Systemd/man/sysctl.d.xml

<?xml version="1.0"?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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  Copyright 2011 Lennart Poettering

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<refentry id="sysctl.d"
          xmlns:xi="http://www.w3.org/2001/XInclude">

        <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-sysctl.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 <literal>#</literal> or <literal>;</literal> are
                ignored.</para>

                <para>Note that either <literal>/</literal> or
                <literal>.</literal> 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. <literal>kernel.domainname=foo</literal>
                and <literal>kernel/domainname=foo</literal> are
                equivalent and will cause <literal>foo</literal> to
                be written to
                <filename>/proc/sys/kernel/domainname</filename>.
                Either
                <literal>net.ipv4.conf.enp3s0/200.forwarding</literal>
                or
                <literal>net/ipv4/conf/enp3s0.200/forwarding</literal>
                may be used to refer to
                <filename>/proc/sys/net/ipv4/conf/enp3s0.200/forwarding</filename>.
                </para>

                <para>The settings configured with
                <filename>sysctl.d</filename> 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,
                <filename>net.ipv4.conf.*</filename>,
                <filename>net.ipv6.conf.*</filename>,
                <filename>net.ipv4.neigh.*</filename> and <filename>net.ipv6.neigh.*</filename>).</para>

                <para>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
                <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> 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 <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry> rule to set those parameters when they become
                available. Alternatively, a slightly simpler and
                less efficient option is to add the module to
                <citerefentry><refentrytitle>modules-load.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>, causing it to be loaded statically
                before sysctl settings are applied (see
                example below).</para>
        </refsect1>

        <xi:include href="standard-conf.xml" xpointer="confd" />

        <refsect1>
                <title>Examples</title>
                <example>
                        <title>Set kernel YP domain name</title>
                        <para><filename>/etc/sysctl.d/domain-name.conf</filename>:
                        </para>

                        <programlisting>kernel.domainname=example.com</programlisting>
                </example>

                <example>
                        <title>Disable packet filter on bridged packets (method one)</title>
                        <para><filename>/etc/udev/rules.d/99-bridge.rules</filename>:
                        </para>

                        <programlisting>ACTION=="add", SUBSYSTEM=="module", KERNEL=="bridge", RUN+="/usr/lib/systemd/systemd-sysctl --prefix=/net/bridge"
</programlisting>

                        <para><filename>/etc/sysctl.d/bridge.conf</filename>:
                        </para>

                        <programlisting>net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0
</programlisting>
                </example>

                <example>
                        <title>Disable packet filter on bridged packets (method two)</title>
                        <para><filename>/etc/modules-load.d/bridge.conf</filename>:
                        </para>

                        <programlisting>bridge</programlisting>

                        <para><filename>/etc/sysctl.d/bridge.conf</filename>:
                        </para>

                        <programlisting>net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0
</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>,
                        <citerefentry><refentrytitle>modprobe</refentrytitle><manvolnum>8</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>