performance-based Red Hat Certified System Administrator (RHCSA) exam (EX200)
https://youtube.com/shorts/VDRzGNo8ERI?si=Gds5ytYewMFizSCR
Red Hat Enterprise Linux 8
Configuring basic system settings
Set up the essential functions of your system and customize your system
environment
Last Updated: 2024-02-20
Red Hat Enterprise Linux 8 Configuring basic system settings
Set up the essential functions of your system and customize your system environment
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Abstract
Perform basic system administration tasks, configure the environment settings, register your
system, and configure network access and system security. Administer users, groups, and file
permissions. Use System Roles for managing system configurations interface on multiple RHEL
systems. Use systemd for efficient service management. Configure the Network Time Protocol
(NTP) with chrony. Backup and restore your system using ReaR. Install and use dynamic
programming languages such as Python 3 and PHP.. . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . Table of Contents
MAKING OPEN SOURCE MORE INCLUSIVE
PROVIDING FEEDBACK ON RED HAT DOCUMENTATION
CHAPTER 1. CONFIGURING AND MANAGING BASIC NETWORK ACCESS
1.1. CONFIGURING THE NETWORK AND HOST NAME IN THE GRAPHICAL INSTALLATION MODE
1.2. CONFIGURING AN ETHERNET CONNECTION BY USING NMCLI
1.3. CONFIGURING AN ETHERNET CONNECTION BY USING NMTUI
1.4. MANAGING NETWORKING IN THE RHEL WEB CONSOLE
1.5. MANAGING NETWORKING USING RHEL SYSTEM ROLES
1.6. ADDITIONAL RESOURCES
CHAPTER 2. REGISTERING THE SYSTEM AND MANAGING SUBSCRIPTIONS
2.1. REGISTERING THE SYSTEM AFTER THE INSTALLATION
2.2. REGISTERING SUBSCRIPTIONS WITH CREDENTIALS IN THE WEB CONSOLE
2.3. REGISTERING A SYSTEM USING RED HAT ACCOUNT ON GNOME
2.4. REGISTERING A SYSTEM USING AN ACTIVATION KEY ON GNOME
2.5. REGISTERING RHEL 8 USING THE INSTALLER GUI
CHAPTER 3. ACCESSING THE RED HAT SUPPORT
3.1. OBTAINING RED HAT SUPPORT THROUGH RED HAT CUSTOMER PORTAL
3.2. TROUBLESHOOTING PROBLEMS USING SOSREPORT
CHAPTER 4. CHANGING BASIC ENVIRONMENT SETTINGS
4.1. CONFIGURING THE DATE AND TIME
4.1.1. Displaying the current date and time
4.2. CONFIGURING THE SYSTEM LOCALE
4.3. CONFIGURING THE KEYBOARD LAYOUT
4.4. CHANGING THE LANGUAGE USING DESKTOP GUI
4.5. ADDITIONAL RESOURCES
CHAPTER 5. USING SECURE COMMUNICATIONS BETWEEN TWO SYSTEMS WITH OPENSSH
5.1. SSH AND OPENSSH
5.2. CONFIGURING AND STARTING AN OPENSSH SERVER
5.3. SETTING AN OPENSSH SERVER FOR KEY-BASED AUTHENTICATION
5.4. GENERATING SSH KEY PAIRS
5.5. USING SSH KEYS STORED ON A SMART CARD
5.6. MAKING OPENSSH MORE SECURE
5.7. CONNECTING TO A REMOTE SERVER USING AN SSH JUMP HOST
5.8. CONNECTING TO REMOTE MACHINES WITH SSH KEYS USING SSH-AGENT
5.9. ADDITIONAL RESOURCES
CHAPTER 6. CONFIGURING BASIC SYSTEM SECURITY
6.1. ENABLING THE FIREWALLD SERVICE
6.2. MANAGING FIREWALL IN THE RHEL 8 WEB CONSOLE
6.3. MANAGING BASIC SELINUX SETTINGS
6.4. ENSURING THE REQUIRED STATE OF SELINUX
6.5. SWITCHING SELINUX MODES IN THE RHEL 8 WEB CONSOLE
6.6. ADDITIONAL RESOURCES
CHAPTER 7. MANAGING SOFTWARE PACKAGES
7.1. SOFTWARE MANAGEMENT TOOLS IN RHEL 8
7.2. APPLICATION STREAMS
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7.3.1. Searching packages with YUM
7.3.2. Listing packages with YUM
7.3.3. Listing repositories with YUM
7.3.4. Displaying package information with YUM
7.3.5. Listing package groups with YUM
7.3.6. Specifying global expressions in YUM input
7.4. INSTALLING SOFTWARE PACKAGES
7.4.1. Installing packages with YUM
7.4.2. Installing a package group with YUM
7.4.3. Specifying a package name in YUM input
7.5. UPDATING SOFTWARE PACKAGES
7.5.1. Checking for updates with YUM
7.5.2. Updating a single package with YUM
7.5.3. Updating a package group with YUM
7.5.4. Updating all packages and their dependencies with YUM
7.5.5. Updating security-related packages with YUM
7.5.6. Automating software updates
7.5.6.1. Installing DNF Automatic
7.5.6.2. DNF Automatic configuration file
7.5.6.3. Enabling DNF Automatic
7.5.6.4. Overview of the systemd timer units included in the dnf-automatic package
7.6. UNINSTALLING SOFTWARE PACKAGES
7.6.1. Removing packages with YUM
7.6.2. Removing a package group with YUM
7.6.3. Specifying a package name in YUM input
7.7. MANAGING SOFTWARE PACKAGE GROUPS
7.7.1. Listing package groups with YUM
7.7.2. Installing a package group with YUM
7.7.3. Removing a package group with YUM
7.7.4. Specifying global expressions in YUM input
7.8. HANDLING PACKAGE MANAGEMENT HISTORY
7.8.1. Listing transactions with YUM
7.8.2. Reverting transactions with YUM
7.8.3. Repeating transactions with YUM
7.8.4. Specifying global expressions in YUM input
7.9. MANAGING SOFTWARE REPOSITORIES
7.9.1. Setting YUM repository options
7.9.2. Adding a YUM repository
7.9.3. Enabling a YUM repository
7.9.4. Disabling a YUM repository
7.10. CONFIGURING YUM
7.10.1. Viewing the current YUM configurations
7.10.2. Setting YUM main options
7.10.3. Using YUM plug-ins
7.10.3.1. Managing YUM plug-ins
7.10.3.2. Enabling YUM plug-ins
7.10.3.3. Disabling YUM plug-ins
CHAPTER 8. INTRODUCTION TO RHEL SYSTEM ROLES
CHAPTER 9. CONFIGURING LOGGING
9.1. CONFIGURING A REMOTE LOGGING SOLUTION
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9.1.2. Installing Rsyslog documentation
9.1.3. Configuring a server for remote logging over TCP
9.1.4. Configuring remote logging to a server over TCP
9.1.5. Configuring TLS-encrypted remote logging
9.1.6. Configuring a server for receiving remote logging information over UDP
9.1.7. Configuring remote logging to a server over UDP
9.1.8. Load balancing helper in Rsyslog
9.1.9. Configuring reliable remote logging
9.1.10. Supported Rsyslog modules
9.1.11. Configuring the netconsole service to log kernel messages to a remote host
9.1.12. Additional resources
9.2. USING THE LOGGING SYSTEM ROLE
9.2.1. The logging System Role
9.2.2. logging System Role parameters
9.2.3. Applying a local logging System Role
9.2.4. Filtering logs in a local logging System Role
9.2.5. Applying a remote logging solution using the logging System Role
9.2.6. Using the logging System Role with TLS
9.2.6.1. Configuring client logging with TLS
9.2.6.2. Configuring server logging with TLS
9.2.7. Using the logging System Roles with RELP
9.2.7.1. Configuring client logging with RELP
9.2.7.2. Configuring server logging with RELP
9.2.8. Additional resources
CHAPTER 10. TROUBLESHOOTING PROBLEMS USING LOG FILES
10.1. SERVICES HANDLING SYSLOG MESSAGES
10.2. SUBDIRECTORIES STORING SYSLOG MESSAGES
10.3. INSPECTING LOG FILES USING THE WEB CONSOLE
10.4. VIEWING LOGS USING THE COMMAND LINE
10.5. ADDITIONAL RESOURCES
CHAPTER 11. MANAGING USERS AND GROUPS
11.1. INTRODUCTION TO MANAGING USER AND GROUP ACCOUNTS
11.1.1. Introduction to users and groups
11.1.2. Configuring reserved user and group IDs
11.1.3. User private groups
11.2. GETTING STARTED WITH MANAGING USER ACCOUNTS
11.2.1. Managing accounts and groups using command line tools
11.2.2. System user accounts managed in the web console
11.2.3. Adding new accounts using the web console
11.3. MANAGING USERS FROM THE COMMAND LINE
11.3.1. Adding a new user from the command line
11.3.2. Adding a new group from the command line
11.3.3. Adding a user to a supplementary group from the command line
11.3.4. Creating a group directory
11.3.5. Removing a user on the command line
11.4. MANAGING USER ACCOUNTS IN THE WEB CONSOLE
11.4.1. System user accounts managed in the web console
11.4.2. Adding new accounts using the web console
11.4.3. Enforcing password expiration in the web console
11.4.4. Terminating user sessions in the web console
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11.5.1. Primary and supplementary user groups
11.5.2. Listing the primary and supplementary groups of a user
11.5.3. Changing the primary group of a user
11.5.4. Adding a user to a supplementary group from the command line
11.5.5. Removing a user from a supplementary group
11.5.6. Changing all of the supplementary groups of a user
11.6. CHANGING AND RESETTING THE ROOT PASSWORD
11.6.1. Changing the root password as the root user
11.6.2. Changing or resetting the forgotten root password as a non-root user
11.6.3. Resetting the root password on boot
CHAPTER 12. MANAGING SUDO ACCESS
12.1. USER AUTHORIZATIONS IN SUDOERS
12.2. GRANTING SUDO ACCESS TO A USER
12.3. ENABLING UNPRIVILEGED USERS TO RUN CERTAIN COMMANDS
CHAPTER 13. MANAGING FILE SYSTEM PERMISSIONS
13.1. MANAGING FILE PERMISSIONS
13.1.1. Base file permissions
13.1.2. User file-creation mode mask
13.1.3. Default file permissions
13.1.4. Changing file permissions using symbolic values
13.1.5. Changing file permissions using octal values
13.2. MANAGING THE ACCESS CONTROL LIST
13.2.1. Displaying the current Access Control List
13.2.2. Setting the Access Control List
13.3. MANAGING THE UMASK
13.3.1. Displaying the current value of the umask
13.3.2. Displaying the default bash umask
13.3.3. Setting the umask using symbolic values
13.3.4. Setting the umask using octal values
13.3.5. Changing the default umask for the non-login shell
13.3.6. Changing the default umask for the login shell
13.3.7. Changing the default umask for a specific user
13.3.8. Setting default permissions for newly created home directories
CHAPTER 14. MANAGING SYSTEMD
14.1. SYSTEMD UNIT FILES LOCATIONS
14.2. MANAGING SYSTEM SERVICES WITH SYSTEMCTL
14.2.1. Listing system services
14.2.2. Displaying system service status
14.2.3. Starting a system service
14.2.4. Stopping a system service
14.2.5. Restarting a system service
14.2.6. Enabling a system service to start at boot
14.2.7. Disabling a system service to start at boot
14.3. BOOTING INTO A TARGET SYSTEM STATE
14.3.1. Target unit files
14.3.2. Changing the default target to boot into
14.3.3. Changing the current target
14.3.4. Booting to rescue mode
14.3.5. Troubleshooting the boot process
14.4. SHUTTING DOWN, SUSPENDING, AND HIBERNATING THE SYSTEM
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14.4.2. Scheduling a system shutdown
14.4.3. Shutting down the system using the systemctl command
14.4.4. Restarting the system
14.4.5. Optimizing power consumption by suspending and hibernating the system
14.4.6. Overview of the power management commands with systemctl
14.4.7. Changing how your system behaves when you press the power button
CHAPTER 15. CONFIGURING TIME SYNCHRONIZATION
15.1. USING THE CHRONY SUITE TO CONFIGURE NTP
15.1.1. Introduction to chrony suite
15.1.2. Using chronyc to control chronyd
15.1.3. Migrating to chrony
15.1.3.1. Migration script
15.2. USING CHRONY
15.2.1. Managing chrony
15.2.2. Checking if chrony is synchronized
15.2.3. Manually adjusting the System Clock
15.2.4. Disabling a chrony dispatcher script
15.2.5. Setting up chrony for a system in an isolated network
15.2.6. Configuring remote monitoring access
15.2.7. Managing time synchronization using RHEL System Roles
15.2.8. Additional resources
15.3. CHRONY WITH HW TIMESTAMPING
15.3.1. Verifying support for hardware timestamping
15.3.2. Enabling hardware timestamping
15.3.3. Configuring client polling interval
15.3.4. Enabling interleaved mode
15.3.5. Configuring server for large number of clients
15.3.6. Verifying hardware timestamping
15.3.7. Configuring PTP-NTP bridge
15.4. ACHIEVING SOME SETTINGS PREVIOUSLY SUPPORTED BY NTP IN CHRONY
15.4.1. Monitoring by ntpq and ntpdc
15.4.2. Using authentication mechanism based on public key cryptography
15.4.3. Using ephemeral symmetric associations
15.4.4. multicast/broadcast client
15.5. OVERVIEW OF NETWORK TIME SECURITY (NTS) IN CHRONY
15.5.1. Enabling Network Time Security (NTS) in the client configuration file
15.5.2. Enabling Network Time Security (NTS) on the server
CHAPTER 16. USING LANGPACKS
16.1. CHECKING LANGUAGES THAT PROVIDE LANGPACKS
16.2. WORKING WITH RPM WEAK DEPENDENCY-BASED LANGPACKS
16.2.1. Listing already installed language support
16.2.2. Checking the availability of language support
16.2.3. Listing packages installed for a language
16.2.4. Installing language support
16.2.5. Removing language support
16.3. SAVING DISK SPACE BY USING GLIBC-LANGPACK-
CHAPTER 17. DUMPING A CRASHED KERNEL FOR LATER ANALYSIS
17.1. WHAT IS KDUMP
17.2. CONFIGURING KDUMP MEMORY USAGE AND TARGET LOCATION IN WEB CONSOLE
17.3. KDUMP USING RHEL SYSTEM ROLES
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CHAPTER 18. RECOVERING AND RESTORING A SYSTEM
18.1. SETTING UP REAR
18.2. USING A REAR RESCUE IMAGE ON THE 64-BIT IBM Z ARCHITECTURE
CHAPTER 19. INSTALLING AND USING DYNAMIC PROGRAMMING LANGUAGES
19.1. INTRODUCTION TO PYTHON
19.1.1. Python versions
19.1.2. Notable differences between Python versions
19.2. INSTALLING AND USING PYTHON
19.2.1. Installing Python 3
19.2.2. Installing additional Python 3 packages
19.2.3. Installing additional Python 3 tools for developers
19.2.4. Installing Python 2
19.2.5. Migrating from Python 2 to Python 3
19.2.6. Using Python
19.3. CONFIGURING THE UNVERSIONED PYTHON
19.3.1. Configuring the unversioned python command directly
19.3.2. Configuring the unversioned python command to the required Python version interactively
19.3.3. Additional resources
19.4. PACKAGING PYTHON 3 RPMS
19.4.1. SPEC file description for a Python package
19.4.2. Common macros for Python 3 RPMs
19.4.3. Automatic provides for Python RPMs
19.5. HANDLING INTERPRETER DIRECTIVES IN PYTHON SCRIPTS
19.5.1. Modifying interpreter directives in Python scripts
19.5.2. Changing /usr/bin/python3 interpreter directives in your custom packages
19.6. USING THE PHP SCRIPTING LANGUAGE
19.6.1. Installing the PHP scripting language
19.6.2. Using the PHP scripting language with a web server
19.6.2.1. Using PHP with the Apache HTTP Server
19.6.2.2. Using PHP with the nginx web server
19.6.3. Running a PHP script using the command-line interface
19.6.4. Additional resources
19.7. GETTING STARTED WITH TCL/TK
19.7.1. Introduction to Tcl/Tk
19.7.2. Notable changes in Tcl/Tk 8.6
19.7.3. Migrating to Tcl/Tk 8.6
19.7.3.1. Migration path for developers of Tcl extensions
19.7.3.2. Migration path for users scripting their tasks with Tcl/Tk
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MAKING OPEN SOURCE MORE INCLUSIVE
Red Hat is committed to replacing problematic language in our code, documentation, and web
properties. We are beginning with these four terms: master, slave, blacklist, and whitelist. Because of the
enormity of this endeavor, these changes will be implemented gradually over several upcoming releases.
For more details, see our CTO Chris Wright’s message .
Red Hat Enterprise Linux 8 Configuring basic system settings
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PROVIDING FEEDBACK ON RED HAT DOCUMENTATION
We appreciate your feedback on our documentation. Let us know how we can improve it.
Submitting feedback through Jira (account required)
1. Log in to the Jira website.
2. Click Create in the top navigation bar.
3. Enter a descriptive title in the Summary field.
4. Enter your suggestion for improvement in the Description field. Include links to the relevant
parts of the documentation.
5. Click Create at the bottom of the dialogue.
PROVIDING FEEDBACK ON RED HAT DOCUMENTATION
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CHAPTER 1. CONFIGURING AND MANAGING BASIC NETWORK
ACCESS
This section describes only basic options on how to configure network settings in Red Hat
Enterprise Linux.
1.1. CONFIGURING THE NETWORK AND HOST NAME IN THE
GRAPHICAL INSTALLATION MODE
Follow the steps in this procedure to configure your network and host name.
Procedure
1. From the Installation Summary window, click Network and Host Name.
2. From the list in the left-hand pane, select an interface. The details are displayed in the righthand pane.
NOTE
There are several types of network device naming standards used to identify
network devices with persistent names, for example, em1 and wl3sp0. For
information about these standards, see the Configuring and managing networking
document.
3. Toggle the ON/OFF switch to enable or disable the selected interface.
NOTE
The installation program automatically detects locally accessible interfaces, and
you cannot add or remove them manually.
4. Click + to add a virtual network interface, which can be either: Team, Bond, Bridge, or VLAN.
5. Click - to remove a virtual interface.
6. Click Configure to change settings such as IP addresses, DNS servers, or routing configuration
for an existing interface (both virtual and physical).
7. Type a host name for your system in the Host Name field.
NOTE
Red Hat Enterprise Linux 8 Configuring basic system settings
10
NOTE
The host name can either be a fully qualified domain name (FQDN) in the
format hostname.domainname, or a short host name without the domain.
Many networks have a Dynamic Host Configuration Protocol (DHCP) service
that automatically supplies connected systems with a domain name. To allow
the DHCP service to assign the domain name to this system, specify only the
short host name.
When using static IP and host name configuration, it depends on the planned
system use case whether to use a short name or FQDN. Red Hat Identity
Management configures FQDN during provisioning but some 3rd party
software products may require short name. In either case, to ensure
availability of both forms in all situations, add an entry for the host in
/etc/hosts in the format IP FQDN short-alias.
The value localhost means that no specific static host name for the target
system is configured, and the actual host name of the installed system is
configured during the processing of the network configuration, for example,
by NetworkManager using DHCP or DNS.
Host names can only contain alphanumeric characters and - or .. Host name
should be equal to or less than 64 characters. Host names cannot start or
end with - and .. To be compliant with DNS, each part of a FQDN should be
equal to or less than 63 characters and the FQDN total length, including dots,
should not exceed 255 characters.
8. Click Apply to apply the host name to the installer environment.
9. Alternatively, in the Network and Hostnamewindow, you can choose the Wireless option. Click
Select network in the right-hand pane to select your wifi connection, enter the password if
required, and click Done.
Additional resources
Performing an advanced RHEL 8 installation
1.2. CONFIGURING AN ETHERNET CONNECTION BY USING NMCLI
If you connect a host to the network over Ethernet, you can manage the connection’s settings on the
command line by using the nmcli utility.
Prerequisites
A physical or virtual Ethernet Network Interface Controller (NIC) exists in the server’s
configuration.
Procedure
1. List the NetworkManager connection profiles:
# nmcli connection show
NAME UUID TYPE DEVICE
Wired connection 1 a5eb6490-cc20-3668-81f8-0314a27f3f75 ethernet enp1s0
By default, NetworkManager creates a profile for each NIC in the host. If you plan to connect
CHAPTER 1. CONFIGURING AND MANAGING BASIC NETWORK ACCESS
11
By default, NetworkManager creates a profile for each NIC in the host. If you plan to connect
this NIC only to a specific network, adapt the automatically-created profile. If you plan to
connect this NIC to networks with different settings, create individual profiles for each network.
2. If you want to create an additional connection profile, enter:
# nmcli connection add con-name ifname type
ethernet
Skip this step to modify an existing profile.
3. Optional: Rename the connection profile:
# nmcli connection modify "Wired connection 1" connection.id "Internal-LAN"
On hosts with multiple profiles, a meaningful name makes it easier to identify the purpose of a
profile.
4. Display the current settings of the connection profile:
# nmcli connection show Internal-LAN
...
connection.interface-name: enp1s0
connection.autoconnect: yes
ipv4.method: auto
ipv6.method: auto
...
5. Configure the IPv4 settings:
To use DHCP, enter:
# nmcli connection modify Internal-LAN ipv4.method auto
Skip this step if ipv4.method is already set to auto (default).
To set a static IPv4 address, network mask, default gateway, DNS servers, and search
domain, enter:
# nmcli connection modify Internal-LAN ipv4.method manual ipv4.addresses
192.0.2.1/24 ipv4.gateway 192.0.2.254 ipv4.dns 192.0.2.200 ipv4.dns-search
example.com
6. Configure the IPv6 settings:
To use stateless address autoconfiguration (SLAAC), enter:
# nmcli connection modify Internal-LAN ipv6.method auto
Skip this step if ipv6.method is already set to auto (default).
To set a static IPv6 address, network mask, default gateway, DNS servers, and search
domain, enter:
Red Hat Enterprise Linux 8 Configuring basic system settings
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# nmcli connection modify Internal-LAN ipv6.method manual ipv6.addresses
2001:db8:1::fffe/64 ipv6.gateway 2001:db8:1::fffe ipv6.dns 2001:db8:1::ffbb
ipv6.dns-search example.com
7. To customize other settings in the profile, use the following command:
# nmcli connection modify
Enclose values with spaces or semicolons in quotes.
8. Activate the profile:
# nmcli connection up Internal-LAN
Verification
1. Display the IP settings of the NIC:
# ip address show enp1s0
2: enp1s0: mtu 1500 qdisc fq_codel state UP
group default qlen 1000
link/ether 52:54:00:17:b8:b6 brd ff:ff:ff:ff:ff:ff
inet 192.0.2.1/24 brd 192.0.2.255 scope global noprefixroute enp1s0
valid_lft forever preferred_lft forever
inet6 2001:db8:1::fffe/64 scope global noprefixroute
valid_lft forever preferred_lft forever
2. Display the IPv4 default gateway:
# ip route show default
default via 192.0.2.254 dev enp1s0 proto static metric 102
3. Display the IPv6 default gateway:
# ip -6 route show default
default via 2001:db8:1::ffee dev enp1s0 proto static metric 102 pref medium
4. Display the DNS settings:
# cat /etc/resolv.conf
search example.com
nameserver 192.0.2.200
nameserver 2001:db8:1::ffbb
If multiple connection profiles are active at the same time, the order of nameserver entries
depend on the DNS priority values in these profile and the connection types.
5. Use the ping utility to verify that this host can send packets to other hosts:
# ping
Troubleshooting
CHAPTER 1. CONFIGURING AND MANAGING BASIC NETWORK ACCESS
13
Verify that the network cable is plugged-in to the host and a switch.
Check whether the link failure exists only on this host or also on other hosts connected to the
same switch.
Verify that the network cable and the network interface are working as expected. Perform
hardware diagnosis steps and replace defect cables and network interface cards.
If the configuration on the disk does not match the configuration on the device, starting or
restarting NetworkManager creates an in-memory connection that reflects the configuration of
the device. For further details and how to avoid this problem, see the NetworkManager
duplicates a connection after restart of NetworkManager service solution.
Additional resources
nm-settings(5) man page
Configuring NetworkManager to avoid using a specific profile to provide a default gateway
Configuring the order of DNS servers
1.3. CONFIGURING AN ETHERNET CONNECTION BY USING NMTUI
If you connect a host to the network over Ethernet, you can manage the connection’s settings in a textbased user interface by using the nmtui application. Use nmtui to create new profiles and to update
existing ones on a host without a graphical interface.
NOTE
In nmtui:
Navigate by using the cursor keys.
Press a button by selecting it and hitting Enter.
Select and deselect checkboxes by using Space.
Prerequisites
A physical or virtual Ethernet Network Interface Controller (NIC) exists in the server’s
configuration.
Procedure
1. If you do not know the network device name you want to use in the connection, display the
available devices:
# nmcli device status
DEVICE TYPE STATE CONNECTION
enp1s0 ethernet unavailable --
...
2. Start nmtui:
# nmtui
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3. Select Edit a connection, and press Enter.
4. Choose whether to add a new connection profile or to modify an existing one:
To create a new profile:
i. Press the Add button.
ii. Select Ethernet from the list of network types, and press Enter.
To modify an existing profile, select the profile from the list, and press Enter.
5. Optional: Update the name of the connection profile.
On hosts with multiple profiles, a meaningful name makes it easier to identify the purpose of a
profile.
6. If you create a new connection profile, enter the network device name into the Device field.
7. Depending on your environment, configure the IP address settings in the IPv4 configuration
and IPv6 configuration areas accordingly. For this, press the button next to these areas, and
select:
Disabled, if this connection does not require an IP address.
Automatic, if a DHCP server dynamically assigns an IP address to this NIC.
Manual, if the network requires static IP address settings. In this case, you must fill further
fields:
i. Press the Show button next to the protocol you want to configure to display additional
fields.
ii. Press the Add button next to Addresses, and enter the IP address and the subnet mask
in Classless Inter-Domain Routing (CIDR) format.
If you do not specify a subnet mask, NetworkManager sets a /32 subnet mask for IPv4
addresses and /64 for IPv6 addresses.
iii. Enter the address of the default gateway.
iv. Press the Add button next to DNS servers, and enter the DNS server address.
v. Press the Add button next to Search domains, and enter the DNS search domain.
Figure 1.1. Example of an Ethernet connection with static IP address settings
CHAPTER 1. CONFIGURING AND MANAGING BASIC NETWORK ACCESS
15
Figure 1.1. Example of an Ethernet connection with static IP address settings
8. Press the OK button to create and automatically activate the new connection.
9. Press the Back button to return to the main menu.
10. Select Quit, and press Enter to close the nmtui application.
Verification
1. Display the IP settings of the NIC:
# ip address show enp1s0
2: enp1s0: mtu 1500 qdisc fq_codel state UP
group default qlen 1000
link/ether 52:54:00:17:b8:b6 brd ff:ff:ff:ff:ff:ff
Red Hat Enterprise Linux 8 Configuring basic system settings
16
inet 192.0.2.1/24 brd 192.0.2.255 scope global noprefixroute enp1s0
valid_lft forever preferred_lft forever
inet6 2001:db8:1::fffe/64 scope global noprefixroute
valid_lft forever preferred_lft forever
2. Display the IPv4 default gateway:
# ip route show default
default via 192.0.2.254 dev enp1s0 proto static metric 102
3. Display the IPv6 default gateway:
# ip -6 route show default
default via 2001:db8:1::ffee dev enp1s0 proto static metric 102 pref medium
4. Display the DNS settings:
# cat /etc/resolv.conf
search example.com
nameserver 192.0.2.200
nameserver 2001:db8:1::ffbb
If multiple connection profiles are active at the same time, the order of nameserver entries
depend on the DNS priority values in these profile and the connection types.
5. Use the ping utility to verify that this host can send packets to other hosts:
# ping
Troubleshooting
Verify that the network cable is plugged-in to the host and a switch.
Check whether the link failure exists only on this host or also on other hosts connected to the
same switch.
Verify that the network cable and the network interface are working as expected. Perform
hardware diagnosis steps and replace defect cables and network interface cards.
If the configuration on the disk does not match the configuration on the device, starting or
restarting NetworkManager creates an in-memory connection that reflects the configuration of
the device. For further details and how to avoid this problem, see the NetworkManager
duplicates a connection after restart of NetworkManager service solution.
Additional resources
Configuring NetworkManager to avoid using a specific profile to provide a default gateway
Configuring the order of DNS servers
1.4. MANAGING NETWORKING IN THE RHEL WEB CONSOLE
In the web console, the Networking menu enables you:
CHAPTER 1. CONFIGURING AND MANAGING BASIC NETWORK ACCESS
17
To display currently received and sent packets
To display the most important characteristics of available network interfaces
To display content of the networking logs.
To add various types of network interfaces (bond, team, bridge, VLAN)
Figure 1.2. Managing Networking in the RHEL web console
1.5. MANAGING NETWORKING USING RHEL SYSTEM ROLES
You can configure the networking connections on multiple target machines using the network role.
The network role allows to configure the following types of interfaces:
Ethernet
Bridge
Bonded
VLAN
MacVLAN
InfiniBand
The required networking connections for each host are provided as a list within the
network_connections variable.
Red Hat Enterprise Linux 8 Configuring basic system settings
18
WARNING
The network role updates or creates all connection profiles on the target system
exactly as specified in the network_connections variable. Therefore, the network
role removes options from the specified profiles if the options are only present on
the system but not in the network_connections variable.
The following example shows how to apply the network role to ensure that an Ethernet connection with
the required parameters exists:
An example playbook applying the network role to set up an Ethernet connection with the
required parameters
Additional resources
Preparing a control node and managed nodes to use RHEL System Roles
1.6. ADDITIONAL RESOURCES
Configuring and managing networking
# SPDX-License-Identifier: BSD-3-Clause
---
- hosts: managed-node-01.example.com
vars:
network_connections:
# Create one Ethernet profile and activate it.
# The profile uses automatic IP addressing
# and is tied to the interface by MAC address.
- name: prod1
state: up
type: ethernet
autoconnect: yes
mac: "00:00:5e:00:53:00"
mtu: 1450
roles:
- rhel-system-roles.network
CHAPTER 1. CONFIGURING AND MANAGING BASIC NETWORK ACCESS
19
CHAPTER 2. REGISTERING THE SYSTEM AND MANAGING
SUBSCRIPTIONS
Subscriptions cover products installed on Red Hat Enterprise Linux, including the operating system
itself.
You can use a subscription to Red Hat Content Delivery Network to track:
Registered systems
Products installed on your systems
Subscriptions attached to the installed products
2.1. REGISTERING THE SYSTEM AFTER THE INSTALLATION
Use the following procedure to register your system if you have not registered it during the installation
process already.
Prerequisites
A valid user account in the Red Hat Customer Portal.
See the Create a Red Hat Login page.
An active subscription for the RHEL system.
For more information about the installation process, see Performing a standard RHEL 8
installation.
Procedure
1. Register and automatically subscribe your system in one step:
# subscription-manager register --username --password --
auto-attach
Registering to: subscription.rhsm.redhat.com:443/subscription
The system has been registered with ID: 37to907c-ece6-49ea-9174-20b87ajk9ee7
The registered system name is: client1.idm.example.com
Installed Product Current Status:
Product Name: Red Hat Enterprise Linux for x86_64
Status: Subscribed
The command prompts you to enter your Red Hat Customer Portal user name and password.
If the registration process fails, you can register your system with a specific pool. For guidance
on how to do it, proceed with the following steps:
a. Determine the pool ID of a subscription that you require:
# subscription-manager list --available
This command displays all available subscriptions for your Red Hat account. For every
subscription, various characteristics are displayed, including the pool ID.
Red Hat Enterprise Linux 8 Configuring basic system settings
20
b. Attach the appropriate subscription to your system by replacing pool_id with the pool ID
determined in the previous step:
# subscription-manager attach --pool=pool_id
NOTE
To register the system with Red Hat Insights, you can use the rhc connect utility. See
Setting up remote host configuration .
Additional resources
Understanding autoattaching subscriptions on the Customer Portal
Understanding the manual registration and subscription on the Customer Portal
2.2. REGISTERING SUBSCRIPTIONS WITH CREDENTIALS IN THE WEB
CONSOLE
Use the following steps to register a newly installed Red Hat Enterprise Linux with account credentials
using the RHEL web console.
Prerequisites
A valid user account on the Red Hat Customer Portal.
See the Create a Red Hat Login page.
Active subscription for your RHEL system.
Procedure
1. Log in to the RHEL web console. For details, see Logging in to the web console .
2. In the Health filed in the Overview page, click the Not registeredwarning, or click
Subscriptions in the main menu to move to page with your subscription information.
.
3. In the Overview filed, click Register.
CHAPTER 2. REGISTERING THE SYSTEM AND MANAGING SUBSCRIPTIONS
21
4. In the Register system dialog box, select that you want to register using your account
credentials.
5. Enter your username.
6. Enter your password.
7. Optionally, enter your organization’s name or ID.
If your account belongs to more than one organization on the Red Hat Customer Portal, you
have to add the organization name or organization ID. To get the org ID, go to your Red Hat
contact point.
If you do not want to connect your system to Red Hat Insights, clear the Insights check box.
8. Click the Register button.
At this point, your Red Hat Enterprise Linux Enterprise Linux system has been successfully registered.
2.3. REGISTERING A SYSTEM USING RED HAT ACCOUNT ON GNOME
Follow the steps in this procedure to enroll your system with your Red Hat account.
Prerequisites
Red Hat Enterprise Linux 8 Configuring basic system settings
22
A valid account on Red Hat customer portal.
See the Create a Red Hat Login page for new user registration.
Procedure
1. Open the system menu, which is accessible from the upper-right screen corner, and click the
Settings icon.
2. In the Details → About section, click Register.
3. Select Registration Server.
4. If you are not using the Red Hat server, enter the server address in the URL field.
5. In the Registration Type menu, select Red Hat Account.
6. Under Registration Details:
Enter your Red Hat account user name in the Login field.
Enter your Red Hat account password in the Password field.
Enter the name of your organization in the Organization field.
7. Click Register.
2.4. REGISTERING A SYSTEM USING AN ACTIVATION KEY ON GNOME
CHAPTER 2. REGISTERING THE SYSTEM AND MANAGING SUBSCRIPTIONS
23
Follow the steps in this procedure to register your system with an activation key. You can get the
activation key from your organization administrator.
Prerequisites
Activation key or keys.
See the Activation Keys page for creating new activation keys.
Procedure
1. Open the system menu, which is accessible from the upper-right screen corner, and click the
Settings icon.
2. In the Details → About section, click Register.
3. Select Registration Server.
4. If you are not using the Red Hat server, enter the server address in the URL field.
5. In the Registration Type menu, select Activation Keys.
6. Under Registration Details:
Enter your activation keys in the Activation Keys field.
Separate your keys by a comma (,).
Enter the name or ID of your organization in the Organization field.
Red Hat Enterprise Linux 8 Configuring basic system settings
24
7. Click Register.
2.5. REGISTERING RHEL 8 USING THE INSTALLER GUI
Use the following steps to register a Red Hat Enterprise Linux 8 using the RHEL installer GUI.
Prerequisites
You have a valid user account on the Red Hat Customer Portal. See the Create a Red Hat Login
page.
You have a valid Activation Key and Organization id.
Procedure
1. From the Installation Summary screen, under Software, click Connect to Red Hat.
2. Authenticate your Red Hat account using the Account or Activation Key option.
3. Optional: In the Set System Purpose field select the Role, SLA, and Usage attribute that you
want to set from the drop-down menu.
At this point, your Red Hat Enterprise Linux 8 system has been successfully registered.
CHAPTER 2. REGISTERING THE SYSTEM AND MANAGING SUBSCRIPTIONS
25
CHAPTER 3. ACCESSING THE RED HAT SUPPORT
This section describes how to effectively troubleshoot your problems using Red Hat support and
sosreport.
To obtain support from Red Hat, use the Red Hat Customer Portal, which provides access to everything
available with your subscription.
3.1. OBTAINING RED HAT SUPPORT THROUGH RED HAT CUSTOMER
PORTAL
The following section describes how to use the Red Hat Customer Portal to get help.
Prerequisites
A valid user account on the Red Hat Customer Portal. See Create a Red Hat Login .
An active subscription for the RHEL system.
Procedure
1. Access Red Hat support:
a. Open a new support case.
b. Initiate a live chat with a Red Hat expert.
c. Contact a Red Hat expert by making a call or sending an email.
3.2. TROUBLESHOOTING PROBLEMS USING SOSREPORT
The sosreport command collects configuration details, system information and diagnostic information
from a Red Hat Enterprise Linux system.
The following section describes how to use the sosreport command to produce reports for your support
cases.
Prerequisites
A valid user account on the Red Hat Customer Portal. See Create a Red Hat Login .
An active subscription for the RHEL system.
A support-case number.
Procedure
1. Install the sos package:
# yum install sos
NOTE
Red Hat Enterprise Linux 8 Configuring basic system settings
26
NOTE
The default minimal installation of Red Hat Enterprise Linux does not include the
sos package, which provides the sosreport command.
2. Generate a report:
# sosreport
3. Attach the report to your support case.
See the How can I attach a file to a Red Hat support case? Red Hat Knowledgebase article for
more information.
Note that when attaching the report, you are prompted to enter the number of the relevant
support case.
Additional resources
What is an sosreport and how to create one in Red Hat Enterprise Linux?
CHAPTER 3. ACCESSING THE RED HAT SUPPORT
27
CHAPTER 4. CHANGING BASIC ENVIRONMENT SETTINGS
Configuration of basic environment settings is a part of the installation process. The following sections
guide you when you change them later. The basic configuration of the environment includes:
Date and time
System locales
Keyboard layout
Language
4.1. CONFIGURING THE DATE AND TIME
Accurate timekeeping is important for several reasons. In Red Hat Enterprise Linux, timekeeping is
ensured by the NTP protocol, which is implemented by a daemon running in user space. The user-space
daemon updates the system clock running in the kernel. The system clock can keep time by using
various clock sources.
Red Hat Enterprise Linux 8 uses the chronyd daemon to implement NTP. chronyd is available from the
chrony package. For more information, see Using the chrony suite to configure NTP .
4.1.1. Displaying the current date and time
To display the current date and time, use either of these steps.
Procedure
1. Enter the date command:
$ date
Mon Mar 30 16:02:59 CEST 2020
2. To see more details, use the timedatectl command:
$ timedatectl
Local time: Mon 2020-03-30 16:04:42 CEST
Universal time: Mon 2020-03-30 14:04:42 UTC
RTC time: Mon 2020-03-30 14:04:41
Time zone: Europe/Prague (CEST, +0200)
System clock synchronized: yes
NTP service: active
RTC in local TZ: no
Additional resources
Configuring time settings using the web console
man date(1) and man timedatectl(1)
4.2. CONFIGURING THE SYSTEM LOCALE
System-wide locale settings are stored in the /etc/locale.conf file that is read at early boot by the
Red Hat Enterprise Linux 8 Configuring basic system settings
28
System-wide locale settings are stored in the /etc/locale.conf file that is read at early boot by the
systemd daemon. Every service or user inherits the locale settings configured in /etc/locale.conf, unless
individual programs or individual users override them.
Procedure
To list available system locale settings:
$ localectl list-locales
C.utf8
aa_DJ
aa_DJ.iso88591
aa_DJ.utf8
...
To display the current status of the system locales settings:
$ localectl status
To set or change the default system locale settings, use a localectl set-locale sub-command as
the root user. For example:
# localectl set-locale LANG=en_US
Additional resources
man localectl(1), man locale(7), and man locale.conf(5)
4.3. CONFIGURING THE KEYBOARD LAYOUT
The keyboard layout settings control the layout used on the text console and graphical user interfaces.
Procedure
To list available keymaps:
$ localectl list-keymaps
ANSI-dvorak
al
al-plisi
amiga-de
amiga-us
...
To display the current status of keymaps settings:
$ localectl status
...
VC Keymap: us
...
To set or change the default system keymap. For example:
CHAPTER 4. CHANGING BASIC ENVIRONMENT SETTINGS
29
# localectl set-keymap us
Additional resources
man localectl(1), man locale(7), and man locale.conf(5)
4.4. CHANGING THE LANGUAGE USING DESKTOP GUI
You can change the system language using the desktop GUI.
Prerequisites
Required language packages are installed on your system
Procedure
1. Open the Settings application from the system menu by clicking on its icon.
2. In Settings, choose Region & Languagefrom the left vertical bar.
3. Click the Language menu.
Red Hat Enterprise Linux 8 Configuring basic system settings
30
4. Select the required region and language from the menu.
If your region and language are not listed, scroll down, and click More to select from available
regions and languages.
5. Click Done.
6. Click Restart for changes to take effect.
CHAPTER 4. CHANGING BASIC ENVIRONMENT SETTINGS
31
NOTE
Some applications do not support certain languages. The text of an application that
cannot be translated into the selected language remains in US English.
Additional resources
Launching applications in GNOME
4.5. ADDITIONAL RESOURCES
Performing a standard RHEL 8 installation
Red Hat Enterprise Linux 8 Configuring basic system settings
32
CHAPTER 5. USING SECURE COMMUNICATIONS BETWEEN
TWO SYSTEMS WITH OPENSSH
SSH (Secure Shell) is a protocol which provides secure communications between two systems using a
client-server architecture and allows users to log in to server host systems remotely. Unlike other
remote communication protocols, such as FTP or Telnet, SSH encrypts the login session, which prevents
intruders to collect unencrypted passwords from the connection.
Red Hat Enterprise Linux includes the basic OpenSSH packages: the general openssh package, the
openssh-server package and the openssh-clients package. Note that the OpenSSH packages require
the OpenSSL package openssl-libs, which installs several important cryptographic libraries that enable
OpenSSH to provide encrypted communications.
5.1. SSH AND OPENSSH
SSH (Secure Shell) is a program for logging into a remote machine and executing commands on that
machine. The SSH protocol provides secure encrypted communications between two untrusted hosts
over an insecure network. You can also forward X11 connections and arbitrary TCP/IP ports over the
secure channel.
The SSH protocol mitigates security threats, such as interception of communication between two
systems and impersonation of a particular host, when you use it for remote shell login or file copying.
This is because the SSH client and server use digital signatures to verify their identities. Additionally, all
communication between the client and server systems is encrypted.
A host key authenticates hosts in the SSH protocol. Host keys are cryptographic keys that are
generated automatically when OpenSSH is first installed, or when the host boots for the first time.
OpenSSH is an implementation of the SSH protocol supported by Linux, UNIX, and similar operating
systems. It includes the core files necessary for both the OpenSSH client and server. The OpenSSH
suite consists of the following user-space tools:
ssh is a remote login program (SSH client).
sshd is an OpenSSH SSH daemon.
scp is a secure remote file copy program.
sftp is a secure file transfer program.
ssh-agent is an authentication agent for caching private keys.
ssh-add adds private key identities to ssh-agent.
ssh-keygen generates, manages, and converts authentication keys for ssh.
ssh-copy-id is a script that adds local public keys to the authorized_keys file on a remote SSH
server.
ssh-keyscan gathers SSH public host keys.
Two versions of SSH currently exist: version 1, and the newer version 2. The OpenSSH suite in RHEL
supports only SSH version 2. It has an enhanced key-exchange algorithm that is not vulnerable to
exploits known in version 1.
OpenSSH, as one of core cryptographic subsystems of RHEL, uses system-wide crypto policies. This
CHAPTER 5. USING SECURE COMMUNICATIONS BETWEEN TWO SYSTEMS WITH OPENSSH
33
ensures that weak cipher suites and cryptographic algorithms are disabled in the default configuration.
To modify the policy, the administrator must either use the update-crypto-policies command to adjust
the settings or manually opt out of the system-wide crypto policies.
The OpenSSH suite uses two sets of configuration files: one for client programs (that is, ssh, scp, and
sftp), and another for the server (the sshd daemon).
System-wide SSH configuration information is stored in the /etc/ssh/ directory. User-specific SSH
configuration information is stored in ~/.ssh/ in the user’s home directory. For a detailed list of
OpenSSH configuration files, see the FILES section in the sshd(8) man page.
Additional resources
Man pages listed by using the man -k ssh command
Using system-wide cryptographic policies
5.2. CONFIGURING AND STARTING AN OPENSSH SERVER
Use the following procedure for a basic configuration that might be required for your environment and
for starting an OpenSSH server. Note that after the default RHEL installation, the sshd daemon is
already started and server host keys are automatically created.
Prerequisites
The openssh-server package is installed.
Procedure
1. Start the sshd daemon in the current session and set it to start automatically at boot time:
# systemctl start sshd
# systemctl enable sshd
2. To specify different addresses than the default 0.0.0.0 (IPv4) or :: (IPv6) for the
ListenAddress directive in the /etc/ssh/sshd_config configuration file and to use a slower
dynamic network configuration, add the dependency on the network-online.target target unit
to the sshd.service unit file. To achieve this, create the
/etc/systemd/system/sshd.service.d/local.conf file with the following content:
[Unit]
Wants=network-online.target
After=network-online.target
3. Review if OpenSSH server settings in the /etc/ssh/sshd_config configuration file meet the
requirements of your scenario.
4. Optionally, change the welcome message that your OpenSSH server displays before a client
authenticates by editing the /etc/issue file, for example:
Welcome to ssh-server.example.com
Warning: By accessing this server, you agree to the referenced terms and conditions.
Ensure that the Banner option is not commented out in /etc/ssh/sshd_config and its value
Red Hat Enterprise Linux 8 Configuring basic system settings
34
Ensure that the Banner option is not commented out in /etc/ssh/sshd_config and its value
contains /etc/issue:
# less /etc/ssh/sshd_config | grep Banner
Banner /etc/issue
Note that to change the message displayed after a successful login you have to edit the
/etc/motd file on the server. See the pam_motd man page for more information.
5. Reload the systemd configuration and restart sshd to apply the changes:
# systemctl daemon-reload
# systemctl restart sshd
Verification
1. Check that the sshd daemon is running:
# systemctl status sshd
● sshd.service - OpenSSH server daemon
Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled)
Active: active (running) since Mon 2019-11-18 14:59:58 CET; 6min ago
Docs: man:sshd(8)
man:sshd_config(5)
Main PID: 1149 (sshd)
Tasks: 1 (limit: 11491)
Memory: 1.9M
CGroup: /system.slice/sshd.service
└─1149 /usr/sbin/sshd -D -oCiphers=aes128-ctr,aes256-ctr,aes128-cbc,aes256-cbc -
oMACs=hmac-sha2-256,>
Nov 18 14:59:58 ssh-server-example.com systemd[1]: Starting OpenSSH server daemon...
Nov 18 14:59:58 ssh-server-example.com sshd[1149]: Server listening on 0.0.0.0 port 22.
Nov 18 14:59:58 ssh-server-example.com sshd[1149]: Server listening on :: port 22.
Nov 18 14:59:58 ssh-server-example.com systemd[1]: Started OpenSSH server daemon.
2. Connect to the SSH server with an SSH client.
# ssh user@ssh-server-example.com
ECDSA key fingerprint is SHA256:dXbaS0RG/UzlTTku8GtXSz0S1++lPegSy31v3L/FAEc.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added 'ssh-server-example.com' (ECDSA) to the list of known hosts.
user@ssh-server-example.com's password:
Additional resources
sshd(8) and sshd_config(5) man pages.
5.3. SETTING AN OPENSSH SERVER FOR KEY-BASED
AUTHENTICATION
To improve system security, enforce key-based authentication by disabling password authentication on
CHAPTER 5. USING SECURE COMMUNICATIONS BETWEEN TWO SYSTEMS WITH OPENSSH
35
To improve system security, enforce key-based authentication by disabling password authentication on
your OpenSSH server.
Prerequisites
The openssh-server package is installed.
The sshd daemon is running on the server.
Procedure
1. Open the /etc/ssh/sshd_config configuration in a text editor, for example:
# vi /etc/ssh/sshd_config
2. Change the PasswordAuthentication option to no:
PasswordAuthentication no
On a system other than a new default installation, check that PubkeyAuthentication no has not
been set and the ChallengeResponseAuthentication directive is set to no. If you are
connected remotely, not using console or out-of-band access, test the key-based login process
before disabling password authentication.
3. To use key-based authentication with NFS-mounted home directories, enable the
use_nfs_home_dirs SELinux boolean:
# setsebool -P use_nfs_home_dirs 1
4. Reload the sshd daemon to apply the changes:
# systemctl reload sshd
Additional resources
sshd(8), sshd_config(5), and setsebool(8) man pages.
5.4. GENERATING SSH KEY PAIRS
Use this procedure to generate an SSH key pair on a local system and to copy the generated public key
to an OpenSSH server. If the server is configured accordingly, you can log in to the OpenSSH server
without providing any password.
IMPORTANT
If you complete the following steps as root, only root is able to use the keys.
Procedure
1. To generate an ECDSA key pair for version 2 of the SSH protocol:
$ ssh-keygen -t ecdsa
Generating public/private ecdsa key pair.
Red Hat Enterprise Linux 8 Configuring basic system settings
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Enter file in which to save the key (/home/joesec/.ssh/id_ecdsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/joesec/.ssh/id_ecdsa.
Your public key has been saved in /home/joesec/.ssh/id_ecdsa.pub.
The key fingerprint is:
SHA256:Q/x+qms4j7PCQ0qFd09iZEFHA+SqwBKRNaU72oZfaCI
joesec@localhost.example.com
The key's randomart image is:
+---[ECDSA 256]---+
|.oo..o=++ |
|.. o .oo . |
|. .. o. o |
|....o.+... |
|o.oo.o +S . |
|.=.+. .o |
|E.*+. . . . |
|.=..+ +.. o |
| . oo*+o. |
+----[SHA256]-----+
You can also generate an RSA key pair by using the -t rsa option with the ssh-keygen
command or an Ed25519 key pair by entering the ssh-keygen -t ed25519 command.
2. To copy the public key to a remote machine:
$ ssh-copy-id joesec@ssh-server-example.com
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are
already installed
joesec@ssh-server-example.com's password:
...
Number of key(s) added: 1
Now try logging into the machine, with: "ssh 'joesec@ssh-server-example.com'" and check to
make sure that only the key(s) you wanted were added.
If you do not use the ssh-agent program in your session, the previous command copies the
most recently modified ~/.ssh/id*.pub public key if it is not yet installed. To specify another
public-key file or to prioritize keys in files over keys cached in memory by ssh-agent, use the
ssh-copy-id command with the -i option.
NOTE
If you reinstall your system and want to keep previously generated key pairs, back up the
~/.ssh/ directory. After reinstalling, copy it back to your home directory. You can do this
for all users on your system, including root.
Verification
1. Log in to the OpenSSH server without providing any password:
$ ssh joesec@ssh-server-example.com
Welcome message.
...
Last login: Mon Nov 18 18:28:42 2019 from ::1
CHAPTER 5. USING SECURE COMMUNICATIONS BETWEEN TWO SYSTEMS WITH OPENSSH
37
Additional resources
ssh-keygen(1) and ssh-copy-id(1) man pages.
5.5. USING SSH KEYS STORED ON A SMART CARD
Red Hat Enterprise Linux enables you to use RSA and ECDSA keys stored on a smart card on OpenSSH
clients. Use this procedure to enable authentication using a smart card instead of using a password.
Prerequisites
On the client side, the opensc package is installed and the pcscd service is running.
Procedure
1. List all keys provided by the OpenSC PKCS #11 module including their PKCS #11 URIs and save
the output to the keys.pub file:
$ ssh-keygen -D pkcs11: > keys.pub
$ ssh-keygen -D pkcs11:
ssh-rsa AAAAB3NzaC1yc2E...KKZMzcQZzx
pkcs11:id=%02;object=SIGN%20pubkey;token=SSH%20key;manufacturer=piv_II?modulepath=/usr/lib64/pkcs11/opensc-pkcs11.so
ecdsa-sha2-nistp256 AAA...J0hkYnnsM=
pkcs11:id=%01;object=PIV%20AUTH%20pubkey;token=SSH%20key;manufacturer=piv_II?
module-path=/usr/lib64/pkcs11/opensc-pkcs11.so
2. To enable authentication using a smart card on a remote server (example.com), transfer the
public key to the remote server. Use the ssh-copy-id command with keys.pub created in the
previous step:
$ ssh-copy-id -f -i keys.pub username@example.com
3. To connect to example.com using the ECDSA key from the output of the ssh-keygen -D
command in step 1, you can use just a subset of the URI, which uniquely references your key, for
example:
$ ssh -i "pkcs11:id=%01?module-path=/usr/lib64/pkcs11/opensc-pkcs11.so" example.com
Enter PIN for 'SSH key':
[example.com] $
4. You can use the same URI string in the ~/.ssh/config file to make the configuration permanent:
$ cat ~/.ssh/config
IdentityFile "pkcs11:id=%01?module-path=/usr/lib64/pkcs11/opensc-pkcs11.so"
$ ssh example.com
Enter PIN for 'SSH key':
[example.com] $
Because OpenSSH uses the p11-kit-proxy wrapper and the OpenSC PKCS #11 module is
registered to PKCS#11 Kit, you can simplify the previous commands:
Red Hat Enterprise Linux 8 Configuring basic system settings
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$ ssh -i "pkcs11:id=%01" example.com
Enter PIN for 'SSH key':
[example.com] $
If you skip the id= part of a PKCS #11 URI, OpenSSH loads all keys that are available in the proxy module.
This can reduce the amount of typing required:
$ ssh -i pkcs11: example.com
Enter PIN for 'SSH key':
[example.com] $
Additional resources
Fedora 28: Better smart card support in OpenSSH
p11-kit(8), opensc.conf(5), pcscd(8), ssh(1), and ssh-keygen(1) man pages
5.6. MAKING OPENSSH MORE SECURE
The following tips help you to increase security when using OpenSSH. Note that changes in the
/etc/ssh/sshd_config OpenSSH configuration file require reloading the sshd daemon to take effect:
# systemctl reload sshd
IMPORTANT
The majority of security hardening configuration changes reduce compatibility with
clients that do not support up-to-date algorithms or cipher suites.
Disabling insecure connection protocols
To make SSH truly effective, prevent the use of insecure connection protocols that are replaced
by the OpenSSH suite. Otherwise, a user’s password might be protected using SSH for one
session only to be captured later when logging in using Telnet. For this reason, consider
disabling insecure protocols, such as telnet, rsh, rlogin, and ftp.
Enabling key-based authentication and disabling password-based authentication
Disabling passwords for authentication and allowing only key pairs reduces the attack surface
and it also might save users’ time. On clients, generate key pairs using the ssh-keygen tool and
use the ssh-copy-id utility to copy public keys from clients on the OpenSSH server. To disable
password-based authentication on your OpenSSH server, edit /etc/ssh/sshd_config and
change the PasswordAuthentication option to no:
PasswordAuthentication no
Key types
Although the ssh-keygen command generates a pair of RSA keys by default, you can instruct it
to generate ECDSA or Ed25519 keys by using the -t option. The ECDSA (Elliptic Curve Digital
Signature Algorithm) offers better performance than RSA at the equivalent symmetric key
CHAPTER 5. USING SECURE COMMUNICATIONS BETWEEN TWO SYSTEMS WITH OPENSSH
39
strength. It also generates shorter keys. The Ed25519 public-key algorithm is an implementation
of twisted Edwards curves that is more secure and also faster than RSA, DSA, and ECDSA.
OpenSSH creates RSA, ECDSA, and Ed25519 server host keys automatically if they are missing.
To configure the host key creation in RHEL, use the sshd-keygen@.service instantiated
service. For example, to disable the automatic creation of the RSA key type:
# systemctl mask sshd-keygen@rsa.service
NOTE
In images with cloud-init enabled, the ssh-keygen units are automatically
disabled. This is because the ssh-keygen template service can interfere with the
cloud-init tool and cause problems with host key generation. To prevent these
problems the etc/systemd/system/sshd-keygen@.service.d/disable-sshdkeygen-if-cloud-init-active.conf drop-in configuration file disables the sshkeygen units if cloud-init is running.
To exclude particular key types for SSH connections, comment out the relevant lines in
/etc/ssh/sshd_config, and reload the sshd service. For example, to allow only Ed25519 host
keys:
# HostKey /etc/ssh/ssh_host_rsa_key
# HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
IMPORTANT
The Ed25519 algorithm is not FIPS-140-compliant, and OpenSSH does not work
with Ed25519 keys in FIPS mode.
Non-default port
By default, the sshd daemon listens on TCP port 22. Changing the port reduces the exposure
of the system to attacks based on automated network scanning and therefore increase security
through obscurity. You can specify the port using the Port directive in the
/etc/ssh/sshd_config configuration file.
You also have to update the default SELinux policy to allow the use of a non-default port. To do
so, use the semanage tool from the policycoreutils-python-utils package:
# semanage port -a -t ssh_port_t -p tcp
Furthermore, update firewalld configuration:
# firewall-cmd --add-port /tcp
# firewall-cmd --remove-port=22/tcp
# firewall-cmd --runtime-to-permanent
In the previous commands, replace with the new port number specified using the
Port directive.
No root login
Red Hat Enterprise Linux 8 Configuring basic system settings
40
If your particular use case does not require the possibility of logging in as the root user, you can
set the PermitRootLogin configuration directive to no in the /etc/ssh/sshd_config file. By
disabling the possibility of logging in as the root user, the administrator can audit which users run
what privileged commands after they log in as regular users and then gain root rights.
Alternatively, set PermitRootLogin to prohibit-password:
PermitRootLogin prohibit-password
This enforces the use of key-based authentication instead of the use of passwords for logging
in as root and reduces risks by preventing brute-force attacks.
Using the X Security extension
The X server in Red Hat Enterprise Linux clients does not provide the X Security extension.
Therefore, clients cannot request another security layer when connecting to untrusted SSH
servers with X11 forwarding. Most applications are not able to run with this extension enabled
anyway.
By default, the ForwardX11Trusted option in the /etc/ssh/ssh_config.d/05-redhat.conf file is
set to yes, and there is no difference between the ssh -X remote_machine (untrusted host)
and ssh -Y remote_machine (trusted host) command.
If your scenario does not require the X11 forwarding feature at all, set the X11Forwarding
directive in the /etc/ssh/sshd_config configuration file to no.
Restricting access to specific users, groups, or domains
The AllowUsers and AllowGroups directives in the /etc/ssh/sshd_config configuration file
server enable you to permit only certain users, domains, or groups to connect to your OpenSSH
server. You can combine AllowUsers and AllowGroups to restrict access more precisely, for
example:
AllowUsers *@192.168.1.* *@10.0.0.* !*@192.168.1.2
AllowGroups example-group
The previous configuration lines accept connections from all users from systems in 192.168.1.*
and 10.0.0.* subnets except from the system with the 192.168.1.2 address. All users must be in
the example-group group. The OpenSSH server denies all other connections.
The OpenSSH server permits only connections that pass all Allow and Deny directives in
/etc/ssh/sshd_config. For example, if the AllowUsers directive lists a user that is not part of a
group listed in the AllowGroups directive, then the user cannot log in.
Note that using allowlists (directives starting with Allow) is more secure than using blocklists
(options starting with Deny) because allowlists block also new unauthorized users or groups.
Changing system-wide cryptographic policies
OpenSSH uses RHEL system-wide cryptographic policies, and the default system-wide
cryptographic policy level offers secure settings for current threat models. To make your
cryptographic settings more strict, change the current policy level:
# update-crypto-policies --set FUTURE
Setting system policy to FUTURE
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41
WARNING
If your system communicates on the internet, you might face
interoperability problems due to the strict setting of the FUTURE policy.
You can also disable only specific ciphers for the SSH protocol through the system-wide cryptographic
policies. See the Customizing system-wide cryptographic policies with subpolicies section in the
Security hardening document for more information.
To opt out of the system-wide cryptographic policies for your OpenSSH server, uncomment the line
with the CRYPTO_POLICY= variable in the /etc/sysconfig/sshd file. After this change, values that you
specify in the Ciphers, MACs, KexAlgoritms, and GSSAPIKexAlgorithms sections in the
/etc/ssh/sshd_config file are not overridden.
See the sshd_config(5) man page for more information.
To opt out of system-wide cryptographic policies for your OpenSSH client, perform one of the following
tasks:
For a given user, override the global ssh_config with a user-specific configuration in the
~/.ssh/config file.
For the entire system, specify the cryptographic policy in a drop-in configuration file located in
the /etc/ssh/ssh_config.d/ directory, with a two-digit number prefix smaller than 5, so that it
lexicographically precedes the 05-redhat.conf file, and with a .conf suffix, for example, 04-
crypto-policy-override.conf.
Additional resources
sshd_config(5), ssh-keygen(1), crypto-policies(7), and update-crypto-policies(8) man pages.
Using system-wide cryptographic policies in the Security hardening document.
How to disable specific algorithms and ciphers for ssh service only article.
5.7. CONNECTING TO A REMOTE SERVER USING AN SSH JUMP HOST
Use this procedure for connecting your local system to a remote server through an intermediary server,
also called jump host.
Prerequisites
A jump host accepts SSH connections from your local system.
A remote server accepts SSH connections only from the jump host.
Procedure
1. Define the jump host by editing the ~/.ssh/config file on your local system, for example:
Red Hat Enterprise Linux 8 Configuring basic system settings
42
Host jump-server1
HostName jump1.example.com
The Host parameter defines a name or alias for the host you can use in ssh commands. The
value can match the real host name, but can also be any string.
The HostName parameter sets the actual host name or IP address of the jump host.
2. Add the remote server jump configuration with the ProxyJump directive to ~/.ssh/config file
on your local system, for example:
Host remote-server
HostName remote1.example.com
ProxyJump jump-server1
3. Use your local system to connect to the remote server through the jump server:
$ ssh remote-server
The previous command is equivalent to the ssh -J jump-server1 remote-server command if
you omit the configuration steps 1 and 2.
NOTE
You can specify more jump servers and you can also skip adding host definitions to the
configurations file when you provide their complete host names, for example:
$ ssh -J jump1.example.com,jump2.example.com,jump3.example.com
remote1.example.com
Change the host name-only notation in the previous command if the user names or SSH
ports on the jump servers differ from the names and ports on the remote server, for
example:
$ ssh -J
johndoe@jump1.example.com:75,johndoe@jump2.example.com:75,johndoe@jump3.e
xample.com:75 joesec@remote1.example.com:220
Additional resources
ssh_config(5) and ssh(1) man pages.
5.8. CONNECTING TO REMOTE MACHINES WITH SSH KEYS USING
SSH-AGENT
To avoid entering a passphrase each time you initiate an SSH connection, you can use the ssh-agent
utility to cache the private SSH key. The private key and the passphrase remain secure.
Prerequisites
You have a remote host with SSH daemon running and reachable through the network.
CHAPTER 5. USING SECURE COMMUNICATIONS BETWEEN TWO SYSTEMS WITH OPENSSH
43
You know the IP address or hostname and credentials to log in to the remote host.
You have generated an SSH key pair with a passphrase and transferred the public key to the
remote machine.
For more information, see Generating SSH key pairs .
Procedure
1. Optional: Verify you can use the key to authenticate to the remote host:
a. Connect to the remote host using SSH:
$ ssh example.user1@198.51.100.1 hostname
b. Enter the passphrase you set while creating the key to grant access to the private key.
$ ssh example.user1@198.51.100.1 hostname
host.example.com
2. Start the ssh-agent.
$ eval $(ssh-agent)
Agent pid 20062
3. Add the key to ssh-agent.
$ ssh-add ~/.ssh/id_rsa
Enter passphrase for ~/.ssh/id_rsa:
Identity added: ~/.ssh/id_rsa (example.user0@198.51.100.12)
Verification
Optional: Log in to the host machine using SSH.
$ ssh example.user1@198.51.100.1
Last login: Mon Sep 14 12:56:37 2020
Note that you did not have to enter the passphrase.
5.9. ADDITIONAL RESOURCES
sshd(8), ssh(1), scp(1), sftp(1), ssh-keygen(1), ssh-copy-id(1), ssh_config(5),
sshd_config(5), update-crypto-policies(8), and crypto-policies(7) man pages.
OpenSSH Home Page
Configuring SELinux for applications and services with non-standard configurations
Controlling network traffic using firewalld
Red Hat Enterprise Linux 8 Configuring basic system settings
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CHAPTER 6. CONFIGURING BASIC SYSTEM SECURITY
Computer security is the protection of computer systems and their hardware, software, information, and
services from theft, damage, disruption, and misdirection. Ensuring computer security is an essential
task, in particular in enterprises that process sensitive data and handle business transactions.
This section covers only the basic security features that you can configure after installation of the
operating system.
6.1. ENABLING THE FIREWALLD SERVICE
A firewall is a network security system that monitors and controls incoming and outgoing network traffic
according to configured security rules. A firewall typically establishes a barrier between a trusted secure
internal network and another outside network.
The firewalld service, which provides a firewall in Red Hat Enterprise Linux, is automatically enabled
during installation.
To enable the firewalld service, follow this procedure.
Procedure
Display the current status of firewalld:
$ systemctl status firewalld
● firewalld.service - firewalld - dynamic firewall daemon
Loaded: loaded (/usr/lib/systemd/system/firewalld.service; disabled; vendor preset:
enabled)
Active: inactive (dead)
...
If firewalld is not enabled and running, switch to the root user, and start the firewalld service
and enable to start it automatically after the system restarts:
# systemctl enable --now firewalld
Verification steps
Check that firewalld is running and enabled:
$ systemctl status firewalld
● firewalld.service - firewalld - dynamic firewall daemon
Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset:
enabled)
Active: active (running)
...
Additional resources
Using and configuring firewalld
man firewalld(1)
CHAPTER 6. CONFIGURING BASIC SYSTEM SECURITY
45
6.2. MANAGING FIREWALL IN THE RHEL 8 WEB CONSOLE
To configure the firewalld service in the web console, navigate to Networking → Firewall.
By default, the firewalld service is enabled.
Procedure
1. To enable or disable firewalld in the web console, switch the Firewall toggle button.
NOTE
Additionally, you can define more fine-grained access through the firewall to a service
using the Add services… button.
6.3. MANAGING BASIC SELINUX SETTINGS
Security-Enhanced Linux (SELinux) is an additional layer of system security that determines which
processes can access which files, directories, and ports. These permissions are defined in SELinux
policies. A policy is a set of rules that guide the SELinux security engine.
SELinux has two possible states:
Disabled
Enabled
When SELinux is enabled, it runs in one of the following modes:
Enabled
Enforcing
Permissive
In enforcing mode, SELinux enforces the loaded policies. SELinux denies access based on SELinux
policy rules and enables only the interactions that are explicitly allowed. Enforcing mode is the safest
SELinux mode and is the default mode after installation.
In permissive mode, SELinux does not enforce the loaded policies. SELinux does not deny access, but
reports actions that break the rules to the /var/log/audit/audit.log log. Permissive mode is the default
mode during installation. Permissive mode is also useful in some specific cases, for example when
troubleshooting problems.
Additional resources
Using SELinux
Red Hat Enterprise Linux 8 Configuring basic system settings
46
6.4. ENSURING THE REQUIRED STATE OF SELINUX
By default, SELinux operates in enforcing mode. However, in specific scenarios, you can set SELinux to
permissive mode or even disable it.
IMPORTANT
Red Hat recommends to keep your system in enforcing mode. For debugging purposes,
you can set SELinux to permissive mode.
Follow this procedure to change the state and mode of SELinux on your system.
Procedure
1. Display the current SELinux mode:
$ getenforce
2. To temporarily set SELinux:
a. To Enforcing mode:
# setenforce Enforcing
b. To Permissive mode:
# setenforce Permissive
NOTE
After reboot, SELinux mode is set to the value specified in the
/etc/selinux/config configuration file.
3. To set SELinux mode to persist across reboots, modify the SELINUX variable in the
/etc/selinux/config configuration file.
For example, to switch SELinux to enforcing mode:
# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
# enforcing - SELinux security policy is enforced.
# permissive - SELinux prints warnings instead of enforcing.
# disabled - No SELinux policy is loaded.
SELINUX=enforcing
...
CHAPTER 6. CONFIGURING BASIC SYSTEM SECURITY
47
WARNING
Disabling SELinux reduces your system security. Avoid disabling SELinux
using the SELINUX=disabled option in the /etc/selinux/config file
because this can result in memory leaks and race conditions causing kernel
panics. Instead, disable SELinux by adding the selinux=0 parameter to the
kernel command line. For more information, see Changing SELinux modes
at boot time.
Additional resources
Changing SELinux states and modes
6.5. SWITCHING SELINUX MODES IN THE RHEL 8 WEB CONSOLE
You can set SELinux mode through the RHEL 8 web console in the SELinux menu item.
By default, SELinux enforcing policy in the web console is on, and SELinux operates in enforcing mode.
By turning it off, you switch SELinux to permissive mode. Note that this selection is automatically
reverted on the next boot to the configuration defined in the /etc/sysconfig/selinux file.
Procedure
1. In the web console, use the Enforce policy toggle button in the SELinux menu item to turn
SELinux enforcing policy on or off.
6.6. ADDITIONAL RESOURCES
Generating SSH key pairs
Setting an OpenSSH server for key-based authentication
Security hardening
Red Hat Enterprise Linux 8 Configuring basic system settings
48
Using SELinux
Securing networks
Deploying the same SELinux configuration on multiple systems
CHAPTER 6. CONFIGURING BASIC SYSTEM SECURITY
49
CHAPTER 7. MANAGING SOFTWARE PACKAGES
7.1. SOFTWARE MANAGEMENT TOOLS IN RHEL 8
In RHEL 8, software installation is enabled by the new version of the YUM tool (YUM v4), which is based
on the DNF technology.
NOTE
Upstream documentation identifies the technology as DNF and the tool is referred to as
DNF in the upstream. As a result, some output returned by the new YUM tool in RHEL 8
mentions DNF.
Although YUM v4used in RHEL 8 is based on DNF, it is compatible with YUM v3 used in RHEL 7. For
software installation, the yum command and most of its options work the same way in RHEL 8 as they
did in RHEL 7.
Selected yum plug-ins and utilities have been ported to the new DNF back end, and can be installed
under the same names as in RHEL 7. Packages also provide compatibility symlinks, so the binaries,
configuration files, and directories can be found in usual locations.
Note that the legacy Python API provided by YUM v3 is no longer available. You can migrate your plugins and scripts to the new API provided by YUM v4(DNF Python API), which is stable and fully
supported. See DNF API Reference for more information.
7.2. APPLICATION STREAMS
RHEL 8 introduces the concept of Application Streams. Multiple versions of user space components are
now delivered and updated more frequently than the core operating system packages. This provides
greater flexibility to customize Red Hat Enterprise Linux without impacting the underlying stability of
the platform or specific deployments.
Components made available as Application Streams can be packaged as modules or RPM packages, and
are delivered through the AppStream repository in RHEL 8. Each Application Stream has a given life
cycle, either the same as RHEL 8 or shorter, more suitable to the particular application. Application
Streams with a shorter life cycle are listed in the Red Hat Enterprise Linux 8 Application Streams Life
Cycle page.
Modules are collections of packages representing a logical unit: an application, a language stack, a
database, or a set of tools. These packages are built, tested, and released together.
Module streams represent versions of the Application Stream components. For example, two streams
(versions) of the PostgreSQL database server are available in the postgresql module: PostgreSQL 10
(the default stream) and PostgreSQL 9.6. Only one module stream can be installed on the system.
Different versions can be used in separate containers.
Detailed module commands are described in the Installing, managing, and removing user-space
components document. For a list of modules available in AppStream, see the Package manifest.
7.3. SEARCHING FOR SOFTWARE PACKAGES
yum allows you to perform a complete set of operations with software packages.
The following section describes how to use yum to:
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Search for packages.
List packages.
List repositories.
Display information about the packages.
List package groups.
Specify global expressions in yum input.
7.3.1. Searching packages with YUM
Use the following procedure to find a package providing a particular application or other content.
Procedure
To search for a package, use:
# yum search term
Replace term with a term related to the package.
Note that yum search command returns term matches within the name and summary of the
packages. This makes the search faster and enables you to search for packages you do not know
the name of, but for which you know a related term.
To include term matches within package descriptions, use:
# yum search --all term
Replace term with a term you want to search for in a package name, summary, or description.
Note that yum search --all enables a more exhaustive but slower search.
7.3.2. Listing packages with YUM
Use the following procedure to list installed and available packages.
Procedure
To list information about all installed and available packages, use:
# yum list --all
To list all packages installed on your system, use:
# yum list --installed
To list all packages in all enabled repositories that are available to install, use:
# yum list --available
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Note that you can filter the results by appending global expressions as arguments. See Specifying global
expressions in yum input
for more details.
7.3.3. Listing repositories with YUM
Use the following procedure to list enabled and disabled repositories.
Procedure
To list all enabled repositories on your system, use:
# yum repolist
To list all disabled repositories on your system, use:
# yum repolist --disabled
To list both enabled and disabled repositories, use:
# yum repolist --all
To list additional information about the repositories, use:
# yum repoinfo
Note that you can filter the results by passing the ID or name of repositories as arguments or by
appending global expressions. See Specifying global expressions in yum input
for more details.
7.3.4. Displaying package information with YUM
You can display various types of information about a package using YUM, for example version, release,
size, loaded plugins, and more.
Procedure
To display information about one or more packages, use:
# yum info package-name
Replace package-name with the name of the package.
Note that you can filter the results by appending global expressions as arguments. See Specifying global
expressions in yum input
for more details.
7.3.5. Listing package groups with YUM
Use yum to view installed package groups and filter the listing results.
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Procedure
To view the number of installed and available groups, use:
# yum group summary
To list all installed and available groups, use:
# yum group list
Note that you can filter the results by appending command line options for the yum group list
command (--hidden, --available). For more available options see the man pages.
To list mandatory and optional packages contained in a particular group, use:
# yum group info group-name
Replace group-name with the name of the group.
Note that you can filter the results by appending global expressions as arguments. See Specifying global
expressions in yum input
for more details.
7.3.6. Specifying global expressions in YUM input
yum commands allow you to filter the results by appending one or more glob expressions as arguments.
You have to escape global expressions when passing them as arguments to the yum command.
Procedure
To ensure global expressions are passed to yum as intended, use one of the following methods:
Double-quote or single-quote the entire global expression.
# yum provides "*/file-name"
Replace file-name with the name of the file.
Escape the wildcard characters by preceding them with a backslash (\) character.
# yum provides \*/file-name
Replace file-name with the name of the file.
7.4. INSTALLING SOFTWARE PACKAGES
The following section describes how to use yum to:
Install packages.
Install a package group.
Specify a package name in yum input.
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7.4.1. Installing packages with YUM
To install a package and all the package dependencies, use:
# yum install package-name
Replace package-name with the name of the package.
To install multiple packages and their dependencies simultaneously, use:
# yum install package-name-1 package-name-2
Replace package-name-1 and package-name-2 with the names of the packages.
When installing packages on a multilib system (AMD64, Intel 64 machine), you can specify the
architecture of the package by appending it to the package name:
# yum install package-name.arch
Replace package-name.arch with the name and architecture of the package.
If you know the name of the binary you want to install, but not the package name, you can use
the path to the binary as an argument:
# yum install /usr/sbin/binary-file
Replace /usr/sbin/binary-file with a path to the binary file.
yum searches through the package lists, finds the package which provides /usr/sbin/binary-file,
and prompts you as to whether you want to install it.
To install a previously-downloaded package from a local directory, use:
# yum install /path/
Replace /path/ with the path to the package.
Note that you can optimize the package search by explicitly defining how to parse the argument. See
Section 7.4.3, “Specifying a package name in YUM input” for more details.
7.4.2. Installing a package group with YUM
The following procedure describes how to install a package group by a group name or by a groupID using
yum.
Procedure
To install a package group by a group name, use:
# yum group install group-name
Or
# yum install @group-name
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Replace group-name with the full name of the group or environmental group.
To install a package group by the groupID, use:
# yum group install groupID
Replace groupID with the ID of the group.
7.4.3. Specifying a package name in YUM input
To optimize the installation and removal process, you can append -n, -na, or -nevra suffixes to yum
install and yum remove commands to explicitly define how to parse an argument:
To install a package using its exact name, use:
# yum install-n name
Replace name with the exact name of the package.
To install a package using its exact name and architecture, use:
# yum install-na name.architecture
Replace name and architecture with the exact name and architecture of the package.
To install a package using its exact name, epoch, version, release, and architecture, use:
# yum install-nevra name-epoch:version-release.architecture
Replace name, epoch, version, release, and architecture with the exact name, epoch, version,
release, and architecture of the package.
7.5. UPDATING SOFTWARE PACKAGES
yum allows you to check if your system has any pending updates. You can list packages that need
updating and choose to update a single package, multiple packages, or all packages at once. If any of the
packages you choose to update have dependencies, they are updated as well.
The following section describes how to use yum to:
Check for updates.
Update a single package.
Update a package group.
Update all packages and their dependencies.
Apply security updates.
Automate software updates.
7.5.1. Checking for updates with YUM
The following procedure describes how to check the available updates for packages installed on your
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The following procedure describes how to check the available updates for packages installed on your
system using yum.
Procedure
To see which packages installed on your system have available updates, use:
# yum check-update
The output returns the list of packages and their dependencies that have an update available.
7.5.2. Updating a single package with YUM
Use the following procedure to update a single package and its dependencies using yum.
To update a package, use:
# yum update package-name
Replace package-name with the name of the package.
IMPORTANT
When applying updates to kernel, yum always installs a new kernel regardless of whether
you are using the yum update or yum install command.
7.5.3. Updating a package group with YUM
Use the following procedure to update a group of packages and their dependencies using yum.
Procedure
To update a package group, use:
# yum group update group-name
Replace group-name with the name of the package group.
7.5.4. Updating all packages and their dependencies with YUM
Use the following procedure to update all packages and their dependencies using yum.
Procedure
To update all packages and their dependencies, use:
# yum update
7.5.5. Updating security-related packages with YUM
Use the following procedure to update packages available packages that have security errata using yum.
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Procedure
To upgrade to the latest available packages that have security errata, use:
# yum update --security
To upgrade to the last security errata packages, use:
# yum update-minimal --security
7.5.6. Automating software updates
To check and download package updates automatically and regularly, you can use the DNF Automatic
tool that is provided by the dnf-automatic package.
DNF Automatic is an alternative command-line interface to yum that is suited for automatic and regular
execution using systemd timers, cron jobs and other such tools.
DNF Automatic synchronizes package metadata as needed and then checks for updates available.
After, the tool can perform one of the following actions depending on how you configure it:
Exit
Download updated packages
Download and apply the updates
The outcome of the operation is then reported by a selected mechanism, such as the standard output or
email.
7.5.6.1. Installing DNF Automatic
The following procedure describes how to install the DNF Automatic tool.
Procedure
To install the dnf-automatic package, use:
# yum install dnf-automatic
Verification steps
To verify the successful installation, confirm the presence of the dnf-automatic package by
running the following command:
# rpm -qi dnf-automatic
7.5.6.2. DNF Automatic configuration file
By default, DNF Automatic uses /etc/dnf/automatic.conf as its configuration file to define its behavior.
The configuration file is separated into the following topical sections:
[commands] section
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Sets the mode of operation of DNF Automatic.
[emitters] section
Defines how the results of DNF Automatic are reported.
[command_email] section
Provides the email emitter configuration for an external command used to send email.
[email] section
Provides the email emitter configuration.
[base] section
Overrides settings from the main configuration file of yum.
With the default settings of the /etc/dnf/automatic.conf file, DNF Automatic checks for available
updates, downloads them, and reports the results as standard output.
WARNING
Settings of the operation mode from the [commands] section are overridden by
settings used by a systemd timer unit for all timer units except dnf-automatic.timer.
Additional resources
For more details on particular sections, see DNF Automatic documentation.
For more details on systemd timer units, see the man dnf-automatic manual pages.
For the overview of the systemd timer units included in the dnf-automatic package, see
Section Overview of the systemd timer units included in the dnf-automatic package Overview of
the systemd timer units included in the dnf-automatic package
7.5.6.3. Enabling DNF Automatic
To run DNF Automatic, you always need to enable and start a specific systemd timer unit. You can use
one of the timer units provided in the dnf-automatic package, or you can write your own timer unit
depending on your needs.
The following section describes how to enable DNF Automatic.
Prerequisites
You specified the behavior of DNF Automatic by modifying the /etc/dnf/automatic.conf
configuration file.
For more information about DNF Automatic configuration file, see Section 2.5.6.2, “DNF Automatic
configuration file”.
Procedure
Select, enable and start a systemd timer unit that fits your needs:
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# systemctl enable --now
where is one of the following timers:
dnf-automatic-download.timer
dnf-automatic-install.timer
dnf-automatic-notifyonly.timer
dnf-automatic.timer
To download available updates, use:
# systemctl enable dnf-automatic-download.timer
# systemctl start dnf-automatic-download.timer
To download and install available updates, use:
# systemctl enable dnf-automatic-install.timer
# systemctl start dnf-automatic-install.timer
To report about available updates, use:
# systemctl enable dnf-automatic-notifyonly.timer
# systemctl start dnf-automatic-notifyonly.timer
Optionally, you can use:
# systemctl enable dnf-automatic.timer
# systemctl start dnf-automatic.timer
In terms of downloading and applying updates, this timer unit behaves according to settings in the
/etc/dnf/automatic.conf configuration file. The default behavior is similar to dnf-automaticdownload.timer: it downloads the updated packages, but it does not install them.
NOTE
Alternatively, you can also run DNF Automatic by executing the /usr/bin/dnf-automatic
file directly from the command line or from a custom script.
Verification steps
To verify that the timer is enabled, run the following command:
# systemctl status
Additional resources
For more information about the dnf-automatic timers, see the man dnf-automatic manual
pages.
For the overview of the systemd timer units included in the dnf-automatic package, see Section
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For the overview of the systemd timer units included in the dnf-automatic package, see Section
Overview of the systemd timer units included in the dnf-automatic package
7.5.6.4. Overview of the systemd timer units included in the dnf-automatic package
The systemd timer units take precedence and override the settings in the /etc/dnf/automatic.conf
configuration file concerning downloading and applying updates.
For example if you set the following option in the /etc/dnf/automatic.conf configuration file, but you
have activated the dnf-automatic-notifyonly.timer unit, the packages will not be downloaded:
download_updates = yes
The dnf-automatic package includes the following systemd timer units:
Timer unit Function Overrides settings in the
/etc/dnf/automatic.conf file?
dnf-automaticdownload.timer
Downloads packages to cache
and makes them available for
updating.
Note: This timer unit does not
install the updated packages. To
perform the installation, you have
to execute the dnf update
command.
Yes
dnf-automatic-install.timer Downloads and installs updated
packages.
Yes
dnf-automaticnotifyonly.timer
Downloads only repository data to
keep repository cache up-to-date
and notifies you about available
updates.
Note: This timer unit does not
download or install the updated
packages
Yes
dnf-automatic.timer The behavior of this timer
concerning downloading and
applying updates is specified by
the settings in the
/etc/dnf/automatic.conf
configuration file.
Default behavior is the same as
for the dnf-automaticdownload.timer unit: it only
downloads packages, but does
not install them.
No
Additional resources
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Additional resources
For more information about the dnf-automatic timers, see the man dnf-automatic manual
pages.
For more information about the /etc/dnf/automatic.conf configuration file, see Section DNF
Automatic configuration file
7.6. UNINSTALLING SOFTWARE PACKAGES
The following section describes how to use yum to:
Remove packages.
Remove a package group.
Specify a package name in yum input.
7.6.1. Removing packages with YUM
Use the following procedure to remove a package either by the group name or the groupID.
Procedure
To remove a particular package and all dependent packages, use:
# yum remove package-name
Replace package-name with the name of the package.
To remove multiple packages and their dependencies simultaneously, use:
# yum remove package-name-1 package-name-2
Replace package-name-1 and package-name-2 with the names of the packages.
NOTE
yum is not able to remove a package without removing depending packages.
Note that you can optimize the package search by explicitly defining how to parse the argument. See
Specifying a package name in yum input for more details.
7.6.2. Removing a package group with YUM
Use the following procedure to remove a package either by the group name or the groupID.
Procedure
To remove a package group by the group name, use:
# yum group remove group-name
Or
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# yum remove @group-name
Replace group-name with the full name of the group.
To remove a package group by the groupID, use:
# yum group remove groupID
Replace groupID with the ID of the group.
7.6.3. Specifying a package name in YUM input
To optimize the installation and removal process, you can append -n, -na, or -nevra suffixes to yum
install and yum remove commands to explicitly define how to parse an argument:
To install a package using its exact name, use:
# yum install-n name
Replace name with the exact name of the package.
To install a package using its exact name and architecture, use:
# yum install-na name.architecture
Replace name and architecture with the exact name and architecture of the package.
To install a package using its exact name, epoch, version, release, and architecture, use:
# yum install-nevra name-epoch:version-release.architecture
Replace name, epoch, version, release, and architecture with the exact name, epoch, version,
release, and architecture of the package.
7.7. MANAGING SOFTWARE PACKAGE GROUPS
A package group is a collection of packages that serve a common purpose (System Tools, Sound and
Video). Installing a package group pulls a set of dependent packages, which saves time considerably.
The following section describes how to use yum to:
List package groups.
Install a package group.
Remove a package group.
Specify global expressions in yum input.
7.7.1. Listing package groups with YUM
Use yum to view installed package groups and filter the listing results.
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Procedure
To view the number of installed and available groups, use:
# yum group summary
To list all installed and available groups, use:
# yum group list
Note that you can filter the results by appending command line options for the yum group list
command (--hidden, --available). For more available options see the man pages.
To list mandatory and optional packages contained in a particular group, use:
# yum group info group-name
Replace group-name with the name of the group.
Note that you can filter the results by appending global expressions as arguments. See Specifying global
expressions in yum input
for more details.
7.7.2. Installing a package group with YUM
The following procedure describes how to install a package group by a group name or by a groupID using
yum.
Procedure
To install a package group by a group name, use:
# yum group install group-name
Or
# yum install @group-name
Replace group-name with the full name of the group or environmental group.
To install a package group by the groupID, use:
# yum group install groupID
Replace groupID with the ID of the group.
7.7.3. Removing a package group with YUM
Use the following procedure to remove a package either by the group name or the groupID.
Procedure
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To remove a package group by the group name, use:
# yum group remove group-name
Or
# yum remove @group-name
Replace group-name with the full name of the group.
To remove a package group by the groupID, use:
# yum group remove groupID
Replace groupID with the ID of the group.
7.7.4. Specifying global expressions in YUM input
yum commands allow you to filter the results by appending one or more glob expressions as arguments.
You have to escape global expressions when passing them as arguments to the yum command.
Procedure
To ensure global expressions are passed to yum as intended, use one of the following methods:
Double-quote or single-quote the entire global expression.
# yum provides "*/file-name"
Replace file-name with the name of the file.
Escape the wildcard characters by preceding them with a backslash (\) character.
# yum provides \*/file-name
Replace file-name with the name of the file.
7.8. HANDLING PACKAGE MANAGEMENT HISTORY
The yum history command allows you to review information about the timeline of yum transactions,
dates and times they occurred, the number of packages affected, whether these transactions
succeeded or were aborted, and if the RPM database was changed between transactions. yum history
command can also be used to undo or redo the transactions.
The following section describes how to use yum to:
List transactions.
Revert transactions.
Repeat transactions.
Specify global expressions in yum input.
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7.8.1. Listing transactions with YUM
Use the following procedure to list the latest transactions, the latest operations for a selected package,
and details of a particular transaction.
Procedure
To display a list of all the latest yum transactions, use:
# yum history
To display a list of all the latest operations for a selected package, use:
# yum history list package-name
Replace package-name with the name of the package. You can filter the command output by
appending global expressions. See Specifying global expressions in yum input for more details.
To examine a particular transaction, use:
# yum history info transactionID
Replace transactionID with the ID of the transaction.
7.8.2. Reverting transactions with YUM
The following procedure describes how to revert a selected transaction or the last transaction using
yum.
Procedure
To revert a particular transaction, use:
# yum history undo transactionID
Replace transactionID with the ID of the transaction.
To revert the last transaction, use:
# yum history undo last
Note that the yum history undo command only reverts the steps that were performed during the
transaction. If the transaction installed a new package, the yum history undo command uninstalls it. If
the transaction uninstalled a package, the yum history undo command reinstalls it. yum history undo
also attempts to downgrade all updated packages to their previous versions, if the older packages are
still available.
7.8.3. Repeating transactions with YUM
Use the following procedure to repeat a selected transaction or the last transaction using yum.
Procedure
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To repeat a particular transaction, use:
# yum history redo transactionID
Replace transactionID with the ID of the transaction.
To repeat the last transaction, use:
# yum history redo last
Note that the yum history redo command only repeats the steps that were performed during the
transaction.
7.8.4. Specifying global expressions in YUM input
yum commands allow you to filter the results by appending one or more glob expressions as arguments.
You have to escape global expressions when passing them as arguments to the yum command.
Procedure
To ensure global expressions are passed to yum as intended, use one of the following methods:
Double-quote or single-quote the entire global expression.
# yum provides "*/file-name"
Replace file-name with the name of the file.
Escape the wildcard characters by preceding them with a backslash (\) character.
# yum provides \*/file-name
Replace file-name with the name of the file.
7.9. MANAGING SOFTWARE REPOSITORIES
The configuration information for yum and related utilities are stored in the /etc/yum.conf file. This file
contains one or more [repository] sections, which allow you to set repository-specific options.
It is recommended to define individual repositories in new or existing .repo files in the
/etc/yum.repos.d/ directory.
Note that the values you define in individual [repository] sections of the /etc/yum.conf file override
values set in the [main] section.
The following section describes how to:
Set [repository] options.
Add a yum repository.
Enable a yum repository.
Disable a yum repository.
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7.9.1. Setting YUM repository options
The /etc/yum.conf configuration file contains the [repository] sections, where repository is a unique
repository ID. The [repository] sections allows you to define individual yum repositories.
NOTE
Do not give custom repositories names used by the Red Hat repositories to avoid
conflicts.
For a complete list of available [repository] options, see the [repository] OPTIONS section of the
yum.conf(5) manual page.
7.9.2. Adding a YUM repository
Procedure
To define a new repository, you can:
Add a [repository] section to the /etc/yum.conf file.
Add a [repository] section to a .repo file in the /etc/yum.repos.d/ directory.
yum repositories commonly provide their own .repo file.
NOTE
It is recommended to define your repositories in a .repo file instead of /etc/yum.conf as
all files with the .repo file extension in this directory are read by yum.
To add a repository to your system and enable it, use:
# yum-config-manager --add-repo repository_URL
Replace repository_url with URL pointing to the repository.
WARNING
Obtaining and installing software packages from unverified or untrusted sources
other than Red Hat certificate-based Content Delivery Network (CDN)
constitutes a potential security risk, and could lead to security, stability,
compatibility, and maintainability issues.
7.9.3. Enabling a YUM repository
Once you added a yum repository to your system, enable it to ensure installation and updates.
Procedure
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To enable a repository, use:
# yum-config-manager --enable repositoryID
Replace repositoryID with the unique repository ID.
To list available repository IDs, see Listing packages with yum.
7.9.4. Disabling a YUM repository
Disable a specific YUM repository to prevent particular packages from installation or update.
Procedure
To disable a yum repository, use:
# yum-config-manager --disable repositoryID
Replace repositoryID with the unique repository ID.
To list available repository IDs, see Listing packages with yum.
7.10. CONFIGURING YUM
The configuration information for yum and related utilities are stored in the /etc/yum.conf file. This file
contains one mandatory [main] section, which enables you to set yum options that have global effect.
The following section describes how to:
View the current yum configurations.
Set yum [main] options.
Use yum plug-ins.
7.10.1. Viewing the current YUM configurations
Use the following procedure to view the current yum configurations.
Procedure
To display the current values of global yum options specified in the [main] section of the
/etc/yum.conf file, use:
# yum config-manager --dump
7.10.2. Setting YUM main options
The /etc/yum.conf configuration file contains one [main] section. The key-value pairs listed below
affect how yum operates and treats repositories.
You can add additional options under the [main] section heading in /etc/yum.conf.
For a complete list of available [main] options, see the [main] OPTIONS section of the yum.conf(5)
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For a complete list of available [main] options, see the [main] OPTIONS section of the yum.conf(5)
manual page.
7.10.3. Using YUM plug-ins
yum provides plug-ins that extend and enhance its operations. Certain plug-ins are installed by default.
The following section describes how to enable, configure, and disable yum plug-ins.
7.10.3.1. Managing YUM plug-ins
Procedure
The plug-in configuration files always contain a [main] section where the enabled= option controls
whether the plug-in is enabled when you run yum commands. If this option is missing, you can add it
manually to the file.
Every installed plug-in has its own configuration file in the /etc/dnf/plugins/ directory. You can enable or
disable plug-in specific options in these files.
7.10.3.2. Enabling YUM plug-ins
The following procedure describes how to disable or enable all YUM plug-ins, disable all plug-ins for a
particular command, or certain YUM plug-ins for a single command.
Procedure
To enable all yum plug-ins:
1. Ensure a line beginning with plugins= is present in the [main] section of the /etc/yum.conf
file.
2. Set the value of plugins= to 1.
plugins=1
7.10.3.3. Disabling YUM plug-ins
To disable all yum plug-ins:
1. Ensure a line beginning with plugins= is present in the [main] section of the /etc/yum.conf
file.
2. Set the value of plugins= to 0.
plugins=0
IMPORTANT
Disabling all plug-ins is not advised. Certain plug-ins provide important yum
services. In particular, the 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
advisable only when diagnosing a potential problem with yum.
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To disable all yum plug-ins for a particular command, append --noplugins option to the
command.
# yum --noplugins update
To disable certain yum plug-ins for a single command, append --disableplugin=plugin-name
option to the command.
# yum update --disableplugin=plugin-name
Replace plugin-name with the name of the plug-in.
Red Hat Enterprise Linux 8 Configuring basic system settings
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CHAPTER 8. INTRODUCTION TO RHEL SYSTEM ROLES
You can automate system administration across multiple systems with RHEL System Roles.
RHEL System Roles is a collection of Ansible roles and modules. By using RHEL System Roles, you can
remotely manage the system configurations of multiple RHEL systems across major versions of RHEL.
To use it to configure systems, you must use the following components:
Control node
A control node is the system from which you run Ansible commands and playbooks. Your control
node can be an Ansible Automation Platform, Red Hat Satellite, or a RHEL 9, 8, or 7 host. For more
information, see Preparing a control node on RHEL 8 .
Managed node
Managed nodes are the servers and network devices that you manage with Ansible. Managed nodes
are also sometimes called hosts. Ansible does not have to be installed on managed nodes. For more
information, see Preparing a managed node .
Ansible playbook
In a playbook, you define the configuration you want to achieve on your managed nodes or a set of
steps for the system on the managed node to perform. Playbooks are Ansible’s configuration,
deployment, and orchestration language.
Inventory
In an inventory file, you list the managed nodes and specify information such as IP address for each
managed node. In the inventory, you can also organize the managed nodes by creating and nesting
groups for easier scaling. An inventory file is also sometimes called a hostfile.
On Red Hat Enterprise Linux 8, you can use the following roles provided by the rhel-system-roles
package, which is available in the AppStream repository:
Role name Role description Chapter title
certificate Certificate Issuance and
Renewal
Requesting certificates using RHEL System Roles
cockpit Web console Installing and configuring web console with the
cockpit RHEL System Role
crypto_policies System-wide
cryptographic policies
Setting a custom cryptographic policy across
systems
firewall Firewalld Configuring firewalld by using System Roles
ha_cluster HA Cluster Configuring a high-availability cluster using System
Roles
kdump Kernel Dumps Configuring kdump using RHEL System Roles
kernel_settings Kernel Settings Using Ansible roles to permanently configure kernel
parameters
CHAPTER 8. INTRODUCTION TO RHEL SYSTEM ROLES
71
logging Logging Using the logging System Role
metrics Metrics (PCP) Monitoring performance using RHEL System Roles
microsoft.sql.server Microsoft SQL Server Configuring Microsoft SQL Server using the
microsoft.sql.server Ansible role
network Networking Using the network RHEL System Role to manage
InfiniBand connections
nbde_client Network Bound Disk
Encryption client
Using the nbde_client and nbde_server System Roles
nbde_server Network Bound Disk
Encryption server
Using the nbde_client and nbde_server System Roles
postfix Postfix Variables of the postfix role in System Roles
postgresql PostgreSQL Installing and configuring PostgreSQL by using the
postgresql RHEL System Role
selinux SELinux Configuring SELinux using System Roles
ssh SSH client Configuring secure communication with the ssh
System Roles
sshd SSH server Configuring secure communication with the ssh
System Roles
storage Storage Managing local storage using RHEL System Roles
tlog Terminal Session
Recording
Configuring a system for session recording using the
tlog RHEL System Role
timesync Time Synchronization Configuring time synchronization using RHEL System
Roles
vpn VPN Configuring VPN connections with IPsec by using the
vpn RHEL System Role
Role name Role description Chapter title
Additional resources
Automating system administration by using RHEL System Roles
Red Hat Enterprise Linux (RHEL) System Roles
/usr/share/doc/rhel-system-roles/ provided by the rhel-system-roles package
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CHAPTER 9. CONFIGURING LOGGING
Most services in Red Hat Enterprise Linux log status messages, warnings, and errors. You can use the
rsyslogd service to log these entries to local files or to a remote logging server.
9.1. CONFIGURING A REMOTE LOGGING SOLUTION
To ensure that logs from various machines in your environment are recorded centrally on a logging
server, you can configure the Rsyslog application to record logs that fit specific criteria from the client
system to the server.
9.1.1. The Rsyslog logging service
The Rsyslog application, in combination with the systemd-journald service, provides local and remote
logging support in Red Hat Enterprise Linux. The rsyslogd daemon continuously reads syslog
messages received by the systemd-journald service from the Journal. rsyslogd then filters and
processes these syslog events and records them to rsyslog log files or forwards them to other services
according to its configuration.
The rsyslogd daemon also provides extended filtering, encryption protected relaying of messages,
input and output modules, and support for transportation using the TCP and UDP protocols.
In /etc/rsyslog.conf, which is the main configuration file for rsyslog, you can specify the rules according
to which rsyslogd handles the messages. Generally, you can classify messages by their source and topic
(facility) and urgency (priority), and then assign an action that should be performed when a message fits
these criteria.
In /etc/rsyslog.conf, you can also see a list of log files maintained by rsyslogd. Most log files are
located in the /var/log/ directory. Some applications, such as httpd and samba, store their log files in a
subdirectory within /var/log/.
Additional resources
The rsyslogd(8) and rsyslog.conf(5) man pages.
Documentation installed with the rsyslog-doc package in the
/usr/share/doc/rsyslog/html/index.html file.
9.1.2. Installing Rsyslog documentation
The Rsyslog application has extensive online documentation that is available at
https://www.rsyslog.com/doc/, but you can also install the rsyslog-doc documentation package locally.
Prerequisites
You have activated the AppStream repository on your system.
You are authorized to install new packages using sudo.
Procedure
Install the rsyslog-doc package:
# yum install rsyslog-doc
CHAPTER 9. CONFIGURING LOGGING
73
Verification
Open the /usr/share/doc/rsyslog/html/index.html file in a browser of your choice, for example:
$ firefox /usr/share/doc/rsyslog/html/index.html &
9.1.3. Configuring a server for remote logging over TCP
The Rsyslog application enables you to both run a logging server and configure individual systems to
send their log files to the logging server. To use remote logging through TCP, configure both the server
and the client. The server collects and analyzes the logs sent by one or more client systems.
With the Rsyslog application, you can maintain a centralized logging system where log messages are
forwarded to a server over the network. To avoid message loss when the server is not available, you can
configure an action queue for the forwarding action. This way, messages that failed to be sent are stored
locally until the server is reachable again. Note that such queues cannot be configured for connections
using the UDP protocol.
The omfwd plug-in provides forwarding over UDP or TCP. The default protocol is UDP. Because the
plug-in is built in, it does not have to be loaded.
By default, rsyslog uses TCP on port 514.
Prerequisites
Rsyslog is installed on the server system.
You are logged in as root on the server.
The policycoreutils-python-utils package is installed for the optional step using the
semanage command.
The firewalld service is running.
Procedure
1. Optional: To use a different port for rsyslog traffic, add the syslogd_port_t SELinux type to
port. For example, enable port 30514:
# semanage port -a -t syslogd_port_t -p tcp 30514
2. Optional: To use a different port for rsyslog traffic, configure firewalld to allow incoming
rsyslog traffic on that port. For example, allow TCP traffic on port 30514:
# firewall-cmd --zone= --permanent --add-port=30514/tcp
success
# firewall-cmd --reload
3. Create a new file in the /etc/rsyslog.d/ directory named, for example, remotelog.conf, and
insert the following content:
# Define templates before the rules that use them
# Per-Host templates for remote systems
template(name="TmplAuthpriv" type="list") {
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constant(value="/var/log/remote/auth/")
property(name="hostname")
constant(value="/")
property(name="programname" SecurePath="replace")
constant(value=".log")
}
template(name="TmplMsg" type="list") {
constant(value="/var/log/remote/msg/")
property(name="hostname")
constant(value="/")
property(name="programname" SecurePath="replace")
constant(value=".log")
}
# Provides TCP syslog reception
module(load="imtcp")
# Adding this ruleset to process remote messages
ruleset(name="remote1"){
authpriv.* action(type="omfile" DynaFile="TmplAuthpriv")
*.info;mail.none;authpriv.none;cron.none
action(type="omfile" DynaFile="TmplMsg")
}
input(type="imtcp" port="30514" ruleset="remote1")
4. Save the changes to the /etc/rsyslog.d/remotelog.conf file.
5. Test the syntax of the /etc/rsyslog.conf file:
# rsyslogd -N 1
rsyslogd: version 8.1911.0-2.el8, config validation run...
rsyslogd: End of config validation run. Bye.
6. Make sure the rsyslog service is running and enabled on the logging server:
# systemctl status rsyslog
7. Restart the rsyslog service.
# systemctl restart rsyslog
8. Optional: If rsyslog is not enabled, ensure the rsyslog service starts automatically after reboot:
# systemctl enable rsyslog
Your log server is now configured to receive and store log files from the other systems in your
environment.
Additional resources
rsyslogd(8), rsyslog.conf(5), semanage(8), and firewall-cmd(1) man pages.
Documentation installed with the rsyslog-doc package in the
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75
Documentation installed with the rsyslog-doc package in the
/usr/share/doc/rsyslog/html/index.html file.
9.1.4. Configuring remote logging to a server over TCP
Follow this procedure to configure a system for forwarding log messages to a server over the TCP
protocol. The omfwd plug-in provides forwarding over UDP or TCP. The default protocol is UDP.
Because the plug-in is built in, you do not have to load it.
Prerequisites
The rsyslog package is installed on the client systems that should report to the server.
You have configured the server for remote logging.
The specified port is permitted in SELinux and open in firewall.
The system contains the policycoreutils-python-utils package, which provides the semanage
command for adding a non-standard port to the SELinux configuration.
Procedure
1. Create a new file in the /etc/rsyslog.d/ directory named, for example, 10-remotelog.conf, and
insert the following content:
*.* action(type="omfwd"
queue.type="linkedlist"
queue.filename="example_fwd"
action.resumeRetryCount="-1"
queue.saveOnShutdown="on"
target="example.com" port="30514" protocol="tcp"
)
Where:
The queue.type="linkedlist" setting enables a LinkedList in-memory queue,
The queue.filename setting defines a disk storage. The backup files are created with the
example_fwd prefix in the working directory specified by the preceding global
workDirectory directive.
The action.resumeRetryCount -1 setting prevents rsyslog from dropping messages when
retrying to connect if server is not responding,
The queue.saveOnShutdown="on" setting saves in-memory data if rsyslog shuts down.
The last line forwards all received messages to the logging server. Port specification is
optional.
With this configuration, rsyslog sends messages to the server but keeps messages in
memory if the remote server is not reachable. A file on disk is created only if rsyslog runs
out of the configured memory queue space or needs to shut down, which benefits the
system performance.
NOTE
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76
NOTE
Rsyslog processes configuration files /etc/rsyslog.d/ in the lexical order.
2. Restart the rsyslog service.
# systemctl restart rsyslog
Verification
To verify that the client system sends messages to the server, follow these steps:
1. On the client system, send a test message:
# logger test
2. On the server system, view the /var/log/messages log, for example:
# cat /var/log/remote/msg/hostname/root.log
Feb 25 03:53:17 hostname root[6064]: test
Where hostname is the host name of the client system. Note that the log contains the user
name of the user that entered the logger command, in this case root.
Additional resources
rsyslogd(8) and rsyslog.conf(5) man pages.
Documentation installed with the rsyslog-doc package in the
/usr/share/doc/rsyslog/html/index.html file.
9.1.5. Configuring TLS-encrypted remote logging
By default, Rsyslog sends remote-logging communication in the plain text format. If your scenario
requires to secure this communication channel, you can encrypt it using TLS.
To use encrypted transport through TLS, configure both the server and the client. The server collects
and analyzes the logs sent by one or more client systems.
You can use either the ossl network stream driver (OpenSSL) or the gtls stream driver (GnuTLS).
NOTE
If you have a separate system with higher security, for example, a system that is not
connected to any network or has stricter authorizations, use the separate system as the
certifying authority (CA).
Prerequisites
You have root access to both the client and server systems.
The rsyslog and rsyslog-openssl packages are installed on the server and the client systems.
If you use the gtls network stream driver, install the rsyslog-gnutls package instead of
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77
If you use the gtls network stream driver, install the rsyslog-gnutls package instead of
rsyslog-openssl.
If you generate certificates using the certtool command, install the gnutls-utils package.
On your logging server, the following certificates are in the /etc/pki/ca-trust/source/anchors/
directory and your system configuration is updated by using the update-ca-trust command:
ca-cert.pem - a CA certificate that can verify keys and certificates on logging servers and
clients.
server-cert.pem - a public key of the logging server.
server-key.pem - a private key of the logging server.
On your logging clients, the following certificates are in the /etc/pki/ca-trust/source/anchors/
directory and your system configuration is updated by using update-ca-trust:
ca-cert.pem - a CA certificate that can verify keys and certificates on logging servers and
clients.
client-cert.pem - a public key of a client.
client-key.pem - a private key of a client.
Procedure
1. Configure the server for receiving encrypted logs from your client systems:
a. Create a new file in the /etc/rsyslog.d/ directory named, for example, securelogser.conf.
b. To encrypt the communication, the configuration file must contain paths to certificate files
on your server, a selected authentication method, and a stream driver that supports TLS
encryption. Add the following lines to the /etc/rsyslog.d/securelogser.conf file:
# Set certificate files
global(
DefaultNetstreamDriverCAFile="/etc/pki/ca-trust/source/anchors/ca-cert.pem"
DefaultNetstreamDriverCertFile="/etc/pki/ca-trust/source/anchors/server-cert.pem"
DefaultNetstreamDriverKeyFile="/etc/pki/ca-trust/source/anchors/server-key.pem"
)
# TCP listener
module(
load="imtcp"
PermittedPeer=["client1.example.com", "client2.example.com"]
StreamDriver.AuthMode="x509/name"
StreamDriver.Mode="1"
StreamDriver.Name="ossl"
)
# Start up listener at port 514
input(
type="imtcp"
port="514"
)
NOTE
Red Hat Enterprise Linux 8 Configuring basic system settings
78
NOTE
If you prefer the GnuTLS driver, use the StreamDriver.Name="gtls"
configuration option. See the documentation installed with the rsyslog-doc
package for more information about less strict authentication modes than
x509/name.
c. Save the changes to the /etc/rsyslog.d/securelogser.conf file.
d. Verify the syntax of the /etc/rsyslog.conf file and any files in the /etc/rsyslog.d/ directory:
# rsyslogd -N 1
rsyslogd: version 8.1911.0-2.el8, config validation run (level 1)...
rsyslogd: End of config validation run. Bye.
e. Make sure the rsyslog service is running and enabled on the logging server:
# systemctl status rsyslog
f. Restart the rsyslog service:
# systemctl restart rsyslog
g. Optional: If Rsyslog is not enabled, ensure the rsyslog service starts automatically after
reboot:
# systemctl enable rsyslog
2. Configure clients for sending encrypted logs to the server:
a. On a client system, create a new file in the /etc/rsyslog.d/ directory named, for example,
securelogcli.conf.
b. Add the following lines to the /etc/rsyslog.d/securelogcli.conf file:
# Set certificate files
global(
DefaultNetstreamDriverCAFile="/etc/pki/ca-trust/source/anchors/ca-cert.pem"
DefaultNetstreamDriverCertFile="/etc/pki/ca-trust/source/anchors/client-cert.pem"
DefaultNetstreamDriverKeyFile="/etc/pki/ca-trust/source/anchors/client-key.pem"
)
# Set up the action for all messages
*.* action(
type="omfwd"
StreamDriver="ossl"
StreamDriverMode="1"
StreamDriverPermittedPeers="server.example.com"
StreamDriverAuthMode="x509/name"
target="server.example.com" port="514" protocol="tcp"
)
NOTE
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79
NOTE
If you prefer the GnuTLS driver, use the StreamDriver.Name="gtls"
configuration option.
c. Save the changes to the /etc/rsyslog.d/securelogser.conf file.
d. Verify the syntax of the /etc/rsyslog.conf file and other files in the /etc/rsyslog.d/
directory:
# rsyslogd -N 1
rsyslogd: version 8.1911.0-2.el8, config validation run (level 1)...
rsyslogd: End of config validation run. Bye.
e. Make sure the rsyslog service is running and enabled on the logging server:
# systemctl status rsyslog
f. Restart the rsyslog service:
# systemctl restart rsyslog
g. Optional: If Rsyslog is not enabled, ensure the rsyslog service starts automatically after
reboot:
# systemctl enable rsyslog
Verification
To verify that the client system sends messages to the server, follow these steps:
1. On the client system, send a test message:
# logger test
2. On the server system, view the /var/log/messages log, for example:
# cat /var/log/remote/msg/hostname/root.log
Feb 25 03:53:17 hostname root[6064]: test
Where hostname is the host name of the client system. Note that the log contains the user
name of the user that entered the logger command, in this case root.
Additional resources
certtool(1), openssl(1), update-ca-trust(8), rsyslogd(8), and rsyslog.conf(5) man pages.
Documentation installed with the rsyslog-doc package at
/usr/share/doc/rsyslog/html/index.html.
Using the logging System Role with TLS .
9.1.6. Configuring a server for receiving remote logging information over UDP
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80
The Rsyslog application enables you to configure a system to receive logging information from remote
systems. To use remote logging through UDP, configure both the server and the client. The receiving
server collects and analyzes the logs sent by one or more client systems. By default, rsyslog uses UDP
on port 514 to receive log information from remote systems.
Follow this procedure to configure a server for collecting and analyzing logs sent by one or more client
systems over the UDP protocol.
Prerequisites
Rsyslog is installed on the server system.
You are logged in as root on the server.
The policycoreutils-python-utils package is installed for the optional step using the
semanage command.
The firewalld service is running.
Procedure
1. Optional: To use a different port for rsyslog traffic than the default port 514:
a. Add the syslogd_port_t SELinux type to the SELinux policy configuration, replacing
portno with the port number you want rsyslog to use:
# semanage port -a -t syslogd_port_t -p udp portno
b. Configure firewalld to allow incoming rsyslog traffic, replacing portno with the port
number and zone with the zone you want rsyslog to use:
# firewall-cmd --zone=zone --permanent --add-port=portno/udp
success
# firewall-cmd --reload
c. Reload the firewall rules:
# firewall-cmd --reload
2. Create a new .conf file in the /etc/rsyslog.d/ directory, for example, remotelogserv.conf, and
insert the following content:
# Define templates before the rules that use them
# Per-Host templates for remote systems
template(name="TmplAuthpriv" type="list") {
constant(value="/var/log/remote/auth/")
property(name="hostname")
constant(value="/")
property(name="programname" SecurePath="replace")
constant(value=".log")
}
template(name="TmplMsg" type="list") {
constant(value="/var/log/remote/msg/")
property(name="hostname")
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81
constant(value="/")
property(name="programname" SecurePath="replace")
constant(value=".log")
}
# Provides UDP syslog reception
module(load="imudp")
# This ruleset processes remote messages
ruleset(name="remote1"){
authpriv.* action(type="omfile" DynaFile="TmplAuthpriv")
*.info;mail.none;authpriv.none;cron.none
action(type="omfile" DynaFile="TmplMsg")
}
input(type="imudp" port="514" ruleset="remote1")
Where 514 is the port number rsyslog uses by default. You can specify a different port instead.
3. Verify the syntax of the /etc/rsyslog.conf file and all .conf files in the /etc/rsyslog.d/ directory:
# rsyslogd -N 1
rsyslogd: version 8.1911.0-2.el8, config validation run...
4. Restart the rsyslog service.
# systemctl restart rsyslog
5. Optional: If rsyslog is not enabled, ensure the rsyslog service starts automatically after reboot:
# systemctl enable rsyslog
Additional resources
rsyslogd(8) , rsyslog.conf(5), semanage(8), and firewall-cmd(1) man pages.
Documentation installed with the rsyslog-doc package in the
/usr/share/doc/rsyslog/html/index.html file.
9.1.7. Configuring remote logging to a server over UDP
Follow this procedure to configure a system for forwarding log messages to a server over the UDP
protocol. The omfwd plug-in provides forwarding over UDP or TCP. The default protocol is UDP.
Because the plug-in is built in, you do not have to load it.
Prerequisites
The rsyslog package is installed on the client systems that should report to the server.
You have configured the server for remote logging as described in Configuring a server for
receiving remote logging information over UDP.
Procedure
1. Create a new .conf file in the /etc/rsyslog.d/ directory, for example, 10-remotelogcli.conf, and
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82
1. Create a new .conf file in the /etc/rsyslog.d/ directory, for example, 10-remotelogcli.conf, and
insert the following content:
*.* action(type="omfwd"
queue.type="linkedlist"
queue.filename="example_fwd"
action.resumeRetryCount="-1"
queue.saveOnShutdown="on"
target="example.com" port="portno" protocol="udp"
)
Where:
The queue.type="linkedlist" setting enables a LinkedList in-memory queue.
The queue.filename setting defines a disk storage. The backup files are created with the
example_fwd prefix in the working directory specified by the preceding global
workDirectory directive.
The action.resumeRetryCount -1 setting prevents rsyslog from dropping messages when
retrying to connect if the server is not responding.
The enabled queue.saveOnShutdown="on" setting saves in-memory data if rsyslog
shuts down.
The portno value is the port number you want rsyslog to use. The default value is 514.
The last line forwards all received messages to the logging server, port specification is
optional.
With this configuration, rsyslog sends messages to the server but keeps messages in
memory if the remote server is not reachable. A file on disk is created only if rsyslog runs
out of the configured memory queue space or needs to shut down, which benefits the
system performance.
NOTE
Rsyslog processes configuration files /etc/rsyslog.d/ in the lexical order.
2. Restart the rsyslog service.
# systemctl restart rsyslog
3. Optional: If rsyslog is not enabled, ensure the rsyslog service starts automatically after reboot:
# systemctl enable rsyslog
Verification
To verify that the client system sends messages to the server, follow these steps:
1. On the client system, send a test message:
# logger test
2. On the server system, view the /var/log/remote/msg/hostname/root.log log, for example:
CHAPTER 9. CONFIGURING LOGGING
83
# cat /var/log/remote/msg/hostname/root.log
Feb 25 03:53:17 hostname root[6064]: test
Where hostname is the host name of the client system. Note that the log contains the user
name of the user that entered the logger command, in this case root.
Additional resources
rsyslogd(8) and rsyslog.conf(5) man pages.
Documentation installed with the rsyslog-doc package at
/usr/share/doc/rsyslog/html/index.html.
9.1.8. Load balancing helper in Rsyslog
The RebindInterval setting specifies an interval at which the current connection is broken and is reestablished. This setting applies to TCP, UDP, and RELP traffic. The load balancers perceive it as a new
connection and forward the messages to another physical target system.
The RebindInterval setting proves to be helpful in scenarios when a target system has changed its IP
address. The Rsyslog application caches the IP address when the connection establishes, therefore, the
messages are sent to the same server. If the IP address changes, the UDP packets will be lost until the
Rsyslog service restarts. Re-establishing the connection will ensure the IP to be resolved by DNS again.
action(type=”omfwd” protocol=”tcp” RebindInterval=”250” target=”example.com” port=”514” …)
action(type=”omfwd” protocol=”udp” RebindInterval=”250” target=”example.com” port=”514” …)
action(type=”omrelp” RebindInterval=”250” target=”example.com” port=”6514” …)
9.1.9. Configuring reliable remote logging
With the Reliable Event Logging Protocol (RELP), you can send and receive syslog messages over TCP
with a much reduced risk of message loss. RELP provides reliable delivery of event messages, which
makes it useful in environments where message loss is not acceptable. To use RELP, configure the
imrelp input module, which runs on the server and receives the logs, and the omrelp output module,
which runs on the client and sends logs to the logging server.
Prerequisites
You have installed the rsyslog, librelp, and rsyslog-relp packages on the server and the client
systems.
The specified port is permitted in SELinux and open in the firewall.
Procedure
1. Configure the client system for reliable remote logging:
a. On the client system, create a new .conf file in the /etc/rsyslog.d/ directory named, for
example,relpclient.conf, and insert the following content:
module(load="omrelp")
*.* action(type="omrelp" target="_target_IP_" port="_target_port_")
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Where:
target_IP is the IP address of the logging server.
target_port is the port of the logging server.
b. Save the changes to the /etc/rsyslog.d/relpclient.conf file.
c. Restart the rsyslog service.
# systemctl restart rsyslog
d. Optional: If rsyslog is not enabled, ensure the rsyslog service starts automatically after
reboot:
# systemctl enable rsyslog
2. Configure the server system for reliable remote logging:
a. On the server system, create a new .conf file in the /etc/rsyslog.d/ directory named, for
example,relpserv.conf, and insert the following content:
ruleset(name="relp"){
*.* action(type="omfile" file="_log_path_")
}
module(load="imrelp")
input(type="imrelp" port="_target_port_" ruleset="relp")
Where:
log_path specifies the path for storing messages.
target_port is the port of the logging server. Use the same value as in the client
configuration file.
b. Save the changes to the /etc/rsyslog.d/relpserv.conf file.
c. Restart the rsyslog service.
# systemctl restart rsyslog
d. Optional: If rsyslog is not enabled, ensure the rsyslog service starts automatically after
reboot:
# systemctl enable rsyslog
Verification
To verify that the client system sends messages to the server, follow these steps:
1. On the client system, send a test message:
# logger test
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85
2. On the server system, view the log at the specified log_path, for example:
# cat /var/log/remote/msg/hostname/root.log
Feb 25 03:53:17 hostname root[6064]: test
Where hostname is the host name of the client system. Note that the log contains the user
name of the user that entered the logger command, in this case root.
Additional resources
rsyslogd(8) and rsyslog.conf(5) man pages.
Documentation installed with the rsyslog-doc package in the
/usr/share/doc/rsyslog/html/index.html file.
9.1.10. Supported Rsyslog modules
To expand the functionality of the Rsyslog application, you can use specific modules. Modules provide
additional inputs (Input Modules), outputs (Output Modules), and other functionalities. A module can
also provide additional configuration directives that become available after you load the module.
You can list the input and output modules installed on your system by entering the following command:
# ls /usr/lib64/rsyslog/{i,o}m*
You can view the list of all available rsyslog modules in the
/usr/share/doc/rsyslog/html/configuration/modules/idx_output.html file after you install the
rsyslog-doc package.
9.1.11. Configuring the netconsole service to log kernel messages to a remote host
When logging to disk or using a serial console is not possible, you can use the netconsole kernel module
and the same-named service to log kernel messages over a network to a remote rsyslog service.
Prerequisites
A system log service, such as rsyslog is installed on the remote host.
The remote system log service is configured to receive incoming log entries from this host.
Procedure
1. Install the netconsole-service package:
# yum install netconsole-service
2. Edit the /etc/sysconfig/netconsole file and set the SYSLOGADDR parameter to the IP
address of the remote host:
# SYSLOGADDR=192.0.2.1
3. Enable and start the netconsole service:
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# systemctl enable --now netconsole
Verification steps
Display the /var/log/messages file on the remote system log server.
Additional resources
Configuring a remote logging solution
9.1.12. Additional resources
Documentation installed with the rsyslog-doc package in the
/usr/share/doc/rsyslog/html/index.html file
rsyslog.conf(5) and rsyslogd(8) man pages
Configuring system logging without journald or with minimized journald usage Knowledgebase
article
Negative effects of the RHEL default logging setup on performance and their mitigations
Knowledgebase article
The Using the Logging System Role chapter
9.2. USING THE LOGGING SYSTEM ROLE
As a system administrator, you can use the logging System Role to configure a RHEL host as a logging
server to collect logs from many client systems.
9.2.1. The logging System Role
With the logging System Role, you can deploy logging configurations on local and remote hosts.
Logging solutions provide multiple ways of reading logs and multiple logging outputs.
For example, a logging system can receive the following inputs:
Local files
systemd/journal
Another logging system over the network
In addition, a logging system can have the following outputs:
Logs stored in the local files in the /var/log directory
Logs sent to Elasticsearch
Logs forwarded to another logging system
With the logging System Role, you can combine the inputs and outputs to fit your scenario. For
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With the logging System Role, you can combine the inputs and outputs to fit your scenario. For
example, you can configure a logging solution that stores inputs from journal in a local file, whereas
inputs read from files are both forwarded to another logging system and stored in the local log files.
9.2.2. logging System Role parameters
In a logging System Role playbook, you define the inputs in the logging_inputs parameter, outputs in
the logging_outputs parameter, and the relationships between the inputs and outputs in the
logging_flows parameter. The logging System Role processes these variables with additional options
to configure the logging system. You can also enable encryption or an automatic port management.
NOTE
Currently, the only available logging system in the logging System Role is Rsyslog.
logging_inputs: List of inputs for the logging solution.
name: Unique name of the input. Used in the logging_flows: inputs list and a part of the
generated config file name.
type: Type of the input element. The type specifies a task type which corresponds to a
directory name in roles/rsyslog/{tasks,vars}/inputs/.
basics: Inputs configuring inputs from systemd journal or unix socket.
kernel_message: Load imklog if set to true. Default to false.
use_imuxsock: Use imuxsock instead of imjournal. Default to false.
ratelimit_burst: Maximum number of messages that can be emitted within
ratelimit_interval. Default to 20000 if use_imuxsock is false. Default to 200 if
use_imuxsock is true.
ratelimit_interval: Interval to evaluate ratelimit_burst. Default to 600 seconds if
use_imuxsock is false. Default to 0 if use_imuxsock is true. 0 indicates rate
limiting is turned off.
persist_state_interval: Journal state is persisted every value messages. Default to
10. Effective only when use_imuxsock is false.
files: Inputs configuring inputs from local files.
remote: Inputs configuring inputs from the other logging system over network.
state: State of the configuration file. present or absent. Default to present.
logging_outputs: List of outputs for the logging solution.
files: Outputs configuring outputs to local files.
forwards: Outputs configuring outputs to another logging system.
remote_files: Outputs configuring outputs from another logging system to local files.
logging_flows: List of flows that define relationships between logging_inputs and
logging_outputs. The logging_flows variable has the following keys:
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name: Unique name of the flow
inputs: List of logging_inputs name values
outputs: List of logging_outputs name values.
logging_manage_firewall: If set to true, the logging role uses the firewall role to automatically
manage port access.
logging_manage_selinux: If set to true, the logging role uses the selinux role to automatically
manage port access.
Additional resources
Documentation installed with the rhel-system-roles package in /usr/share/ansible/roles/rhelsystem-roles.logging/README.html
9.2.3. Applying a local logging System Role
Prepare and apply an Ansible playbook to configure a logging solution on a set of separate machines.
Each machine records logs locally.
Prerequisites
You have prepared the control node and the managed nodes
You are logged in to the control node as a user who can run playbooks on the managed nodes.
The account you use to connect to the managed nodes has sudo permissions on them.
The managed nodes or groups of managed nodes on which you want to run this playbook are
listed in the Ansible inventory file.
NOTE
You do not have to have the rsyslog package installed, because the System Role installs
rsyslog when deployed.
Procedure
1. Create a playbook file, for example, ~/logging-playbook.yml, with the following content:
---
- name: Deploying basics input and implicit files output
hosts: all
roles:
- rhel-system-roles.logging
vars:
logging_inputs:
- name: system_input
type: basics
logging_outputs:
- name: files_output
type: files
logging_flows:
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2. Validate the playbook syntax:
# ansible-playbook ~/logging-playbook.yml --syntax-check
Note that this command only validates the syntax and does not protect against a wrong but valid
configuration.
3. Run the playbook:
# ansible-playbook ~/logging-playbook.yml
Verification
1. Test the syntax of the /etc/rsyslog.conf file:
# rsyslogd -N 1
rsyslogd: version 8.1911.0-6.el8, config validation run...
rsyslogd: End of config validation run. Bye.
2. Verify that the system sends messages to the log:
a. Send a test message:
# logger test
b. View the /var/log/messages log, for example:
# cat /var/log/messages
Aug 5 13:48:31 root[6778]: test
Where is the host name of the client system. Note that the log contains the
user name of the user that entered the logger command, in this case root.
9.2.4. Filtering logs in a local logging System Role
You can deploy a logging solution which filters the logs based on the rsyslog property-based filter.
Prerequisites
You have prepared the control node and the managed nodes
You are logged in to the control node as a user who can run playbooks on the managed nodes.
The account you use to connect to the managed nodes has sudo permissions on them.
The managed nodes or groups of managed nodes on which you want to run this playbook are
listed in the Ansible inventory file.
NOTE
- name: flow1
inputs: [system_input]
outputs: [files_output]
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NOTE
You do not have to have the rsyslog package installed, because the System Role installs
rsyslog when deployed.
Procedure
1. Create a new playbook file, for example, ~/log-filter-playbook.yml, with the following content:
Using this configuration, all messages that contain the error string are logged in
/var/log/errors.log, and all other messages are logged in /var/log/others.log.
You can replace the error property value with the string by which you want to filter.
You can modify the variables according to your preferences.
2. Validate the playbook syntax:
# ansible-playbook ~/log-filter-playbook.yml --syntax-check
Note that this command only validates the syntax and does not protect against a wrong but valid
configuration.
3. Run the playbook:
# ansible-playbook ~/log-filter-playbook.yml
Verification
---
- name: Deploying files input and configured files output
hosts: all
roles:
- linux-system-roles.logging
vars:
logging_inputs:
- name: files_input
type: basics
logging_outputs:
- name: files_output0
type: files
property: msg
property_op: contains
property_value: error
path: /var/log/errors.log
- name: files_output1
type: files
property: msg
property_op: "!contains"
property_value: error
path: /var/log/others.log
logging_flows:
- name: flow0
inputs: [files_input]
outputs: [files_output0, files_output1]
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1. Test the syntax of the /etc/rsyslog.conf file:
# rsyslogd -N 1
rsyslogd: version 8.1911.0-6.el8, config validation run...
rsyslogd: End of config validation run. Bye.
2. Verify that the system sends messages that contain the error string to the log:
a. Send a test message:
# logger error
b. View the /var/log/errors.log log, for example:
# cat /var/log/errors.log
Aug 5 13:48:31 hostname root[6778]: error
Where hostname is the host name of the client system. Note that the log contains the user
name of the user that entered the logger command, in this case root.
Additional resources
Documentation installed with the rhel-system-roles package in /usr/share/ansible/roles/rhelsystem-roles.logging/README.html
9.2.5. Applying a remote logging solution using the logging System Role
Follow these steps to prepare and apply a Red Hat Ansible Core playbook to configure a remote logging
solution. In this playbook, one or more clients take logs from systemd-journal and forward them to a
remote server. The server receives remote input from remote_rsyslog and remote_files and outputs
the logs to local files in directories named by remote host names.
Prerequisites
You have prepared the control node and the managed nodes
You are logged in to the control node as a user who can run playbooks on the managed nodes.
The account you use to connect to the managed nodes has sudo permissions on them.
NOTE
You do not have to have the rsyslog package installed, because the System Role installs
rsyslog when deployed.
Procedure
1. Create a playbook file, for example, ~/logging-playbook.yml, with the following content:
---
- name: Deploying remote input and remote_files output
hosts: server
roles:
- rhel-system-roles.logging
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Where is the logging server.
NOTE
You can modify the parameters in the playbook to fit your needs.
vars:
logging_inputs:
- name: remote_udp_input
type: remote
udp_ports: [ 601 ]
- name: remote_tcp_input
type: remote
tcp_ports: [ 601 ]
logging_outputs:
- name: remote_files_output
type: remote_files
logging_flows:
- name: flow_0
inputs: [remote_udp_input, remote_tcp_input]
outputs: [remote_files_output]
- name: Deploying basics input and forwards output
hosts: clients
roles:
- rhel-system-roles.logging
vars:
logging_inputs:
- name: basic_input
type: basics
logging_outputs:
- name: forward_output0
type: forwards
severity: info
target:
udp_port: 601
- name: forward_output1
type: forwards
facility: mail
target:
tcp_port: 601
logging_flows:
- name: flows0
inputs: [basic_input]
outputs: [forward_output0, forward_output1]
[basic_input]
[forward_output0, forward_output1]
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WARNING
The logging solution works only with the ports defined in the SELinux policy
of the server or client system and open in the firewall. The default SELinux
policy includes ports 601, 514, 6514, 10514, and 20514. To use a different
port, modify the SELinux policy on the client and server systems .
2. Create a new inventory file inventory.ini that lists your servers and clients:
[servers]
server ansible_host=
[clients]
client ansible_host=
Where:
is the logging server.
is the logging client.
3. Validate the playbook syntax:
# ansible-playbook ~/logging-playbook.yml --syntax-check
Note that this command only validates the syntax and does not protect against a wrong but valid
configuration.
4. Run the playbook on your inventory.
# ansible-playbook -i ~/inventory.ini ~/logging-playbook.yml
Verification
1. On both the client and the server system, test the syntax of the /etc/rsyslog.conf file:
# rsyslogd -N 1
rsyslogd: version 8.1911.0-6.el8, config validation run (level 1), master config
/etc/rsyslog.conf
rsyslogd: End of config validation run. Bye.
2. Verify that the client system sends messages to the server:
a. On the client system, send a test message:
# logger test
b. On the server system, view the /var/log//messages log, for example:
# cat /var/log//messages
Aug 5 13:48:31 root[6778]: test
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Where is the host name of the client system. Note that the log
contains the user name of the user that entered the logger command, in this case root.
Additional resources
Preparing a control node and managed nodes to use RHEL System Roles
Documentation installed with the rhel-system-roles package in /usr/share/ansible/roles/rhelsystem-roles.logging/README.html
RHEL System Roles KB article
9.2.6. Using the logging System Role with TLS
Transport Layer Security (TLS) is a cryptographic protocol designed to allow secure communication
over the computer network.
As an administrator, you can use the logging RHEL System Role to configure a secure transfer of logs
using Red Hat Ansible Automation Platform.
9.2.6.1. Configuring client logging with TLS
You can use an Ansible playbook with the logging System Role to configure logging on RHEL clients
and transfer logs to a remote logging system using TLS encryption.
This procedure creates a private key and certificate, and configures TLS on all hosts in the clients group
in the Ansible inventory. The TLS protocol encrypts the message transmission for secure transfer of logs
over the network.
NOTE
You do not have to call the certificate System Role in the playbook to create the
certificate. The logging System Role calls it automatically.
In order for the CA to be able to sign the created certificate, the managed nodes must be
enrolled in an IdM domain.
Prerequisites
You have prepared the control node and the managed nodes
You are logged in to the control node as a user who can run playbooks on the managed nodes.
The account you use to connect to the managed nodes has sudo permissions on them.
The managed nodes or groups of managed nodes on which you want to run this playbook are
listed in the Ansible inventory file.
The managed nodes are enrolled in an IdM domain.
Procedure
1. Create a playbook file, for example ~/tls-client-logging-playbook.yml, with the following
content:
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The playbook uses the following parameters:
logging_certificates
The value of this parameter is passed on to certificate_requests in the certificate role and
used to create a private key and certificate.
logging_pki_files
Using this parameter, you can configure the paths and other settings that logging uses to
find the CA, certificate, and key files used for TLS, specified with one or more of the
following sub-parameters: ca_cert, ca_cert_src, cert, cert_src, private_key,
private_key_src, and tls.
NOTE
If you are using logging_certificates to create the files on the target node, do
not use ca_cert_src, cert_src, and private_key_src, which are used to copy
files not created by logging_certificates.
ca_cert
Represents the path to the CA certificate file on the target node. Default path is
/etc/pki/tls/certs/ca.pem and the file name is set by the user.
cert
Represents the path to the certificate file on the target node. Default path is
---
- name: Deploying files input and forwards output with certs
hosts: clients
roles:
- rhel-system-roles.logging
vars:
logging_certificates:
- name: logging_cert
dns: ['localhost', 'www.example.com']
ca: ipa
logging_pki_files:
- ca_cert: /local/path/to/ca_cert.pem
cert: /local/path/to/logging_cert.pem
private_key: /local/path/to/logging_cert.pem
logging_inputs:
- name: input_name
type: files
input_log_path: /var/log/containers/*.log
logging_outputs:
- name: output_name
type: forwards
target: your_target_host
tcp_port: 514
tls: true
pki_authmode: x509/name
permitted_server: 'server.example.com'
logging_flows:
- name: flow_name
inputs: [input_name]
outputs: [output_name]
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Represents the path to the certificate file on the target node. Default path is
/etc/pki/tls/certs/server-cert.pem and the file name is set by the user.
private_key
Represents the path to the private key file on the target node. Default path is
/etc/pki/tls/private/server-key.pem and the file name is set by the user.
ca_cert_src
Represents the path to the CA certificate file on the control node which is copied to the
target host to the location specified by ca_cert. Do not use this if using
logging_certificates.
cert_src
Represents the path to a certificate file on the control node which is copied to the target
host to the location specified by cert. Do not use this if using logging_certificates.
private_key_src
Represents the path to a private key file on the control node which is copied to the target
host to the location specified by private_key. Do not use this if using logging_certificates.
tls
Setting this parameter to true ensures secure transfer of logs over the network. If you do not
want a secure wrapper, you can set tls: false.
2. Validate the playbook syntax:
# ansible-playbook ~/tls-client-logging-playbook.yml --syntax-check
Note that this command only validates the syntax and does not protect against a wrong but valid
configuration.
3. Run the playbook:
# ansible-playbook ~/tls-client-logging-playbook.yml
Additional resources
Requesting certificates using RHEL System Roles .
9.2.6.2. Configuring server logging with TLS
You can use an Ansible playbook with the logging System Role to configure logging on RHEL servers
and set them to receive logs from a remote logging system using TLS encryption.
This procedure creates a private key and certificate, and configures TLS on all hosts in the server group
in the Ansible inventory.
NOTE
You do not have to call the certificate System Role in the playbook to create the
certificate. The logging System Role calls it automatically.
In order for the CA to be able to sign the created certificate, the managed nodes must be
enrolled in an IdM domain.
Prerequisites
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You have prepared the control node and the managed nodes
You are logged in to the control node as a user who can run playbooks on the managed nodes.
The account you use to connect to the managed nodes has sudo permissions on them.
The managed nodes or groups of managed nodes on which you want to run this playbook are
listed in the Ansible inventory file.
The managed nodes are enrolled in an IdM domain.
Procedure
1. Create a playbook file, for example ~/tls-server-logging-playbook.yml, with the following
content:
The playbook uses the following parameters:
logging_certificates
The value of this parameter is passed on to certificate_requests in the certificate role and
used to create a private key and certificate.
logging_pki_files
---
- name: Deploying remote input and remote_files output with certs
hosts: server
roles:
- rhel-system-roles.logging
vars:
logging_certificates:
- name: logging_cert
dns: ['localhost', 'www.example.com']
ca: ipa
logging_pki_files:
- ca_cert: /local/path/to/ca_cert.pem
cert: /local/path/to/logging_cert.pem
private_key: /local/path/to/logging_cert.pem
logging_inputs:
- name: input_name
type: remote
tcp_ports: 514
tls: true
permitted_clients: ['clients.example.com']
logging_outputs:
- name: output_name
type: remote_files
remote_log_path: /var/log/remote/%FROMHOST%/%PROGRAMNAME:::secpathreplace%.log
async_writing: true
client_count: 20
io_buffer_size: 8192
logging_flows:
- name: flow_name
inputs: [input_name]
outputs: [output_name]
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Using this parameter, you can configure the paths and other settings that logging uses to
find the CA, certificate, and key files used for TLS, specified with one or more of the
following sub-parameters: ca_cert, ca_cert_src, cert, cert_src, private_key,
private_key_src, and tls.
NOTE
If you are using logging_certificates to create the files on the target node, do
not use ca_cert_src, cert_src, and private_key_src, which are used to copy
files not created by logging_certificates.
ca_cert
Represents the path to the CA certificate file on the target node. Default path is
/etc/pki/tls/certs/ca.pem and the file name is set by the user.
cert
Represents the path to the certificate file on the target node. Default path is
/etc/pki/tls/certs/server-cert.pem and the file name is set by the user.
private_key
Represents the path to the private key file on the target node. Default path is
/etc/pki/tls/private/server-key.pem and the file name is set by the user.
ca_cert_src
Represents the path to the CA certificate file on the control node which is copied to the
target host to the location specified by ca_cert. Do not use this if using
logging_certificates.
cert_src
Represents the path to a certificate file on the control node which is copied to the target
host to the location specified by cert. Do not use this if using logging_certificates.
private_key_src
Represents the path to a private key file on the control node which is copied to the target
host to the location specified by private_key. Do not use this if using logging_certificates.
tls
Setting this parameter to true ensures secure transfer of logs over the network. If you do not
want a secure wrapper, you can set tls: false.
2. Validate the playbook syntax:
# ansible-playbook ~/tls-server-logging-playbook.yml --syntax-check
Note that this command only validates the syntax and does not protect against a wrong but valid
configuration.
3. Run the playbook on your inventory file:
# ansible-playbook ~/tls-server-logging-playbook.yml
Additional resources
Requesting certificates using RHEL System Roles .
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9.2.7. Using the logging System Roles with RELP
Reliable Event Logging Protocol (RELP) is a networking protocol for data and message logging over the
TCP network. It ensures reliable delivery of event messages and you can use it in environments that do
not tolerate any message loss.
The RELP sender transfers log entries in form of commands and the receiver acknowledges them once
they are processed. To ensure consistency, RELP stores the transaction number to each transferred
command for any kind of message recovery.
You can consider a remote logging system in between the RELP Client and RELP Server. The RELP
Client transfers the logs to the remote logging system and the RELP Server receives all the logs sent by
the remote logging system.
Administrators can use the logging System Role to configure the logging system to reliably send and
receive log entries.
9.2.7.1. Configuring client logging with RELP
You can use the logging System Role to configure logging in RHEL systems that are logged on a local
machine and can transfer logs to the remote logging system with RELP by running an Ansible playbook.
This procedure configures RELP on all hosts in the clients group in the Ansible inventory. The RELP
configuration uses Transport Layer Security (TLS) to encrypt the message transmission for secure
transfer of logs over the network.
Prerequisites
You have prepared the control node and the managed nodes
You are logged in to the control node as a user who can run playbooks on the managed nodes.
The account you use to connect to the managed nodes has sudo permissions on them.
The managed nodes or groups of managed nodes on which you want to run this playbook are
listed in the Ansible inventory file.
Procedure
1. Create a playbook file, for example ~/relp-client-logging-playbook.yml, with the following
content:
---
- name: Deploying basic input and relp output
hosts: clients
roles:
- rhel-system-roles.logging
vars:
logging_inputs:
- name: basic_input
type: basics
logging_outputs:
- name: relp_client
type: relp
target: logging.server.com
port: 20514
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The playbooks uses following settings:
target
This is a required parameter that specifies the host name where the remote logging system
is running.
port
Port number the remote logging system is listening.
tls
Ensures secure transfer of logs over the network. If you do not want a secure wrapper you
can set the tls variable to false. By default tls parameter is set to true while working with
RELP and requires key/certificates and triplets {ca_cert, cert, private_key} and/or
{ca_cert_src, cert_src, private_key_src}.
If the {ca_cert_src, cert_src, private_key_src} triplet is set, the default locations
/etc/pki/tls/certs and /etc/pki/tls/private are used as the destination on the managed
node to transfer files from control node. In this case, the file names are identical to the
original ones in the triplet
If the {ca_cert, cert, private_key} triplet is set, files are expected to be on the default
path before the logging configuration.
If both triplets are set, files are transferred from local path from control node to specific
path of the managed node.
ca_cert
Represents the path to CA certificate. Default path is /etc/pki/tls/certs/ca.pem and the file
name is set by the user.
cert
Represents the path to certificate. Default path is /etc/pki/tls/certs/server-cert.pem and
the file name is set by the user.
private_key
Represents the path to private key. Default path is /etc/pki/tls/private/server-key.pem and
the file name is set by the user.
ca_cert_src
Represents local CA certificate file path which is copied to the target host. If ca_cert is
specified, it is copied to the location.
cert_src
Represents the local certificate file path which is copied to the target host. If cert is
specified, it is copied to the location.
tls: true
ca_cert: /etc/pki/tls/certs/ca.pem
cert: /etc/pki/tls/certs/client-cert.pem
private_key: /etc/pki/tls/private/client-key.pem
pki_authmode: name
permitted_servers:
- '*.server.example.com'
logging_flows:
- name: example_flow
inputs: [basic_input]
outputs: [relp_client]
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private_key_src
Represents the local key file path which is copied to the target host. If private_key is
specified, it is copied to the location.
pki_authmode
Accepts the authentication mode as name or fingerprint.
permitted_servers
List of servers that will be allowed by the logging client to connect and send logs over TLS.
inputs
List of logging input dictionary.
outputs
List of logging output dictionary.
2. Validate the playbook syntax:
# ansible-playbook ~/relp-client-logging-playbook.yml --syntax-check
Note that this command only validates the syntax and does not protect against a wrong but valid
configuration.
3. Run the playbook:
# ansible-playbook ~/relp-client-logging-playbook.yml
9.2.7.2. Configuring server logging with RELP
You can use the logging System Role to configure logging in RHEL systems as a server and can receive
logs from the remote logging system with RELP by running an Ansible playbook.
This procedure configures RELP on all hosts in the server group in the Ansible inventory. The RELP
configuration uses TLS to encrypt the message transmission for secure transfer of logs over the
network.
Prerequisites
You have prepared the control node and the managed nodes
You are logged in to the control node as a user who can run playbooks on the managed nodes.
The account you use to connect to the managed nodes has sudo permissions on them.
The managed nodes or groups of managed nodes on which you want to run this playbook are
listed in the Ansible inventory file.
Procedure
1. Create a playbook file, for example ~/relp-server-logging-playbook.yml, with the following
content:
---
- name: Deploying remote input and remote_files output
hosts: server
roles:
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The playbooks uses the following settings:
port
Port number the remote logging system is listening.
tls
Ensures secure transfer of logs over the network. If you do not want a secure wrapper you
can set the tls variable to false. By default tls parameter is set to true while working with
RELP and requires key/certificates and triplets {ca_cert, cert, private_key} and/or
{ca_cert_src, cert_src, private_key_src}.
If the {ca_cert_src, cert_src, private_key_src} triplet is set, the default locations
/etc/pki/tls/certs and /etc/pki/tls/private are used as the destination on the managed
node to transfer files from control node. In this case, the file names are identical to the
original ones in the triplet
If the {ca_cert, cert, private_key} triplet is set, files are expected to be on the default
path before the logging configuration.
If both triplets are set, files are transferred from local path from control node to specific
path of the managed node.
ca_cert
Represents the path to CA certificate. Default path is /etc/pki/tls/certs/ca.pem and the file
name is set by the user.
cert
Represents the path to the certificate. Default path is /etc/pki/tls/certs/server-cert.pem
and the file name is set by the user.
private_key
Represents the path to private key. Default path is /etc/pki/tls/private/server-key.pem and
the file name is set by the user.
ca_cert_src
Represents local CA certificate file path which is copied to the target host. If ca_cert is
- rhel-system-roles.logging
vars:
logging_inputs:
- name: relp_server
type: relp
port: 20514
tls: true
ca_cert: /etc/pki/tls/certs/ca.pem
cert: /etc/pki/tls/certs/server-cert.pem
private_key: /etc/pki/tls/private/server-key.pem
pki_authmode: name
permitted_clients:
- '*example.client.com'
logging_outputs:
- name: remote_files_output
type: remote_files
logging_flows:
- name: example_flow
inputs: relp_server
outputs: remote_files_output
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Represents local CA certificate file path which is copied to the target host. If ca_cert is
specified, it is copied to the location.
cert_src
Represents the local certificate file path which is copied to the target host. If cert is
specified, it is copied to the location.
private_key_src
Represents the local key file path which is copied to the target host. If private_key is
specified, it is copied to the location.
pki_authmode
Accepts the authentication mode as name or fingerprint.
permitted_clients
List of clients that will be allowed by the logging server to connect and send logs over TLS.
inputs
List of logging input dictionary.
outputs
List of logging output dictionary.
2. Validate the playbook syntax:
# ansible-playbook ~/relp-server-logging-playbook.yml --syntax-check
Note that this command only validates the syntax and does not protect against a wrong but valid
configuration.
3. Run the playbook:
# ansible-playbook ~/relp-server-logging-playbook.yml
9.2.8. Additional resources
Preparing a control node and managed nodes to use RHEL System Roles
Documentation installed with the rhel-system-roles package in /usr/share/ansible/roles/rhelsystem-roles.logging/README.html.
RHEL System Roles
ansible-playbook(1) man page.
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CHAPTER 10. TROUBLESHOOTING PROBLEMS USING LOG
FILES
Log files contain messages about the system, including the kernel, services, and applications running on
it. These contain information that helps troubleshoot issues or monitor system functions. The logging
system in Red Hat Enterprise Linux is based on the built-in syslog protocol. Particular programs use
this system to record events and organize them into log files, which are useful when auditing the
operating system and troubleshooting various problems.
10.1. SERVICES HANDLING SYSLOG MESSAGES
The following two services handle syslog messages:
The systemd-journald daemon
The Rsyslog service
The systemd-journald daemon collects messages from various sources and forwards them to Rsyslog
for further processing. The systemd-journald daemon collects messages from the following sources:
Kernel
Early stages of the boot process
Standard and error output of daemons as they start up and run
Syslog
The Rsyslog service sorts the syslog messages by type and priority and writes them to the files in the
/var/log directory. The /var/log directory persistently stores the log messages.
10.2. SUBDIRECTORIES STORING SYSLOG MESSAGES
The following subdirectories under the /var/log directory store syslog messages.
/var/log/messages - all syslog messages except the following
/var/log/secure - security and authentication-related messages and errors
/var/log/maillog - mail server-related messages and errors
/var/log/cron - log files related to periodically executed tasks
/var/log/boot.log - log files related to system startup
10.3. INSPECTING LOG FILES USING THE WEB CONSOLE
Follow the steps in this procedure to inspect the log files using the RHEL web console.
Procedure
1. Log into the RHEL web console. For details see Logging in to the web console .
2. Click Logs.
Figure 10.1. Inspecting the log files in the RHEL 8 web console
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Figure 10.1. Inspecting the log files in the RHEL 8 web console
10.4. VIEWING LOGS USING THE COMMAND LINE
The Journal is a component of systemd that helps to view and manage log files. It addresses problems
connected with traditional logging, closely integrated with the rest of the system, and supports various
logging technologies and access management for the log files.
You can use the journalctl command to view messages in the system journal using the command line,
for example:
$ journalctl -b | grep kvm
May 15 11:31:41 localhost.localdomain kernel: kvm-clock: Using msrs 4b564d01 and 4b564d00
May 15 11:31:41 localhost.localdomain kernel: kvm-clock: cpu 0, msr 76401001, primary cpu clock
...
Table 10.1. Viewing system information
Command Description
journalctl Shows all collected journal entries.
journalctl FILEPATH Shows logs related to a specific file. For example, the
journalctl /dev/sda command displays logs related
to the /dev/sda file system.
journalctl -b Shows logs for the current boot.
journalctl -k -b -1 Shows kernel logs for the current boot.
Table 10.2. Viewing information about specific services
Command Description
journalctl -b
_SYSTEMD_UNIT=
Filters log to show entries matching the systemd
service.
journalctl -b
_SYSTEMD_UNIT=
_PID=
Combines matches. For example, this command
shows logs for systemd-units that match
and the PID.
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journalctl -b
_SYSTEMD_UNIT=
_PID= +
_SYSTEMD_UNIT=
The plus sign (+) separator combines two expressions
in a logical OR. For example, this command shows all
messages from the service
process with the PID plus all messages from the
service (from any of its
processes).
journalctl -b
_SYSTEMD_UNIT=
_SYSTEMD_UNIT=
This command shows all entries matching either
expression, referring to the same field. Here, this
command shows logs matching a systemd-unit
or a systemd-unit
.
Command Description
Table 10.3. Viewing logs related to specific boots
Command Description
journalctl --list-boots Shows a tabular list of boot numbers, their IDs, and
the timestamps of the first and last message
pertaining to the boot. You can use the ID in the next
command to view detailed information.
journalctl --boot=ID
_SYSTEMD_UNIT=
Shows information about the specified boot ID.
10.5. ADDITIONAL RESOURCES
man journalctl(1)
Configuring a remote logging solution
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CHAPTER 11. MANAGING USERS AND GROUPS
Preventing unauthorized access to files and processes requires an accurate user and group
management. If you do not manage accounts centrally or you require a user account or group only on a
specific system, you can create them locally on this host.
11.1. INTRODUCTION TO MANAGING USER AND GROUP ACCOUNTS
The control of users and groups is a core element of Red Hat Enterprise Linux (RHEL) system
administration. Each RHEL user has distinct login credentials and can be assigned to various groups to
customize their system privileges.
11.1.1. Introduction to users and groups
A user who creates a file is the owner of that file and the group owner of that file. The file is assigned
separate read, write, and execute permissions for the owner, the group, and those outside that group.
The file owner can be changed only by the root user. Access permissions to the file can be changed by
both the root user and the file owner. A regular user can change group ownership of a file they own to a
group of which they are a member of.
Each user is associated with a unique numerical identification number called user ID (UID). Each group is
associated with a group ID (GID). Users within a group share the same permissions to read, write, and
execute files owned by that group.
11.1.2. Configuring reserved user and group IDs
RHEL reserves user and group IDs below 1000 for system users and groups. You can find the reserved
user and group IDs in the setup package. To view reserved user and group IDs, use:
cat /usr/share/doc/setup*/uidgid
It is recommended to assign IDs to the new users and groups starting at 5000, as the reserved range
can increase in the future.
To make the IDs assigned to new users start at 5000 by default, modify the UID_MIN and GID_MIN
parameters in the /etc/login.defs file.
Procedure
To modify and make the IDs assigned to new users start at 5000 by default:
1. Open the /etc/login.defs file in an editor of your choice.
2. Find the lines that define the minimum value for automatic UID selection.
# Min/max values for automatic uid selection in useradd
#
UID_MIN 1000
3. Modify the UID_MIN value to start at 5000.
# Min/max values for automatic uid selection in useradd
#
UID_MIN 5000
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4. Find the lines that define the minimum value for automatic GID selection.
# Min/max values for automatic gid selection in groupadd
#
GID_MIN 1000
5. Modify the GID_MIN value to start at 5000.
# Min/max values for automatic gid selection in groupadd
#
GID_MIN 5000
The dynamically assigned UIDs and GIDs for the regular users now start at 5000.
NOTE
The UID’s and GID’s of users and groups created before you changed the
UID_MIN and GID_MIN values do not change.
This will allow new user’s group to have same 5000+ ID as UID and GID.
WARNING
Do not raise IDs reserved by the system above 1000 by changing
SYS_UID_MAX to avoid conflict with systems that retain the 1000 limit.
11.1.3. User private groups
RHEL uses the user private group (UPG) system configuration, which makes UNIX groups easier to
manage. A user private group is created whenever a new user is added to the system. The user private
group has the same name as the user for which it was created and that user is the only member of the
user private group.
UPGs simplify the collaboration on a project between multiple users. In addition, UPG system
configuration makes it safe to set default permissions for a newly created file or directory, as it allows
both the user, and the group this user is a part of, to make modifications to the file or directory.
A list of all groups is stored in the /etc/group configuration file.
11.2. GETTING STARTED WITH MANAGING USER ACCOUNTS
Red Hat Enterprise Linux is a multi-user operating system, which enables multiple users on different
computers to access a single system installed on one machine. Every user operates under its own
account, and managing user accounts thus represents a core element of Red Hat Enterprise Linux
system administration.
The following are the different types of user accounts:
Normal user accounts:
Normal accounts are created for users of a particular system. Such accounts can be added,
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Normal accounts are created for users of a particular system. Such accounts can be added,
removed, and modified during normal system administration.
System user accounts:
System user accounts represent a particular applications identifier on a system. Such accounts
are generally added or manipulated only at software installation time, and they are not modified
later.
WARNING
System accounts are presumed to be available locally on a system. If these
accounts are configured and provided remotely, such as in the instance of
an LDAP configuration, system breakage and service start failures can
occur.
For system accounts, user IDs below 1000 are reserved. For normal accounts, you can use IDs
starting at 1000. However, the recommended practice is to assign IDs starting at 5000. For
assigning IDs, see the /etc/login.defs file.
Group:
A group is an entity which ties together multiple user accounts for a common purpose, such as
granting access to particular files.
11.2.1. Managing accounts and groups using command line tools
Use the following basic command-line tools to manage user accounts and groups.
To display user and group IDs:
$ id
uid=1000(example.user) gid=1000(example.user) groups=1000(example.user),10(wheel)
context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
To create a new user account:
# useradd example.user
To assign a new password to a user account belonging to example.user:
# passwd example.user
To add a user to a group:
# usermod -a -G example.group example.user
Additional resources
man useradd(8), man passwd(1), and man usermod(8)
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11.2.2. System user accounts managed in the web console
With user accounts displayed in the RHEL web console you can:
Authenticate users when accessing the system.
Set the access rights to the system.
The RHEL web console displays all user accounts located in the system. Therefore, you can see at least
one user account just after the first login to the web console.
After logging into the RHEL web console, you can perform the following operations:
Create new users accounts.
Change their parameters.
Lock accounts.
Terminate user sessions.
11.2.3. Adding new accounts using the web console
Use the following steps for adding user accounts to the system and setting administration rights to the
accounts through the RHEL web console.
Prerequisites
The RHEL web console must be installed and accessible. For details, see Installing the web
console.
Procedure
1. Log in to the RHEL web console.
2. Click Accounts.
3. Click Create New Account.
4. In the Full Name field, enter the full name of the user.
The RHEL web console automatically suggests a user name from the full name and fills it in the
User Name field. If you do not want to use the original naming convention consisting of the first
letter of the first name and the whole surname, update the suggestion.
5. In the Password/Confirm fields, enter the password and retype it for verification that your
password is correct.
The color bar below the fields shows you the security level of the entered password, which does
not allow you to create a user with a weak password.
6. Click Create to save the settings and close the dialog box.
7. Select the newly created account.
8. In the Groups drop down menu, select the groups that you want to add to the new account.
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Now you can see the new account in the Accounts settings and you can use its credentials to
connect to the system.
11.3. MANAGING USERS FROM THE COMMAND LINE
You can manage users and groups using the command-line interface (CLI). This enables you to add,
remove, and modify users and user groups in Red Hat Enterprise Linux environment.
11.3.1. Adding a new user from the command line
You can use the useradd utility to add a new user.
Prerequisites
Root access
Procedure
To add a new user, use:
# useradd options username
Replace options with the command-line options for the useradd command, and replace
username with the name of the user.
Example 11.1. Adding a new user
To add the user sarah with user ID 5000, use:
# useradd -u 5000 sarah
Verification steps
To verify the new user is added, use the id utility.
# id sarah
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The output returns:
uid=5000(sarah) gid=5000(sarah) groups=5000(sarah)
Additional resources
useradd man page
11.3.2. Adding a new group from the command line
You can use the groupadd utility to add a new group.
Prerequisites
Root access
Procedure
To add a new group, use:
# groupadd options group-name
Replace options with the command-line options for the groupadd command, and replace
group-name with the name of the group.
Example 11.2. Adding a new group
To add the group sysadmins with group ID 5000, use:
# groupadd -g 5000 sysadmins
Verification steps
To verify the new group is added, use the tail utility.
# tail /etc/group
The output returns:
sysadmins:x:5000:
Additional resources
groupadd man page
11.3.3. Adding a user to a supplementary group from the command line
You can add a user to a supplementary group to manage permissions or enable access to certain files or
devices.
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Prerequisites
root access
Procedure
To add a group to the supplementary groups of the user, use:
# usermod --append -G group-name username
Replace group-name with the name of the group, and replace username with the name of the
user.
Example 11.3. Adding a user to a supplementary group
To add the user sysadmin to the group system-administrators, use:
# usermod --append -G system-administrators sysadmin
Verification steps
To verify the new groups is added to the supplementary groups of the user sysadmin, use:
# groups sysadmin
The output displays:
sysadmin : sysadmin system-administrators
11.3.4. Creating a group directory
Under the UPG system configuration, you can apply the set-group identification permission (setgid bit)
to a directory. The setgid bit makes managing group projects that share a directory simpler. When you
apply the setgid bit to a directory, files created within that directory are automatically assigned to a
group that owns the directory. Any user that has the permission to write and execute within this group
can now create, modify, and delete files in the directory.
The following section describes how to create group directories.
Prerequisites
Root access
Procedure
1. Create a directory:
# mkdir directory-name
Replace directory-name with the name of the directory.
2. Create a group:
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# groupadd group-name
Replace group-name with the name of the group.
3. Add users to the group:
# usermod --append -G group-name username
Replace group-name with the name of the group, and replace username with the name of the
user.
4. Associate the user and group ownership of the directory with the group-name group:
# chgrp group-name directory-name
Replace group-name with the name of the group, and replace directory-name with the name of
the directory.
5. Set the write permissions to allow the users to create and modify files and directories and set
the setgid bit to make this permission be applied within the directory-name directory:
# chmod g+rwxs directory-name
Replace directory-name with the name of the directory.
Now all members of the group-name group can create and edit files in the directory-name
directory. Newly created files retain the group ownership of group-name group.
Verification steps
To verify the correctness of set permissions, use:
# ls -ld directory-name
Replace directory-name with the name of the directory.
The output returns:
drwxrwsr-x. 2 root group-name 6 Nov 25 08:45 directory-name
11.3.5. Removing a user on the command line
You can remove a user account using the command line. In addition to removing the user account, you
can optionally remove the user data and metadata, such as their home directory and configuration files.
Prerequisites
You have root access.
The user currently exists.
Ensure that the user is logged out:
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# loginctl terminate-user user-name
Procedure
To only remove the user account, and not the user data:
# userdel user-name
To remove the user, the data, and the metadata:
a. Remove the user, their home directory, their mail spool, and their SELinux user mapping:
# userdel --remove --selinux-user user-name
b. Remove additional user metadata:
# rm -rf /var/lib/AccountsService/users/user-name
This directory stores information that the system needs about the user before the home
directory is available. Depending on the system configuration, the home directory might not
be available until the user authenticates at the login screen.
IMPORTANT
If you do not remove this directory and you later recreate the same user, the
recreated user will still use certain settings inherited from the removed user.
Additional resources
The userdel(8) man page.
11.4. MANAGING USER ACCOUNTS IN THE WEB CONSOLE
The RHEL web console offers a graphical interface that enables you to execute a wide range of
administrative tasks without accessing your terminal directly. For example, you can add, edit or remove
system user accounts.
After reading this section, you will know:
From where the existing accounts come from.
How to add new accounts.
How to set password expiration.
How and when to terminate user sessions.
Prerequisites
Set up the RHEL web console. For details, see Getting started using the RHEL web console .
Log in to the RHEL web console with an account that has administrator permissions assigned.
For details, see Logging in to the RHEL web console .
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11.4.1. System user accounts managed in the web console
With user accounts displayed in the RHEL web console you can:
Authenticate users when accessing the system.
Set the access rights to the system.
The RHEL web console displays all user accounts located in the system. Therefore, you can see at least
one user account just after the first login to the web console.
After logging into the RHEL web console, you can perform the following operations:
Create new users accounts.
Change their parameters.
Lock accounts.
Terminate user sessions.
11.4.2. Adding new accounts using the web console
Use the following steps for adding user accounts to the system and setting administration rights to the
accounts through the RHEL web console.
Prerequisites
The RHEL web console must be installed and accessible. For details, see Installing the web
console.
Procedure
1. Log in to the RHEL web console.
2. Click Accounts.
3. Click Create New Account.
4. In the Full Name field, enter the full name of the user.
The RHEL web console automatically suggests a user name from the full name and fills it in the
User Name field. If you do not want to use the original naming convention consisting of the first
letter of the first name and the whole surname, update the suggestion.
5. In the Password/Confirm fields, enter the password and retype it for verification that your
password is correct.
The color bar below the fields shows you the security level of the entered password, which does
not allow you to create a user with a weak password.
6. Click Create to save the settings and close the dialog box.
7. Select the newly created account.
8. In the Groups drop down menu, select the groups that you want to add to the new account.
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Now you can see the new account in the Accounts settings and you can use its credentials to
connect to the system.
11.4.3. Enforcing password expiration in the web console
By default, user accounts have set passwords to never expire. You can set system passwords to expire
after a defined number of days. When the password expires, the next login attempt will prompt for a
password change.
Procedure
1. Log in to the RHEL 8 web console.
2. Click Accounts.
3. Select the user account for which you want to enforce password expiration.
4. Click edit on the Password line.
5. In the Password expiration dialog box, select Require password change every … daysand
enter a positive whole number representing the number of days after which the password
expires.
6. Click Change.
The web console immediately shows the date of the future password change request on the
Password line.
11.4.4. Terminating user sessions in the web console
A user creates user sessions when logging into the system. Terminating user sessions means to log the
user out from the system. It can be helpful if you need to perform administrative tasks sensitive to
configuration changes, for example, system upgrades.
In each user account in the RHEL 8web console, you can terminate all sessions for the account except
for the web console session you are currently using. This prevents you from loosing access to your
system.
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Procedure
1. Log in to the RHEL 8 web console.
2. Click Accounts.
3. Click the user account for which you want to terminate the session.
4. Click Terminate Session.
If the Terminate Session button is inactive, the user is not logged in to the system.
The RHEL web console terminates the sessions.
11.5. EDITING USER GROUPS USING THE COMMAND LINE
A user belongs to a certain set of groups that allow a logical collection of users with a similar access to
files and folders. You can edit the primary and supplementary user groups from the command line to
change the user’s permissions.
11.5.1. Primary and supplementary user groups
A group is an entity which ties together multiple user accounts for a common purpose, such as granting
access to particular files.
On Linux, user groups can act as primary or supplementary. Primary and supplementary groups have the
following properties:
Primary group
Every user has just one primary group at all times.
You can change the user’s primary group.
Supplementary groups
You can add an existing user to an existing supplementary group to manage users with the
same security and access privileges within the group.
Users can be members of zero or multiple supplementary groups.
11.5.2. Listing the primary and supplementary groups of a user
You can list the groups of users to see which primary and supplementary groups they belong to.
Procedure
Display the names of the primary and any supplementary group of a user:
$ groups user-name
Replace user-name with the name of the user. If you do not provide a user name, the command
displays the group membership for the current user. The first group is the primary group
followed by the optional supplementary groups.
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Example 11.4. Listing of groups for user sarah:
$ groups sarah
The output displays:
sarah : sarah wheel developer
User sarah has a primary group sarah and is a member of supplementary groups wheel and
developer.
Example 11.5. Listing of groups for user marc:
$ groups marc
The output displays:
marc : marc
User marc has only a primary group marc and no supplementary groups.
11.5.3. Changing the primary group of a user
You can change the primary group of an existing user to a new group.
Prerequisites:
1. root access
2. The new group must exist
Procedure
Change the primary group of a user:
# usermod -g group-name user-name
Replace group-name with the name of the new primary group, and replace user-name with the
name of the user.
NOTE
When you change a user’s primary group, the command also automatically
changes the group ownership of all files in the user’s home directory to the new
primary group. You must fix the group ownership of files outside of the user’s
home directory manually.
Example 11.6. Example of changing the primary group of a user:
If the user sarah belongs to the primary group sarah1, and you want to change the primary
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If the user sarah belongs to the primary group sarah1, and you want to change the primary
group of the user to sarah2, use:
# usermod -g sarah2 sarah
Verification steps
Verify that you changed the primary group of the user:
$ groups sarah
The output displays:
sarah : sarah2
11.5.4. Adding a user to a supplementary group from the command line
You can add a user to a supplementary group to manage permissions or enable access to certain files or
devices.
Prerequisites
root access
Procedure
To add a group to the supplementary groups of the user, use:
# usermod --append -G group-name username
Replace group-name with the name of the group, and replace username with the name of the
user.
Example 11.7. Adding a user to a supplementary group
To add the user sysadmin to the group system-administrators, use:
# usermod --append -G system-administrators sysadmin
Verification steps
To verify the new groups is added to the supplementary groups of the user sysadmin, use:
# groups sysadmin
The output displays:
sysadmin : sysadmin system-administrators
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11.5.5. Removing a user from a supplementary group
You can remove an existing user from a supplementary group to limit their permissions or access to files
and devices.
Prerequisites
root access
Procedure
Remove a user from a supplementary group:
# gpasswd -d user-name group-name
Replace user-name with the name of the user, and replace group-name with the name of the
supplementary group.
Example 11.8. Removing user from a supplementary group
If the user sarah has a primary group sarah2, and belongs to the secondary groups wheel
and developers, and you want to remove that user from the group developers, use:
# gpasswd -d sarah developers
Verification steps
Verify that you removed the user sarah from the secondary group developers:
$ groups sarah
The output displays:
sarah : sarah2 wheel
11.5.6. Changing all of the supplementary groups of a user
You can overwrite the list of supplementary groups that you want the user to remain a member of.
Prerequisites
root access
The supplementary groups must exist
Procedure
Overwrite a list of user’s supplementary groups:
# usermod -G group-names username
Replace group-names with the name of one or more supplementary groups. To add the user to
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Replace group-names with the name of one or more supplementary groups. To add the user to
several supplementary groups at once, separate the group names using commas and no
intervening spaces. For example: wheel,developer.
Replace user-name with the name of the user.
IMPORTANT
If the user is currently a member of a group that you do not specify, the
command removes the user from the group.
Example 11.9. Changing the list of supplementary groups of a user
If the user sarah has a primary group sarah2, and belongs to the supplementary group
wheel, and you want the user to belong to three more supplementary groups developer,
sysadmin, and security, use:
# usermod -G wheel,developer,sysadmin,security sarah
Verification steps
Verify that you set the list of the supplementary groups correct:
# groups sarah
The output displays:
sarah : sarah2 wheel developer sysadmin security
11.6. CHANGING AND RESETTING THE ROOT PASSWORD
If the existing root password is no longer satisfactory or is forgotten, you can change or reset it both as
the root user and a non-root user.
11.6.1. Changing the root password as the root user
You can use the passwd command to change the root password as the root user.
Prerequisites
Root access
Procedure
To change the root password, use:
# passwd
You are prompted to enter your current password before you can change it.
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11.6.2. Changing or resetting the forgotten root password as a non-root user
You can use the passwd command to change or reset the forgotten root password as a non-root user.
Prerequisites
You are able to log in as a non-root user.
You are a member of the administrative wheel group.
Procedure
To change or reset the root password as a non-root user that belongs to the wheel group, use:
$ sudo passwd root
You are prompted to enter your current non-root password before you can change the root
password.
11.6.3. Resetting the root password on boot
If you are unable to log in as a non-root user or do not belong to the administrative wheel group, you can
reset the root password on boot by switching into a specialized chroot jail environment.
Procedure
1. Reboot the system and, on the GRUB 2 boot screen, press the e key to interrupt the boot
process.
The kernel boot parameters appear.
load_video
set gfx_payload=keep
insmod gzio
linux ($root)/vmlinuz-4.18.0-80.e18.x86_64 root=/dev/mapper/rhel-root ro crash\
kernel=auto resume=/dev/mapper/rhel-swap rd.lvm.lv/swap rhgb quiet
initrd ($root)/initramfs-4.18.0-80.e18.x86_64.img $tuned_initrd
2. Go to the end of the line that starts with linux.
linux ($root)/vmlinuz-4.18.0-80.e18.x86_64 root=/dev/mapper/rhel-root ro crash\
kernel=auto resume=/dev/mapper/rhel-swap rd.lvm.lv/swap rhgb quiet
Press Ctrl+e to jump to the end of the line.
3. Add rd.break to the end of the line that starts with linux.
linux ($root)/vmlinuz-4.18.0-80.e18.x86_64 root=/dev/mapper/rhel-root ro crash\
kernel=auto resume=/dev/mapper/rhel-swap rd.lvm.lv/swap rhgb quiet rd.break
4. Press Ctrl+x to start the system with the changed parameters.
The switch_root prompt appears.
5. Remount the file system as writable:
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mount -o remount,rw /sysroot
The file system is mounted as read-only in the /sysroot directory. Remounting the file system
as writable allows you to change the password.
6. Enter the chroot environment:
chroot /sysroot
The sh-4.4# prompt appears.
7. Reset the root password:
passwd
Follow the instructions displayed by the command line to finalize the change of the root
password.
8. Enable the SELinux relabeling process on the next system boot:
touch /.autorelabel
9. Exit the chroot environment:
exit
10. Exit the switch_root prompt:
exit
11. Wait until the SELinux relabeling process is finished. Note that relabeling a large disk might take
a long time. The system reboots automatically when the process is complete.
Verification steps
1. To verify that the root password is successfully changed, log in as a normal user and open the
Terminal.
2. Run the interactive shell as root:
$ su
3. Enter your new root password.
4. Print the user name associated with the current effective user ID:
# whoami
The output returns:
root
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CHAPTER 12. MANAGING SUDO ACCESS
System administrators can grant sudo access to allow non-root users to execute administrative
commands that are normally reserved for the root user. As a result, non-root users can enter such
commands without logging in to the root user account.
12.1. USER AUTHORIZATIONS IN SUDOERS
The /etc/sudoers file specifies which users can run which commands using the sudo command. The
rules can apply to individual users and user groups. You can also use aliases to simplify defining rules for
groups of hosts, commands, and even users. Default aliases are defined in the first part of the
/etc/sudoers file.
When a user tries to use sudo privileges to run a command that is not allowed in the /etc/sudoers file,
the system records a message containing username : user NOT in sudoers to the journal log.
The default /etc/sudoers file provides information and examples of authorizations. You can activate a
specific example rule by removing the # comment character from the beginning of the line. The
authorizations section relevant for user is marked with the following introduction:
## Next comes the main part: which users can run what software on
## which machines (the sudoers file can be shared between multiple
## systems).
You can use the following format to create new sudoers authorizations and to modify existing
authorizations:
username hostname=path/to/command
Where:
username is the name of the user or group, for example, user1 or %group1.
hostname is the name of the host on which the rule applies.
path/to/command is the complete absolute path to the command. You can also limit the user to
only performing a command with specific options and arguments by adding those options after
the command path. If you do not specify any options, the user can use the command with all
options.
You can replace any of these variables with ALL to apply the rule to all users, hosts, or commands.
WARNING
With overly permissive rules, such as ALL ALL=(ALL) ALL, all users are able to run
all commands as all users on all hosts. This can lead to security risks.
You can specify the arguments negatively using the ! operator. For example, use !root to specify all
users except the root user. Note that using the allowlists to allow specific users, groups, and commands,
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is more secure than using the blocklists to disallowing specific users, groups, and commands. By using
the allowlists you also block new unauthorized users or groups.
WARNING
Avoid using negative rules for commands because users can overcome such rules by
renaming commands using the alias command.
The system reads the /etc/sudoers file from beginning to end. Therefore, if the file contains multiple
entries for a user, the entries are applied in order. In case of conflicting values, the system uses the last
match, even if it is not the most specific match.
The preferred way of adding new rules to sudoers is by creating new files in the /etc/sudoers.d/
directory instead of entering rules directly to the /etc/sudoers file. This is because the contents of this
directory are preserved during system updates. In addition, it is easier to fix any errors in the separate
files than in the /etc/sudoers file. The system reads the files in the /etc/sudoers.d directory when it
reaches the following line in the /etc/sudoers file:
#includedir /etc/sudoers.d
Note that the number sign # at the beginning of this line is part of the syntax and does not mean the line
is a comment. The names of files in that directory must not contain a period . and must not end with a
tilde ~.
Additional resources
sudo(8) and sudoers(5) man pages
12.2. GRANTING SUDO ACCESS TO A USER
System administrators can grant sudo access to allow non-root users to execute administrative
commands. The sudo command provides users with administrative access without using the password
of the root user.
When users need to perform an administrative command, they can precede that command with sudo.
The command is then executed as if they were the root user.
Be aware of the following limitations:
Only users listed in the /etc/sudoers configuration file can use the sudo command.
The command is executed in the shell of the user, not in the root shell.
Prerequisites
root access
Procedure
1. As root, open the /etc/sudoers file.
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# visudo
The /etc/sudoers file defines the policies applied by the sudo command.
2. In the /etc/sudoers file, find the lines that grant sudo access to users in the administrative
wheel group.
## Allows people in group wheel to run all commands
%wheel ALL=(ALL) ALL
3. Make sure the line that starts with %wheel does not have the # comment character before it.
4. Save any changes, and exit the editor.
5. Add users you want to grant sudo access to into the administrative wheel group.
# usermod --append -G wheel
Replace with the name of the user.
Verification steps
Verify that the user is added to the administrative wheel group:
# id
uid=5000() gid=5000() groups=5000(),10(wheel)
Additional resources
sudo(8), visudo(8), and sudoers(5) man pages
12.3. ENABLING UNPRIVILEGED USERS TO RUN CERTAIN COMMANDS
As an administrator, you can allow unprivileged users to enter certain commands on specific
workstations by configuring a policy in the /etc/sudoers.d/ directory.
For example, you can enable the user to install programs on the host.example.com
workstation using the dnf command with sudo privileges.
Prerequisites
You must have root access to the system.
Procedure
1. As root, create a new sudoers.d directory under /etc/:
# mkdir -p /etc/sudoers.d/
2. Create a new file in the /etc/sudoers.d directory:
# visudo -f /etc/sudoers.d/
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The file opens automatically.
3. Add the following line to the /etc/sudoers.d/ file:
= /usr/bin/dnf
To allow two and more commands on the same host on one line, you can list them separated by
a , comma followed by a space.
4. Optional: To receive email notifications every time the user attempts to use
sudo privileges, add the following lines to the file:
Defaults mail_always
Defaults mailto=""
5. Save the changes, and exit the editor.
Verification
1. To verify if the user can run the dnf command with sudo privileges, switch the
account:
# su -
2. Enter the sudo dnf command:
$ sudo dnf
[sudo] password for :
Enter the sudo password for the user .
3. The system displays the list of dnf commands and options:
...
usage: dnf [options] COMMAND
...
If the system returns the is not in the sudoers file. This incident will be
reported error message, you have not created the file for in /etc/sudoers.d/.
If you receive the is not allowed to run sudo on error
message, you have not completed the configuration correctly. Ensure that you are logged in as
root and that you followed the steps thoroughly.
Additional resources
sudo(8), visudo(8), and sudoers(5) man pages
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CHAPTER 13. MANAGING FILE SYSTEM PERMISSIONS
File system permissions control the ability of user and group accounts to read, modify, and execute the
contents of the files and to enter directories. Set permissions carefully to protect your data against
unauthorized access.
13.1. MANAGING FILE PERMISSIONS
Every file or directory has three levels of ownership:
User owner (u).
Group owner (g).
Others (o).
Each level of ownership can be assigned the following permissions:
Read (r).
Write (w).
Execute (x).
Note that the execute permission for a file allows you to execute that file. The execute permission for a
directory allows you to access the contents of the directory, but not execute it.
When a new file or directory is created, the default set of permissions are automatically assigned to it.
The default permissions for a file or directory are based on two factors:
Base permission.
The user file-creation mode mask (umask).
13.1.1. Base file permissions
Whenever a new file or directory is created, a base permission is automatically assigned to it. Base
permissions for a file or directory can be expressed in symbolic or octal values.
Permission Symbolic value Octal value
No permission --- 0
Execute --x 1
Write -w- 2
Write and execute -wx 3
Read r-- 4
Read and execute r-x 5
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Read and write rw- 6
Read, write, execute rwx 7
The base permission for a directory is 777 (drwxrwxrwx), which grants everyone the permissions to
read, write, and execute. This means that the directory owner, the group, and others can list the
contents of the directory, create, delete, and edit items within the directory, and descend into it.
Note that individual files within a directory can have their own permission that might prevent you from
editing them, despite having unrestricted access to the directory.
The base permission for a file is 666 (-rw-rw-rw-), which grants everyone the permissions to read and
write. This means that the file owner, the group, and others can read and edit the file.
Example 13.1. Permissions for a file
If a file has the following permissions:
$ ls -l
-rwxrw----. 1 sysadmins sysadmins 2 Mar 2 08:43 file
- indicates it is a file.
rwx indicates that the file owner has permissions to read, write, and execute the file.
rw- indicates that the group has permissions to read and write, but not execute the file.
--- indicates that other users have no permission to read, write, or execute the file.
. indicates that the SELinux security context is set for the file.
Example 13.2. Permissions for a directory
If a directory has the following permissions:
$ ls -dl directory
drwxr-----. 1 sysadmins sysadmins 2 Mar 2 08:43 directory
d indicates it is a directory.
rwx indicates that the directory owner has the permissions to read, write, and access the
contents of the directory.
As a directory owner, you can list the items (files, subdirectories) within the directory, access
the content of those items, and modify them.
r-x indicates that the group has permissions to read the content of the directory, but not
write - create new entries or delete files. The x permission means that you can also access
the directory using the cd command.
--- indicates that other users have no permission to read, write, or access the contents of the
directory.
As someone who is not a user owner, or as group owner of the directory, you cannot list the
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As someone who is not a user owner, or as group owner of the directory, you cannot list the
items within the directory, access information about those items, or modify them.
. indicates that the SELinux security context is set for the directory.
NOTE
The base permission that is automatically assigned to a file or directory is not the default
permission the file or directory ends up with. When you create a file or directory, the base
permission is altered by the umask. The combination of the base permission and the
umask creates the default permission for files and directories.
13.1.2. User file-creation mode mask
The user file-creation mode mask (umask) is variable that controls how file permissions are set for newly
created files and directories. The umask automatically removes permissions from the base permission
value to increase the overall security of a Linux system. The umask can be expressed in symbolic or octal
values.
Permission Symbolic value Octal value
Read, write, and execute rwx 0
Read and write rw- 1
Read and execute r-x 2
Read r-- 3
Write and execute -wx 4
Write -w- 5
Execute --x 6
No permissions --- 7
The default umask for a standard user is 0002. The default umask for a root user is 0022.
The first digit of the umask represents special permissions (sticky bit, ). The last three digits of the
umask represent the permissions that are removed from the user owner ( u), group owner (g), and
others (o) respectively.
Example 13.3. Applying the umask when creating a file
The following example illustrates how the umask with an octal value of 0137 is applied to the file with
the base permission of 777, to create the file with the default permission of 640.
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13.1.3. Default file permissions
The default permissions are set automatically for all newly created files and directories. The value of the
default permissions is determined by applying the umask to the base permission.
Example 13.4. Default permissions for a directory created by a standard user
When a standard user creates a new directory, the umask is set to 002 (rwxrwxr-x), and the base
permissions for a directory are set to 777 (rwxrwxrwx). This brings the default permissions to 775
(drwxrwxr-x).
Symbolic value Octal value
Base permission rwxrwxrwx 777
Umask rwxrwxr-x 002
Default permission rwxrwxr-x 775
This means that the directory owner and the group can list the contents of the directory, create, delete,
and edit items within the directory, and descend into it. Other users can only list the contents of the
directory and descend into it.
Example 13.5. Default permissions for a file created by a standard user
When a standard user creates a new file, the umask is set to 002 (rwxrwxr-x), and the base
permissions for a file are set to 666 (rw-rw-rw-). This brings the default permissions to 664 (-rw-rw-r-
-).
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Symbolic value Octal value
Base permission rw-rw-rw- 666
Umask rwxrwxr-x 002
Default permission rw-rw-r-- 664
This means that the file owner and the group can read and edit the file, while other users can only
read the file.
Example 13.6. Default permissions for a directory created by the root user
When a root user creates a new directory, the umask is set to 022 (rwxr-xr-x), and the base
permissions for a directory are set to 777 (rwxrwxrwx). This brings the default permissions to 755
(rwxr-xr-x).
Symbolic value Octal value
Base permission rwxrwxrwx 777
Umask rwxr-xr-x 022
Default permission rwxr-xr-x 755
This means that the directory owner can list the contents of the directory, create, delete, and edit
items within the directory, and descend into it. The group and others can only list the contents of the
directory and descend into it.
Example 13.7. Default permissions for a file created by the root user
When a root user creates a new file, the umask is set to 022 (rwxr-xr-x), and the base permissions
for a file are set to 666 (rw-rw-rw-). This brings the default permissions to 644 (-rw-r—r--).
Symbolic value Octal value
Base permission rw-rw-rw- 666
Umask rwxr-xr-x 022
Default permission rw-r—r-- 644
This means that the file owner can read and edit the file, while the group and others can only read
the file.
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NOTE
For security reasons, regular files cannot have execute permissions by default, even if the
umask is set to 000 (rwxrwxrwx). However, directories can be created with execute
permissions.
13.1.4. Changing file permissions using symbolic values
You can use the chmod utility with symbolic values (a combination letters and signs) to change file
permissions for a file or directory.
You can assign the following permissions:
Read (r)
Write (w)
Execute (x)
Permissions can be assigned to the following levels of ownership:
User owner (u)
Group owner (g)
Other (o)
All (a)
To add or remove permissions you can use the following signs:
+ to add the permissions on top of the existing permissions
- to remove the permissions from the existing permission
= to remove the existing permissions and explicitly define the new ones
Procedure
To change the permissions for a file or directory, use:
$ chmod file-name
Replace with the level of ownership you want to set the permissions for. Replace
with one of the signs. Replace with the permissions you want to
assign. Replace file-name with the name of the file or directory. For example, to grant everyone
the permissions to read, write, and execute (rwx) my-script.sh, use the chmod a=rwx myscript.sh command.
See Base file permissions for more details.
Verification steps
To see the permissions for a particular file, use:
$ ls -l file-name
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Replace file-name with the name of the file.
To see the permissions for a particular directory, use:
$ ls -dl directory-name
Replace directory-name with the name of the directory.
To see the permissions for all the files within a particular directory, use:
$ ls -l directory-name
Replace directory-name with the name of the directory.
Example 13.8. Changing permissions for files and directories
To change file permissions for my-file.txt from -rw-rw-r-- to -rw------, use:
1. Display the current permissions for my-file.txt:
$ ls -l my-file.txt
-rw-rw-r--. 1 username username 0 Feb 24 17:56 my-file.txt
2. Remove the permissions to read, write, and execute (rwx) the file from group owner (g)
and others (o):
$ chmod go= my-file.txt
Note that any permission that is not specified after the equals sign (=) is automatically
prohibited.
3. Verify that the permissions for my-file.txt were set correctly:
$ ls -l my-file.txt
-rw-------. 1 username username 0 Feb 24 17:56 my-file.txt
To change file permissions for my-directory from drwxrwx--- to drwxrwxr-x, use:
1. Display the current permissions for my-directory:
$ ls -dl my-directory
drwxrwx---. 2 username username 4096 Feb 24 18:12 my-directory
2. Add the read and execute (r-x) access for all users (a):
$ chmod o+rx my-directory
3. Verify that the permissions for my-directory and its content were set correctly:
$ ls -dl my-directory
drwxrwxr-x. 2 username username 4096 Feb 24 18:12 my-directory
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13.1.5. Changing file permissions using octal values
You can use the chmod utility with octal values (numbers) to change file permissions for a file or
directory.
Procedure
To change the file permissions for an existing file or directory, use:
$ chmod octal_value file-name
Replace file-name with the name of the file or directory. Replace octal_value with an octal value.
See Base file permissions for more details.
13.2. MANAGING THE ACCESS CONTROL LIST
Each file and directory can only have one user owner and one group owner at a time. If you want to grant
a user permissions to access specific files or directories that belong to a different user or group while
keeping other files and directories private, you can utilize Linux Access Control Lists (ACLs).
13.2.1. Displaying the current Access Control List
You can use the getfacl utility to display the current ACL.
Procedure
To display the current ACL for a particular file or directory, use:
$ getfacl file-name
Replace file-name with the name of the file or directory.
13.2.2. Setting the Access Control List
You can use the setfacl utility to set the ACL for a file or directory.
Prerequisites
root access.
Procedure
To set the ACL for a file or directory, use:
# setfacl -m u:username:symbolic_value file-name
Replace username with the name of the user, symbolic_value with a symbolic value, and file-name with
the name of the file or directory. For more information see the setfacl man page.
Example 13.9. Modifying permissions for a group project
The following example describes how to modify permissions for the group-project file owned by the
root user that belongs to the root group so that this file is:
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Not executable by anyone.
The user andrew has the rw- permissions.
The user susan has the --- permissions.
Other users have the r-- permissions.
Procedure
# setfacl -m u:andrew:rw- group-project
# setfacl -m u:susan:--- group-project
Verification steps
To verify that the user andrew has the rw- permission, the user susan has the ---
permission, and other users have the r-- permission, use:
$ getfacl group-project
The output returns:
# file: group-project
# owner: root
# group: root
user:andrew:rwuser:susan:---
group::r--
mask::rwother::r--
13.3. MANAGING THE UMASK
You can use the umask utility to display, set, or change the current or default value of the umask.
13.3.1. Displaying the current value of the umask
You can use the umask utility to display the current value of the umask in symbolic or octal mode.
Procedure
To display the current value of the umask in symbolic mode, use:
$ umask -S
To display the current value of the umask in the octal mode, use:
$ umask
NOTE
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NOTE
When displaying the umask in octal mode, you may notice it displayed as a four
digit number (0002 or 0022). The first digit of the umask represents a special bit
(sticky bit, SGID bit, or SUID bit). If the first digit is set to 0, the special bit is not
set.
13.3.2. Displaying the default bash umask
There are a number of shells you can use, such as bash, ksh, zsh and tcsh. Those shells can behave as
login or non-login shells. You can invoke the login shell by opening a native or a GUI terminal.
To determine whether you are executing a command in a login or a non-login shell, use the echo $0
command.
Example 13.10. Determining if you are working in a login or a non-login bash shell
If the output of the echo $0 command returns bash, you are executing the command in a
non-login shell.
$ echo $0
bash
The default umask for the non-login shell is set in the /etc/bashrc configuration file.
If the output of the echo $0 command returns -bash, you are executing the command in a
login shell.
# echo $0
-bash
The default umask for the login shell is set in the /etc/profile configuration file.
Procedure
To display the default bash umask for the non-login shell, use:
$ grep umask /etc/bashrc
The output returns:
# By default, we want umask to get set. This sets it for non-login shell.
umask 002
umask 022
To display the default bash umask for the login shell, use:
$ grep umask /etc/profile
The output returns:
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# By default, we want umask to get set. This sets it for login shell
umask 002
umask 022
13.3.3. Setting the umask using symbolic values
You can use the umask utility with symbolic values (a combination letters and signs) to set the umask
for the current shell session
You can assign the following permissions:
Read (r)
Write (w)
Execute (x)
Permissions can be assigned to the following levels of ownership:
User owner (u)
Group owner (g)
Other (o)
All (a)
To add or remove permissions you can use the following signs:
+ to add the permissions on top of the existing permissions
- to remove the permissions from the existing permission
= to remove the existing permissions and explicitly define the new ones
NOTE
Any permission that is not specified after the equals sign (=) is automatically
prohibited.
Procedure
To set the umask for the current shell session, use:
$ umask -S
Replace with the level of ownership you want to set the umask for. Replace
with one of the signs. Replace with the permissions you want to
assign. For example, to set the umask to u=rwx,g=rwx,o=rwx, use umask -S a=rwx.
See User file-creation mode for more details.
NOTE
The umask is only valid for the current shell session.
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13.3.4. Setting the umask using octal values
You can use the umask utility with octal values (numbers) to set the umask for the current shell session.
Procedure
To set the umask for the current shell session, use:
$ umask octal_value
Replace octal_value with an octal value. See User file-creation mode mask for more details.
NOTE
The umask is only valid for the current shell session.
13.3.5. Changing the default umask for the non-login shell
You can change the default bash umask for standard users by modifying the /etc/bashrc file.
Prerequisites
root access
Procedure
1. As root, open the /etc/bashrc file in the editor.
2. Modify the following sections to set a new default bash umask:
if [ $UID -gt 199 ] && [ “id -gn” = “id -un” ]; then
umask 002
else
umask 022
fi
Replace the default octal value of the umask (002) with another octal value. See User filecreation mode mask for more details.
3. Save the changes and exit the editor.
13.3.6. Changing the default umask for the login shell
You can change the default bash umask for the root user by modifying the /etc/profile file.
Prerequisites
root access
Procedure
1. As root, open the /etc/profile file in the editor.
2. Modify the following sections to set a new default bash umask:
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if [ $UID -gt 199 ] && [ “/usr/bin/id -gn” = “/usr/bin/id -un” ]; then
umask 002
else
umask 022
fi
Replace the default octal value of the umask (022) with another octal value. See User filecreation mode mask for more details.
3. Save the changes and exit the editor.
13.3.7. Changing the default umask for a specific user
You can change the default umask for a specific user by modifying the .bashrc for that user.
Procedure
Append the line that specifies the octal value of the umask into the .bashrc file for the
particular user.
$ echo 'umask octal_value' >> /home/username/.bashrc
Replace octal_value with an octal value and replace username with the name of the user. See
User file-creation mode mask for more details.
13.3.8. Setting default permissions for newly created home directories
You can change the permission modes for home directories of newly created users by modifying the
/etc/login.defs file.
Procedure
1. As root, open the /etc/login.defs file in the editor.
2. Modify the following section to set a new default HOME_MODE:
# HOME_MODE is used by useradd(8) and newusers(8) to set the mode for new
# home directories.
# If HOME_MODE is not set, the value of UMASK is used to create the mode.
HOME_MODE 0700
Replace the default octal value (0700) with another octal value. The selected mode will be used
to create the permissions for the home directory.
3. If HOME_MODE is set, save the changes and exit the editor.
4. If HOME_MODE is not set, modify the UMASK to set the mode for the newly created home
directories:
# Default initial "umask" value used by login(1) on non-PAM enabled systems.
# Default "umask" value for pam_umask(8) on PAM enabled systems.
# UMASK is also used by useradd(8) and newusers(8) to set the mode for new
# home directories if HOME_MODE is not set.
# 022 is the default value, but 027, or even 077, could be considered
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# for increased privacy. There is no One True Answer here: each sysadmin
# must make up their mind.
UMASK 022
Replace the default octal value (022) with another octal value. See User file-creation mode
mask for more details.
5. Save the changes and exit the editor.
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CHAPTER 14. MANAGING SYSTEMD
As a system administrator, you can manage critical aspects of your system with systemd. Serving as a
system and service manager for Linux operating systems, systemd software suite provides tools and
services for controlling, reporting, and system initialization. Key features of systemd include:
Parallel start of system services during boot
On-demand activation of daemons
Dependency-based service control logic
The basic object that systemd manages is a systemd unit, a representation of system resources and
services. A systemd unit consists of a name, type and a configuration file that defines and manages a
particular task. You can use unit files to configure system behavior. See the following examples of
various systemd unit types:
Service
Controls and manages individual system services.
Target
Represents a group of units that define system states.
Device
Manages hardware devices and their availability.
Mount
Handles file system mounting.
Timer
Schedules tasks to run at specific intervals.
NOTE
To display all available unit types:
# systemctl -t help
14.1. SYSTEMD UNIT FILES LOCATIONS
You can find the unit configuration files in one of the following directories:
Table 14.1. systemd unit files locations
Directory Description
/usr/lib/systemd/system/ systemd unit files distributed with installed RPM
packages.
/run/systemd/system/ systemd unit files created at run time. This
directory takes precedence over the directory with
installed service unit files.
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/etc/systemd/system/ systemd unit files created by using thesystemctl
enable command as well as unit files added for
extending a service. This directory takes precedence
over the directory with runtime unit files.
Directory Description
The default configuration of systemd is defined during the compilation and you can find the
configuration in the /etc/systemd/system.conf file. By editing this file, you can modify the default
configuration by overriding values for systemd units globally.
For example, to override the default value of the timeout limit, which is set to 90 seconds, use the
DefaultTimeoutStartSec parameter to input the required value in seconds.
DefaultTimeoutStartSec=required value
14.2. MANAGING SYSTEM SERVICES WITH SYSTEMCTL
As a system administrator, you can manage system services by using the systemctl utility. You can
perform various tasks, such as starting, stopping, restarting running services, enabling and disabling
services to start at boot, listing available services, and displaying system services statuses.
14.2.1. Listing system services
You can list all currently loaded service units and display the status of all available service units.
Procedure
Use the systemctl command to perform any of the following tasks:
List all currently loaded service units:
$ systemctl list-units --type service
UNIT LOAD ACTIVE SUB DESCRIPTION
abrt-ccpp.service loaded active exited Install ABRT coredump hook
abrt-oops.service loaded active running ABRT kernel log watcher
abrtd.service loaded active running ABRT Automated Bug Reporting Tool
...
systemd-vconsole-setup.service loaded active exited Setup Virtual Console
tog-pegasus.service loaded active running OpenPegasus CIM Server
LOAD = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, or a generalization of SUB.
SUB = The low-level unit activation state, values depend on unit type.
46 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'
By default, the systemctl list-units command displays only active units. For each service unit
file, the command provides an overview of the following parameters:
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UNIT
The full name of the service unit
LOAD
The load state of the configuration file
ACTIVE orSUB
The current high-level and low-level unit file activation state
DESCRIPTION
A short description of the unit’s purpose and functionality
List all loaded units regardless of their state, by using the following command with the --all or
-a command line option:
$ systemctl list-units --type service --all
List the status (enabled or disabled) of all available service units:
$ systemctl list-unit-files --type service
UNIT FILE STATE
abrt-ccpp.service enabled
abrt-oops.service enabled
abrtd.service enabled
...
wpa_supplicant.service disabled
ypbind.service disabled
208 unit files listed.
For each service unit, this command displays:
UNIT FILE
The full name of the service unit
STATE
The information whether the service unit is enabled or disabled to start automatically during
boot
Additional resources
Displaying system service status
14.2.2. Displaying system service status
You can inspect any service unit to get detailed information and verify the state of the service, whether
it is enabled to start during boot or currently running. You can also view services that are ordered to start
after or before a particular service unit.
Procedure
Use the systemctl command to perform any of the following tasks:
Display detailed information about a service unit that corresponds to a system service:
$ systemctl status .service
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Replace with the name of the service unit you want to inspect (for example, gdm).
This command displays the following information:
The name of the selected service unit followed by a short description
One or more fields described in Available service unit information
The execution of the service unit: if the unit is executed by the root user
The most recent log entries
Table 14.2. Available service unit information
Field Description
Loaded Information whether the service unit has been
loaded, the absolute path to the unit file, and a
note whether the unit is enabled to start
during boot.
Active Information whether the service unit is running
followed by a time stamp.
Main PID The process ID and the name of the
corresponding system service.
Status Additional information about the
corresponding system service.
Process Additional information about related
processes.
CGroup Additional information about related control
groups (cgroups).
Example 14.1. Displaying service status
The service unit for the GNOME Display Manager is named gdm.service. To determine the
current status of this service unit, type the following at a shell prompt:
# systemctl status gdm.service
gdm.service - GNOME Display Manager
Loaded: loaded (/usr/lib/systemd/system/gdm.service; enabled)
Active: active (running) since Thu 2013-10-17 17:31:23 CEST; 5min ago
Main PID: 1029 (gdm)
CGroup: /system.slice/gdm.service
├─1029 /usr/sbin/gdm
└─1047 /usr/bin/Xorg :0 -background none -verbose -auth /r...
Oct 17 17:31:23 localhost systemd[1]: Started GNOME Display Manager.
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Verify that a particular service unit is running:
$ systemctl is-active .service
Determine whether a particular service unit is enabled to start during boot:
$ systemctl is-enabled .service
NOTE
Both systemctl is-active and systemctl is-enabled commands return an exit
status of 0 if the specified service unit is running or enabled.
Check what services systemd orders to start before the specified service unit
# systemctl list-dependencies --after .service
For example, to view the list of services ordered to start before gdm, enter:
# systemctl list-dependencies --after gdm.service
gdm.service
├─dbus.socket
├─getty@tty1.service
├─livesys.service
├─plymouth-quit.service
├─system.slice
├─systemd-journald.socket
├─systemd-user-sessions.service
└─basic.target
[output truncated]
Check what services systemd orders to start after the specified service unit:
# systemctl list-dependencies --before .service
For example, to view the list of services systemd orders to start after gdm, enter:
# systemctl list-dependencies --before gdm.service
gdm.service
├─dracut-shutdown.service
├─graphical.target
│ ├─systemd-readahead-done.service
│ ├─systemd-readahead-done.timer
│ └─systemd-update-utmp-runlevel.service
└─shutdown.target
├─systemd-reboot.service
└─final.target
└─systemd-reboot.service
Additional resources
Listing system services
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14.2.3. Starting a system service
You can start system service in the current session by using the start command.
Prerequisites
Root access
Procedure
Start a system service in the current session:
# systemctl start .service
Replace with the name of the service unit you want to start (for example,
httpd.service).
NOTE
In systemd, positive and negative dependencies between services exist. Starting
a particular service may require starting one or more other services (positive
dependency) or stopping one or more services ( negative dependency).
When you attempt to start a new service, systemd resolves all dependencies
automatically, without explicit notification to the user. This means that if you are
already running a service, and you attempt to start another service with a
negative dependency, the first service is automatically stopped.
For example, if you are running the postfix service, and you attempt to start the
sendmail service, systemd first automatically stops postfix, because these two
services are conflicting and cannot run on the same port.
Additional resources
systemctl(1) man page
Enabling a system service to start at boot
Displaying system service status
14.2.4. Stopping a system service
If you want to stop a system service in the current session, use the stop command.
Prerequisites
Root access
Procedure
Stop a system service:
# systemctl stop .service
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Replace with the name of the service unit you want to stop (for example, bluetooth).
Additional resources
systemctl(1) man page
Disabling a system service to start at boot
Displaying system service status
14.2.5. Restarting a system service
You can restart system service in the current session using the restart command to perform the
following actions:
Stop the selected service unit in the current session and immediately start it again.
Restart a service unit only if the corresponding service is already running.
Reload configuration of a system service without interrupting its execution.
Prerequisites
Root access
Procedure
Restart a system service:
# systemctl restart .service
Replace with the name of the service unit you want to restart (for example, httpd).
NOTE
If the selected service unit is not running, this command starts it too.
Optional: Restart a service unit only if the corresponding service is already running:
# systemctl try-restart .service
Optional: Reload the configuration without interrupting service execution:
# systemctl reload .service
NOTE
System services that do not support this feature, ignore this command. To restart
such services, use the reload-or-restart and reload-or-try-restart commands
instead.
Additional resources
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systemctl man page
Displaying system service status
14.2.6. Enabling a system service to start at boot
You can enable a service to start automatically at boot, these changes apply with the next reboot.
Prerequisites
Root access
The service you want to enable must not be masked. If you have a masked service, unmask it
first:
# systemctl unmask .service
Procedure
Enable a service to start at boot:
# systemctl enable .service
Replace with the name of the service unit you want to enable (for example, httpd).
Optional: You can also enable and start a service by using a single command:
# systemctl enable --now .service
Additional resources
systemctl (1) man page
Displaying system service status
Starting a system service
14.2.7. Disabling a system service to start at boot
You can prevent a service unit from starting automatically at boot time. If you disable a service, it will not
start at boot, but you can start it manually. You can also mask a service, so that it cannot be started
manually. Masking is a way of disabling a service that makes the service permanently unusable until it is
unmasked again.
Prerequisites
Root access
Procedure
Disable a service to start at boot:
# systemctl disable .service
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Replace with the name of the service unit you want to disable (for example,
bluetooth).
Optional: If you want to make a service permanently unusable, mask the service:
# systemctl mask .service
This command replaces the /etc/systemd/system/name.service file with a symbolic link to
/dev/null, rendering the actual unit file inaccessible to systemd.
Additional resources
systemctl (1) man page
Displaying system service status
Stopping a system service
14.3. BOOTING INTO A TARGET SYSTEM STATE
As a system administrator, you can control the boot process of your system, and define the state you
want your system to boot into. This is called a systemd target, and it is a set of systemd units that your
system starts to reach a certain level of functionality. While working with systemd targets, you can view
the default target, select a target at runtime, change the default boot target, boot into emergency or
rescue target.
14.3.1. Target unit files
Targets in systemd are groups of related units that act as synchronization points during the start of your
system. Target unit files, which end with the .target file extension, represent the systemd targets. The
purpose of target units is to group together various systemd units through a chain of dependencies.
Consider the following examples:
The graphical.target unit for starting a graphical session, starts system services such as the
GNOME Display Manager (gdm.service) or Accounts Service (accounts-daemon.service),
and also activates the multi-user.target unit.
Similarly, the multi-user.target unit starts other essential system services such as
NetworkManager (NetworkManager.service) or D-Bus (dbus.service) and activates another
target unit named basic.target.
You can set the following systemd targets as default or current targets:
Table 14.3. Common systemd targets
rescue unit target that pulls in the base system and spawns a rescue shell
multi-user unit target for setting up a multi-user system
graphical unit target for setting up a graphical login screen
emergency unit target that starts an emergency shell on the main console
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Additional resources
systemd.special(7) man page
systemd.target(5) man page
14.3.2. Changing the default target to boot into
When a system starts, systemd activates the default.target symbolic link, which points to the true
target unit. You can find the currently selected default target unit in the
/etc/systemd/system/default.target file. Each target represents a certain level of functionality and is
used for grouping other units. Additionally, target units serve as synchronization points during boot. You
can change the default target your system boots into. When you set a default target unit, the current
target remains unchanged until the next reboot.
Prerequisites
Root access
Procedure
1. Determine the current default target unit systemd uses to start the system:
# systemctl get-default
graphical.target
2. List the currently loaded targets:
# systemctl list-units --type target
3. Configure the system to use a different target unit by default:
# systemctl set-default .target
Replace with the name of the target unit you want to use by default.
Example:
# systemctl set-default multi-user.target
Removed /etc/systemd/system/default.target
Created symlink /etc/systemd/system/default.target -> /usr/lib/systemd/system/multiuser.target
4. Verify the default target unit:
# systemctl get-default
multi-user.target
5. Apply the changes by rebooting:
# reboot
Additional resources
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systemctl(1) man page
systemd.special(7) man page
bootup(7) man page
14.3.3. Changing the current target
On a running system, you can change the target unit in the current boot without reboot. If you switch to
a different target, systemd starts all services and their dependencies that this target requires, and stops
all services that the new target does not enable. Isolating a different target affects only the current boot.
Procedure
1. Optional: Determine the current target:
# systemctl get-default
graphical.target
2. Optional: Display the list of targets you can select:
# systemctl list-units --type target
NOTE
You can only isolate targets that have the AllowIsolate=yes option set in the
unit files.
3. Change to a different target unit in the current boot:
# systemctl isolate .target
Replace with the name of the target unit you want to use in the current boot.
Example:
# systemctl isolate multi-user.target
This command starts the target unit named multi-user and all dependent units, and immediately
stops all other unit.
Additional resources
systemctl(1) man page
14.3.4. Booting to rescue mode
You can boot to the rescue mode that provides a single-user environment for troubleshooting or repair
if the system cannot get to a later target, and the regular booting process fails. In rescue mode, the
system attempts to mount all local file systems and start certain important system services, but it does
not activate network interfaces.
Prerequisites
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Root access
Procedure
To enter the rescue mode, change the current target in the current session:
# systemctl rescue
Broadcast message from root@localhost on pts/0 (Fri 2023-03-24 18:23:15 CEST):
The system is going down to rescue mode NOW!
NOTE
This command is similar to systemctl isolate rescue.target, but it also sends an
informative message to all users that are currently logged into the system.
To prevent systemd from sending a message, enter the following command with
the --no-wall command-line option:
# systemctl --no-wall rescue
Troubleshooting steps
If your system is not able to enter the rescue mode, you can boot to emergency mode, which provides
the most minimal environment possible. In emergency mode, the system mounts the root file system
only for reading, does not attempt to mount any other local file systems, does not activate network
interfaces, and only starts a few essential services.
14.3.5. Troubleshooting the boot process
As a system administrator, you can select a non-default target at boot time to troubleshoot the boot
process. Changing the target at boot time affects only a single boot. You can boot to emergency mode,
which provides the most minimal environment possible.
Procedure
1. Reboot the system, and interrupt the boot loader menu countdown by pressing any key except
the Enter key, which would initiate a normal boot.
2. Move the cursor to the kernel entry that you want to start.
3. Press the E key to edit the current entry.
4. Move to the end of the line that starts with linux and press Ctrl+E to jump to the end of the line:
linux ($root)/vmlinuz-5.14.0-70.22.1.e19_0.x86_64 root=/dev/mapper/rhel-root ro crash\
kernel=auto resume=/dev/mapper/rhel-swap rd.lvm.lv/swap rhgb quiet
5. To choose an alternate boot target, append the systemd.unit= parameter to the end of the line
that starts with linux:
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linux ($root)/vmlinuz-5.14.0-70.22.1.e19_0.x86_64 root=/dev/mapper/rhel-root ro crash\
kernel=auto resume=/dev/mapper/rhel-swap rd.lvm.lv/swap rhgb quiet
systemd.unit=.target
Replace with the name of the target unit you want to use. For example,
systemd.unit=emergency.target
6. Press Ctrl+X to boot with these settings.
14.4. SHUTTING DOWN, SUSPENDING, AND HIBERNATING THE
SYSTEM
As a system administrator, you can use different power management options to manage power
consumption, perform a proper shutdown to ensure that all data is saved, or restart the system to apply
changes and updates.
14.4.1. System shutdown
To shut down the system, you can either use the systemctl utility directly, or call this utility through the
shutdown command.
Using the shutdown has the following advantages:
You can schedule a shutdown by using the time argument. This also gives users warning that a
system shutdown has been scheduled.
You can cancel the shutdown.
Additional resources
Overview of the power management commands with systemctl
14.4.2. Scheduling a system shutdown
As a system administrator, you can schedule a delayed shutdown to give users time to save their work
and log off the system. Use the shutdown command to perform the following operations:
Shut down the system and power off the machine at a certain time
Shut down and halt the system without powering off the machine
Cancel a pending shutdown
Prerequisites
Root access
Procedure
Use the shutdown command to perform any of the following tasks:
Specify the time at which you want to shut down the system and power off the machine:
# shutdown --poweroff hh:mm
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Where hh:mm is the time in the 24-hour time notation. To prevent new logins, the /run/nologin
file is created 5 minutes before system shutdown.
When you use the time argument, you can notify users logged in to the system of the planned
shutdown by specifying an optional wall message, for example shutdown --poweroff 13:59
"Attention. The system will shut down at 13:59".
Shut down and halt the system after a delay, without powering off the machine:
# shutdown --halt +m
Where +m is the delay time in minutes. You can use the now keyword as an alias for +0.
Cancel a pending shutdown:
# shutdown -c
Additional resources
shutdown(8) manual page
Shutting down the system using the systemctl command
14.4.3. Shutting down the system using the systemctl command
As a system administrator, you can shut down the system and power off the machine or shut down and
halt the system without powering off the machine by using the systemctl command.
Prerequisites
Root access
Procedure
Use the systemctl command to perform any of the following tasks:
Shut down the system and power off the machine:
# systemctl poweroff
Shut down and halt the system without powering off the machine:
# systemctl halt
NOTE
By default, running either of these commands causes systemd to send an informative
message to all users that are currently logged into the system. To prevent systemd from
sending this message, run the selected command with the --no-wall command line
option.
14.4.4. Restarting the system
When you restart the system, systemd stops all running programs and services, the system shuts down,
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When you restart the system, systemd stops all running programs and services, the system shuts down,
and then immediately starts again. Restarting the system can be helpful in the following situations:
After installing new software or updates
After making changes to system settings
When troubleshooting system issues
Prerequisites
Root access
Procedure
Restart the system:
# systemctl reboot
NOTE
By default, when you use this command, systemd sends an informative message to all
users that are currently logged into the system. To prevent systemd from sending this
message, run this command with the --no-wall option.
14.4.5. Optimizing power consumption by suspending and hibernating the system
As a system administrator, you can manage power consumption, save energy on your systems, and
preserve the current state of your system. To do so, apply one of the following modes:
Suspend
Suspending saves the system state in RAM and with the exception of the RAM module, powers off
most of the devices in the machine. When you turn the machine back on, the system then restores its
state from RAM without having to boot again. Because the system state is saved in RAM and not on
the hard disk, restoring the system from suspend mode is significantly faster than from hibernation.
However, the suspended system state is also vulnerable to power outages.
Hibernate
Hibernating saves the system state on the hard disk drive and powers off the machine. When you
turn the machine back on, the system then restores its state from the saved data without having to
boot again. Because the system state is saved on the hard disk and not in RAM, the machine does
not have to maintain electrical power to the RAM module. However, as a consequence, restoring the
system from hibernation is significantly slower than restoring it from suspend mode.
Hybrid sleep
This combines elements of both hibernation and suspending. The system first saves the current
state on the the hard disk drive, and enters a low-power state similar to suspending, which allows the
system to resume more quickly. The benefit of hybrid sleep is that if the system loses power during
the sleep state, it can still recover the previous state from the saved image on the hard disk, similar to
hibernation.
Suspend-then-hibernate
This mode first suspends the system, which results in saving the current system state to RAM and
putting the system in a low-power mode. The system hibernates if it remains suspended for a
specific period of time that you can define in the HibernateDelaySec parameter. Hibernation saves
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the system state to the hard disk drive and shuts down the system completely. The suspend-thenhibernate mode provides the benefit of conserving battery power while you are still able to quickly
resume work. Additionally, this mode ensures that your data is saved in case of a power failure.
Prerequisites
Root access
Procedure
Choose the appropriate method for power saving:
Suspend the system:
# systemctl suspend
Hibernate the system:
# systemctl hibernate
Hibernate and suspend the system:
# systemctl hybrid-sleep
Suspend and then hibernate the system:
# systemctl suspend-then-hibernate
14.4.6. Overview of the power management commands with systemctl
You can use the following list of the systemctl commands to control the power management of your
system.
Table 14.4. Overview of the systemctl power management commands
systemctl command Description
systemctl halt Halts the system.
systemctl poweroff Powers off the system.
systemctl reboot Restarts the system.
systemctl suspend Suspends the system.
systemctl hibernate Hibernates the system.
systemctl hybrid-sleep Hibernates and suspends the system.
14.4.7. Changing how your system behaves when you press the power button
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When you press the power button on your computer, it shuts down the system by default. You can
customize this behavior according to your preferences.
Prerequisites
Administrative access.
Procedure
1. Open the /etc/systemd/logind.conf configuration file.
2. Look for the line that says HandlePowerKey=poweroff.
3. If the line starts with the # symbol, remove it to enable the setting.
4. Replace poweroff with one of the following options:
poweroff to shut down the computer.
reboot for a system reboot.
halt to initiate a system halt.
kexec for a kexec-based reboot.
suspend to suspend the system.
hibernate to initiate system hibernation.
ignore to do nothing.
For example, to reboot the system upon pressing the power button, use this setting:
HandlePowerKey=reboot
5. Save your changes and close the editor.
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CHAPTER 15. CONFIGURING TIME SYNCHRONIZATION
Accurate timekeeping in an IT environment is important. A consistent time across all network devices
improves the traceability of log files and certain protocols rely on synchronized clocks. For example,
Kerberos uses time stamps to prevent replay attacks.
15.1. USING THE CHRONY SUITE TO CONFIGURE NTP
Accurate timekeeping is important for several reasons in IT. In networking for example, accurate time
stamps in packets and logs are required. In Linux systems, the NTP protocol is implemented by a
daemon running in user space.
The user space daemon updates the system clock running in the kernel. The system clock can keep time
by using various clock sources. Usually, the Time Stamp Counter (TSC) is used. The TSC is a CPU
register which counts the number of cycles since it was last reset. It is very fast, has a high resolution,
and there are no interruptions.
Starting with Red Hat Enterprise Linux 8, the NTP protocol is implemented by the chronyd daemon,
available from the repositories in the chrony package.
The following sections describe how to use the chrony suite to configure NTP.
15.1.1. Introduction to chrony suite
chrony is an implementation of the Network Time Protocol (NTP). You can use chrony:
To synchronize the system clock with NTP servers
To synchronize the system clock with a reference clock, for example a GPS receiver
To synchronize the system clock with a manual time input
As an NTPv4(RFC 5905) server or peer to provide a time service to other computers in the
network
chrony performs well in a wide range of conditions, including intermittent network connections, heavily
congested networks, changing temperatures (ordinary computer clocks are sensitive to temperature),
and systems that do not run continuously, or run on a virtual machine.
Typical accuracy between two machines synchronized over the Internet is within a few milliseconds, and
for machines on a LAN within tens of microseconds. Hardware timestamping or a hardware reference
clock may improve accuracy between two machines synchronized to a sub-microsecond level.
chrony consists of chronyd, a daemon that runs in user space, and chronyc, a command line program
which can be used to monitor the performance of chronyd and to change various operating parameters
when it is running.
The chrony daemon, chronyd, can be monitored and controlled by the command line utility chronyc.
This utility provides a command prompt which allows entering a number of commands to query the
current state of chronyd and make changes to its configuration. By default, chronyd accepts only
commands from a local instance of chronyc, but it can be configured to accept monitoring commands
also from remote hosts. The remote access should be restricted.
15.1.2. Using chronyc to control chronyd
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You can control chronyd by using the chronyc command line utility.
Procedure
1. To make changes to the local instance of chronyd using the command line utility chronyc in
interactive mode, enter the following command as root:
# chronyc
chronyc must run as root if some of the restricted commands are to be used.
The chronyc command prompt will be displayed as follows:
chronyc>
2. To list all of the commands, type help.
3. Alternatively, the utility can also be invoked in non-interactive command mode if called together
with a command as follows:
chronyc command
NOTE
Changes made using chronyc are not permanent, they will be lost after a chronyd
restart. For permanent changes, modify /etc/chrony.conf.
15.1.3. Migrating to chrony
In Red Hat Enterprise Linux 7, users could choose between ntp and chrony to ensure accurate
timekeeping. For differences between ntp and chrony, ntpd and chronyd, see Differences between
ntpd and chronyd.
Starting with Red Hat Enterprise Linux 8, ntp is no longer supported. chrony is enabled by default. For
this reason, you might need to migrate from ntp to chrony.
Migrating from ntp to chrony is straightforward in most cases. The corresponding names of the
programs, configuration files and services are:
Table 15.1. Corresponding names of the programs, configuration files and services when migrating
from ntp to chrony
ntp name chrony name
/etc/ntp.conf /etc/chrony.conf
/etc/ntp/keys /etc/chrony.keys
ntpd chronyd
ntpq chronyc
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ntpd.service chronyd.service
ntp-wait.service chrony-wait.service
ntp name chrony name
The ntpdate and sntp utilities, which are included in the ntp distribution, can be replaced with chronyd
using the -q option or the -t option. The configuration can be specified on the command line to avoid
reading /etc/chrony.conf. For example, instead of running ntpdate ntp.example.com, chronyd could
be started as:
# chronyd -q 'server ntp.example.com iburst'
2018-05-18T12:37:43Z chronyd version 3.3 starting (+CMDMON +NTP +REFCLOCK +RTC
+PRIVDROP +SCFILTER +SIGND +ASYNCDNS +SECHASH +IPV6 +DEBUG)
2018-05-18T12:37:43Z Initial frequency -2.630 ppm
2018-05-18T12:37:48Z System clock wrong by 0.003159 seconds (step)
2018-05-18T12:37:48Z chronyd exiting
The ntpstat utility, which was previously included in the ntp package and supported only ntpd, now
supports both ntpd and chronyd. It is available in the ntpstat package.
15.1.3.1. Migration script
A Python script called ntp2chrony.py is included in the documentation of the chrony package
(/usr/share/doc/chrony). The script automatically converts an existing ntp configuration to chrony. It
supports the most common directives and options in the ntp.conf file. Any lines that are ignored in the
conversion are included as comments in the generated chrony.conf file for review. Keys that are
specified in the ntp key file, but are not marked as trusted keys in ntp.conf are included in the generated
chrony.keys file as comments.
By default, the script does not overwrite any files. If /etc/chrony.conf or /etc/chrony.keys already exist,
the -b option can be used to rename the file as a backup. The script supports other options. The --help
option prints all supported options.
An example of an invocation of the script with the default ntp.conf provided in the ntp package is:
# python3 /usr/share/doc/chrony/ntp2chrony.py -b -v
Reading /etc/ntp.conf
Reading /etc/ntp/crypto/pw
Reading /etc/ntp/keys
Writing /etc/chrony.conf
Writing /etc/chrony.keys
The only directive ignored in this case is disable monitor, which has a chrony equivalent in the
noclientlog directive, but it was included in the default ntp.conf only to mitigate an amplification attack.
The generated chrony.conf file typically includes a number of allow directives corresponding to the
restrict lines in ntp.conf. If you do not want to run chronyd as an NTP server, remove all allow directives
from chrony.conf.
15.2. USING CHRONY
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The following sections describe how to install, start, and stop chronyd, and how to check if chrony is
synchronized. Sections also describe how to manually adjust System Clock.
15.2.1. Managing chrony
The following procedure describes how to install, start, stop, and check the status of chronyd.
Procedure
1. The chrony suite is installed by default on Red Hat Enterprise Linux. To ensure that it is, run the
following command as root:
# yum install chrony
The default location for the chrony daemon is /usr/sbin/chronyd. The command line utility will
be installed to /usr/bin/chronyc.
2. To check the status of chronyd, issue the following command:
$ systemctl status chronyd
chronyd.service - NTP client/server
Loaded: loaded (/usr/lib/systemd/system/chronyd.service; enabled)
Active: active (running) since Wed 2013-06-12 22:23:16 CEST; 11h ago
3. To start chronyd, issue the following command as root:
# systemctl start chronyd
To ensure chronyd starts automatically at system start, issue the following command as root:
# systemctl enable chronyd
4. To stop chronyd, issue the following command as root:
# systemctl stop chronyd
To prevent chronyd from starting automatically at system start, issue the following command
as root:
# systemctl disable chronyd
15.2.2. Checking if chrony is synchronized
The following procedure describes how to check if chrony is synchronized with the use of the tracking,
sources, and sourcestats commands.
Procedure
1. To check chrony tracking, issue the following command:
$ chronyc tracking
Reference ID : CB00710F (ntp-server.example.net)
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Stratum : 3
Ref time (UTC) : Fri Jan 27 09:49:17 2017
System time : 0.000006523 seconds slow of NTP time
Last offset : -0.000006747 seconds
RMS offset : 0.000035822 seconds
Frequency : 3.225 ppm slow
Residual freq : 0.000 ppm
Skew : 0.129 ppm
Root delay : 0.013639022 seconds
Root dispersion : 0.001100737 seconds
Update interval : 64.2 seconds
Leap status : Normal
2. The sources command displays information about the current time sources that chronyd is
accessing. To check chrony sources, issue the following command:
$ chronyc sources
210 Number of sources = 3
MS Name/IP address Stratum Poll Reach LastRx Last sample
===========================================================================
====
#* GPS0 0 4 377 11 -479ns[ -621ns] /- 134ns
^? a.b.c 2 6 377 23 -923us[ -924us] +/- 43ms
^ d.e.f 1 6 377 21 -2629us[-2619us] +/- 86ms
You can specify the optional -v argument to print more verbose information. In this case, extra
caption lines are shown as a reminder of the meanings of the columns.
3. The sourcestats command displays information about the drift rate and offset estimation
process for each of the sources currently being examined by chronyd. To check chrony source
statistics, issue the following command:
$ chronyc sourcestats
210 Number of sources = 1
Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev
===========================================================================
====
abc.def.ghi 11 5 46m -0.001 0.045 1us 25us
The optional argument -v can be specified, meaning verbose. In this case, extra caption lines are
shown as a reminder of the meanings of the columns.
Additional resources
chronyc(1) man page
15.2.3. Manually adjusting the System Clock
The following procedure describes how to manually adjust the System Clock.
Procedure
1. To step the system clock immediately, bypassing any adjustments in progress by slewing, issue
the following command as root:
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# chronyc makestep
If the rtcfile directive is used, the real-time clock should not be manually adjusted. Random adjustments
would interfere with chrony's need to measure the rate at which the real-time clock drifts.
15.2.4. Disabling a chrony dispatcher script
The chrony dispatcher script manages the online and offline state of the NTP servers. As a system
administrator, you can disable the dispatcher script to keep chronyd polling the servers constantly.
If you enable NetworkManager on your system to manage networking configuration, the
NetworkManager executes the chrony dispatcher script during interface reconfiguration, stop or start
operations. However, if you configure certain interfaces or routes outside of NetworkManager, you can
encounter the following situation:
1. The dispatcher script might run when no route to the NTP servers exists, causing the NTP
servers to switch to the offline state.
2. If you establish the route later, the script does not run again by default, and the NTP servers
remain in the offline state.
To ensure that chronyd can synchronize with your NTP servers, which have separately managed
interfaces, disable the dispatcher script.
Prerequisites
You installed NetworkManager on your system and enabled it.
Root access
Procedure
1. To disable the chrony dispatcher script, edit the /etc/NetworkManager/dispatcher.d/20-
chrony-onoffline file as follows:
#!/bin/sh
exit 0
NOTE
When you upgrade or reinstall the chrony package, the packaged version of the
dispatcher script replaces your modified dispatcher script.
15.2.5. Setting up chrony for a system in an isolated network
For a network that is never connected to the Internet, one computer is selected to be the primary
timeserver. The other computers are either direct clients of the server, or clients of clients. On the
server, the drift file must be manually set with the average rate of drift of the system clock. If the server
is rebooted, it will obtain the time from surrounding systems and calculate an average to set its system
clock. Thereafter it resumes applying adjustments based on the drift file. The drift file will be updated
automatically when the settime command is used.
The following procedure describes how to set up chrony for a system in an isolated network.
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Procedure
1. On the system selected to be the server, using a text editor running as root, edit
/etc/chrony.conf as follows:
driftfile /var/lib/chrony/drift
commandkey 1
keyfile /etc/chrony.keys
initstepslew 10 client1 client3 client6
local stratum 8
manual
allow 192.0.2.0
Where 192.0.2.0 is the network or subnet address from which the clients are allowed to connect.
2. On the systems selected to be direct clients of the server, using a text editor running as root,
edit the /etc/chrony.conf as follows:
server ntp1.example.net
driftfile /var/lib/chrony/drift
logdir /var/log/chrony
log measurements statistics tracking
keyfile /etc/chrony.keys
commandkey 24
local stratum 10
initstepslew 20 ntp1.example.net
allow 192.0.2.123
Where 192.0.2.123 is the address of the server, and ntp1.example.net is the host name of the
server. Clients with this configuration will resynchronize with the server if it restarts.
On the client systems which are not to be direct clients of the server, the /etc/chrony.conf file should be
the same except that the local and allow directives should be omitted.
In an isolated network, you can also use the local directive that enables a local reference mode, which
allows chronyd operating as an NTP server to appear synchronized to real time, even when it was never
synchronized or the last update of the clock happened a long time ago.
To allow multiple servers in the network to use the same local configuration and to be synchronized to
one another, without confusing clients that poll more than one server, use the orphan option of the
local directive which enables the orphan mode. Each server needs to be configured to poll all other
servers with local. This ensures that only the server with the smallest reference ID has the local
reference active and other servers are synchronized to it. When the server fails, another one will take
over.
15.2.6. Configuring remote monitoring access
chronyc can access chronyd in two ways:
Internet Protocol, IPv4 or IPv6.
Unix domain socket, which is accessible locally by the root or chrony user.
By default, chronyc connects to the Unix domain socket. The default path is
/var/run/chrony/chronyd.sock. If this connection fails, which can happen for example when chronyc is
running under a non-root user, chronyc tries to connect to 127.0.0.1 and then ::1.
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Only the following monitoring commands, which do not affect the behavior of chronyd, are allowed from
the network:
activity
manual list
rtcdata
smoothing
sources
sourcestats
tracking
waitsync
The set of hosts from which chronyd accepts these commands can be configured with the cmdallow
directive in the configuration file of chronyd, or the cmdallow command in chronyc. By default, the
commands are accepted only from localhost (127.0.0.1 or ::1).
All other commands are allowed only through the Unix domain socket. When sent over the network,
chronyd responds with a Not authorised error, even if it is from localhost.
The following procedure describes how to access chronyd remotely with chronyc.
Procedure
1. Allow access from both IPv4 and IPv6 addresses by adding the following to the
/etc/chrony.conf file:
bindcmdaddress 0.0.0.0
or
bindcmdaddress ::
2. Allow commands from the remote IP address, network, or subnet by using the cmdallow
directive.
Add the following content to the /etc/chrony.conf file:
cmdallow 192.168.1.0/24
3. Open port 323 in the firewall to connect from a remote system:
# firewall-cmd --zone=public --add-port=323/udp
Optionally, you can open port 323 permanently using the --permanent option:
# firewall-cmd --permanent --zone=public --add-port=323/udp
4. If you opened port 323 permanently, reload the firewall configuration:
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# firewall-cmd --reload
Additional resources
chrony.conf(5) man page
15.2.7. Managing time synchronization using RHEL System Roles
You can manage time synchronization on multiple target machines using the timesync role. The
timesync role installs and configures an NTP or PTP implementation to operate as an NTP or PTP client
to synchronize the system clock.
Note that using the timesync role also facilitates migration to chrony, because you can use the same
playbook on all versions of Red Hat Enterprise Linux starting with RHEL 6 regardless of whether the
system uses ntp or chrony to implement the NTP protocol.
WARNING
The timesync role replaces the configuration of the given or detected provider
service on the managed host. Previous settings are lost, even if they are not
specified in the role variables. The only preserved setting is the choice of provider if
the timesync_ntp_provider variable is not defined.
The following example shows how to apply the timesync role in a situation with just one pool of servers.
Example 15.1. An example playbook applying the timesync role for a single pool of servers
---
- hosts: timesync-test
vars:
timesync_ntp_servers:
- hostname: 2.rhel.pool.ntp.org
pool: yes
iburst: yes
roles:
- rhel-system-roles.timesync
For a detailed reference on timesync role variables, install the rhel-system-roles package, and see the
README.md or README.html files in the /usr/share/doc/rhel-system-roles/timesync directory.
Additional resources
Preparing a control node and managed nodes to use RHEL System Roles
15.2.8. Additional resources
chronyc(1) man page
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chronyd(8) man page
Frequently Asked Questions
15.3. CHRONY WITH HW TIMESTAMPING
Hardware timestamping is a feature supported in some Network Interface Controller (NICs) which
provides accurate timestamping of incoming and outgoing packets. NTP timestamps are usually created
by the kernel and chronyd with the use of the system clock. However, when HW timestamping is
enabled, the NIC uses its own clock to generate the timestamps when packets are entering or leaving
the link layer or the physical layer. When used with NTP, hardware timestamping can significantly
improve the accuracy of synchronization. For best accuracy, both NTP servers and NTP clients need to
use hardware timestamping. Under ideal conditions, a sub-microsecond accuracy may be possible.
Another protocol for time synchronization that uses hardware timestamping is PTP.
Unlike NTP, PTP relies on assistance in network switches and routers. If you want to reach the best
accuracy of synchronization, use PTP on networks that have switches and routers with PTP support, and
prefer NTP on networks that do not have such switches and routers.
The following sections describe how to:
Verify support for hardware timestamping
Enable hardware timestamping
Configure client polling interval
Enable interleaved mode
Configure server for large number of clients
Verify hardware timestamping
Configure PTP-NTP bridge
15.3.1. Verifying support for hardware timestamping
To verify that hardware timestamping with NTP is supported by an interface, use the ethtool -T
command. An interface can be used for hardware timestamping with NTP if ethtool lists the
SOF_TIMESTAMPING_TX_HARDWARE and SOF_TIMESTAMPING_TX_SOFTWARE capabilities
and also the HWTSTAMP_FILTER_ALL filter mode.
Example 15.2. Verifying support for hardware timestamping on a specific interface
# ethtool -T eth0
Output:
Timestamping parameters for eth0:
Capabilities:
hardware-transmit (SOF_TIMESTAMPING_TX_HARDWARE)
software-transmit (SOF_TIMESTAMPING_TX_SOFTWARE)
hardware-receive (SOF_TIMESTAMPING_RX_HARDWARE)
software-receive (SOF_TIMESTAMPING_RX_SOFTWARE)
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software-system-clock (SOF_TIMESTAMPING_SOFTWARE)
hardware-raw-clock (SOF_TIMESTAMPING_RAW_HARDWARE)
PTP Hardware Clock: 0
Hardware Transmit Timestamp Modes:
off (HWTSTAMP_TX_OFF)
on (HWTSTAMP_TX_ON)
Hardware Receive Filter Modes:
none (HWTSTAMP_FILTER_NONE)
all (HWTSTAMP_FILTER_ALL)
ptpv1-l4-sync (HWTSTAMP_FILTER_PTP_V1_L4_SYNC)
ptpv1-l4-delay-req (HWTSTAMP_FILTER_PTP_V1_L4_DELAY_REQ)
ptpv2-l4-sync (HWTSTAMP_FILTER_PTP_V2_L4_SYNC)
ptpv2-l4-delay-req (HWTSTAMP_FILTER_PTP_V2_L4_DELAY_REQ)
ptpv2-l2-sync (HWTSTAMP_FILTER_PTP_V2_L2_SYNC)
ptpv2-l2-delay-req (HWTSTAMP_FILTER_PTP_V2_L2_DELAY_REQ)
ptpv2-event (HWTSTAMP_FILTER_PTP_V2_EVENT)
ptpv2-sync (HWTSTAMP_FILTER_PTP_V2_SYNC)
ptpv2-delay-req (HWTSTAMP_FILTER_PTP_V2_DELAY_REQ)
15.3.2. Enabling hardware timestamping
To enable hardware timestamping, use the hwtimestamp directive in the /etc/chrony.conf file. The
directive can either specify a single interface, or a wildcard character can be used to enable hardware
timestamping on all interfaces that support it. Use the wildcard specification in case that no other
application, like ptp4l from the linuxptp package, is using hardware timestamping on an interface.
Multiple hwtimestamp directives are allowed in the chrony configuration file.
Example 15.3. Enabling hardware timestamping by using the hwtimestamp directive
hwtimestamp eth0
hwtimestamp eth1
hwtimestamp *
15.3.3. Configuring client polling interval
The default range of a polling interval (64-1024 seconds) is recommended for servers on the Internet.
For local servers and hardware timestamping, a shorter polling interval needs to be configured in order
to minimize offset of the system clock.
The following directive in /etc/chrony.conf specifies a local NTP server using one second polling
interval:
server ntp.local minpoll 0 maxpoll 0
15.3.4. Enabling interleaved mode
NTP servers that are not hardware NTP appliances, but rather general purpose computers running a
software NTP implementation, like chrony, will get a hardware transmit timestamp only after sending a
packet. This behavior prevents the server from saving the timestamp in the packet to which it
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corresponds. In order to enable NTP clients receiving transmit timestamps that were generated after
the transmission, configure the clients to use the NTP interleaved mode by adding the xleave option to
the server directive in /etc/chrony.conf:
server ntp.local minpoll 0 maxpoll 0 xleave
15.3.5. Configuring server for large number of clients
The default server configuration allows a few thousands of clients at most to use the interleaved mode
concurrently. To configure the server for a larger number of clients, increase the clientloglimit directive
in /etc/chrony.conf. This directive specifies the maximum size of memory allocated for logging of
clients' access on the server:
clientloglimit 100000000
15.3.6. Verifying hardware timestamping
To verify that the interface has successfully enabled hardware timestamping, check the system log. The
log should contain a message from chronyd for each interface with successfully enabled hardware
timestamping.
Example 15.4. Log messages for interfaces with enabled hardware timestamping
chronyd[4081]: Enabled HW timestamping on eth0
chronyd[4081]: Enabled HW timestamping on eth1
When chronyd is configured as an NTP client or peer, you can have the transmit and receive
timestamping modes and the interleaved mode reported for each NTP source by the chronyc ntpdata
command:
Example 15.5. Reporting the transmit, receive timestamping and interleaved mode for each NTP
source
# chronyc ntpdata
Output:
Remote address : 203.0.113.15 (CB00710F)
Remote port : 123
Local address : 203.0.113.74 (CB00714A)
Leap status : Normal
Version : 4
Mode : Server
Stratum : 1
Poll interval : 0 (1 seconds)
Precision : -24 (0.000000060 seconds)
Root delay : 0.000015 seconds
Root dispersion : 0.000015 seconds
Reference ID : 47505300 (GPS)
Reference time : Wed May 03 13:47:45 2017
Offset : -0.000000134 seconds
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Peer delay : 0.000005396 seconds
Peer dispersion : 0.000002329 seconds
Response time : 0.000152073 seconds
Jitter asymmetry: +0.00
NTP tests : 111 111 1111
Interleaved : Yes
Authenticated : No
TX timestamping : Hardware
RX timestamping : Hardware
Total TX : 27
Total RX : 27
Total valid RX : 27
Example 15.6. Reporting the stability of NTP measurements
# chronyc sourcestats
With hardware timestamping enabled, stability of NTP measurements should be in tens or hundreds
of nanoseconds, under normal load. This stability is reported in the Std Dev column of the output of
the chronyc sourcestats command:
Output:
210 Number of sources = 1
Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev
ntp.local 12 7 11 +0.000 0.019 +0ns 49ns
15.3.7. Configuring PTP-NTP bridge
If a highly accurate Precision Time Protocol (PTP) primary timeserver is available in a network that does
not have switches or routers with PTP support, a computer may be dedicated to operate as a PTP client
and a stratum-1 NTP server. Such a computer needs to have two or more network interfaces, and be
close to the primary timeserver or have a direct connection to it. This will ensure highly accurate
synchronization in the network.
Configure the ptp4l and phc2sys programs from the linuxptp packages to use one interface to
synchronize the system clock using PTP.
Configure chronyd to provide the system time using the other interface:
Example 15.7. Configuring chronyd to provide the system time using the other interface
bindaddress 203.0.113.74
hwtimestamp eth1
local stratum 1
15.4. ACHIEVING SOME SETTINGS PREVIOUSLY SUPPORTED BY NTP
IN CHRONY
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Some settings that were in previous major version of Red Hat Enterprise Linux supported by ntp, are not
supported by chrony. The following sections list such settings, and describe ways to achieve them on a
system with chrony.
15.4.1. Monitoring by ntpq and ntpdc
chronyd cannot be monitored by the ntpq and ntpdc utilities from the ntp distribution, because
chrony does not support the NTP modes 6 and 7. It supports a different protocol and chronyc is the
client implementation. For more information, see the chronyc(1) man page.
To monitor the status of the system clock sychronized by chronyd, you can:
Use the tracking command
Use the ntpstat utility, which supports chrony and provides a similar output as it used to with
ntpd
Example 15.8. Using the tracking command
$ chronyc -n tracking
Reference ID : 0A051B0A (10.5.27.10)
Stratum : 2
Ref time (UTC) : Thu Mar 08 15:46:20 2018
System time : 0.000000338 seconds slow of NTP time
Last offset : +0.000339408 seconds
RMS offset : 0.000339408 seconds
Frequency : 2.968 ppm slow
Residual freq : +0.001 ppm
Skew : 3.336 ppm
Root delay : 0.157559142 seconds
Root dispersion : 0.001339232 seconds
Update interval : 64.5 seconds
Leap status : Normal
Example 15.9. Using the ntpstat utility
$ ntpstat
synchronised to NTP server (10.5.27.10) at stratum 2
time correct to within 80 ms
polling server every 64 s
15.4.2. Using authentication mechanism based on public key cryptography
In Red Hat Enterprise Linux 7, ntp supported Autokey, which is an authentication mechanism based on
public key cryptography.
In Red Hat Enterprise Linux 8, chronyd supports Network Time Security (NTS), a modern secure
authentication mechanism, instead of Autokey. For more information, see Overview of Network Time
Security (NTS) in chrony.
15.4.3. Using ephemeral symmetric associations
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In Red Hat Enterprise Linux 7, ntpd supported ephemeral symmetric associations, which can be
mobilized by packets from peers which are not specified in the ntp.conf configuration file. In Red Hat
Enterprise Linux 8, chronyd needs all peers to be specified in chrony.conf. Ephemeral symmetric
associations are not supported.
Note that using the client/server mode enabled by the server or pool directive is more secure
compared to the symmetric mode enabled by the peer directive.
15.4.4. multicast/broadcast client
Red Hat Enterprise Linux 7 supported the broadcast/multicast NTP mode, which simplifies
configuration of clients. With this mode, clients can be configured to just listen for packets sent to a
multicast/broadcast address instead of listening for specific names or addresses of individual servers,
which may change over time.
In Red Hat Enterprise Linux 8, chronyd does not support the broadcast/multicast mode. The main
reason is that it is less accurate and less secure than the ordinary client/server and symmetric modes.
There are several options of migration from an NTP broadcast/multicast setup:
Configure DNS to translate a single name, such as ntp.example.com, to multiple addresses of
different servers
Clients can have a static configuration using only a single pool directive to synchronize with
multiple servers. If a server from the pool becomes unreacheable, or otherwise unsuitable for
synchronization, the clients automatically replace it with another server from the pool.
Distribute the list of NTP servers over DHCP
When NetworkManager gets a list of NTP servers from the DHCP server, chronyd is
automatically configured to use them. This feature can be disabled by adding PEERNTP=no to
the /etc/sysconfig/network file.
Use the Precision Time Protocol (PTP)
This option is suitable mainly for environments where servers change frequently, or if a larger
group of clients needs to be able to synchronize to each other without having a designated
server.
PTP was designed for multicast messaging and works similarly to the NTP broadcast mode. A
PTP implementation is available in the linuxptp package.
PTP normally requires hardware timestamping and support in network switches to perform well.
However, PTP is expected to work better than NTP in the broadcast mode even with software
timestamping and no support in network switches.
In networks with very large number of PTP clients in one communication path, it is
recommended to configure the PTP clients with the hybrid_e2e option to reduce the amount
of network traffic generated by the clients. You can configure a computer running chronyd as
an NTP client, and possibly NTP server, to operate also as a primary PTP timeserver to
distribute synchronized time to a large number of computers using multicast messaging.
15.5. OVERVIEW OF NETWORK TIME SECURITY (NTS) IN CHRONY
Network Time Security (NTS) is an authentication mechanism for Network Time Protocol (NTP),
designed to scale substantial clients. It verifies that the packets received from the server machines are
unaltered while moving to the client machine. Network Time Security (NTS) includes a Key
Establishment (NTS-KE) protocol that automatically creates the encryption keys used between the
server and its clients.
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WARNING
NTS is not compatible with the FIPS and OSPP profile. When you enable the FIPS
and OSPP profile, chronyd that is configured with NTS can abort with a fatal
message. You can disable the OSPP profile and FIPS mode for chronyd service by
adding the GNUTLS_FORCE_FIPS_MODE=0 to the /etc/sysconfig/chronyd file.
15.5.1. Enabling Network Time Security (NTS) in the client configuration file
By default, Network Time Security (NTS) is not enabled. You can enable NTS in the /etc/chrony.conf.
For that, perform the following steps:
Prerequisites
Server with the NTS support
Procedure
In the client configuration file:
1. Specify the server with the nts option in addition to the recommended iburst option.
For example:
server time.example.com iburst nts
server nts.netnod.se iburst nts
server ptbtime1.ptb.de iburst nts
2. To avoid repeating the Network Time Security-Key Establishment (NTS-KE) session during
system boot, add the following line to chrony.conf, if it is not present:
ntsdumpdir /var/lib/chrony
3. Add the following line to /etc/sysconfig/network to disable synchronization with Network Time
Protocol (NTP) servers provided by DHCP:
PEERNTP=no
4. Save your changes.
5. Restart the chronyd service:
systemctl restart chronyd
Verification
Verify if the NTS keys were successfully established:
# chronyc -N authdata
Name/IP address Mode KeyID Type KLen Last Atmp NAK Cook CLen
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================================================================
time.example.com NTS 1 15 256 33m 0 0 8 100
nts.sth1.ntp.se NTS 1 15 256 33m 0 0 8 100
nts.sth2.ntp.se NTS 1 15 256 33m 0 0 8 100
The KeyID, Type, and KLen should have non-zero values. If the value is zero, check the system
log for error messages from chronyd.
Verify the client is making NTP measurements:
# chronyc -N sources
MS Name/IP address Stratum Poll Reach LastRx Last sample
=========================================================
time.example.com 3 6 377 45 +355us[ +375us] +/- 11ms
nts.sth1.ntp.se 1 6 377 44 +237us[ +237us] +/- 23ms
nts.sth2.ntp.se 1 6 377 44 -170us[ -170us] +/- 22ms
The Reach column should have a non-zero value; ideally 377. If the value rarely gets 377 or
never gets to 377, it indicates that NTP requests or responses are getting lost in the network.
Additional resources
chrony.conf(5) man page
15.5.2. Enabling Network Time Security (NTS) on the server
If you run your own Network Time Protocol (NTP) server, you can enable the server Network Time
Security (NTS) support to facilitate its clients to synchronize securely.
If the NTP server is a client of other servers, that is, it is not a Stratum 1 server, it should use NTS or
symmetric key for its synchronization.
Prerequisites
Server private key in PEM format
Server certificate with required intermediate certificates in PEM format
Procedure
1. Specify the private key and the certificate file in chrony.conf. For example:
ntsserverkey /etc/pki/tls/private/.key
ntsservercert /etc/pki/tls/certs/.crt
2. Ensure that both the key and certificate files are readable by the chrony system user, by setting
the group ownership. For example:
# chown :chrony /etc/pki/tls//.
3. Ensure the ntsdumpdir /var/lib/chrony directive is present in the chrony.conf.
4. Restart the chronyd service:
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# systemctl restart chronyd
IMPORTANT
If the server has a firewall, it needs to allow both the UDP 123 and TCP 4460
ports for NTP and Network Time Security-Key Establishment (NTS-KE).
Verification
Perform a quick test from a client machine with the following command:
$ chronyd -Q -t 3 'server
ntp-server.example.net iburst nts maxsamples 1'
2021-09-15T13:45:26Z chronyd version 4.1 starting (+CMDMON +NTP +REFCLOCK +RTC
+PRIVDROP +SCFILTER +SIGND +ASYNCDNS +NTS +SECHASH +IPV6 +DEBUG)
2021-09-15T13:45:26Z Disabled control of system clock
2021-09-15T13:45:28Z System clock wrong by 0.002205 seconds (ignored)
2021-09-15T13:45:28Z chronyd exiting
The System clock wrong message indicates the NTP server is accepting NTS-KE connections
and responding with NTS-protected NTP messages.
Verify the NTS-KE connections and authenticated NTP packets observed on the server:
# chronyc serverstats
NTP packets received : 7
NTP packets dropped : 0
Command packets received : 22
Command packets dropped : 0
Client log records dropped : 0
NTS-KE connections accepted: 1
NTS-KE connections dropped : 0
Authenticated NTP packets: 7
If the value of the NTS-KE connections accepted and Authenticated NTP packets field is a
non-zero value, it means that at least one client was able to connect to the NTS-KE port and
send an authenticated NTP request.
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CHAPTER 16. USING LANGPACKS
Langpacks are meta-packages which install extra add-on packages containing translations, dictionaries
and locales for every package installed on the system.
On a Red Hat Enterprise Linux 8 system, langpacks installation is based on the langpacks-
language meta-packages and RPM weak dependencies (Supplements tag).
There are two prerequisites to be able to use langpacks for a selected language. If these prerequisites
are fulfilled, the language meta-packages pull their langpack for the selected language automatically in
the transaction set.
Prerequisites
The langpacks- language meta-package for the selected language has been
installed on the system.
On Red Hat Enterprise Linux 8, the langpacks meta packages are installed automatically with
the initial installation of the operating system using the Anaconda installer, because these
packages are available in the in Application Stream repository.
For more information, see Checking languages that provide langpacks .
The base package, for which you want to search the locale packages, has already been installed
on the system.
16.1. CHECKING LANGUAGES THAT PROVIDE LANGPACKS
Folow this procedure to check which languages provide langpacks.
Procedure
Execute the following command:
# yum list langpacks-*
16.2. WORKING WITH RPM WEAK DEPENDENCY-BASED LANGPACKS
This section describes multiple actions that you may want to perform when querying RPM weak
dependency-based langpacks, installing or removing language support.
16.2.1. Listing already installed language support
To list the already installed language support, use this procedure.
Procedure
Execute the following command:
# yum list installed langpacks*
16.2.2. Checking the availability of language support
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To check if language support is available for any language, use the following procedure.
Procedure
Execute the following command:
# yum list available langpacks*
16.2.3. Listing packages installed for a language
To list what packages get installed for any language, use the following procedure:
Procedure
Execute the following command:
# yum repoquery --whatsupplements langpacks-
16.2.4. Installing language support
To add new a language support, use the following procedure.
Procedure
Execute the following command:
# yum install langpacks-
16.2.5. Removing language support
To remove any installed language support, use the following procedure.
Procedure
Execute the following command:
# yum remove langpacks-
16.3. SAVING DISK SPACE BY USING GLIBC-LANGPACK-
Currently, all locales are stored in the /usr/lib/locale/locale-archive file, which requires a lot of disk
space.
On systems where disk space is a critical issue, such as containers and cloud images, or only a few locales
are needed, you can use the glibc locale langpack packages (glibc-langpack-).
To install locales individually, and thus gain a smaller package installation footprint, use the following
procedure.
Procedure
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Execute the following command:
# yum install glibc-langpack-
When installing the operating system with Anaconda, glibc-langpack- is installed for the
language you used during the installation and also for the languages you selected as additional
languages. Note that glibc-all-langpacks, which contains all locales, is installed by default, so some
locales are duplicated. If you installed glibc-langpack- for one or more selected
languages, you can delete glibc-all-langpacks after the installation to save the disk space.
Note that installing only selected glibc-langpack- packages instead of glibc-alllangpacks has impact on run time performance.
NOTE
If disk space is not an issue, keep all locales installed by using the glibc-all-langpacks
package.
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CHAPTER 17. DUMPING A CRASHED KERNEL FOR LATER
ANALYSIS
To analyze why a system crashed, you can use the kdump service to save the contents of the system’s
memory for later analysis. This section provides a brief introduction to kdump, and information about
configuring kdump using the RHEL web console or using the corresponding RHEL system role.
17.1. WHAT IS KDUMP
kdump is a service which provides a crash dumping mechanism and generates a dump file, known as
crash dump or a vmcore file. The vmcore file has the contents of the system memory that helps in
analysis and troubleshooting. kdump uses the kexec system call to boot into the second kernel, a
capture kernel without a reboot and then captures the contents of the crashed kernel’s memory and
saves it into a file. The second kernel is available in a reserved part of the system memory.
IMPORTANT
A kernel crash dump can be the only information available if a system failure occur.
Therefore, operational kdump is important in mission-critical environments. Red Hat
advises to regularly update and test kexec-tools in your normal kernel update cycle. This
is especially important when you install new kernel features.
You can enable kdump for all installed kernels on a machine or only for specified kernels. This is useful
when there are multiple kernels used on a machine, some of which are stable enough that there is no
concern that they could crash. When you install kdump, a default /etc/kdump.conf file is created. The
/etc/kdump.conf file includes the default minimum kdump configuration, which you can edit to
customize the kdump configuration.
17.2. CONFIGURING KDUMP MEMORY USAGE AND TARGET
LOCATION IN WEB CONSOLE
You can configure the memory reserve for the kdump kernel and also specify the target location to
capture the vmcore dump file with the RHEL web console interface.
Procedure
1. In the web console, open the Kernel Dump tab and start the kdump service by setting the
Kernel crash dumpswitch to on.
2. Configure the kdump memory usage in the command line.
3. In the Kernel Dump tab, go to Crash dump location and click the link with the path to the
dump location.
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4. Specify the target directory for saving the vmcore dump file:
For a local filesystem, select Local Filesystem from the drop-down menu.
For a remote system by using the SSH protocol, select Remote over SSH from the dropdown menu and specify the following fields:
In the Server field, enter the remote server address
In the ssh key field, enter the ssh key location
In the Directory field, enter the target directory
For a remote system by using the NFS protocol, select Remote over NFS from the dropdown menu and specify the following fields:
In the Server field, enter the remote server address
In the Export field, enter the location of the shared folder of an NFS server
In the Directory field, enter the target directory
NOTE
You can reduce the size of the vmcore file by selecting the
Compression check box.
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Verification
1. Click the Test configuration.
2. Click Crash system under Test kdump settings.
WARNING
When you initiate the system crash, the kernel’s operation stops and results
in a system crash with data loss.
Additional resources
Supported kdump targets
Using secure communications between two systems with OpenSSH
Getting started using the RHEL web console
17.3. KDUMP USING RHEL SYSTEM ROLES
RHEL System Roles is a collection of Ansible roles and modules that provide a consistent configuration
interface to remotely manage multiple RHEL systems. The kdump role enables you to set basic kernel
dump parameters on multiple systems.
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WARNING
The kdump role replaces the kdump configuration of the managed hosts entirely
by replacing the /etc/kdump.conf file. Additionally, if the kdump role is applied, all
previous kdump settings are also replaced, even if they are not specified by the role
variables, by replacing the /etc/sysconfig/kdump file.
The following example playbook shows how to apply the kdump system role to set the location of the
crash dump files:
---
- hosts: kdump-test
vars:
kdump_path: /var/crash
roles:
- rhel-system-roles.kdump
For a detailed reference on kdump role variables, install the rhel-system-roles package, and see the
README.md or README.html files in the /usr/share/doc/rhel-system-roles/kdump directory.
Additional resources
Introduction to RHEL System Roles
17.4. ADDITIONAL RESOURCES
Installing kdump
Configuring kdump on the command line
Configuring kdump in the web console
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CHAPTER 18. RECOVERING AND RESTORING A SYSTEM
To recover and restore a system using an existing backup, Red Hat Enterprise Linux provides the Relaxand-Recover (ReaR) utility.
You can use the utility as a disaster recovery solution and also for system migration.
The utility enables you to perform the following tasks:
Produce a bootable image and restore the system from an existing backup, using the image.
Replicate the original storage layout.
Restore user and system files.
Restore the system to a different hardware.
Additionally, for disaster recovery, you can also integrate certain backup software with ReaR.
Setting up ReaR involves the following high-level steps:
1. Install ReaR.
2. Modify ReaR configuration file, to add backup method details.
3. Create rescue system.
4. Generate backup files.
18.1. SETTING UP REAR
Use the following steps to install the package for using the Relax-and-Recover (ReaR) utility, create a
rescue system, configure and generate a backup.
Prerequisites
Necessary configurations as per the backup restore plan are ready.
Note that you can use the NETFS backup method, a fully-integrated and built-in method with
ReaR.
Procedure
1. Install the ReaR utility by running the following command:
# yum install rear
2. Modify the ReaR configuration file in an editor of your choice, for example:
# vi /etc/rear/local.conf
3. Add the backup setting details to /etc/rear/local.conf. For example, in the case of the NETFS
backup method, add the following lines:
BACKUP=NETFS
BACKUP_URL=backup.location
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Replace backup.location by the URL of your backup location.
4. To configure ReaR to keep the previous backup archive when the new one is created, also add
the following line to the configuration file:
NETFS_KEEP_OLD_BACKUP_COPY=y
5. To make the backups incremental, meaning that only the changed files are backed up on each
run, add the following line:
BACKUP_TYPE=incremental
6. Create a rescue system:
# rear mkrescue
7. Take a backup as per the restore plan. For example, in the case of the NETFS backup method,
run the following command:
# rear mkbackuponly
Alternatively, you can create the rescue system and the backup in a single step by running the
following command:
# rear mkbackup
This command combines the functionality of the rear mkrescue and rear mkbackuponly
commands.
18.2. USING A REAR RESCUE IMAGE ON THE 64-BIT IBM Z
ARCHITECTURE
Basic Relax and Recover (ReaR) functionality is now available on the 64-bit IBM Z architecture as a
Technology Preview. You can create a ReaR rescue image on IBM Z only in the z/VM environment.
Backing up and recovering logical partitions (LPARs) has not been tested.
IMPORTANT
ReaR on the 64-bit IBM Z architecture is supported only with the rear package version
2.6-9.el8 or later. Earlier versions are available as a Technology Preview feature only. For
more information about the support scope of Red Hat Technology Preview features, see
https://access.redhat.com/support/offerings/techpreview.
The only output method currently available is Initial Program Load (IPL). IPL produces a kernel and an
initial RAM disk (initrd) that can be used with the zIPL boot loader.
Prerequisites
ReaR is installed.
To install ReaR, run the yum install rear command
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Procedure
Add the following variables to the /etc/rear/local.conf to configure ReaR for producing a rescue image
on the 64-bit IBM Z architecture:
1. To configure the IPL output method, add OUTPUT=IPL.
2. To configure the backup method and destination, add BACKUP and BACKUP_URL variables.
For example:
BACKUP=NETFS
BACKUP_URL=nfs:///
IMPORTANT
The local backup storage is currently not supported on the 64-bit IBM Z
architecture.
3. Optionally, you can also configure the OUTPUT_URL variable to save the kernel and initrd files.
By default, the OUTPUT_URL is aligned with BACKUP_URL.
4. To perform backup and rescue image creation:
# rear mkbackup
5. This creates the kernel and initrd files at the location specified by the BACKUP_URL or
OUTPUT_URL (if set) variable, and a backup using the specified backup method.
6. To recover the system, use the ReaR kernel and initrd files created in step 3, and boot from a
Direct Attached Storage Device (DASD) or a Fibre Channel Protocol (FCP)-attached SCSI
device prepared with the zipl boot loader, kernel, and initrd. For more information, see Using a
Prepared DASD.
7. When the rescue kernel and initrd get booted, it starts the ReaR rescue environment. Proceed
with system recovery.
WARNING
Currently, the rescue process reformats all the DASDs (Direct Attached Storage
Devices) connected to the system. Do not attempt a system recovery if there is any
valuable data present on the system storage devices. This also includes the device
prepared with the zipl boot loader, ReaR kernel, and initrd that were used to boot
into the rescue environment. Ensure to keep a copy.
Additional resources
Installing under z/VM
Using a Prepared DASD
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CHAPTER 19. INSTALLING AND USING DYNAMIC
PROGRAMMING LANGUAGES
Red Hat provides different programming languages, such as Python, PHP, and Tcl/TK. Use them to
develop own applications and services.
19.1. INTRODUCTION TO PYTHON
Python is a high-level programming language that supports multiple programming paradigms, such as
object-oriented, imperative, functional, and procedural paradigms. Python has dynamic semantics and
can be used for general-purpose programming.
With Red Hat Enterprise Linux, many packages that are installed on the system, such as packages
providing system tools, tools for data analysis, or web applications, are written in Python. To use these
packages, you must have the python* packages installed.
19.1.1. Python versions
Two incompatible versions of Python are widely used, Python 2.x and Python 3.x. RHEL 8 provides the
following versions of Python.
Table 19.1. Python versions in RHEL 8
Version Package to
install
Command examples Available since Life cycle
Python 3.6 python3,
python36
python3, python3.6,
pip3, pip3.6
RHEL 8.0 full RHEL 8
Python 2.7 python2 python2, pip2 RHEL 8.0 shorter
Python 3.8 python38 python3.8, pip3.8 RHEL 8.2 shorter
Python 3.9 python39 python3.9, pip3.9 RHEL 8.4 shorter
Python 3.11 python3.11 python3.11, pip3.11 RHEL 8.8 shorter
For details about the length of support, see Red Hat Enterprise Linux Life Cycle and Red Hat Enterprise
Linux Application Streams Life Cycle.
Each of the Python versions up to 3.9 is distributed in a separate module. Python 3.11 is distributed as a
suite of non-modular RPM packages, including the python3.11 package.
You can install multiple Python versions in parallel on the same RHEL 8 system.
IMPORTANT
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IMPORTANT
Always specify the version of Python when installing it, invoking it, or otherwise
interacting with it. For example, use python3 instead of python in package and
command names. All Python-related commands must also include the version, for
example, pip3, pip2, pip3.8, pip3.9, or pip3.11.
The unversioned python command (/usr/bin/python) is not available by default in RHEL
8. You can configure it using the alternatives command; for instructions, see Configuring
the unversioned Python
Any manual changes to /usr/bin/python, except changes made using the alternatives
command, might be overwritten upon an update.
As a system administrator, use Python 3 for the following reasons:
Python 3 represents the main development direction of the Python project.
Support for Python 2 in the upstream community ended in 2020.
Popular Python libraries are discontinuing Python 2 support in upstream.
Python 2 in Red Hat Enterprise Linux 8 will have a shorter life cycle and aims to facilitate a
smoother transition to Python 3 for customers.
For developers, Python 3 has the following advantages over Python 2:
Python 3 enables you to write expressive, maintainable, and correct code more easily.
Code written in Python 3 will have greater longevity.
Python 3 has new features, including asyncio, f-strings, advanced unpacking, keyword-only
arguments, and chained exceptions.
However, legacy software might require /usr/bin/python to be configured to Python 2. For this reason,
no default python package is distributed with Red Hat Enterprise Linux 8, and you can choose between
using Python 2 and 3 as /usr/bin/python, as described in Configuring the unversioned Python.
IMPORTANT
System tools in Red Hat Enterprise Linux 8 use Python version 3.6 provided by the
internal platform-python package, which is not intended to be used directly by
customers. It is recommended to use the python3 or python3.6 command from the
python36 package for Python 3.6, or to use later Python versions.
Do not remove the platform-python package from RHEL 8 because other packages
require it.
19.1.2. Notable differences between Python versions
Python versions included in RHEL 8 differ in various aspects.
Python bindings
The python38 and python39 modules and the python3.11 package suite do not include the same
bindings to system tools (RPM, DNF, SELinux, and others) that are provided for the python36 module.
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Therefore, use python36 in instances where the greatest compatibility with the base operating system
or binary compatibility is necessary. In unique instances where system bindings are necessary together
with later versions of various Python modules, use the python36 module in combination with third-party
upstream Python modules installed through pip into Python’s venv or virtualenv environments.
Python 3.11 virtual environments must be created using venv instead of virtualenv
The virtualenv utility in RHEL 8, provided by the python3-virtualenv package, is not compatible with
Python 3.11. An attempt to create a virtual environment by using virtualenv will fail with the following
error message:
$ virtualenv -p python3.11 venv3.11
Running virtualenv with interpreter /usr/bin/python3.11
ERROR: Virtual environments created by virtualenv < 20 are not compatible with Python 3.11.
ERROR: Use python3.11 -m venv instead.
To create Python 3.11 virtual environments, use the python3.11 -m venv command instead, which uses
the venv module from the standard library.
19.2. INSTALLING AND USING PYTHON
In Red Hat Enterprise Linux 8, Python 3 is distributed in versions 3.6, 3.8, and 3.9, provided by the
python36, python38, and python39 modules, and the python3.11 package suite in the AppStream
repository.
WARNING
Using the unversioned python command to install or run Python does not work by
default due to ambiguity. Always specify the version of Python, or configure the
system default version by using the alternatives command.
19.2.1. Installing Python 3
By design, you can install RHEL 8 modules in parallel, including the python27, python36, python38, and
python39 modules, and the python3.11 package suite.
You can install Python 3.8, Python 3.9, and Python 3.11, including packages built for each version, in
parallel with Python 3.6 on the same system, with the exception of the mod_wsgi module. Due to a
limitation of the Apache HTTP Server, only one of the python3-mod_wsgi, python38-mod_wsgi,
python39-mod_wsgi, or python3.11-mod_wsgi packages can be installed on a system.
Procedure
To install Python 3.6 from the python36 module, use:
# yum install python3
The python36:3.6 module stream is enabled automatically.
To install Python 3.8 from the python38 module, use:
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191
# yum install python38
The python38:3.8 module stream is enabled automatically.
To install Python 3.9 from the python39 module, use:
# yum install python39
The python39:3.9 module stream is enabled automatically.
To install Python 3.11 from the python3.11 RPM package, use:
# yum install python3.11
Verification steps
To verify the Python version installed on your system, use the --version option with the python
command specific for your required version of Python.
For Python 3.6:
$ python3 --version
For Python 3.8:
$ python3.8 --version
For Python 3.9:
$ python3.9 --version
For Python 3.11:
$ python3.11 --version
Additional resources
Installing, managing, and removing user-space components
19.2.2. Installing additional Python 3 packages
Packages with add-on modules for Python 3.6 generally use the python3- prefix, packages for Python
3.8 include the python38- prefix, packages for Python 3.9 include the python39- prefix, and packages
for Python 3.11 include the python3.11- prefix. Always include the prefix when installing additional
Python packages, as shown in the examples below.
Procedure
To install the Requests module for Python 3.6, use:
# yum install python3-requests
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To install the Cython extension to Python 3.8, use:
# yum install python38-Cython
To install the pip package installer from Python 3.9, use:
# yum install python39-pip
To install the pip package installer from Python 3.11, use:
# yum install python3.11-pip
Additional resources
Upstream documentation about Python add-on modules
19.2.3. Installing additional Python 3 tools for developers
Additional Python tools for developers are distributed mostly through the CodeReady Linux Builder
(CRB) repository in the respective python38-devel or python39-devel module, or the python3.11-*
packages.
The python3-pytest package (for Python 3.6) and its dependencies are available in the AppStream
repository.
The CRB repository provides:
The python38-devel module, which contains the python38-pytest package and its
dependencies.
The python39-devel module, which contains the python39-pytest package and its
dependencies, and the python39-debug and python39-Cython packages.
The python3.11-* packages, which include:
python3.11-pytest and its dependencies
python3.11-idle
python3.11-debug
python3.11-Cython
IMPORTANT
The content in the CodeReady Linux Builder repository is unsupported by Red Hat.
NOTE
Not all upstream Python-related packages are available in RHEL.
To install the python3*-pytest package, use the following procedure.
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193
Procedure
1. For Python 3.8 and later, enable the CodeReady Linux Builder repository:
# subscription-manager repos --enable codeready-builder-for-rhel-8-x86_64-rpms
2. For Python 3.8 or 3.9, enable the respective python3*-devel module, for example:
# yum module enable python39-devel
3. Install the python3*-pytest package:
For Python 3.6:
# yum install python3-pytest
For Python 3.8:
# yum install python38-pytest
For Python 3.9:
# yum install python39-pytest
For Python 3.11:
# yum install python3.11-pytest
Additional resources
How to enable and make use of content within CodeReady Linux Builder
Package manifest
19.2.4. Installing Python 2
Some applications and scripts have not yet been fully ported to Python 3 and require Python 2 to run.
Red Hat Enterprise Linux 8 allows parallel installation of Python 3 and Python 2. If you need the Python
2 functionality, install the python27 module, which is available in the AppStream repository.
WARNING
Note that Python 3 is the main development direction of the Python project.
Support for Python 2 is being phased out. The python27 module has a shorter
support period than Red Hat Enterprise Linux 8.
Procedure
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To install Python 2.7 from the python27 module, use:
# yum install python2
The python27:2.7 module stream is enabled automatically.
Packages with add-on modules for Python 2 generally use the python2- prefix. Always include the prefix
when installing additional Python packages, as shown in the examples below.
To install the Requests module for Python 2, use:
# yum install python2-requests
To install the Cython extension to Python 2, use:
# yum install python2-Cython
Verification steps
To verify the Python version installed on your system, use:
$ python2 --version
NOTE
By design, you can install RHEL 8 modules in parallel, including the python27, python36,
python38, and python39 modules.
Additional resources
Installing, managing, and removing user-space components in RHEL 8
19.2.5. Migrating from Python 2 to Python 3
As a developer, you may want to migrate your former code that is written in Python 2 to Python 3.
For more information about how to migrate large code bases to Python 3, see The Conservative Python
3 Porting Guide.
Note that after this migration, the original Python 2 code becomes interpretable by the Python 3
interpreter and stays interpretable for the Python 2 interpreter as well.
19.2.6. Using Python
When running the Python interpreter or Python-related commands, always specify the version.
Prerequisites
Ensure that the required version of Python is installed.
If you want to download and install third-party applications for Python 3.11, install the
python3.11-pip package.
Procedure
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Procedure
To run the Python 3.6 interpreter or related commands, use, for example:
$ python3
$ python3 -m venv --help
$ python3 -m pip install package
$ pip3 install package
To run the Python 3.8 interpreter or related commands, use, for example:
$ python3.8
$ python3.8 -m venv --help
$ python3.8 -m pip install package
$ pip3.8 install package
To run the Python 3.9 interpreter or related commands, use, for example:
$ python3.9
$ python3.9 -m venv --help
$ python3.9 -m pip install package
$ pip3.9 install package
To run the Python 3.11 interpreter or related commands, use, for example:
$ python3.11
$ python3.11 -m venv --help
$ python3.11 -m pip install package
$ pip3.11 install package
To run the Python 2 interpreter or related commands, use, for example:
$ python2
$ python2 -m pip install package
$ pip2 install package
19.3. CONFIGURING THE UNVERSIONED PYTHON
System administrators can configure the unversioned python command, located at /usr/bin/python,
using the alternatives command. Note that the required package, python3, python38, python39,
python3.11, or python2, must be installed before configuring the unversioned command to the
respective version.
IMPORTANT
The /usr/bin/python executable is controlled by the alternatives system. Any manual
changes may be overwritten upon an update.
Additional Python-related commands, such as pip3, do not have configurable
unversioned variants.
19.3.1. Configuring the unversioned python command directly
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You can configure the unversioned python command directly to a selected version of Python.
Prerequisites
Ensure that the required version of Python is installed.
Procedure
To configure the unversioned python command to Python 3.6, use:
# alternatives --set python /usr/bin/python3
To configure the unversioned python command to Python 3.8, use:
# alternatives --set python /usr/bin/python3.8
To configure the unversioned python command to Python 3.9, use:
# alternatives --set python /usr/bin/python3.9
To configure the unversioned python command to Python 3.11, use:
# alternatives --set python /usr/bin/python3.11
To configure the unversioned python command to Python 2, use:
# alternatives --set python /usr/bin/python2
19.3.2. Configuring the unversioned python command to the required Python
version interactively
You can configure the unversioned python command to the required Python version interactively.
Prerequisites
Ensure that the required version of Python is installed.
Procedure
1. To configure the unversioned python command interactively, use:
# alternatives --config python
2. Select the required version from the provided list.
3. To reset this configuration and remove the unversioned python command, use:
# alternatives --auto python
19.3.3. Additional resources
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alternatives(8) and unversioned-python(1) man pages
19.4. PACKAGING PYTHON 3 RPMS
Most Python projects use Setuptools for packaging, and define package information in the setup.py
file. For more information about Setuptools packaging, see the Setuptools documentation.
You can also package your Python project into an RPM package, which provides the following
advantages compared to Setuptools packaging:
Specification of dependencies of a package on other RPMs (even non-Python)
Cryptographic signing
With cryptographic signing, content of RPM packages can be verified, integrated, and tested
with the rest of the operating system.
19.4.1. SPEC file description for a Python package
A SPEC file contains instructions that the rpmbuild utility uses to build an RPM. The instructions are
included in a series of sections. A SPEC file has two main parts in which the sections are defined:
Preamble (contains a series of metadata items that are used in the Body)
Body (contains the main part of the instructions)
An RPM SPEC file for Python projects has some specifics compared to non-Python RPM SPEC files.
Most notably, a name of any RPM package of a Python library must always include the prefix
determining the version, for example, python3 for Python 3.6, python38 for Python 3.8, python39 for
Python 3.9, or python3.11 for Python 3.11.
Other specifics are shown in the following SPEC file example for thepython3-detox package. For
description of such specifics, see the notes below the example.
%global modname detox 1
Name: python3-detox 2
Version: 0.12
Release: 4%{?dist}
Summary: Distributing activities of the tox tool
License: MIT
URL: https://pypi.io/project/detox
Source0: https://pypi.io/packages/source/d/%{modname}/%{modname}-%{version}.tar.gz
BuildArch: noarch
BuildRequires: python36-devel 3
BuildRequires: python3-setuptools
BuildRequires: python36-rpm-macros
BuildRequires: python3-six
BuildRequires: python3-tox
BuildRequires: python3-py
BuildRequires: python3-eventlet
%?python_enable_dependency_generator 4
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1
2
3
4
5
6
The modname macro contains the name of the Python project. In this example it is detox.
When packaging a Python project into RPM, the python3 prefix always needs to be added to the
original name of the project. The original name here is detox and the name of the RPMis
python3-detox.
BuildRequires specifies what packages are required to build and test this package. In
BuildRequires, always include items providing tools necessary for building Python packages:
python36-devel and python3-setuptools. The python36-rpm-macros package is required so
that files with /usr/bin/python3 interpreter directives are automatically changed to
/usr/bin/python3.6.
Every Python package requires some other packages to work correctly. Such packages need to be
specified in the SPEC file as well. To specify the dependencies, you can use the
%python_enable_dependency_generator macro to automatically use dependencies defined in
the setup.py file. If a package has dependencies that are not specified using Setuptools, specify
them within additional Requires directives.
The %py3_build and %py3_install macros run the setup.py build and setup.py install commands,
respectively, with additional arguments to specify installation locations, the interpreter to use, and
other details.
The check section provides a macro that runs the correct version of Python. The %{__python3}
macro contains a path for the Python 3 interpreter, for example /usr/bin/python3. We recommend
to always use the macro rather than a literal path.
%description
Detox is the distributed version of the tox python testing tool. It makes efficient use of multiple CPUs
by running all possible activities in parallel.
Detox has the same options and configuration that tox has, so after installation you can run it in the
same way and with the same options that you use for tox.
$ detox
%prep
%autosetup -n %{modname}-%{version}
%build
%py3_build 5
%install
%py3_install
%check
%{__python3} setup.py test 6
%files -n python3-%{modname}
%doc CHANGELOG
%license LICENSE
%{_bindir}/detox
%{python3_sitelib}/%{modname}/
%{python3_sitelib}/%{modname}-%{version}*
%changelog
...
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19.4.2. Common macros for Python 3 RPMs
In a SPEC file, always use the macros that are described in the following Macros for Python 3 RPMs
table rather than hardcoding their values.
In macro names, always use python3 or python2 instead of unversioned python. Configure the
particular Python 3 version in the BuildRequires section of the SPEC file to python36-rpm-macros,
python38-rpm-macros, python39-rpm-macros, or python3.11-rpm-macros.
Table 19.2. Macros for Python 3 RPMs
Macro Normal Definition Description
%{__python3} /usr/bin/python3 Python 3 interpreter
%{python3_version} 3.6 The full version of the Python 3
interpreter.
%{python3_sitelib} /usr/lib/python3.6/site-packages Where pure-Python modules are
installed.
%{python3_sitearch} /usr/lib64/python3.6/sitepackages
Where modules containing
architecture-specific extensions
are installed.
%py3_build Runs the setup.py build
command with arguments suitable
for a system package.
%py3_install Runs the setup.py install
command with arguments suitable
for a system package.
19.4.3. Automatic provides for Python RPMs
When packaging a Python project, make sure that the following directories are included in the resulting
RPM if these directories are present:
.dist-info
.egg-info
.egg-link
From these directories, the RPM build process automatically generates virtual pythonX.Ydist provides,
for example, python3.6dist(detox). These virtual provides are used by packages that are specified by
the %python_enable_dependency_generator macro.
19.5. HANDLING INTERPRETER DIRECTIVES IN PYTHON SCRIPTS
In Red Hat Enterprise Linux 8, executable Python scripts are expected to use interpreter directives (also
known as hashbangs or shebangs) that explicitly specify at a minimum the major Python version. For
example:
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#!/usr/bin/python3
#!/usr/bin/python3.6
#!/usr/bin/python3.8
#!/usr/bin/python3.9
#!/usr/bin/python3.11
#!/usr/bin/python2
The /usr/lib/rpm/redhat/brp-mangle-shebangs buildroot policy (BRP) script is run automatically when
building any RPM package, and attempts to correct interpreter directives in all executable files.
The BRP script generates errors when encountering a Python script with an ambiguous interpreter
directive, such as:
#!/usr/bin/python
or
#!/usr/bin/env python
19.5.1. Modifying interpreter directives in Python scripts
Modify interpreter directives in the Python scripts that cause the build errors at RPM build time.
Prerequisites
Some of the interpreter directives in your Python scripts cause a build error.
Procedure
To modify interpreter directives, complete one of the following tasks:
Apply the pathfix.py script from the platform-python-devel package:
# pathfix.py -pn -i %{__python3} PATH …
Note that multiple PATHs can be specified. If a PATH is a directory, pathfix.py recursively
scans for any Python scripts matching the pattern ^[a-zA-Z0-9_]+\.py$, not only those with an
ambiguous interpreter directive. Add this command to the %prep section or at the end of the
%install section.
Modify the packaged Python scripts so that they conform to the expected format. For this
purpose, pathfix.py can be used outside the RPM build process, too. When running pathfix.py
outside an RPM build, replace %{__python3} from the example above with a path for the
interpreter directive, such as /usr/bin/python3.
If the packaged Python scripts require a version other than Python 3.6, adjust the preceding commands
to include the required version.
19.5.2. Changing /usr/bin/python3 interpreter directives in your custom packages
By default, interpreter directives in the form of /usr/bin/python3 are replaced with interpreter directives
pointing to Python from the platform-python package, which is used for system tools with Red Hat
Enterprise Linux. You can change the /usr/bin/python3 interpreter directives in your custom packages
to point to a specific version of Python that you have installed from the AppStream repository.
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Procedure
To build your package for a specific version of Python, add the python*-rpm-macros
subpackage of the respective python package to the BuildRequires section of the SPEC file.
For example, for Python 3.6, include the following line:
BuildRequires: python36-rpm-macros
As a result, the /usr/bin/python3 interpreter directives in your custom package are
automatically converted to /usr/bin/python3.6.
NOTE
To prevent the BRP script from checking and modifying interpreter directives, use the
following RPM directive:
%undefine __brp_mangle_shebangs
19.6. USING THE PHP SCRIPTING LANGUAGE
Hypertext Preprocessor (PHP) is a general-purpose scripting language mainly used for server-side
scripting, which enables you to run the PHP code using a web server.
In RHEL 8, the PHP scripting language is provided by the php module, which is available in multiple
streams (versions).
Depending on your use case, you can install a specific profile of the selected module stream:
common - The default profile for server-side scripting using a web server. It includes several
widely used extensions.
minimal - This profile installs only the command-line interface for scripting with PHP without
using a web server.
devel - This profile includes packages from the common profile and additional packages for
development purposes.
19.6.1. Installing the PHP scripting language
You can install a selected version of the php module.
Procedure
To install a php module stream with the default profile, use:
# yum module install php:stream
Replace stream with the version of PHP you wish to install.
For example, to install PHP 8.0:
# yum module install php:8.0
The default common profile installs also the php-fpm package, and preconfigures PHP for use
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The default common profile installs also the php-fpm package, and preconfigures PHP for use
with the Apache HTTP Server or nginx.
To install a specific profile of a php module stream, use:
# yum module install php:stream/profile
Replace stream with the desired version and profile with the name of the profile you wish to
install.
For example, to install PHP 8.0 for use without a web server:
# yum module install php:8.0/minimal
Additional resources
If you want to upgrade from an earlier version of PHP available in RHEL 8, see Switching to a
later stream.
For more information about managing RHEL 8 modules and streams, see Installing, managing,
and removing user-space components.
19.6.2. Using the PHP scripting language with a web server
19.6.2.1. Using PHP with the Apache HTTP Server
In Red Hat Enterprise Linux 8, the Apache HTTP Server enables you to run PHP as a FastCGI process
server. FastCGI Process Manager (FPM) is an alternative PHP FastCGI daemon that allows a website to
manage high loads. PHP uses FastCGI Process Manager by default in RHEL 8.
You can run the PHP code using the FastCGI process server.
Prerequisites
The PHP scripting language is installed on your system.
See Installing the PHP scripting language.
Procedure
1. Install the httpd module:
# yum module install httpd:2.4
2. Start the Apache HTTP Server:
# systemctl start httpd
Or, if the Apache HTTP Server is already running on your system, restart the httpd service
after installing PHP:
# systemctl restart httpd
3. Start the php-fpm service:
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# systemctl start php-fpm
4. Optional: Enable both services to start at boot time:
# systemctl enable php-fpm httpd
5. To obtain information about your PHP settings, create the index.php file with the following
content in the /var/www/html/ directory:
# echo '' > /var/www/html/index.php
6. To run the index.php file, point the browser to:
http:///
7. Optional: Adjust configuration if you have specific requirements:
/etc/httpd/conf/httpd.conf - generic httpd configuration
/etc/httpd/conf.d/php.conf - PHP-specific configuration for httpd
/usr/lib/systemd/system/httpd.service.d/php-fpm.conf - by default, the php-fpm service
is started with httpd
/etc/php-fpm.conf - FPM main configuration
/etc/php-fpm.d/www.conf - default www pool configuration
Example 19.1. Running a "Hello, World!" PHP script using the Apache HTTP Server
1. Create a hello directory for your project in the /var/www/html/ directory:
# mkdir hello
2. Create a hello.php file in the /var/www/html/hello/ directory with the following content:
#
3. Start the Apache HTTP Server:
# systemctl start httpd
4. To run the hello.php file, point the browser to:
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http:///hello/hello.php
As a result, a web page with the “Hello, World!” text is displayed.
Additional resources
Setting up the Apache HTTP web server
19.6.2.2. Using PHP with the nginx web server
You can run PHP code through the nginx web server.
Prerequisites
The PHP scripting language is installed on your system.
See Installing the PHP scripting language.
Procedure
1. Install an nginx module stream:
# yum module install nginx:stream
Replace stream with the version of nginx you wish to install.
For example, to install nginx version 1.18:
# yum module install nginx:1.18
2. Start the nginx server:
# systemctl start nginx
Or, if the nginx server is already running on your system, restart the nginx service after
installing PHP:
# systemctl restart nginx
3. Start the php-fpm service:
# systemctl start php-fpm
4. Optional: Enable both services to start at boot time:
# systemctl enable php-fpm nginx
5. To obtain information about your PHP settings, create the index.php file with the following
content in the /usr/share/nginx/html/ directory:
# echo '' > /usr/share/nginx/html/index.php
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6. To run the index.php file, point the browser to:
http:///
7. Optional: Adjust configuration if you have specific requirements:
/etc/nginx/nginx.conf - nginx main configuration
/etc/nginx/conf.d/php-fpm.conf - FPM configuration for nginx
/etc/php-fpm.conf - FPM main configuration
/etc/php-fpm.d/www.conf - default www pool configuration
Example 19.2. Running a "Hello, World!" PHP script using the nginx server
1. Create a hello directory for your project in the /usr/share/nginx/html/ directory:
# mkdir hello
2. Create a hello.php file in the /usr/share/nginx/html/hello/ directory with the following
content:
#
3. Start the nginx server:
# systemctl start nginx
4. To run the hello.php file, point the browser to:
http:///hello/hello.php
As a result, a web page with the “Hello, World!” text is displayed.
Additional resources
Setting up and configuring NGINX
19.6.3. Running a PHP script using the command-line interface
A PHP script is usually run using a web server, but also can be run using the command-line interface.
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If you want to run php scripts using only command-line, install the minimal profile of a php module
stream.
See Installing the PHP scripting language.
Prerequisites
The PHP scripting language is installed on your system.
See Installing the PHP scripting language.
Procedure
1. In a text editor, create a filename.php file
Replace filename with the name of your file.
2. Execute the created filename.php file from the command line:
# php filename.php
Example 19.3. Running a "Hello, World!" PHP script using the command-line interface
1. Create a hello.php file with the following content using a text editor:
2. Execute the hello.php file from the command line:
# php hello.php
As a result, “Hello, World!” is printed.
19.6.4. Additional resources
httpd(8) — The manual page for the httpd service containing the complete list of its commandline options.
httpd.conf(5) — The manual page for httpd configuration, describing the structure and location
of the httpd configuration files.
nginx(8) — The manual page for the nginx web server containing the complete list of its
command-line options and list of signals.
php-fpm(8) — The manual page for PHP FPM describing the complete list of its command-line
options and configuration files.
19.7. GETTING STARTED WITH TCL/TK
19.7.1. Introduction to Tcl/Tk
Tool command language (Tcl) is a dynamic programming language. The interpreter for this language,
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Tool command language (Tcl) is a dynamic programming language. The interpreter for this language,
together with the C library, is provided by the tcl package.
Using Tcl paired with Tk (Tcl/Tk) enables creating cross-platform GUI applications. Tk is provided by
the tk package.
Note that Tk can refer to any of the following:
A programming toolkit for multiple languages
A Tk C library bindings available for multiple languages, such as C, Ruby, Perl and Python
A wish interpreter that instantiates a Tk console
A Tk extension that adds a number of new commands to a particular Tcl interpreter
For more information about Tcl/Tk, see the Tcl/Tk manual or Tcl/Tk documentation web page.
19.7.2. Notable changes in Tcl/Tk 8.6
Red Hat Enterprise Linux 7 used Tcl/Tk 8.5. With Red Hat Enterprise Linux 8, Tcl/Tk version 8.6 is
provided in the Base OS repository.
Major changes in Tcl/Tk 8.6 compared to Tcl/Tk 8.5 are:
Object-oriented programming support
Stackless evaluation implementation
Enhanced exceptions handling
Collection of third-party packages built and installed with Tcl
Multi-thread operations enabled
SQL database-powered scripts support
IPv6 networking support
Built-in Zlib compression
List processing
Two new commands, lmap and dict map are available, which allow the expression of
transformations over Tcl containers.
Stacked channels by script
Two new commands, chan push and chan pop are available, which allow to add or remove
transformations to or from I/O channels.
Major changes in Tk include:
Built-in PNG image support
Busy windows
A new command, tk busy is available, which disables user interaction for a window or a widget
and shows the busy cursor.
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New font selection dialog interface
Angled text support
Moving things on a canvas support
For the detailed list of changes between Tcl 8.5 and Tcl 8.6, see Changes in Tcl/Tk 8.6.
19.7.3. Migrating to Tcl/Tk 8.6
Red Hat Enterprise Linux 7 used Tcl/Tk 8.5. With Red Hat Enterprise Linux 8, Tcl/Tk version 8.6 is
provided in the Base OS repository.
This section describes migration path to Tcl/Tk 8.6 for:
Developers writing Tcl extensions or embedding Tcl interpreter into their applications
Users scripting tasks with Tcl/Tk
19.7.3.1. Migration path for developers of Tcl extensions
To make your code compatible with Tcl 8.6, use the following procedure.
Procedure
1. Rewrite the code to use the interp structure. For example, if your code reads
interp→errorLine, rewrite it to use the following function:
Tcl_GetErrorLine(interp)
This is necessary because Tcl 8.6 limits direct access to members of the interp structure.
2. To make your code compatible with both Tcl 8.5 and Tcl 8.6, use the following code snippet in
a header file of your C or C++ application or extension that includes the Tcl library:
# include
# if !defined(Tcl_GetErrorLine)
# define Tcl_GetErrorLine(interp) (interp→errorLine)
# endif
19.7.3.2. Migration path for users scripting their tasks with Tcl/Tk
In Tcl 8.6, most scripts work the same way as with the previous version of Tcl.
To migrate you code into Tcl 8.6, use this procedure.
Procedure
When writing a portable code, make sure to not use the commands that are no longer supported
in Tk 8.6:
tkIconList_Arrange
tkIconList_AutoScan
tkIconList_Btn1
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tkIconList_Config
tkIconList_Create
tkIconList_CtrlBtn1
tkIconList_Curselection
tkIconList_DeleteAll
tkIconList_Double1
tkIconList_DrawSelection
tkIconList_FocusIn
tkIconList_FocusOut
tkIconList_Get
tkIconList_Goto
tkIconList_Index
tkIconList_Invoke
tkIconList_KeyPress
tkIconList_Leave1
tkIconList_LeftRight
tkIconList_Motion1
tkIconList_Reset
tkIconList_ReturnKey
tkIconList_See
tkIconList_Select
tkIconList_Selection
tkIconList_ShiftBtn1
tkIconList_UpDown
Note that you can check the list of unsupported commands also in the
/usr/share/tk8.6/unsupported.tcl file.
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