssh_knownhostsproxy Options

Short Argument Long Argument Description
HOSTNAME Gives the host name of the host to check and connect to. In the OpenSSH configuration file, this can be a token, %h.
PROXY_COMMAND Passes a proxy command to use to connect to the SSH client. This is similar to running ssh -o ProxyCommand=value. This option is used when running sss_ssh_knownhostsproxy from the command line or through another script, but is not necessary in the OpenSSH configuration file.
-d sssd_domain --domain sssd_domain Only searches for public keys in entries in the specified domain. If not given, SSSD searches for keys in all configured domains.
-p port --port port Uses this port to connect to the SSH client. By default, this is port 22.
To use this SSSD tool, add or edit two parameters to the ssh_config or ~/.ssh/config file:
  • Specify the command to use to connect to the SSH client (ProxyCommand). This is the sss_ssh_knownhostsproxy, with the desired arguments and host name.
  • Specify the location of the SSSD hosts file (GlobalKnownHostsFile).
For example, this looks for public keys in all configured SSSD domains and connects over whatever port and host are supplied:
ProxyCommand /usr/bin/sss_ssh_knownhostsproxy -p %p %h
GlobalKnownHostsFile /var/lib/sss/pubconf/known_hosts

Configuring OpenSSH to Use SSSD for User Keys

SSSD can provide user public keys to OpenSSH. The keys are read by the SSH daemon, sshd, directly from the output of the sss_ssh_authorizedkeys tool and are not stored in a file.
To configure sshd to read a user's public keys from an external program, in this case the sss_ssh_authorizedkeys tool, use the AuthorizedKeysCommand directive in the /etc/ssh/sshd_config file.
The sss_ssh_authorizedkeys tool can be used to acquire SSH public keys from the user entries in the Identity Management (IPA) domain and output them in OpenSSH authorized_keys format. The command has the following format:
sss_ssh_authorizedkeys [-d sssd_domain] USER

Table 12.5. sss_ssh_authorizedkeys Options

Short Argument Long Argument Description
USER The user name or account name for which to obtain the public key. In the OpenSSH configuration file, this can be represented by a token, %u.
-d sssd_domain --domain sssd_domain Only search for public keys in entries in the specified domain. If not given, SSSD searches for keys in all configured domains.
This feature is configured in /etc/ssh/sshd_config as follows:
AuthorizedKeysCommand /usr/bin/sss_ssh_authorizedkeys
AuthorizedKeysCommandRunAs nobody
These and further options are documented in the sshd_config(5) man page. Note that the sshd service must be restarted for any changes to take effect.

12.2.10. SSSD and Identity Providers (Domains)

SSSD recognizes domains, which are entries within the SSSD configuration file associated with different, external data sources. Domains are a combination of an identity provider (for user information) and, optionally, other providers such as authentication (for authentication requests) and for other operations, such as password changes. (The identity provider can also be used for all operations, if all operations are performed within a single domain or server.)
SSSD works with different LDAP identity providers (including OpenLDAP, Red Hat Directory Server, and Microsoft Active Directory) and can use native LDAP authentication, Kerberos authentication, or provider-specific authentication protocols (such as Active Directory).
A domain configuration defines the identity provider, the authentication provider, and any specific configuration to access the information in those providers. There are several types of identity and authentication providers:
  • LDAP, for general LDAP servers
  • Active Directory (an extension of the LDAP provider type)
  • Identity Management (an extension of the LDAP provider type)
  • Local, for the local SSSD database
  • Proxy
  • Kerberos (authentication provider only)
The identity and authentication providers can be configured in different combinations in the domain entry. The possible combinations are listed in Table 12.6, “Identity Store and Authentication Type Combinations”.

Table 12.6. Identity Store and Authentication Type Combinations

Identification Provider Authentication Provider
Identity Management (LDAP) Identity Management (LDAP)
Active Directory (LDAP) Active Directory (LDAP)
Active Directory (LDAP) Kerberos
LDAP LDAP
LDAP Kerberos
proxy LDAP
proxy Kerberos
proxy proxy
Along with the domain entry itself, the domain name must be added to the list of domains that SSSD will query. For example:
[sssd]
domains = LOCAL,Name
...

[domain/Name]
id_provider = type
auth_provider = type
provider_specific = value
global = value
global attributes are available to any type of domain, such as cache and time out settings. Each identity and authentication provider has its own set of required and optional configuration parameters.

Table 12.7. General [domain] Configuration Parameters

Parameter Value Format Description
id_provider string Specifies the data back end to use for this domain. The supported identity back ends are:
  • ldap
  • ipa (Identity Management in Red Hat Enterprise Linux)
  • ad (Microsoft Active Directory)
  • proxy, for a legacy NSS provider, such as nss_nis. Using a proxy ID provider also requires specifying the legacy NSS library to load to start successfully, set in the proxy_lib_name option.
  • local, the SSSD internal local provider
auth_provider string Sets the authentication provider used for the domain. The default value for this option is the value of id_provider. The supported authentication providers are ldap, ipa, ad, krb5 (Kerberos), proxy, and none.
min_id,max_id integer Optional. Specifies the UID and GID range for the domain. If a domain contains entries that are outside that range, they are ignored. The default value for min_id is 1; the default value for max_id is 0, which is unlimited.

Important

The default min_id value is the same for all types of identity provider. If LDAP directories are using UID numbers that start at one, it could cause conflicts with users in the local /etc/passwd file. To avoid these conflicts, set min_id to 1000 or higher as possible.
cache_credentials Boolean Optional. Specifies whether to store user credentials in the local SSSD domain database cache. The default value for this parameter is false. Set this value to true for domains other than the LOCAL domain to enable offline authentication.
entry_cache_timeout integer Optional. Specifies how long, in seconds, SSSD should cache positive cache hits. A positive cache hit is a successful query.
use_fully_qualified_names Boolean Optional. Specifies whether requests to this domain require fully-qualified domain names. If set to true, all requests to this domain must use fully-qualified domain names. It also means that the output from the request displays the fully-qualified name. Restricting requests to fully-qualified user names allows SSSD to differentiate between domains with users with conflicting user names.
If use_fully_qualified_names is set to false, it is possible to use the fully-qualified name in the requests, but only the simplified version is displayed in the output.
SSSD can only parse names based on the domain name, not the realm name. The same name can be used for both domains and realms, however.

12.2.11. Creating Domains: LDAP

An LDAP domain means that SSSD uses an LDAP directory as the identity provider (and, optionally, also as an authentication provider). SSSD supports several major directory services:
  • Red Hat Directory Server
  • OpenLDAP
  • Identity Management (IdM or IPA)
  • Microsoft Active Directory 2008 R2

Note

All of the parameters available to a general LDAP identity provider are also available to Identity Management and Active Directory identity providers, which are subsets of the LDAP provider.

Parameters for Configuring an LDAP Domain

An LDAP directory can function as both an identity provider and an authentication provider. The configuration requires enough information to identify and connect to the user directory in the LDAP server, but the way that those connection parameters are defined is flexible.
Other options are available to provide more fine-grained control, like specifying a user account to use to connect to the LDAP server or using different LDAP servers for password operations. The most common options are listed in Table 12.8, “LDAP Domain Configuration Parameters”.

Note

Server-side password policies always take precedence over the policy enabled from the client side. For example, when setting the ldap_pwd_policy=shadow option, the policies defined with the shadow LPAD attributes for a user have no effect on whether the password policy is enabled on the OpenLDAP server.

Tip

Many other options are listed in the man page for LDAP domain configuration, sssd-ldap(5).

Table 12.8. LDAP Domain Configuration Parameters

Parameter Description
ldap_uri Gives a comma-separated list of the URIs of the LDAP servers to which SSSD will connect. The list is given in order of preference, so the first server in the list is tried first. Listing additional servers provides failover protection. This can be detected from the DNS SRV records if it is not given.
ldap_search_base
Gives the base DN to use for performing LDAP user operations.

Important

If used incorrectly, ldap_search_base might cause SSSD lookups to fail.
With an AD provider, setting ldap_search_base is not required. The AD provider automatically discovers all the necessary information. Red Hat recommends not to set the parameter in this situation and instead rely on what the AD provider discovers.
ldap_tls_reqcert Specifies how to check for SSL server certificates in a TLS session. There are four options:
  • never disables requests for certificates.
  • allow requests a certificate, but proceeds normally even if no certificate is given or a bad certificate is given.
  • try requests a certificate and proceeds normally if no certificate is given, If a bad certificate is given, the session terminates.
  • demand and hard are the same option. This requires a valid certificate or the session is terminated.
The default is hard.
ldap_tls_cacert Gives the full path and file name to the file that contains the CA certificates for all of the CAs that SSSD recognizes. SSSD will accept any certificate issued by these CAs.
This uses the OpenLDAP system defaults if it is not given explicitly.
ldap_referrals Sets whether SSSD will use LDAP referrals, meaning forwarding queries from one LDAP database to another. SSSD supports database-level and subtree referrals. For referrals within the same LDAP server, SSSD will adjust the DN of the entry being queried. For referrals that go to different LDAP servers, SSSD does an exact match on the DN. Setting this value to true enables referrals; this is the default.
Referrals can negatively impact overall performance because of the time spent attempting to trace referrals. Disabling referral checking can significantly improve performance.
ldap_schema Sets what version of schema to use when searching for user entries. This can be rfc2307, rfc2307bis, ad, or ipa. The default is rfc2307.
In RFC 2307, group objects use a multi-valued attribute, memberuid, which lists the names of the users that belong to that group. In RFC 2307bis, group objects use the member attribute, which contains the full distinguished name (DN) of a user or group entry. RFC 2307bis allows nested groups using the member attribute. Because these different schema use different definitions for group membership, using the wrong LDAP schema with SSSD can affect both viewing and managing network resources, even if the appropriate permissions are in place.
For example, with RFC 2307bis, all groups are returned when using nested groups or primary/secondary groups.
$ id
uid=500(myserver) gid=500(myserver) groups=500(myserver),510(myothergroup)
If SSSD is using RFC 2307 schema, only the primary group is returned.
This setting only affects how SSSD determines the group members. It does not change the actual user data.
ldap_search_timeout Sets the time, in seconds, that LDAP searches are allowed to run before they are canceled and cached results are returned.
When an LDAP search times out, SSSD automatically switches to offline mode.
ldap_network_timeout Sets the time, in seconds, SSSD attempts to poll an LDAP server after a connection attempt fails. The default is six seconds.
ldap_opt_timeout Sets the time, in seconds, to wait before aborting synchronous LDAP operations if no response is received from the server. This option also controls the timeout when communicating with the KDC in case of a SASL bind. The default is five seconds.

LDAP Domain Example

The LDAP configuration is very flexible, depending on your specific environment and the SSSD behavior. These are some common examples of an LDAP domain, but the SSSD configuration is not limited to these examples.

Note

Along with creating the domain entry, add the new domain to the list of domains for SSSD to query in the sssd.conf file. For example:
domains = LOCAL,LDAP1,AD,PROXYNIS

Example 12.2. A Basic LDAP Domain Configuration

An LDAP domain requires three things:
  • An LDAP server
  • The search base
  • A way to establish a secure connection
The last item depends on the LDAP environment. SSSD requires a secure connection since it handles sensitive information. This connection can be a dedicated TLS/SSL connection or it can use Start TLS.
Using a dedicated TLS/SSL connection uses an LDAPS connection to connect to the server and is therefore set as part of the ldap_uri option:
# An LDAP domain
[domain/LDAP]
cache_credentials = true

id_provider = ldap
auth_provider = ldap

ldap_uri = ldaps://ldap.example.com:636
ldap_search_base = dc=example,dc=com
Using Start TLS requires a way to input the certificate information to establish a secure connection dynamically over an insecure port. This is done using the ldap_id_use_start_tls option to use Start TLS and then ldap_tls_cacert to identify the CA certificate which issued the SSL server certificates.
# An LDAP domain
[domain/LDAP]
cache_credentials = true

id_provider = ldap
auth_provider = ldap

ldap_uri = ldap://ldap.example.com
ldap_search_base = dc=example,dc=com
ldap_id_use_start_tls = true
ldap_tls_reqcert = demand
ldap_tls_cacert = /etc/pki/tls/certs/ca-bundle.crt

12.2.12. Creating Domains: Identity Management (IdM)

The Identity Management (IdM or IPA) identity provider is an extension of a generic LDAP provider. All of the configuration options for an LDAP provider are available to the IdM provider, as well as some additional parameters which allow SSSD to work as a client of the IdM domain and extend IdM functionality.
Identity Management can work as a provider for identities, authentication, access control rules, and passwords, all of the *_provider parameters for a domain. Additionally, Identity Management has configuration options within its own domain to manage SELinux policies, automount information, and host-based access control. All of those features in IdM domains can be tied to SSSD configuraiton, allowing those security-related policies to be applied and cached for system users.

Example 12.3. Basic IdM Provider

An IdM provider, like an LDAP provider, can be set to serve several different services, including identity, authentication, and access control
For IdM servers, there are two additional settings which are very useful (although not required):
  • Use the specific IdM schema rather than the default RFC 2307 schema.
  • Set SSSD to update the Identity Management domain's DNS server with the IP address of this client when the client first connects to the IdM domain.
[sssd]
domains = local,example.com
...

[domain/example.com]
id_provider = ipa
ipa_server = ipaserver.example.com
ipa_hostname = ipa1.example.com
auth_provider = ipa
access_provider = ipa
chpass_provider = ipa

# set which schema to use
ldap_schema = ipa

# automatically update IdM DNS records
ipa_dyndns_update = true
Identity Management defines and maintains security policies and identities for users across a Linux domain. This includes access control policies, SELinux policies, and other rules. Some of these elements in the IdM domain interact directly with SSSD, using SSSD as an IdM client — and those features can be managed in the IdM domain entry in sssd.conf.
Most of the configuration parameters relate to setting schema elements (which is not relevant in most deployments because IdM uses a fixed schema) and never need to be changed. In fact, none of the features in IdM require client-side settings. But there may be circumstances where tweaking the behavior is helpful.

Example 12.4. IdM Provider with SELinux

IdM can define SELinux user policies for system users, so it can work as an SELinux provider for SSSD. This is set in the selinux_provider parameter. The provider defaults to the id_provider value, so this is not necessary to set explicitly to support SELinux rules. However, it can be useful to explicitly disable SELinux support for the IdM provider in SSSD.
selinux_provider = ipa

Example 12.5. IdM Provider with Host-Based Access Control

IdM can define host-based access controls, restricting access to services or entire systems based on what host a user is using to connect or attempting to connect to. This rules can be evaluated and enforced by SSSD as part of the access provider behavior.
For host-based access controls to be in effect, the Identity Management server must be the access provider, at a minimum.
There are two options which can be set for how SSSD evaluates host-based access control rules:
  • SSSD can evaluate what machine (source host) the user is using to connect to the IdM resource; this is disabled by default, so that only the target host part of the rule is evaluated.
  • SSSD can refresh the host-based access control rules in its cache at a specified interval.
For example:
access_provider = ipa	
ipa_hbac_refresh = 120

# check for source machine rules; disabled by default
ipa_hbac_support_srchost = true

Example 12.6. Identity Management with Cross-Realm Kerberos Trusts

Identity Management (IdM or IPA) can be configured with trusted relationships between Active Directory DNS domains and Kerberos realms. This allows Active Directory users to access services and hosts on Linux systems.
There are two configuration settings in SSSD that are used with cross-realm trusts:
  • A service that adds required data to Kerberos tickets
  • A setting to support subdomains
Kerberos Ticket Data
Microsoft uses a special authorization structure called privileged access certificates or MS-PAC. A PAC is embedded in a Kerberos ticket as a way of identifying the entity to other Windows clients and servers in the Windows domain.
SSSD has a special PAC service which generates the additional data for Kerberos tickets. When using an Active Directory domain, it may be necessary to include the PAC data for Windows users. In that case, enable the pac service in SSSD:
[sssd]
services = nss, pam, pac
...
Windows Subdomains
Normally, a domain entry in SSSD corresponds directly to a single identity provider. However, with IdM cross-realm trusts, the IdM domain can trust another domain, so that the domains are transparent to each other. SSSD can follow that trusted relationship, so that if an IdM domain is configured, any Windows domain is also automatically searched and supported by SSSD — without having to be configured in a domain section in SSSD.
This is configured by adding the subdomains_provider parameter to the IdM domain section. This is actually an optional parameter; if a subdomain is discovered, then SSSD defaults to using the ipa provider type. However, this parameter can also be used to disable subdomain fetches by setting a value of none.
[domain/IDM]
...	
subdomains_provider = ipa
get_domains_timeout = 300

12.2.13. Creating Domains: Active Directory

The Active Directory identity provider is an extension of a generic LDAP provider. All of the configuration options for an LDAP provider are available to the Active Directory provider, as well as some additional parameters related to user accounts and identity mapping between Active Directory and system users.
There are some fundamental differences between standard LDAP servers and an Active Directory server. When configuring an Active Directory provider, there are some configuration areas, then, which require specific configuration:
  • Identities using a Windows security ID must be mapped to the corresponding Linux system user ID.
  • Searches must account for the range retrieval extension.
  • There may be performance issues with LDAP referrals.

Mapping Active Directory Securiy IDs and Linux User IDs

There are inherent structural differences between how Windows and Linux handle system users and in the user schemas used in Active Directory and standard LDAPv3 directory services. When using an Active Directory identity provider with SSSD to manage system users, it is necessary to reconcile the Active Directory-style user to the new SSSD user. There are two ways to do this:
  • Using Services for Unix to insert POSIX attributes on Windows user and group entries, and then having those attributes pulled into PAM/NSS
  • Using ID mapping on SSSD to create a map between Active Directory security IDs (SIDs) and the generated UIDs on Linux
ID mapping is the simplest option for most environments because it requires no additional packages or configuration on Active Directory.

The Mechanism of ID Mapping

Linux/Unix systems use a local user ID number and group ID number to identify users on the system. These UID:GID numbers are a simple integer, such as 501:501. These numbers are simple because they are always created and administered locally, even for systems which are part of a larger Linux/Unix domain.
Microsoft Windows and Active Directory use a different user ID structure to identify users, groups, and machines. Each ID is constructed of different segments that identify the security version, the issuing authority type, the machine, and the identity itself. For example:
S-1-5-21-3623811015-3361044348-30300820-1013
The third through sixth blocks are the machine identifier:
S-1-5-21-3623811015-3361044348-30300820-1013
The last block is the relative identifier (RID) which identifies the specific entity:
S-1-5-21-3623811015-3361044348-30300820-1013
A range of possible ID numbers are always assigned to SSSD. (This is a local range, so it is the same for every machine.)
|_____________________________|
|                             |
minimum ID                    max ID
This range is divided into 10,000 sections (by default), with each section allocated 200,000 IDs.
| slice 1 | slice 2 |   ...   |
|_________|_________|_________|
|         |         |         |
minimum ID                    max ID
When a new Active Directory domain is detected, the SID is hashed. Then, SSSD takes the modulus of the hash and the number of available sections to determine which ID section to assign to the Active Directory domain. This is a reliably consistent means of assigning ID sections, so the same ID range is assigned to the same Active Directory domain on most client machines.
| Active  | Active  |         |
|Directory|Directory|         |
|domain 1 |domain 2 |   ...   |
|         |         |         |
| slice 1 | slice 2 |   ...   |
|_________|_________|_________|
|         |         |         |
minimum ID                    max ID

Note

While the method of assigning ID sections is consistent, ID mapping is based on the order that an Active Directory domain is encountered on a client machine — so it may not result in consistent ID range assignments on all Linux client machines. If consistency is required, then consider disabling ID mapping and using explicit POSIX attributes.

ID Mapping Parameters

ID mapping is enabled in two parameters, one to enable the mapping and one to load the appropriate Active Directory user schema:
ldap_id_mapping = True
ldap_schema = ad

Note

When ID mapping is enabled, the uidNumber and gidNumber attributes are ignored. This prevents any manually-assigned values. If any values must be manually assigned, then all values must be manually assigned, and ID mapping should be disabled.

Mapping Users

When an Active Directory user attempts to log into a local system service for the first time, an entry for that user is created in the SSSD cache. The remote user is set up much like a system user:
  • A system UID is created for the user based on his SID and the ID range for that domain.
  • A GID is created for the user, which is identical to the UID.
  • A private group is created for the user.
  • A home directory is created, based on the home directory format in the sssd.conf file.
  • A shell is created, according to the system defaults or the setting in the sssd.conf file.
  • If the user belongs to any groups in the Active Directory domain, then, using the SID, SSSD adds the user to those groups on the Linux system.

Active Directory Users and Range Retrieval Searches

Microsoft Active Directory has an attribute, MaxValRange, which sets a limit on how many values for a multi-valued attribute will be returned. This is the range retrieval search extension. Essentially, this runs multiuple mini-searches, each returning a subset of the results within a given range, until all matches are returned.
For example, when doing a search for the member attribute, each entry could have multiple values, and there can be multiple entries with that attribute. If there are 2000 matching results (or more), then MaxValRange limits how many are displayed at once; this is the value range. The given attribute then has an additional flag set, showing which range in the set the result is in:
attribute:range=low-high:value
For example, results 100 to 500 in a search:
member;range=99-499: cn=John Smith...
This is described in the Microsoft documentation at http://msdn.microsoft.com/en-us/library/cc223242.aspx.
SSSD supports range retrievals with Active Directory providers as part of user and group management, without any additional configuration.
However, some LDAP provider attributes which are available to configure searches — such as ldap_user_search_base — are not performant with range retrievals. Be cautious when configuring search bases in the Active Directory provider domain and consider what searches may trigger a range retrieval.

Performance and LDAP Referrals

Referrals can negatively impact overall performance because of the time spent attempting to trace referrals. There is particularly bad performance degradation when referral chasing is used with an Active Directory identity provider. Disabling referral checking can significantly improve performance.
LDAP referrals are enabled by default, so they must be explicitly disabled in the LDAP domain configuration. For example:
ldap_referrals = false

Active Directory as Other Provider Types

Active Directory can be used as an identity provider and as an access, password, and authentication provider.
There are a number of options in the generic LDAP provider configuration which can be used to configure an Active Directory provider. Using the ad value is a short-cut which automatically pulls in the parameters and values to configure a given provider for Active Directory. For example, using access_provider = ad to configure an Active Directory access provider expands to this configuration using the explicit LDAP provider parameters:
access_provider = ldap
ldap_access_order = expire
ldap_account_expire_policy = ad

Procedure 12.6. Configuring an Active Directory Identity Provider

Active Directory can work as a provider for identities, authentication, access control rules, and passwords, all of the *_provider parameters for a domain. Additionally, it is possible to load the native Active Directory schema for user and group entries, rather than using the default RFC 2307.
  1. Make sure that both the Active Directory and Linux systems have a properly configured environment.
    • Name resolution must be properly configured, particularly if service discovery is used with SSSD.
    • The clocks on both systems must be in sync for Kerberos to work properly.
  2. Set up the Linux system as an Active Directory client and enroll it within the Active Directory domain. This is done by configuring the Kerberos and Samba services on the Linux system.
    1. Set up Kerberos to use the Active Directory Kerberos realm.
      1. Open the Kerberos client configuration file.
        ~]# vim /etc/krb5.conf
      2. Configure the [logging] and [libdefaults] sections so that they connect to the Active Directory realm.
        [logging]
         default = FILE:/var/log/krb5libs.log
        
        [libdefaults]
         default_realm = EXAMPLE.COM
         dns_lookup_realm = true
         dns_lookup_kdc = true
         ticket_lifetime = 24h
         renew_lifetime = 7d
         rdns = false
         forwardable = false
        If autodiscovery is not used with SSSD, then also configure the [realms] and [domain_realm] sections to explicitly define the Active Directory server.
    2. Configure the Samba server to connect to the Active directory server.
      1. Open the Samba configuration file.
        ~]# vim /etc/samba/smb.conf
      2. Set the Active Directory domain information in the [global] section.
        [global]
           workgroup = EXAMPLE
           client signing = yes
           client use spnego = yes
           kerberos method = secrets and keytab
           log file = /var/log/samba/%m.log
           password server = AD.EXAMPLE.COM
           realm = EXAMPLE.COM
           security = ads
    3. Add the Linux machine to the Active Directory domain.
      1. Obtain Kerberos credentials for a Windows administrative user.
        ~]# kinit Administrator
      2. Add the machine to the domain using the net command.
        ~]# net ads join -k
        Joined 'server' to dns domain 'example.com'
        This creates a new keytab file, /etc/krb5.keytab.
        List the keys for the system and check that the host principal is there.
        ~]# klist -k
  3. Use authconfig to enable SSSD for system authentication.
    # authconfig --update --enablesssd --enablesssdauth
  4. Set the Active Directory domain as an identity provider in the SSSD configuration, as shown in Example 12.7, “An Active Directory 2008 R2 Domain” and Example 12.8, “An Active Directory 2008 R2 Domain with ID Mapping”.
  5. Restart the SSH service to load the new PAM configuration.
    ~]# service restart sshd
  6. Restart SSSD after changing the configuration file.
    ~]# service sssd restart

Example 12.7. An Active Directory 2008 R2 Domain

~]# vim /etc/sssd/sssd.conf

[sssd]
config_file_version = 2
domains = ad.example.com
services = nss, pam

...

[domain/ad.example.com]
id_provider = ad
ad_server = ad.example.com
ad_hostname = ad.example.com
auth_provider = ad
chpass_provider = ad
access_provider = ad

# defines user/group schema type
ldap_schema = ad

# using explicit POSIX attributes in the Windows entries
ldap_id_mapping = False

# caching credentials
cache_credentials = true

# access controls
ldap_access_order = expire
ldap_account_expire_policy = ad
ldap_force_upper_case_realm = true

# performance
ldap_referrals = false
There are two parameters that are critical for ID mapping: the Active Directory schema must be loaded (ldap_schema) and ID mapping must be explicitly enabled (ldap_id_mapping).

Example 12.8. An Active Directory 2008 R2 Domain with ID Mapping

~]# vim /etc/sssd/sssd.conf

[sssd]
config_file_version = 2
domains = ad.example.com
services = nss, pam

...

[domain/ad.example.com]
id_provider = ad
ad_server = ad.example.com
ad_hostname = ad.example.com
auth_provider = ad
chpass_provider = ad
access_provider = ad

# defines user/group schema type
ldap_schema = ad

# for SID-UID mapping
ldap_id_mapping = True

# caching credentials
cache_credentials = true

# access controls
ldap_access_order = expire
ldap_account_expire_policy = ad
ldap_force_upper_case_realm = true

# performance
ldap_referrals = false
All of the potential configuration attributes for an Active Directory domain are listed in the sssd-ldap(5) and sssd-ad(5) man pages.

12.2.14. Configuring Domains: Active Directory as an LDAP Provider (Alternative)

While Active Directory can be configured as a type-specific identity provider, it can also be configured as a pure LDAP provider with a Kerberos authentication provider.

Procedure 12.7. Configuring Active Directory as an LDAP Provider

  1. It is recommended that SSSD connect to the Active Directory server using SASL, which means that the local host must have a service keytab for the Windows domain on the Linux host.
    This keytab can be created using Samba.
    1. Configure the /etc/krb5.conf file to use the Active Directory realm.
      [logging]
       default = FILE:/var/log/krb5libs.log
      
      [libdefaults]
       default_realm = AD.EXAMPLE.COM
       dns_lookup_realm = true
       dns_lookup_kdc = true
       ticket_lifetime = 24h
       renew_lifetime = 7d
       rdns = false
       forwardable = false
      
      [realms]
      # Define only if DNS lookups are not working
      # AD.EXAMPLE.COM = {
      #  kdc = server.ad.example.com
      #  admin_server = server.ad.example.com
      #  master_kdc = server.ad.example.com
      # }
      
      [domain_realm]
      # Define only if DNS lookups are not working
      # .ad.example.com = AD.EXAMPLE.COM
      # ad.example.com = AD.EXAMPLE.COM
    2. Set the Samba configuration file, /etc/samba/smb.conf, to point to the Windows Kerberos realm.
      [global]
         workgroup = EXAMPLE
         client signing = yes
         client use spnego = yes
         kerberos method = secrets and keytab
         log file = /var/log/samba/%m.log
         password server = AD.EXAMPLE.COM
         realm = EXAMPLE.COM
         security = ads
      
    3. To initialize Kerberos, type the following command as root:
      ~]# kinit Administrator@EXAMPLE.COM
    4. Then, run the net ads command to log in as an administrator principal. This administrator account must have sufficient rights to add a machine to the Windows domain, but it does not require domain administrator privileges.
      ~]# net ads join -U Administrator
    5. Run net ads again to add the host machine to the domain. This can be done with the host principal (host/FQDN) or, optionally, with the NFS service (nfs/FQDN).
      ~]# net ads join createupn="host/rhel-server.example.com@AD.EXAMPLE.COM" -U Administrator
  2. Make sure that the Services for Unix package is installed on the Windows server.
  3. Set up the Windows domain which will be used with SSSD.
    1. On the Windows machine, open Server Manager.
    2. Create the Active Directory Domain Services role.
    3. Create a new domain, such as ad.example.com.
    4. Add the Identity Management for UNIX service to the Active Directory Domain Services role. Use the Unix NIS domain as the domain name in the configuration.
  4. On the Active Directory server, create a group for the Linux users.
    1. Open Administrative Tools and select Active Directory Users and Computers.
    2. Select the Active Directory domain, ad.example.com.
    3. In the Users tab, right-click and select Create a New Group.
    4. Name the new group unixusers, and save.
    5. Double-click the unixusers group entry, and open the Users tab.
    6. Open the Unix Attributes tab.
    7. Set the NIS domain to the NIS domain that was configured for ad.example.com and, optionally, set a group ID (GID) number.
  5. Configure a user to be part of the Unix group.
    1. Open Administrative Tools and select Active Directory Users and Computers.
    2. Select the Active Directory domain, ad.example.com.
    3. In the Users tab, right-click and select Create a New User.
    4. Name the new user aduser, and make sure that the User must change password at next logon and Lock account checkboxes are not selected.
      Then save the user.
    5. Double-click the aduser user entry, and open the Unix Attributes tab. Make sure that the Unix configuration matches that of the Active Directory domain and the unixgroup group:
      • The NIS domain, as created for the Active Directory domain
      • The UID
      • The login shell, to /bin/bash
      • The home directory, to /home/aduser
      • The primary group name, to unixusers

    TIP

    Password lookups on large directories can take several seconds per request. The initial user lookup is a call to the LDAP server. Unindexed searches are much more resource-intensive, and therefore take longer, than indexed searches because the server checks every entry in the directory for a match. To speed up user lookups, index the attributes that are searched for by SSSD:
    • uid
    • uidNumber
    • gidNumber
    • gecos
  6. On the Linux system, configure the SSSD domain.
    ~]# vim /etc/sssd/sssd.conf
    For a complete list of LDAP provider parameters, see the sssd-ldap(5) man pages.

    Example 12.9. An Active Directory 2008 R2 Domain with Services for Unix

    [sssd]
    config_file_version = 2
    domains = ad.example.com
    services = nss, pam
    
    ...
    
    [domain/ad.example.com]
    cache_credentials = true
    
    # for performance
    ldap_referrals = false
    
    id_provider = ldap
    auth_provider = krb5
    chpass_provider = krb5
    access_provider = ldap
    
    ldap_schema = rfc2307bis
    
    ldap_sasl_mech = GSSAPI
    ldap_sasl_authid = host/rhel-server.example.com@AD.EXAMPLE.COM 
    
    #provide the schema for services for unix
    ldap_schema = rfc2307bis
    
    ldap_user_search_base = ou=user accounts,dc=ad,dc=example,dc=com
    ldap_user_object_class = user
    ldap_user_home_directory = unixHomeDirectory
    ldap_user_principal = userPrincipalName
    
    # optional - set schema mapping
    # parameters are listed in sssd-ldap
    ldap_user_object_class = user
    ldap_user_name = sAMAccountName
    
    ldap_group_search_base = ou=groups,dc=ad,dc=example,dc=com
    ldap_group_object_class = group
    
    ldap_access_order = expire
    ldap_account_expire_policy = ad
    ldap_force_upper_case_realm = true
    ldap_referrals = false
    
    krb5_realm = AD-REALM.EXAMPLE.COM
    # required
    krb5_canonicalize = false
  7. Restart SSSD.
    ~]# service sssd restart

12.2.15. Domain Options: Setting Username Formats

One of the primary actions that SSSD performs is mapping a local system user to an identity in the remote identity provider. SSSD uses a combination of the user name and the domain back end name to create the login identity.
As long as they belong to different domains, SSSD can recognize different users with the same user name. For example, SSSD can successfully authenticate both jsmith in the ldap.example.com domain and jsmith in the ldap.otherexample.com domain.
The name format used to construct full user name is (optionally) defined universally in the [sssd] section of the configuration and can then be defined individually in each domain section.
Usernames for different services — LDAP, Samba, Active Directory, Identity Management, even the local system — all have different formats. The expression that SSSD uses to identify user name/domain name sets must be able to interpret names in different formats. This expression is set in the re_expression parameter.
In the global default, this filter constructs a name in the form name@domain:
(?P<name>[^@]+)@?(?P<domain>[^@]*$)

Note

The regular expression format is Python syntax.
The domain part may be supplied automatically, based on the domain name of the identity provider. Therefore, a user can log in as jsmith and if the user belongs to the LOCAL domain (for example), then his user name is interpreted by SSSD as jsmith@LOCAL.
However, other identity providers may have other formats. Samba, for example, has a very strict format so that user name must match the form DOMAIN\username. For Samba, then, the regular expression must be:
(?P<domain>[^\\]*?)\\?(?P<name>[^\\]+$)
Some providers, such as Active Directory, support multiple different name formats. Active Directory and Identity Management, for example, support three different formats by default:
  • username
  • username@domain.name
  • DOMAIN\username
The default value for Active Directory and Identity Management providers, then, is a more complex filter that allows all three name formats:
(((?P<domain>[^\\]+)\\(?P<name>.+$))|((?P<name>[^@]+)@(?P<domain>.+$))|(^(?P<name>[^@\\]+)$)) 

Note

Requesting information with the fully-qualified name, such as jsmith@ldap.example.com, always returns the proper user account. If there are multiple users with the same user name in different domains, specifying only the user name returns the user for whichever domain comes first in the lookup order.
While re_expression is the most important method for setting user name formats, there are two other options which are useful for other applications.
Default Domain Name Value
The first sets a default domain name to be used with all users, default_domain_suffix. (This is a global setting, available in the [sssd] section only.) There may be a case where multiple domains are configured but only one stores user data and the others are used for host or service identities. Setting a default domain name allows users to log in with only their user name, not specifying the domain name (which would be required for users outside the primary domain).
[sssd]
...
default_domain_suffix = USERS.EXAMPLE.COM
Full Name Format for Output
The other parameter is related to re_expression, only instead of defining how to interpret a user name, it defines how to print an identified name. The full_name_format parameter sets how the user name and domain name (once determined) are displayed.
full_name_format = %1$s@%2$s

12.2.16. Domain Options: Enabling Offline Authentication

User identities are always cached, as well as information about the domain services. However, user credentials are not cached by default. This means that SSSD always checks with the back end identity provider for authentication requests. If the identity provider is offline or unavailable, there is no way to process those authentication requests, so user authentication could fail.
It is possible to enable offline credentials caching, which stores credentials (after successful login) as part of the user account in the SSSD cache. Therefore, even if an identity provider is unavailable, users can still authenticate, using their stored credentials. Offline credentials caching is primarily configured in each individual domain entry, but there are some optional settings that can be set in the PAM service section, because credentials caching interacts with the local PAM service as well as the remote domain.
[domain/EXAMPLE]
cache_credentials = true
There are optional parameters that set when those credentials expire. Expiration is useful because it can prevent a user with a potentially outdated account or credentials from accessing local services indefinitely.
The credentials expiration itself is set in the PAM service, which processes authentication requests for the system.
[sssd]
services = nss,pam
...

[pam]
offline_credentials_expiration = 3
...

[domain/EXAMPLE]
cache_credentials = true
...
offline_credentials_expiration sets the number of days after a successful login that a single credentials entry for a user is preserved in cache. Setting this to zero (0) means that entries are kept forever.
While not related to the credentials cache specifically, each domain has configuration options on when individual user and service caches expire:
  • account_cache_expiration sets the number of days after a successful login that the entire user account entry is removed from the SSSD cache. This must be equal to or longer than the individual offline credentials cache expiration period.
  • entry_cache_timeout sets a validity period, in seconds, for all entries stored in the cache before SSSD requests updated information from the identity provider. There are also individual cache timeout parameters for group, service, netgroup, sudo, and autofs entries; these are listed in the sssd.conf man page. The default time is 5400 seconds (90 minutes).
For example:
[sssd]
services = nss,pam
...

[pam]
offline_credentials_expiration = 3
...

[domain/EXAMPLE]
cache_credentials = true
account_cache_expiration = 7
entry_cache_timeout = 14400
...

12.2.17. Domain Options: Setting Password Expirations

Password policies generally set an expiration time, after which passwords expire and must be replaced. Password expiration policies are evaluated on the server side through the identity provider, then a warning can be processed and displayed in SSSD through its PAM service.
There are two ways to display password expiration warnings:
  • The pam_pwd_expiration_warning parameter defines the global default setting for all domains on how far in advance of the password expiration to display a warning. This is set for the PAM service.
  • The pwd_expiration_warning parameter defines the per-domain setting on how far in advance of the password expiration to display a warning.
    When using a domain-level password expiration warning, an authentication provider (auth_provider) must also be configured for the domain.
For example:
[sssd]
services = nss,pam
...

[pam]
pam_pwd_expiration_warning = 3
...

[domain/EXAMPLE]
id_provider = ipa
auth_provider = ipa
pwd_expiration_warning = 7
The password expiration warning must be sent from the server to SSSD for the warning to be displayed. If no password warning is sent from the server, no message is displayed through SSSD, even if the password expiration time is within the period set in SSSD.
If the password expiration warning is not set in SSSD or is set to 0, then the SSSD password warning filter is not applied and the server-side password warning is automatically displayed.

Note

As long as the password warning is sent from the server, the PAM or domain password expirations in effect override the password warning settings on the back end identity provider. For example, consider a back end identity provider that has the warning period set at 28 days, but the PAM service in SSSD has it set to 7 days. The provider sends the warning to SSSD starting at 28 days, but the warning is not displayed locally until 7 days, according to the password expiration set in the SSSD configuration.

Password Expiration Warnings for Non-Password Authentication

By default, password expiration is verified only if the user enters the password during authentication. However, you can configure SSSD to perform the expiration check and display the warning even when a non-password authentication method is used, for example, during SSH login.
To enable password expiration warnings with non-password authentication methods:
  1. Make sure the access_provider parameter is set to ldap in the sssd.conf file.
  2. Make sure the ldap_pwd_policy parameter is set in sssd.conf. In most situations, the appropriate value is shadow.
  3. Add one of the following pwd_expire_* values to the ldap_access_order parameter in sssd.conf. If the password is about to expire, each one of these values only displays the expiration warning. In addition:
    • pwd_expire_policy_reject prevents the user from logging in if the password is already expired.
    • pwd_expire_policy_warn allows the user to log in even if the password is already expired.
    • pwd_expire_policy_renew prompts the user to immediately change the password if the user attempts to log in with an expired password.
    For example:
    [domain/EXAMPLE]
    access_provider = ldap
    ldap_pwd_policy = shadow
    ldap_access_order = pwd_expire_policy_warn
    
For more details on using ldap_access_order and its values, see the sssd-ldap(5) man page.

12.2.18. Domain Options: Using DNS Service Discovery

DNS service discovery, defined in RFC 2782, allows applications to check the SRV records in a given domain for certain services of a certain type; it then returns any servers discovered of that type.
With SSSD, the identity and authentication providers can either be explicitly defined (by IP address or host name) or they can be discovered dynamically, using service discovery. If no provider server is listed — for example, if id_provider = ldap is set without a corresponding ldap_uri parameter — then discovery is automatically used.
The DNS discovery query has this format:
_service._protocol.domain
For example, a scan for an LDAP server using TCP in the example.com domain looks like this:
_ldap._tcp.example.com

Note

For every service with which to use service discovery, add a special DNS record to the DNS server:
_service._protocol._domain TTL priority weight port hostname
For SSSD, the service type is LDAP by default, and almost all services use TCP (except for Kerberos, which starts with UDP). For service discovery to be enabled, the only thing that is required is the domain name. The default is to use the domain portion of the machine host name, but another domain can be specified (using the dns_discovery_domain parameter).
So, by default, no additional configuration needs to be made for service discovery — with one exception. The password change provider has server discovery disabled by default, and it must be explicitly enabled by setting a service type.
[domain/EXAMPLE]
...
chpass_provider = ldap
ldap_chpass_dns_service_name = ldap
While no configuration is necessary, it is possible for server discovery to be customized by using a different DNS domain (dns_discovery_domain) or by setting a different service type to scan for. For example:
[domain/EXAMPLE]
id _provider = ldap

dns_discovery_domain = corp.example.com
ldap_dns_service_name = ldap

chpass_provider = krb5
ldap_chpass_dns_service_name = kerberos
Lastly, service discovery is never used with backup servers; it is only used for the primary server for a provider. What this means is that discovery can be used initially to locate a server, and then SSSD can fall back to using a backup server. To use discovery for the primary server, use _srv_ as the primary server value, and then list the backup servers. For example:
[domain/EXAMPLE]
id _provider = ldap
ldap_uri = _srv_
ldap_backup_uri = ldap://ldap2.example.com

auth_provider = krb5
krb5_server = _srv_
krb5_backup_server = kdc2.example.com

chpass_provider = krb5
ldap_chpass_dns_service_name = kerberos
ldap_chpass_uri = _srv_
ldap_chpass_backup_uri = kdc2.example.com

Note

Service discovery cannot be used with backup servers, only primary servers.
If a DNS lookup fails to return an IPv4 address for a host name, SSSD attempts to look up an IPv6 address before returning a failure. This only ensures that the asynchronous resolver identifies the correct address.
The host name resolution behavior is configured in the lookup family order option in the sssd.conf configuration file.

12.2.19. Domain Options: Using IP Addresses in Certificate Subject Names (LDAP Only)

Using an IP address in the ldap_uri option instead of the server name may cause the TLS/SSL connection to fail. TLS/SSL certificates contain the server name, not the IP address. However, the subject alternative name field in the certificate can be used to include the IP address of the server, which allows a successful secure connection using an IP address.

Procedure 12.8. Using IP Addresses in Certificate Subject Names

  1. Convert an existing certificate into a certificate request. The signing key (-signkey) is the key of the issuer of whatever CA originally issued the certificate. If this is done by an external CA, it requires a separate PEM file; if the certificate is self-signed, then this is the certificate itself. For example:
    openssl x509 -x509toreq -in old_cert.pem -out req.pem -signkey key.pem
    With a self-signed certificate:
    openssl x509 -x509toreq -in old_cert.pem -out req.pem -signkey old_cert.pem
  2. Edit the /etc/pki/tls/openssl.cnf configuration file to include the server's IP address under the [ v3_ca ] section:
    subjectAltName = IP:10.0.0.10
  3. Use the generated certificate request to generate a new self-signed certificate with the specified IP address:
    openssl x509 -req -in req.pem -out new_cert.pem -extfile ./openssl.cnf -extensions v3_ca -signkey old_cert.pem
    The -extensions option sets which extensions to use with the certificate. For this, it should be v3_ca to load the appropriate section.
  4. Copy the private key block from the old_cert.pem file into the new_cert.pem file to keep all relevant information in one file.
When creating a certificate through the certutil utility provided by the nss-tools package, note that certutil supports DNS subject alternative names for certificate creation only.

12.2.20. Creating Domains: Proxy

A proxy with SSSD is just a relay, an intermediary configuration. SSSD connects to its proxy service, and then that proxy loads the specified libraries. This allows SSSD to use some resources that it otherwise would not be able to use. For example, SSSD only supports LDAP and Kerberos as authentication providers, but using a proxy allows SSSD to use alternative authentication methods like a fingerprint scanner or smart card.

Table 12.9. Proxy Domain Configuration Parameters

Parameter Description
proxy_pam_target Specifies the target to which PAM must proxy as an authentication provider. The PAM target is a file containing PAM stack information in the default PAM directory, /etc/pam.d/.
This is used to proxy an authentication provider.

Important

Ensure that the proxy PAM stack does not recursively include pam_sss.so.
proxy_lib_name Specifies which existing NSS library to proxy identity requests through.
This is used to proxy an identity provider.

Example 12.10. Proxy Identity and Kerberos Authentication

The proxy library is loaded using the proxy_lib_name parameter. This library can be anything as long as it is compatible with the given authentication service. For a Kerberos authentication provider, it must be a Kerberos-compatible library, like NIS.
[domain/PROXY_KRB5]
auth_provider = krb5
krb5_server = kdc.example.com
krb5_realm = EXAMPLE.COM

id_provider = proxy
proxy_lib_name = nis
cache_credentials = true

Example 12.11. LDAP Identity and Proxy Authentication

The proxy library is loaded using the proxy_pam_target parameter. This library must be a PAM module that is compatible with the given identity provider. For example, this uses a PAM fingerprint module with LDAP:
[domain/LDAP_PROXY]
id_provider = ldap
ldap_uri = ldap://example.com
ldap_search_base = dc=example,dc=com

auth_provider = proxy
proxy_pam_target = sssdpamproxy
cache_credentials = true
After the SSSD domain is configured, make sure that the specified PAM files are configured. In this example, the target is sssdpamproxy, so create a /etc/pam.d/sssdpamproxy file and load the PAM/LDAP modules:
auth          required      pam_frprint.so
account       required      pam_frprint.so
password      required      pam_frprint.so
session       required      pam_frprint.so

Example 12.12. Proxy Identity and Authentication

SSSD can have a domain with both identity and authentication proxies. The only configuration given then are the proxy settings, proxy_pam_target for the authentication PAM module and proxy_lib_name for the service, like NIS or LDAP.
This example illustrates a possible configuration, but this is not a realistic configuration. If LDAP is used for identity and authentication, then both the identity and authentication providers should be set to the LDAP configuration, not a proxy.
[domain/PROXY_PROXY]
auth_provider = proxy
id_provider = proxy
proxy_lib_name = ldap
proxy_pam_target = sssdproxyldap
cache_credentials = true
Once the SSSD domain is added, then update the system settings to configure the proxy service:
  1. Create a /etc/pam.d/sssdproxyldap file which requires the pam_ldap.so module:
    auth          required      pam_ldap.so
    account       required      pam_ldap.so
    password      required      pam_ldap.so
    session       required      pam_ldap.so
  2. Make sure the nss-pam-ldapd package is installed.
    ~]# yum install nss-pam-ldapd
  3. Edit the /etc/nslcd.conf file, the configuration file for the LDAP name service daemon, to contain the information for the LDAP directory:
    uid nslcd
    gid ldap
    uri ldaps://ldap.example.com:636
    base dc=example,dc=com
    ssl on
    tls_cacertdir /etc/openldap/cacerts

12.2.21. Creating Domains: Kerberos Authentication

Both LDAP and proxy identity providers can use a separate Kerberos domain to supply authentication. Configuring a Kerberos authentication provider requires the key distribution center (KDC) and the Kerberos domain. All of the principal names must be available in the specified identity provider; if they are not, SSSD constructs the principals using the format username@REALM.

Note

Kerberos can only provide authentication; it cannot provide an identity database.
SSSD assumes that the Kerberos KDC is also a Kerberos kadmin server. However, production environments commonly have multiple, read-only replicas of the KDC and only a single kadmin server. Use the krb5_kpasswd option to specify where the password changing service is running or if it is running on a non-default port. If the krb5_kpasswd option is not defined, SSSD tries to use the Kerberos KDC to change the password.
The basic Kerberos configuration options are listed in Table 12.10, “Kerberos Authentication Configuration Parameters”. The sssd-krb5(5) man page has more information about Kerberos configuration options.

Example 12.13. Basic Kerberos Authentication

# A domain with identities provided by LDAP and authentication by Kerberos
[domain/KRBDOMAIN]
id_provider = ldap
chpass_provider = krb5
ldap_uri = ldap://ldap.example.com
ldap_search_base = dc=example,dc=com
ldap-tls_reqcert = demand
ldap_tls_cacert = /etc/pki/tls/certs/ca-bundle.crt

auth_provider = krb5
krb5_server = kdc.example.com
krb5_backup_server = kerberos.example.com
krb5_realm = EXAMPLE.COM
krb5_kpasswd = kerberos.admin.example.com
krb5_auth_timeout = 15

Example 12.14. Setting Kerberos Ticket Renewal Options

The Kerberos authentication provider, among other tasks, requests ticket granting tickets (TGT) for users and services. These tickets are used to generate other tickets dynamically for specific services, as accessed by the ticket principal (the user).
The TGT initially granted to the user principal is valid only for the lifetime of the ticket (by default, whatever is configured in the configured KDC). After that, the ticket cannot be renewed or extended. However, not renewing tickets can cause problems with some services when they try to access a service in the middle of operations and their ticket has expired.
Kerberos tickets are not renewable by default, but ticket renewal can be enabled using the krb5_renewable_lifetime and krb5_renew_interval parameters.
The lifetime for a ticket is set in SSSD with the krb5_lifetime parameter. This specifies how long a single ticket is valid, and overrides any values in the KDC.
Ticket renewal itself is enabled in the krb5_renewable_lifetime parameter, which sets the maximum lifetime of the ticket, counting all renewals.
For example, the ticket lifetime is set at one hour and the renewable lifetime is set at 24 hours:
krb5_lifetime = 1h
krb5_renewable_lifetime = 1d
This means that the ticket expires every hour and can be renewed continually up to one day.
The lifetime and renewable lifetime values can be in seconds (s), minutes (m), hours (h), or days (d).
The other option — which must also be set for ticket renewal — is the krb5_renew_interval parameter, which sets how frequently SSSD checks to see if the ticket needs to be renewed. At half of the ticket lifetime (whatever that setting is), the ticket is renewed automatically. (This value is always in seconds.)
krb5_lifetime = 1h
krb5_renewable_lifetime = 1d
krb5_renew_interval = 60s

Note

If the krb5_renewable_lifetime value is not set or the krb5_renew_interval parameter is not set or is set to zero (0), then ticket renewal is disabled. Both krb5_renewable_lifetime and krb5_renew_interval are required for ticket renewal to be enabled.

Table 12.10. Kerberos Authentication Configuration Parameters

Parameter Description
chpass_provider Specifies which service to use for password change operations. This is assumed to be the same as the authentication provider. To use Kerberos, set this to krb5.
krb5_server Gives the primary Kerberos server, by IP address or host names, to which SSSD will connect.
krb5_backup_server Gives a comma-separated list of IP addresses or host names of Kerberos servers to which SSSD will connect if the primary server is not available. The list is given in order of preference, so the first server in the list is tried first.
After an hour, SSSD will attempt to reconnect to the primary service specified in the krb5_server parameter.
When using service discovery for KDC or kpasswd servers, SSSD first searches for DNS entries that specify UDP as the connection protocol, and then falls back to TCP.
krb5_realm Identifies the Kerberos realm served by the KDC.
krb5_lifetime Requests a Kerberos ticket with the specified lifetime in seconds (s), minutes (m), hours (h) or days (d).
krb5_renewable_lifetime Requests a renewable Kerberos ticket with a total lifetime that is specified in seconds (s), minutes (m), hours (h) or days (d).
krb5_renew_interval Sets the time, in seconds, for SSSD to check if tickets should be renewed. Tickets are renewed automatically once they exceed half their lifetime. If this option is missing or set to zero, then automatic ticket renewal is disabled.
krb5_store_password_if_offline Sets whether to store user passwords if the Kerberos authentication provider is offline, and then to use that cache to request tickets when the provider is back online. The default is false, which does not store passwords.
krb5_kpasswd Lists alternate Kerberos kadmin servers to use if the change password service is not running on the KDC.
krb5_ccname_template Gives the directory to use to store the user's credential cache. This can be templatized, and the following tokens are supported:
  • %u, the user's login name
  • %U, the user's login UID
  • %p, the user's principal name
  • %r, the realm name
  • %h, the user's home directory
  • %d, the value of the krb5ccache_dir parameter
  • %P, the process ID of the SSSD client.
  • %%, a literal percent sign (%)
  • XXXXXX, a string at the end of the template which instructs SSSD to create a unique filename safely
For example:
krb5_ccname_template = FILE:%d/krb5cc_%U_XXXXXX
krb5_ccachedir Specifies the directory to store credential caches. This can be templatized, using the same tokens as krb5_ccname_template, except for %d and %P. If %u, %U, %p, or %h are used, then SSSD creates a private directory for each user; otherwise, it creates a public directory.
krb5_auth_timeout Gives the time, in seconds, before an online authentication or change password request is aborted. If possible, the authentication request is continued offline. The default is 15 seconds.

12.2.22. Creating Domains: Access Control

SSSD provides a rudimentary access control for domain configuration, allowing either simple user allow/deny lists or using the LDAP back end itself.

Using the Simple Access Provider

The Simple Access Provider allows or denies access based on a list of user names or groups.
The Simple Access Provider is a way to restrict access to certain, specific machines. For example, if a company uses laptops, the Simple Access Provider can be used to restrict access to only a specific user or a specific group, even if a different user authenticated successfully against the same authentication provider.
The most common options are simple_allow_users and simple_allow_groups, which grant access explicitly to specific users (either the given users or group members) and deny access to everyone else. It is also possible to create deny lists (which deny access only to explicit people and implicitly allow everyone else access).
The Simple Access Provider adheres to the following four rules to determine which users should or should not be granted access:
  • If both the allow and deny lists are empty, access is granted.
  • If any list is provided, allow rules are evaluated first, and then deny rules. Practically, this means that deny rules supersede allow rules.
  • If an allowed list is provided, then all users are denied access unless they are in the list.
  • If only deny lists are provided, then all users are allowed access unless they are in the list.
This example grants access to two users and anyone who belongs to the IT group; implicitly, all other users are denied:
[domain/example.com]
access_provider = simple
simple_allow_users = jsmith,bjensen
simple_allow_groups = itgroup

Note

The LOCAL domain in SSSD does not support simple as an access provider.
Other options are listed in the sssd-simple man page, but these are rarely used.

Using the Access Filters

An LDAP, Active Directory, or Identity Management server can provide access control rules for a domain. The associated options (ldap_access_filter for LDAP and IdM and ad_access_filter for AD) specify which users are granted access to the specified host. The user filter must be used or all users are denied access. See the examples below:
[domain/example.com]
access_provider = ldap
ldap_access_filter = memberOf=cn=allowedusers,ou=Groups,dc=example,dc=com
[domain/example.com]
access_provider = ad
ad_access_filter = memberOf=cn=allowedusers,ou=Groups,dc=example,dc=com

Note

Offline caching for LDAP access providers is limited to determining whether the user's last online login attempt was successful. Users that were granted access during their last login will continue to be granted access while offline.
SSSD can also check results by the authorizedService or host attribute in an entry. In fact, all options — LDAP filter, authorizedService, and host — can be evaluated, depending on the user entry and the configuration. The ldap_access_order parameter lists all access control methods to use, in order of how they should be evaluated.
[domain/example.com]
access_provider = ldap
ldap_access_filter = memberOf=cn=allowedusers,ou=Groups,dc=example,dc=com
ldap_access_order = filter, host, authorized_service
The attributes in the user entry to use to evaluate authorized services or allowed hosts can be customized. Additional access control parameters are listed in the sssd-ldap(5) man page.

12.2.23. Creating Domains: Primary Server and Backup Servers

Identity and authentication providers for a domain can be configured for automatic failover. SSSD attempts to connect to the specified, primary server first. If that server cannot be reached, then SSSD then goes through the listed backup servers, in order.

Note

SSSD tries to connect to the primary server every 30 seconds, until the connection can be re-established, and then switches from the backup to the primary.
All of the major service areas have optional settings for primary and backup servers[3].

Table 12.11. Primary and Secondary Server Parameters

Service Area Primary Server Attribute Backup Server Attribute
LDAP identity provider ldap_uri ldap_backup_uri
Active Directory identity provider ad_server ad_backup_server
Identity Management (IdM or IPA) identity provider ipa_server ipa_backup_server
Kerberos authentication provider krb5_server krb5_backup_server
Kerberos authentication provider krb5_server krb5_backup_server
Password change provider ldap_chpass_uri ldap_chpass_backup_uri
One and only one server can be set as the primary server. (And, optionally, the primary server can be set to service discovery, using _srv_ rather than a host name.) Multiple backup servers can be set, in a comma-separate list. The backup server list is in order of preference, so the first server listed is tried first.
[domain/EXAMPLE]
id_provider = ad
ad_server = ad.example.com
ad_backup_server = ad1.example.com, ad-backup.example.com

12.2.24. Installing SSSD Utilities

Additional tools to handle the SSSD cache, user entries, and group entries are contained in the sssd-tools package. This package is not required, but it is useful to install to help administer user accounts.
~]# yum install sssd-tools

Note

The sssd-tools package is provided by the Optional subscription channel. See Section 7.4.8, “Adding the Optional and Supplementary Repositories” for more information on Red Hat additional channels.

12.2.25. SSSD and UID and GID Numbers

When a user is created — using system tools such as useradd or through an application such as Red Hat Identity Management or other client tools — the user is automatically assigned a user ID number and a group ID number.
When the user logs into a system or service, SSSD caches that user name with the associated UID/GID numbers. The UID number is then used as the identifying key for the user. If a user with the same name but a different UID attempts to log into the system, then SSSD treats it as two different users with a name collision.
What this means is that SSSD does not recognize UID number changes. It interprets it as a different and new user, not an existing user with a different UID number. If an existing user changes the UID number, that user is prevented from logging into SSSD and associated services and domains. This also has an impact on any client applications which use SSSD for identity information; the user with the conflict will not be found or accessible to those applications.

Important

UID/GID changes are not supported in SSSD.
If a user for some reason has a changed UID/GID number, then the SSSD cache must be cleared for that user before that user can log in again. For example:
~]# sss_cache -u jsmith
Cleaning the SSSD cache is covered in Section 12.2.28, “Purging the SSSD Cache”.

12.2.26. Creating Local System Users

There can be times when it is useful to seed users into the SSSD database rather than waiting for users to login and be added.

Note

Adding user accounts manually requires the sssd-tools package to be installed.
When creating new system users, it is possible to create a user within the SSSD local identity provider domain. This can be useful for creating new system users, for troubleshooting SSSD configuration, or for creating specialized or nested groups.
New users can be added using the sss_useradd command.
At its most basic, the sss_useradd command only requires the new user name.
~]# sss_useradd jsmith
There are other options (listed in the sss_useradd(8) man page) which can be used to set attributes on the account, like the UID and GID, the home directory, or groups which the user belongs to.
~]# sss_useradd --UID 501 --home /home/jsmith --groups admin,dev-group jsmith

12.2.27. Seeding Users into the SSSD Cache During Kickstart

Note

Adding user accounts manually requires the sssd-tools package to be installed.
With SSSD, users in a remote domain are not available in a local system until that identity is retrieved from the identity provider. However, some network interfaces are not available until a user has logged in — which is not possible if the user identity is somewhere over the network. In that case, it is possible to seed the SSSD cache with that user identity, associated with the appropriate domain, so that the user can log in locally and active the appropriate interfaces.
This is done using the sss_seed utility:
sss_seed --domain EXAMPLE.COM --username testuser --password-file /tmp/sssd-pwd.txt
This utility requires options that identify, at a minimum, the user name, domain name, and password.
  • --domain gives the domain name from the SSSD configuration. This domain must already exist in the SSSD configuration.
  • --username for the short name of the user account.
  • --password-file for the path and name of a file containing a temporary password for the seed entry. If the user account already exists in the SSSD cache, then the temporary password in this file overwrites the stored password in the SSSD cache.
Additional account configuration options are listed in the sss_seed(8) man page.
This would almost always be run as part of a kickstart or automated setup, so it would be part of a larger set of scripts, which would also enable SSSD, set up an SSSD domain, and create the password file. For example:
function make_sssd {
cat <<- _EOF_
[sssd]
domains = LOCAL
services = nss,pam

[nss]

[pam]

[domain/LOCAL]
id_provider = local
auth_provider = local
access_provider = permit
				
_EOF_
}

make_sssd >> /etc/sssd/sssd.conf

authconfig --enablesssd --enablesssdauth --update

function make_pwdfile {
cat <<1 _EOF_
password
_EOF_
}

make_pwdfile >> /tmp/sssd-pwd.txt

sss_seed --domain EXAMPLE.COM --username testuser --password-file /tmp/sssd-pwd.txt

12.2.28. Managing the SSSD Cache

SSSD can define multiple domains of the same type and different types of domain. SSSD maintains a separate database file for each domain, meaning each domain has its own cache. These cache files are stored in the /var/lib/sss/db/ directory.

Purging the SSSD Cache

As LDAP updates are made to the identity provider for the domains, it can be necessary to clear the cache to reload the new information quickly.
The cache purge utility, sss_cache, invalidates records in the SSSD cache for a user, a domain, or a group. Invalidating the current records forces the cache to retrieve the updated records from the identity provider, so changes can be realized quickly.

Note

This utility is included with SSSD in the sssd package.
Most commonly, this is used to clear the cache and update all records:
~]# sss_cache -E
The sss_cache command can also clear all cached entries for a particular domain:
~]# sss_cache -Ed LDAP1
If the administrator knows that a specific record (user, group, or netgroup) has been updated, then sss_cache can purge the records for that specific account and leave the rest of the cache intact:
~]# sss_cache -u jsmith

Table 12.12. Common sss_cache Options

Short Argument Long Argument Description
-E --everything Invalidates all cached entries with the exception of sudo rules.
-d name --domain name Invalidates cache entries for users, groups, and other entries only within the specified domain.
-G --groups Invalidates all group records. If -g is also used, -G takes precedence and -g is ignored.
-g name --group name Invalidates the cache entry for the specified group.
-N --netgroups Invalidates cache entries for all netgroup cache records. If -n is also used, -N takes precedence and -n is ignored.
-n name --netgroup name Invalidates the cache entry for the specified netgroup.
-U --users Invalidates cache entries for all user records. If the -u option is also used, -U takes precedence and -u is ignored.
-u name --user name Invalidates the cache entry for the specified user.

Deleting Domain Cache Files

All cache files are named for the domain. For example, for a domain named exampleldap, the cache file is named cache_exampleldap.ldb.
Be careful when you delete a cache file. This operation has significant effects:
  • Deleting the cache file deletes all user data, both identification and cached credentials. Consequently, do not delete a cache file unless the system is online and can authenticate with a user name against the domain's servers. Without a credentials cache, offline authentication will fail.
  • If the configuration is changed to reference a different identity provider, SSSD will recognize users from both providers until the cached entries from the original provider time out.
    It is possible to avoid this by purging the cache, but the better option is to use a different domain name for the new provider. When SSSD is restarted, it creates a new cache file with the new name and the old file is ignored.

12.2.29. Downgrading SSSD

When downgrading — either downgrading the version of SSSD or downgrading the operating system itself — then the existing SSSD cache needs to be removed. If the cache is not removed, then SSSD process is dead but a PID file remains. The SSSD logs show that it cannot connect to any of its associated domains because the cache version is unrecognized.
(Wed Nov 28 21:25:50 2012) [sssd] [sysdb_domain_init_internal] (0x0010): Unknown DB version [0.14], expected [0.10] for domain AD!
Users are then no longer recognized and are unable to authenticate to domain services and hosts.
After downgrading the SSSD version:
  1. Delete the existing cache database files.
    ~]# rm -rf /var/lib/sss/db/*
  2. Restart the SSSD process.
    ~]# service sssd restart
    Stopping sssd:                                             [FAILED]
    Starting sssd:                                             [  OK  ]

12.2.30. Using NSCD with SSSD

SSSD is not designed to be used with the NSCD daemon. Even though SSSD does not directly conflict with NSCD, using both services can result in unexpected behavior, especially with how long entries are cached.
The most common evidence of a problem is conflicts with NFS. When using Network Manager to manage network connections, it may take several minutes for the network interface to come up. During this time, various services attempt to start. If these services start before the network is up and the DNS servers are available, these services fail to identify the forward or reverse DNS entries they need. These services will read an incorrect or possibly empty resolv.conf file. This file is typically only read once, and so any changes made to this file are not automatically applied. This can cause NFS locking to fail on the machine where the NSCD service is running, unless that service is manually restarted.
To avoid this problem, enable caching for hosts and services in the /etc/nscd.conf file and rely on the SSSD cache for the passwd, group, and netgroup entries.
Change the /etc/nscd.conf file:
enable-cache hosts yes
enable-cache passwd no
enable-cache group no
enable-cache netgroup no
With NSCD answering hosts requests, these entries will be cached by NSCD and returned by NSCD during the boot process. All other entries are handled by SSSD.

12.2.31. Troubleshooting SSSD

Setting Debug Logs for SSSD Domains

Each domain sets its own debug log level. Increasing the log level can provide more information about problems with SSSD or with the domain configuration.
To change the log level, set the debug_level parameter for each section in the sssd.conf file for which to produce extra logs. For example:
[domain/LDAP]
cache_credentials = true
debug_level = 9

Table 12.13. Debug Log Levels

Level Description
0 Fatal failures. Anything that would prevent SSSD from starting up or causes it to cease running.
1 Critical failures. An error that doesn't kill the SSSD, but one that indicates that at least one major feature is not going to work properly.
2 Serious failures. An error announcing that a particular request or operation has failed.
3 Minor failures. These are the errors that would percolate down to cause the operation failure of 2.
4 Configuration settings.
5 Function data.
6 Trace messages for operation functions.
7 Trace messages for internal control functions.
8 Contents of function-internal variables that may be interesting.
9 Extremely low-level tracing information.

Note

In versions of SSSD older than 1.8, debug log levels could be set globally in the [sssd] section. Now, each domain and service must configure its own debug log level.
To copy the global SSSD debug log levels into each configuration area in the SSSD configuration file, use the sssd_update_debug_levels.py script.
python -m SSSDConfig.sssd_update_debug_levels.py

Checking SSSD Log Files

SSSD uses a number of log files to report information about its operation, located in the /var/log/sssd/ directory. SSSD produces a log file for each domain, as well as an sssd_pam.log and an sssd_nss.log file.
Additionally, the /var/log/secure file logs authentication failures and the reason for the failure.

Problems with SSSD Configuration

Q: SSSD fails to start
Q: I don't see any groups with 'id' or group members with 'getent group'.
Q: Authentication fails against LDAP.
Q: Connecting to LDAP servers on non-standard ports fail.
Q: NSS fails to return user information
Q: NSS returns incorrect user information
Q: Setting the password for the local SSSD user prompts twice for the password
Q: I am trying to use sudo rules with an Identity Management (IPA) provider, but no sudo rules are being found, even though sudo is properly configured.
Q: Password lookups on large directories can take several seconds per request. How can this be improved?
Q: An Active Directory identity provider is properly configured in my sssd.conf file, but SSSD fails to connect to it, with GSS-API errors.
Q: I configured SSSD for central authentication, but now several of my applications (such as Firefox or Adobe) will not start.
Q: SSSD is showing an automount location that I removed.
Q:
SSSD fails to start
A:
SSSD requires that the configuration file be properly set up, with all the required entries, before the daemon will start.
  • SSSD requires at least one properly configured domain before the service will start. Without a domain, attempting to start SSSD returns an error that no domains are configured:
    # sssd -d4
    
    [sssd] [ldb] (3): server_sort:Unable to register control with rootdse!
    [sssd] [confdb_get_domains] (0): No domains configured, fatal error!
    [sssd] [get_monitor_config] (0): No domains configured.
    
    Edit the /etc/sssd/sssd.conf file and create at least one domain.
  • SSSD also requires at least one available service provider before it will start. If the problem is with the service provider configuration, the error message indicates that there are no services configured:
    [sssd] [get_monitor_config] (0): No services configured!
    
    Edit the /etc/sssd/sssd.conf file and configure at least one service provider.

    Important

    SSSD requires that service providers be configured as a comma-separated list in a single services entry in the /etc/sssd/sssd.conf file. If services are listed in multiple entries, only the last entry is recognized by SSSD.
Q:
I don't see any groups with 'id' or group members with 'getent group'.
A:
This may be due to an incorrect ldap_schema setting in the [domain/DOMAINNAME] section of sssd.conf.
SSSD supports RFC 2307 and RFC 2307bis schema types. By default, SSSD uses the more common RFC 2307 schema.
The difference between RFC 2307 and RFC 2307bis is the way which group membership is stored in the LDAP server. In an RFC 2307 server, group members are stored as the multi-valued memberuid attribute, which contains the name of the users that are members. In an RFC2307bis server, group members are stored as the multi-valued member or uniqueMember attribute which contains the DN of the user or group that is a member of this group. RFC2307bis allows nested groups to be maintained as well.
If group lookups are not returning any information:
  1. Set ldap_schema to rfc2307bis.
  2. Delete /var/lib/sss/db/cache_DOMAINNAME.ldb.
  3. Restarting SSSD.
If that doesn't work, add this line to sssd.conf:
ldap_group_name = uniqueMember
Then delete the cache and restart SSSD again.
Q:
Authentication fails against LDAP.
A:
To perform authentication, SSSD requires that the communication channel be encrypted. This means that if sssd.conf is configured to connect over a standard protocol (ldap://), it attempts to encrypt the communication channel with Start TLS. If sssd.conf is configured to connect over a secure protocol (ldaps://), then SSSD uses SSL.
This means that the LDAP server must be configured to run in SSL or TLS. TLS must be enabled for the standard LDAP port (389) or SSL enabled on the secure LDAPS port (636). With either SSL or TLS, the LDAP server must also be configured with a valid certificate trust.
An invalid certificate trust is one of the most common issues with authenticating against LDAP. If the client does not have proper trust of the LDAP server certificate, it is unable to validate the connection, and SSSD refuses to send the password. The LDAP protocol requires that the password be sent in plaintext to the LDAP server. Sending the password in plaintext over an unencrypted connection is a security problem.
If the certificate is not trusted, a syslog message is written, indicating that TLS encryption could not be started. The certificate configuration can be tested by checking if the LDAP server is accessible apart from SSSD. For example, this tests an anonymous bind over a TLS connection to test.example.com:
$ ldapsearch -x -ZZ -h test.example.com -b dc=example,dc=com
If the certificate trust is not properly configured, the test fails with this error:
ldap_start_tls: Connect error (-11) additional info: TLS error -8179:Unknown code ___f 13
To trust the certificate:
  1. Obtain a copy of the public CA certificate for the certificate authority used to sign the LDAP server certificate and save it to the local system.
  2. Add a line to the sssd.conf file that points to the CA certificate on the filesystem.
    ldap_tls_cacert = /path/to/cacert
  3. If the LDAP server uses a self-signed certificate, remove the ldap_tls_reqcert line from the sssd.conf file.
    This parameter directs SSSD to trust any certificate issued by the CA certificate, which is a security risk with a self-signed CA certificate.
Q:
Connecting to LDAP servers on non-standard ports fail.
A:
When running SELinux in enforcing mode, the client's SELinux policy has to be modified to connect to the LDAP server over the non-standard port. For example:
# semanage port -a -t ldap_port_t -p tcp 1389
Q:
NSS fails to return user information
A:
This usually means that SSSD cannot connect to the NSS service.
  • Ensure that NSS is running:
    # service sssd status
  • If NSS is running, make sure that the provider is properly configured in the [nss] section of the /etc/sssd/sssd.conf file. Especially check the filter_users and filter_groups attributes.
  • Make sure that NSS is included in the list of services that SSSD uses.
  • Check the configuration in the /etc/nsswitch.conf