<?xml version="1.0"?>

<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<refentry id="sysctl.d">

<refentryinfo>

<title>sysctl.d</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>Developer</contrib>

<firstname>Lennart</firstname>

<surname>Poettering</surname>

<email>lennart@poettering.net</email>

</author>

</authorgroup>

</refentryinfo>

<refmeta>

<refentrytitle>sysctl.d</refentrytitle>

<manvolnum>5</manvolnum>

</refmeta>

<refnamediv>

<refname>sysctl.d</refname>

<refpurpose>Configure kernel parameters at boot</refpurpose>

</refnamediv>

<refsynopsisdiv>

<para><filename>/etc/sysctl.d/*.conf</filename></para>

<para><filename>/run/sysctl.d/*.conf</filename></para>

<para><filename>/usr/lib/sysctl.d/*.conf</filename></para>

</refsynopsisdiv>

<refsect1>

<title>Description</title>

<para>At boot,

<citerefentry><refentrytitle>systemd-binfmt.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>

reads configuration files from the above directories

to configure

<citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>

kernel parameters.</para>

</refsect1>

<refsect1>

<title>Configuration Format</title>

<para>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.</para>

<para>Note that both / and . are accepted as label

separators within sysctl variable

names. <literal>kernel.domainname=foo</literal> and

<literal>kernel/domainname=foo</literal> hence are

entirely equivalent.</para>

<para>Each configuration file shall be named in the

style of <filename>&lt;program&gt;.conf</filename>.

Files in <filename>/etc/</filename> override files

with the same name in <filename>/usr/lib/</filename>

and <filename>/run/</filename>. Files in

<filename>/run/</filename> override files with the same

name in <filename>/usr/lib/</filename>. Packages

should install their configuration files in

<filename>/usr/lib/</filename>. Files in

<filename>/etc/</filename> 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

alphabetical order, regardless in which of the

directories they reside, to guarantee that a specific

configuration file takes precedence over another file

with an alphabetically earlier name, if both files

contain the same variable setting.</para>

<para>If the administrator wants to disable a

configuration file supplied by the vendor the

recommended way is to place a symlink to

<filename>/dev/null</filename> in

<filename>/etc/sysctl.d/</filename> bearing the

same file name.</para>

</refsect1>

<refsect1>

<title>Example</title>

<example>

<title>/etc/sysctl.d/domain-name.conf example:</title>

<programlisting># Set kernel YP domain name

kernel.domainname=example.com</programlisting>

</example>

</refsect1>

<refsect1>

<title>See Also</title>

<para>

<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,

<citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sysctl.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>