Configuring System Settings

3 Configuring System Settings

This chapter describes the files and virtual file systems that you can use to change the configuration settings for the system.

Also see Configure System Settings on Oracle Linux for a hands-on tutorial on how to configure system settings as described in this chapter.

About the /etc/sysconfig Files

The /etc/sysconfig directory contains files that control the system's configuration. The contents of this directory depend on the packages that you have installed on the system.

Certain files that you might find in the /etc/sysconfig directory include the following:

atd

Specifies command line arguments for the atd daemon.

autofs

Defines custom options for automatically mounting devices and controlling the operation of the automounter.

crond

Passes arguments to the crond daemon at boot time.

chronyd

Passes arguments to the chronyd daemon used for NTP services at boot time.

firewalld

Passes arguments to the firewall daemon (firewalld) at boot time.

grub

Specifies default settings for the GRUB 2 bootloader. This file is a symbolic link to /etc/default/grub. For more information, see About the GRUB 2 Bootloader.

named

Passes arguments to the name service daemon at boot time. The named daemon is a Domain Name System (DNS) server that's part of the Berkeley Internet Name Domain (BIND) distribution. This server maintains a table that associates host names with IP addresses on the network.

samba

Passes arguments to the smbd, nmbd, and winbindd daemons at boot time to support file-sharing connectivity for Windows clients, NetBIOS-over-IP naming service, and connection management to domain controllers.

selinux

Controls the state of SELinux on the system. This file is a symbolic link to /etc/selinux/config.

For more information, see Oracle Linux: Administering SELinux.

snapper

Defines a list of btrfs file systems and thinly provisioned LVM volumes whose contents can be recorded as snapshots by the snapper utility.

For more information, see Oracle Linux 8: Managing Local File Systems .

sysstat

Configures logging parameters for system activity data collector utilities such as sar.

For more information, see /usr/share/doc/initscripts*/sysconfig.txt.

About the /proc Virtual File System

The files in the /proc directory hierarchy contain information about the system hardware and the processes that are running on the system. You can change the configuration of the kernel by writing to certain files that have write permission.

Files that are under the /proc directory are virtual files that the kernel creates on demand to present a browsable view of the underlying data structures and system information. As such, /proc is an example of a virtual file system. Most virtual files are listed as 0 bytes in size, but they contain large amount of information when viewed.

Virtual files such as /proc/interrupts, /proc/meminfo, /proc/mounts, and /proc/partitions provide a view of the system’s hardware. Other files, such as /proc/filesystems and the files under /proc/sys, provide information about the system's configuration and through which you can change configurations as needed.

Files that contain information about related topics are grouped into virtual directories. A separate directory exists in the /proc directory for each process that's running on the system. The directory's name corresponds to the numeric process ID. For example, /proc/1 corresponds to the systemd process that has a PID of 1.

To examine virtual files, you can use commands such as cat, less, and view, as shown in the following example:

cat /proc/cpuinfo

processor         : 0
vendor_id         : GenuineIntel
cpu family        : 6
model             : 42
model name        : Intel(R) Core(TM) i5-2520M CPU @ 2.50GHz
stepping          : 7
cpu MHz           : 2393.714
cache size        : 6144 KB
physical id       : 0
siblings          : 2
core id           : 0
cpu cores         : 2
apicid            : 0
initial apicid    : 0
fpu               : yes
fpu_exception     : yes
cpuid level       : 5
wp                : yes
...

For files that contain nonhuman-readable content, you can use utilities such as lspci, free, top, and sysctl to access information. For example, the lspci command lists PCI devices on a system:

sudo lspci

00:00.0 Host bridge: Intel Corporation 440FX - 82441FX PMC [Natoma] (rev 02)
00:01.0 ISA bridge: Intel Corporation 82371SB PIIX3 ISA [Natoma/Triton II]
00:01.1 IDE interface: Intel Corporation 82371AB/EB/MB PIIX4 IDE (rev 01)
00:02.0 VGA compatible controller: InnoTek Systemberatung GmbH VirtualBox Graphics Adapter
00:03.0 Ethernet controller: Intel Corporation 82540EM Gigabit Ethernet Controller (rev 02)
00:04.0 System peripheral: InnoTek Systemberatung GmbH VirtualBox Guest Service
00:05.0 Multimedia audio controller: Intel Corporation 82801AA AC'97 Audio Controller (rev 01)
00:06.0 USB controller: Apple Inc. KeyLargo/Intrepid USB
00:07.0 Bridge: Intel Corporation 82371AB/EB/MB PIIX4 ACPI (rev 08)
00:0b.0 USB controller: Intel Corporation 82801FB/FBM/FR/FW/FRW (ICH6 Family) USB2 EHCI Controller
00:0d.0 SATA controller: Intel Corporation 82801HM/HEM (ICH8M/ICH8M-E) SATA Controller [AHCI mode]
        (rev 02)
...

Virtual Files and Directories Under /proc

The following table describes the most useful virtual files and directories under the /proc directory hierarchy.

Table 3-1 Useful Virtual Files and Directories Under the /proc Directory

Virtual File or Directory	Description
`PID` (Directory)	Provides information about the process with the process ID (PID). The directory's owner and group is same as the process's. Useful files under the directory include: `cmdline` Command path. `cwd` Symbolic link to the process's current working directory. `environ` Environment variables. `exe` Symbolic link to the command executable. `fd/N` File descriptors. `maps` Memory maps to executable and library files. `root` Symbolic link to the effective root directory for the process. `stack` The contents of the kernel stack. `status` Run state and memory usage.
`buddyinfo`	Provides information for diagnosing memory fragmentation.
`bus` (directory)	Contains information about the various buses (such as `pci` and `usb`) that are available on the system. You can use commands such as `lspci`, `lspcmcia`, and `lsusb` to display information for such devices.
`cgroups`	Provides information about the resource control groups that are in use on the system.
`cmdline`	Lists parameters passed to the kernel at boot time.
`cpuinfo`	Provides information about the system's CPUs.
`crypto`	Provides information about all installed cryptographic cyphers.
`devices`	Lists the names and major device numbers of all currently configured characters and block devices.
`dma`	Lists the direct memory access (DMA) channels that are currently in use.
`driver` (directory)	Contains information about drivers used by the kernel, such as those for nonvolatile RAM (`nvram`), the real-time clock (`rtc`), and memory allocation for sound (`snd-page-alloc`).
`execdomains`	Lists the execution domains for binaries that the Oracle Linux kernel provides.
`filesystems`	Lists the file system types that the kernel provides. Entries marked with `nodev` aren't in use.
`fs` (directory)	Contains information about mounted file systems, organized by file system type.
`interrupts`	Records the number of interrupts per interrupt request queue (IRQ) for each CPU after system startup.
`iomem`	Lists the system memory map for each physical device.
`ioports`	Lists the range of I/O port addresses that the kernel uses with devices.
`irq` (directory)	Contains information about each IRQ. You can configure the affinity between each IRQ and the system CPUs.
`kcore`	Presents the system's physical memory in `core` file format that you can examine using a debugger such as `crash` or `gdb`. This file isn't human-readable.
`kmsg`	Records kernel-generated messages, which are picked up by programs such as `dmesg`.
`loadavg`	Displays the system load averages (number of queued processes) for the past 1, 5, and 15 minutes, the number of running processes, the total number of processes, and the PID of the process that's running.
`locks`	Displays information about the file locks that the kernel is currently holding on behalf of processes. The information provided includes: lock class (`FLOCK` or `POSIX`) lock type (`ADVISORY` or `MANDATORY`) access type (`READ` or `WRITE`) process ID major device, minor device, and inode numbers bounds of the locked region
`mdstat`	Lists information about multiple-disk RAID devices.
`meminfo`	Reports the system's usage of memory in more detail than is available using the `free` or `top` commands.
`modules`	Displays information about the modules that are currently loaded into the kernel. The `lsmod` command formats and displays the same information, excluding the kernel memory offset of a module.
`mounts`	Lists information about all mounted file systems.
`net` (directory)	Provides information about networking protocol, parameters, and statistics. Each directory and virtual file describes aspects of the configuration of the system's network.
`partitions`	Lists the major and minor device numbers, number of blocks, and name of partitions mounted by the system.
`scsi/device_info`	Provides information about SCSI devices.
`scsi/scsi` and `scsi/sg/*`	Provide information about configured SCSI devices, including vendor, model, channel, ID, and LUN data .
`self`	Symbolic link to the process that's examining `/proc`.
`slabinfo`	Provides detailed information about slab memory usage.
`softirqs`	Displays information about software interrupts (`softirqs`). A `softirq` is similar to a hardware interrupt (`hardirq`) and configures the kernel to perform asynchronous processing that would take too long during a hardware interrupt.
`stat`	Records information about the system from when it was started, including: `cpu` Total CPU time (measured in `jiffies`) spent in user mode, low-priority user mode, system mode, idle, waiting for I/O, handling hardirq events, and handling softirq events. `cpuN` Times for CPU N.
`swaps`	Provides information about swap devices. The units of size and usage are in kilobytes.
`sys` (directory)	Provides information about the system and also enables you to enable, disable, or modify kernel features. You can write new settings to any file that has write permission. See Modifying Kernel Parameters. The following subdirectory hierarchies of `/proc/sys` contain virtual files, some of whose values you can alter: `dev` Device parameters. `fs` File system parameters. `kernel` Kernel configuration parameters. `net` Networking parameters.
`sysvipc` (directory)	Provides information about the usage of System V Interprocess Communication (IPC) resources for messages (`msg`), semaphores (`sem`), and shared memory (`shm`).
`tty` (directory)	Provides information about the available and currently used terminal devices on the system. The `drivers` virtual file lists the devices that are currently configured.
`vmstat`	Provides information about virtual memory usage.

For more information, see the proc(5) manual page.

Modifying Kernel Parameters

Some virtual files under /proc, and especially under /proc/sys, are writable. You can adjust settings in the kernel through these files. For example, to change the hostname, you would revise the /proc/sys/kernel/hostname file as follows:

echo www.mydomain.com > /proc/sys/kernel/hostname

Other files take binary or Boolean values, such as the setting of IP forwarding, which is defined in /proc/sys/net/ipv4/ip_forward:

cat /proc/sys/net/ipv4/ip_forward

echo 1 > /proc/sys/net/ipv4/ip_forward
cat /proc/sys/net/ipv4/ip_forward

You can use the sysctl command to view or modify values under the /proc/sys directory.

Note:

Even root can't bypass the file access permissions of virtual file entries under /proc. If you change the value of a read-only entry such as /proc/partitions, no kernel code exists to service the write() system call.

To display the current kernel settings, use the following command:

sysctl -a

kernel.sched_child_runs_first = 0
kernel.sched_min_granularity_ns = 2000000
kernel.sched_latency_ns = 10000000
kernel.sched_wakeup_granularity_ns = 2000000
kernel.sched_shares_ratelimit = 500000
...

Note:

The delimiter character in the name of a setting is a period (.) rather than a slash (/) in a path relative to /proc/sys, such as net.ipv4.ip_forward. This setting represents net/ipv4/ip_forward. As another example, kernel.msgmax represents kernel/msgmax.

To display an individual setting, specify its name as the argument to sysctl:

sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 0

To change the value of a setting, use the following command format:

sysctl -w net.ipv4.ip_forward=1
net.ipv4.ip_forward = 1

Changes that you make in this way remain in force only until the system is rebooted. To make configuration changes persist after the system is rebooted, you must add them to the /etc/sysctl.d directory as a configuration file. Any changes that you make to the files in this directory take effect when the system reboots or if you run the sysctl --system command, for example:

echo 'net.ipv4.ip_forward=1' > /etc/sysctl.d/ip_forward.conf
grep -r ip_forward /etc/sysctl.d

/etc/sysctl.d/ip_forward.conf:net.ipv4.ip_forward=1

sysctl net.ipv4.ip_forward

net.ipv4.ip_forward = 0

sysctl --system

* Applying /usr/lib/sysctl.d/00-system.conf ...
net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0
* Applying /usr/lib/sysctl.d/50-default.conf ...
kernel.sysrq = 16
kernel.core_uses_pid = 1
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.default.promote_secondaries = 1
net.ipv4.conf.all.promote_secondaries = 1
fs.protected_hardlinks = 1
fs.protected_symlinks = 1
* Applying /etc/sysctl.d/99-sysctl.conf ...
* Applying /etc/sysctl.d/ip_forward.conf ...
net.ipv4.ip_forward = 1
* Applying /etc/sysctl.conf ...

sysctl net.ipv4.ip_forward

net.ipv4.ip_forward = 1

For more information, see the sysctl(8) and sysctl.d(5) manual pages.

Parameters That Control System Performance

The following parameters control various aspects of system performance:

fs.file-max

Specifies the maximum number of open files for all processes. Increase the value of this parameter if you see messages about running out of file handles.

kernel.io_uring_disabled

Specifies the disabled setting for creating io_uring instances. io_uring provides an interface to handle asynchronous I/O operations that can significantly improve performance for storage and networking. io_uring is supported with UEK and is enabled by default when running UEK on Oracle Linux.

You can set the following values for the io_uring parameter:

kernel.io_uring_disabled=0 (default). This setting specifies all processes can create io_uring instances.
kernel.io_uring_disabled=1. This setting specifies only processes with CAP_SYS_ADMIN privileges can create io_uring instances.
kernel.io_uring_disabled=2. This setting specifies that io_uring instance creation is disabled for all users.

net.core.netdev_max_backlog

Specifies the size of the receiver backlog queue, which is used if an interface receives packets faster than the kernel can process them. If this queue is too small, packets are lost at the receiver, rather than on the network.

net.core.rmem_max

Specifies the maximum read socket buffer size. To minimize network packet loss, this buffer must be large enough to handle incoming network packets.

net.core.wmem_max

Specifies the maximum write socket buffer size. To minimize network packet loss, this buffer must be large enough to handle outgoing network packets.

net.ipv4.tcp_available_congestion_control

Displays the TCP congestion avoidance algorithms that are available for use. Use the modprobe command if you need to load additional modules such as tcp_htcp to implement the htcp algorithm.

net.ipv4.tcp_congestion_control

Specifies which TCP congestion avoidance algorithm is used.

net.ipv4.tcp_max_syn_backlog

Specifies the number of outstanding SYN requests that are allowed. Increase the value of this parameter if you see synflood warnings in the logs that are caused by the server being overloaded by legitimate connection attempts.

net.ipv4.tcp_rmem

Specifies minimum, default, and maximum receive buffer sizes that are used for a TCP socket. The maximum value can't be larger than net.core.rmem_max.

net.ipv4.tcp_wmem

Specifies minimum, default, and maximum send buffer sizes that are used for a TCP socket. The maximum value can't be larger than net.core.wmem_max.

vm.swappiness

Specifies how likely the kernel is to write loaded pages to swap rather than drop pages from the system page cache. When set to 0, swapping only occurs to avoid an out of memory condition. When set to 100, the kernel swaps aggressively. For a desktop system, setting a lower value can improve system responsiveness by decreasing latency. The default value is 60.

Caution:

This parameter is intended for use with laptop computers to reduce power consumption by the hard disk. Do not adjust this value on server systems.

Parameters That Control Kernel Panics

The following parameters control the circumstances under which a kernel panic can occur:

kernel.hung_task_panic

If set to 1, the kernel panics if any kernel or user thread sleeps in the TASK_UNINTERRUPTIBLE state (D state) for more than kernel.hung_task_timeout_secs seconds. A process remains in D state while waiting for I/O to complete. You can't stop or interrupt a process in this state.

The default value is 0, which disables the panic.

Tip:

To diagnose a hung thread, you can examine /proc/PID/stack, which displays the kernel stack for both kernel and user threads.

kernel.hung_task_timeout_secs

Specifies how long a user or kernel thread can remain in D state before a warning message is generated or the kernel panics, if the value of kernel.hung_task_panic is 1. The default value is 120 seconds. A value of 0 disables the timeout.

kernel.nmi_watchdog

If set to 1 (default), enables the nonmaskable interrupt (NMI) watchdog thread in the kernel. To use the NMI switch or the OProfile system profiler to generate an undefined NMI, set the value of kernel.nmi_watchdog to 0.

kernel.panic

Specifies the number of seconds after a panic before a system automatically resets itself.

If the value is 0, which is the default value, the system bcomes suspended, and you can collect detailed information about the panic for troubleshooting.

To enable automatic reset, set a nonzero value. If you require a memory image (vmcore), leave enough time for Kdump to create this image. The suggested value is 30 seconds, although large systems require a longer time.

kernel.panic_on_io_nmi

If set to 0 (default), the system tries to continue operations if the kernel detects an I/O channel check (IOCHK) NMI that typically indicates a uncorrectable hardware error. If set to 1, the system panics.

kernel.panic_on_oops

If set to 0, the system tries to continue operations if the kernel detects an oops or BUG condition. If set to 1 (default), the system delays a few seconds to give the kernel log daemon, klogd, time to record the oops output before the panic occurs.

In an OCFS2 cluster. set the value to 1 to specify that a system must panic if a kernel oops occurs. If a kernel thread required for cluster operation fails, the system must reset itself. Otherwise, another node might not detect whether a node is slow to respond or unable to respond, causing cluster operations to halt.

kernel.panic_on_unrecovered_nmi

If set to 0 (default), the system tries to continue operations if the kernel detects an NMI that usually indicates an uncorrectable parity or ECC memory error. If set to 1, the system panics.

kernel.softlockup_panic

If set to 0 (default), the system tries to continue operations if the kernel detects a soft-lockup error that causes the NMI watchdog thread to fail to update its timestamp for more than twice the value of kernel.watchdog_thresh seconds. If set to 1, the system panics.

kernel.unknown_nmi_panic

If set to 1, the system panics if the kernel detects an undefined NMI. You would usually generate an undefined NMI by manually pressing an NMI switch. As the NMI watchdog thread also uses the undefined NMI, set the value of kernel.unknown_nmi_panic to 0 if you set kernel.nmi_watchdog to 1.

kernel.watchdog_thresh

Specifies the interval between generating an NMI performance monitoring interrupt that the kernel uses to check for hard-lockup and soft-lockup errors. A hard-lockup error is assumed if a CPU is unresponsive to the interrupt for more than kernel.watchdog_thresh seconds. The default value is 10 seconds. A value of 0 disables the detection of lockup errors.

vm.panic_on_oom

If set to 0 (default), the kernel’s OOM-killer scans through the entire task list and stops a memory-hogging process to avoid a panic. If set to 1, the kernel panics but can survive under certain conditions. If a process limits allocations to certain nodes by using memory policies or cpusets, and those nodes reach memory exhaustion status, the OOM-killer can stop one process. No panic occurs in this case because other nodes’ memory might be free and the system as a whole might not yet be out of memory. If set to 2, the kernel always panics when an OOM condition occurs. Settings of 1 and 2 are for intended for use with clusters, depending on the defined failover policy.

About the /sys Virtual File System

In addition to the /proc file system, the kernel exports information to the /sys virtual file system (sysfs). Programs such as the dynamic device manager (udev), use /sys to access device and device driver information.

Note:

/sys exposes kernel data structures and control points, which implies that the directory contains circular references, where a directory links to an ancestor directory. Thus, a find command used on /sys might never stop.

Virtual Directories Under the /sys Directory

The following table describes some useful virtual directories under the /sys directory hierarchy.

Table 3-2 Virtual Directories Under /sys

Virtual Directory	Description
`block`	Contains subdirectories for block devices. For example: `/sys/block/sda`.
`bus`	Contains subdirectories for each physical bus type, such as `pci`, `pcmcia`, `scsi`, or `usb`. Under each bus type, the `devices` directory lists discovered devices, and the `drivers` directory contains directories for each device driver.
`class`	Contains subdirectories for every class of device that's registered with the kernel.
`dev`	Contains the `char/` and `block/` directories. Inside these two directories are symlinks named major:minor. These symlinks point to the `sysfs` directory for the particular device. The `/sys/dev` directory provides a quick way to look up the `sysfs` interface for a device from the result of the `stat(2)` operation.
`devices`	Contains the global device hierarchy of all devices on the system. The platform directory contains peripheral devices such as device controllers that are specific to a particular platform. The `system` directory contains non peripheral devices such as CPUs and APICs. The `virtual` directory contains virtual and pseudo devices. See Managing System Devices.
`firmware`	Contains subdirectories for firmware objects.
`fs`	Contains subdirectories for file system objects.
`kernel`	Contains subdirectories for other kernel objects
`module`	Contains subdirectories for each module loaded into the kernel. You can alter some parameter values for loaded modules. See About Module Parameters.
`power`	Contains attributes that control the system's power state.

For more information, see https://www.kernel.org/doc/Documentation/filesystems/sysfs.txt.

Configuring System Language (Locale) and Keyboard Settings

System-wide preferences for language and keyboard are stored in the locale configuration file (/etc/locale.conf). You can query and change these settings as needed using localectl command. Note that the systemd process reads the locale configuration file at boot and applies these settings to every system-wide service, user interface, and user profile, unless they're overridden by other programs or users. For more information about configuring these system-wide settings, see:

Note:

System -wide preferences for language and keyboard are also configurable during installation. For details on how to configure these settings at installation, see Oracle Linux 9: Installing Oracle Linux or Oracle Linux 8: Installing Oracle Linux.

Changing the Language Setting

The system locale language setting defines the language in which text appears in the Linux user interfaces (text-based and graphical).

To query and change the language setting on the system, follow these steps:

To check the current language locale set on the system, type:
```
localectl status
```
For example, the following system language locale output indicates: English (en) as the language, US as the country code, and UTF-8 as the codeset.
```
 System Locale: LANG=en_US.UTF-8       
```
To list all possible language locales available on the system, type:
```
localectl list-locales
```
To search the output for a specific language locale, use the grep command. For example, to list all possible English locales available for configuration, type:
```
localectl list-locales | grep en
```

To list all language packs already installed on your system and all language packs available on the ol8_appstream repository, and type:

sudo dnf list langpacks-*

For example, the following shows that this system has Spanish, French, Japanese, and Russian language packs installed followed by a truncated list of language packs available on ol8_appstream.

sudo dnf list langpacks-*
Last metadata expiration check: 1:37:24 ago on Thu 18 Apr 2024 08:14:05 AM EDT.
Installed Packages
langpacks-es.noarch                    1.0-12.el8                 @ol8_appstream
langpacks-fr.noarch                    1.0-12.el8                 @ol8_appstream
langpacks-ja.noarch                    1.0-12.el8                 @ol8_appstream
langpacks-ru.noarch                    1.0-12.el8                 @ol8_appstream
Available Packages
langpacks-af.noarch                    1.0-12.el8                 ol8_appstream 
langpacks-am.noarch                    1.0-12.el8                 ol8_appstream 
langpacks-ar.noarch                    1.0-12.el8                 ol8_appstream 
...

Use dnf to install a language pack. For example, the following installs the Japanese language pack:
```
sudo dnf install langpacks-ja.noarch
```
To set the default language locale on the system, type:
```
sudo localectl set-locale LANG=locale_name
```
Where:
- locale_name is replaced with the name retrieved earlier from the list-locales output.
For example, to set British English as the system language locale, type:
```
sudo localectl set-locale LANG=en_GB.utf8
```
Note:
Locale options are typically listed in the following format: LANGUAGE_COUNTRY.CODESET[@MODIFIERS]. The LANGUAGE is an ISO 639 language code, for example, en for English and COUNTRY is an ISO 3166 country code. The two letter country code in this example is GB for Great Britain and the United Kingdom. The CODESET is the character set or encoding, for example, utf-8.
For more information on how to configure language locale options on the system, see the locale manual page.

Installing Language Locales Individually

To reduce storage space required for languages, you can choose to install individual glibc locale langpack packages (glibc-langpack-<locale_code>).

To list all installed and all available glibc Langpack packages, run the following command:

sudo dnf list glibc-langpack*

To install a language pack, run the following command:

sudo dnf install glibc-langpack-language_code

In the previous command, language_code is the language code you want to install. For example, the following example installs Japanese.

sudo dnf install glibc-langpack-ja.x86_64

Changing the Keyboard Layout

The keyboard layout settings enable you to specify a keymap locale for the Linux user interfaces (text-based and graphical).

To query and change the keyboard layout settings on the system, follow these steps:

To check the current keyboard layout configuration on the system, type:
```
localectl status
```
For example, the following keyboard layout output indicates a US country code for the virtual console keymap and a US country code for the X11 layout.
```
 System Locale: LANG=en_US.UTF-8
       VC Keymap: us
      X11 Layout: us
```
To list all possible keyboard layout configurations available, type:
```
localectl list-keymaps
```
To search the output for a specific keymap name, use the grep command. For example, to list British compatible keyboard layouts, type:
```
localectl list-keymaps | grep gb
```
To set the default keyboard layout on the system, type:
```
sudo localectl set-keymap keymap_name
```
Where:
- keymap_name is replaced with the name of the keymap retrieved earlier from the list-keymaps output.
Note that the keymap name change applies to both the virtual console and the x11 layout settings. If you want the X11 layout to differ from the virtual console keymap, use the --no-convert option, for example:
```
sudo localectl --no-convert set-x11-keymap keymap_name
```
The no-convert option retains the previous x11 keyboard layout setting.

For more information on how to use the localectl command line utility to change keyboard system settings, see thelocalectl manual page.

Configuring System Date and Time Settings

System time is based on the POSIX time standard, where time is measured as the number of seconds that have elapsed from 00:00:00 Coordinated Universal Time (UTC), Thursday, January 1, 1970. A day is defined as 86400 seconds and leap seconds are subtracted automatically.

Date and time representation on a system can be set to match a specific timezone. To list the available timezones, run:

timedatectl list-timezones

To set the system timezone to match a value returned from the available timezones, you can run:

timedatectl set-timezone America/Los_Angeles

Substitute America/Los_Angeles with a valid timezone entry.

This command sets a symbolic link from /etc/localtime to point to the appropriate zone information file in /usr/share/zoneinfo/. The setting takes effect immediately. Some long running processes that use /etc/localtime to detect the current system timezone might not detect a change in system timezone until the process is restarted.

Note that timezones are largely used for display purposes or to handle user input. Changing timezone doesn't change the time for the system clock. You can change the presentation for system time in any console by setting the TZ environment variable. For example, to see the current time in Tokyo, you can run:

TZ="Asia/Tokyo" date

You can check the system's current date and time configuration by running the timedatectl command on its own:

timedatectl

               Local time: Wed 2021-07-17 00:50:58 EDT                                                                                                                                                                                                     
           Universal time: Wed 2021-07-17 04:50:58 UTC                                                                                                                                                                                                     
                 RTC time: Wed 2021-07-17 04:50:55                                                                                                                                                                                                         
                Time zone: America/New_York (EDT, -0400)                                                                                                                                                                                                   
System clock synchronized: yes                                                                                                                                                                                                                             
              NTP service: active                                                                                                                                                                                                                          
          RTC in local TZ: no

To set system time manually, use the timedatectl set-time command:

timedatectl set-time "2021-07-17 01:59:59"

This command sets the current system time based on the time specified assuming the currently set system timezone. The command also updates the system Real Time Clock (RTC).

Tip:

See Learn How to Localize Your Installation on Oracle Linux for a hands-on tutorial that describes how to use tools to configure system parameters such as date, time, and locale.

Consider configuring the system to use network time synchronization for more accurate time-keeping. Using network time synchronization is important especially when setting up high-availability or when using network-based file systems.

For more information about configuring the network time services that use NTP, see Oracle Linux 8: Setting Up Networking.

Tip:

See Configure Chrony on Oracle Linux for a hands-on tutorial on setting up and configuring the chronyd service.

If you configure an NTP service, enable NTP by running the following command:

timedatectl set-ntp true

This command enables and starts the chronyd service, if available.

Configuring the Watchdog Service

Watchdog is an Oracle Linux service that runs in the background to monitor host availability and processes and reports back to the kernel. If the Watchdog service fails to notify the kernel that the system is healthy, the kernel typically automatically reboots the system.

To install the Watchdog package, run:

sudo dnf install watchdog

To configure the Watchdog service, edit the /etc/watchdog.conf file. The watchdog.conf file includes all Watchdog configuration properties. For information on how to edit this file, see the watchdog.conf(5) manual page.

To enable and start the Watchdog service, run:

sudo systemctl enable --now watchdog

The Watchdog service immediately starts and runs in the background.

Note:

The Watchdog service starts and runs immediately after a power reset.