systemd-sysctl.service

systemd

systemd-sysctl

Configure kernel parameters at boot

/usr/lib/systemd/systemd-sysctl

OPTIONS

CONFIGFILE

systemd-sysctl.service

Description

systemd-sysctl.service is an early boot service that configures sysctl(8) kernel parameters by invoking /usr/lib/systemd/systemd-sysctl.

When invoked with no arguments, /usr/lib/systemd/systemd-sysctl applies all directives from configuration files listed in sysctl.d(5). When invoked with positional arguments, the configuration specified by the command line arguments is executed. If the string - is specified instead of a filename, the configuration is read from standard input. If the argument is a file name (without any slashes), all configuration directories are searched for a matching file and the file found that has the highest priority is executed. If the argument is a path, that file is used directly without searching the configuration directories for any other matching file.

In addition, --prefix= option may be used to limit which sysctl settings are applied.

See sysctl.d(5) for information about the configuration of sysctl settings. After sysctl configuration is changed on disk, it must be written to the files in /proc/sys/ before it takes effect. It is possible to update specific settings, or simply to reload all configuration, see Examples below.

Options

--prefix=
Only apply rules with the specified prefix.

--strict
Always return non-zero exit code on failure (including invalid sysctl variable name and insufficient permissions), unless the sysctl variable name is prefixed with a "-" character.

--verify
After systemd-sysctl successfully writes a value to a sysctl variable, the variable is read back and verified to match the value that was written. If the variable cannot be read back, or if the returned value differs from the written value, the write operation is considered to have failed. To detect such failures reliably, it is recommended to also specify --strict, and to ensure that the settings being applied are not prefixed with - (see sysctl.d(5) for details). This mode is disabled by default, since the format accepted by the kernel may differ from the format returned when the variable is read back, or the kernel may normalize the input. As a result, verification may not work reliably in all cases. Therefore, this option is best used together with explicitly specified configuration files or settings provided through --inline, or with --prefix= to restrict the set of sysctl variables being written.

--inline
Treat each positional argument as a separate configuration line instead of a file name. When specified, at least one positional argument must be specified.

--save=FILENAME
Before applying the loaded sysctl settings, write them to /run/sysctl.d/ using the specified filename. If the filename does not end with .conf, the suffix is appended. This option requires one or more positional arguments. May be combined with --inline. This may be useful for creating runtime sysctl configuration files or overriding existing sysctl configuration files.

--revert=FILENAME
Before loading and applying the sysctl settings, removes the specified sysctl configuration file under /run/sysctl.d/. If the filename does not end with .conf, the suffix is appended. This may be useful for removing configuration files created by --save=.

Credentials

systemd-sysctl supports the service credentials logic as implemented by ImportCredential=/LoadCredential=/SetCredential= (see systemd.exec(5) for details). The following credentials are used when passed in:

sysctl.extra
The contents of this credential may contain additional lines to operate on. The credential contents should follow the same format as any other sysctl.d/ drop-in configuration file. If this credential is passed it is processed after all of the drop-in files read from the file system. The settings configured in the credential hence take precedence over those in the file system.

Note that by default the systemd-sysctl.service unit file is set up to inherit the sysctl.extra credential from the service manager.

Examples

Reset all sysctl settings

systemctl restart systemd-sysctl

View coredump handler configuration

# sysctl kernel.core_pattern
kernel.core_pattern = |/usr/libexec/abrt-hook-ccpp %s %c %p %u %g %t %P %I

Update and verify coredump handler configuration

# /usr/lib/systemd/systemd-sysctl --prefix kernel.core_pattern --strict --verify

This searches all the directories listed in sysctl.d(5) for configuration files and writes /proc/sys/kernel/core_pattern. The sysctl variable is read back and verified. If writing or verification fails, the command exits with a non-zero status, unless the corresponding setting is prefixed with -.

Update coredump handler configuration according to a specific file

# /usr/lib/systemd/systemd-sysctl 50-coredump.conf

This applies all the settings found in 50-coredump.conf. Either /etc/sysctl.d/50-coredump.conf, or /run/sysctl.d/50-coredump.conf, or /usr/lib/sysctl.d/50-coredump.conf will be used, in the order of preference.

Disable IPv6 on an interface and save the specified setting

# /usr/lib/systemd/systemd-sysctl --save=99-disable-ipv6-foo - <<EOF
net.ipv6.conf.foo.disable_ipv6=1
EOF

This disables IPv6 on the network interface foo, and creates /run/sysctl.d/99-disable-ipv6-foo.conf.

Remove a runtime sysctl configuration file

# /usr/lib/systemd/systemd-sysctl --revert=99-disable-ipv6-foo --prefix=/net/ipv6/conf/foo

This removes /run/sysctl.d/99-disable-ipv6-foo.conf, and applies the remaining sysctl settings for the network interface foo.

See sysctl(8) for various ways to directly apply sysctl settings.