SYSCTL.D(5)sysctl.dSYSCTL.D(5)NAMEsysctl.d - Configure kernel parameters at boot
SYNOPSIS
/etc/sysctl.d/*.conf
/run/sysctl.d/*.conf
/usr/lib/sysctl.d/*.conf
DESCRIPTION
At boot, systemd-sysctl.service(8) reads configuration files from the
above directories to configure sysctl(8) kernel parameters.
CONFIGURATION FORMAT
The configuration files contain a list of variable assignments,
separated by newlines. Empty lines and lines whose first non-whitespace
character is "#" or ";" are ignored.
Each configuration file shall be named in the style of program.conf.
Files in /etc/ override files with the same name in /usr/lib/ and
/run/. Files in /run/ override files with the same name in /usr/lib/.
Packages should install their configuration files in /usr/lib/. Files
in /etc/ are reserved for the local administrator, who may use this
logic to override the configuration files installed by vendor packages.
All configuration files are sorted by their filename in lexicographic
order, regardless of which of the directories they reside in. If
multiple files specify the same variable name, the entry in the file
with the lexicographically latest name will be applied. It is
recommended to prefix all filenames with a two-digit number and a dash,
to simplify the ordering of the files.
Note that either "/" or "." may be used as separators within sysctl
variable names. If the first separator is a slash, remaining slashes
and dots are left intact. If the first separator is a dot, dots and
slashes are interchanged. "kernel.domainname=foo" and
"kernel/domainname=foo" are equivalent and will cause "foo" to be
written to /proc/sys/kernel/domainname. Either
"net.ipv4.conf.enp3s0/200.forwarding" or
"net/ipv4/conf/enp3s0.200/forwarding" may be used to refer to
/proc/sys/net/ipv4/conf/enp3s0.200/forwarding.
If the administrator wants to disable a configuration file supplied by
the vendor, the recommended way is to place a symlink to /dev/null in
/etc/sysctl.d/ bearing the same filename.
The settings configured with sysctl.d files will be applied early on
boot. The network interface-specific options will also be applied
individually for each network interface as it shows up in the system.
(More specifically, net.ipv4.conf.*, net.ipv6.conf.*, net.ipv4.neigh.*
and net.ipv6.neigh.*).
Many sysctl parameters only become available when certain kernel
modules are loaded. Modules are usually loaded on demand, e.g. when
certain hardware is plugged in or network brought up. This means that
systemd-sysctl.service(8) which runs during early boot will not
configure such parameters if they become available after it has run. To
set such parameters, it is recommended to add an udev(7) rule to set
those parameters when they become available. Alternatively, a slightly
simpler and less efficient option is to add the module to modules-
load.d(5), causing it to be loaded statically before sysctl settings
are applied (see example below).
EXAMPLES
Example 1. Set kernel YP domain name
/etc/sysctl.d/domain-name.conf:
kernel.domainname=example.com
Example 2. Disable packet filter on the bridge (method one)
/etc/udev/rules.d/99-bridge.conf:
ACTION=="add", SUBSYSTEM=="module", KERNEL=="bridge", RUN+="/usr/lib/systemd/systemd-sysctl --prefix=/proc/sys/net/bridge"
/etc/sysctl.d/bridge.conf:
net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0
Example 3. Disable packet filter on the bridge (method two)
/etc/modules-load.d/bridge.conf:
bridge
/etc/sysctl.d/bridge.conf:
net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0
SEE ALSOsystemd(1), systemd-sysctl.service(8), systemd-delta(1), sysctl(8),
sysctl.conf(5)modprobe(8)systemd 208SYSCTL.D(5)
