SYSCTL.D(5)                                  sysctl.d                                 SYSCTL.D(5)



NAME
       sysctl.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 bridged packets (method one)

       /etc/udev/rules.d/99-bridge.conf:

           ACTION=="add", SUBSYSTEM=="module", KERNEL=="bridge", RUN+="/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 bridged packets (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 ALSO
       systemd(1), systemd-sysctl.service(8), systemd-delta(1), sysctl(8),
       sysctl.conf(5)modprobe(8)



systemd 215                                                                           SYSCTL.D(5)