man/sysctl.d.xml

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   6   This file is part of systemd.
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   8   Copyright 2011 Lennart Poettering
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  23 <refentry id="sysctl.d"
  24     xmlns:xi="http://www.w3.org/2001/XInclude">
  25
  26   <refentryinfo>
  27     <title>sysctl.d</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>Developer</contrib>
  33         <firstname>Lennart</firstname>
  34         <surname>Poettering</surname>
  35         <email>lennart@poettering.net</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>sysctl.d</refentrytitle>
  42     <manvolnum>5</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>sysctl.d</refname>
  47     <refpurpose>Configure kernel parameters at boot</refpurpose>
  48   </refnamediv>
  49
  50   <refsynopsisdiv>
  51     <para><filename>/etc/sysctl.d/*.conf</filename></para>
  52     <para><filename>/run/sysctl.d/*.conf</filename></para>
  53     <para><filename>/usr/lib/sysctl.d/*.conf</filename></para>
  54   </refsynopsisdiv>
  55
  56   <refsect1>
  57     <title>Description</title>
  58
  59     <para>At boot,
  60     <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  61     reads configuration files from the above directories to configure
  62     <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  63     kernel parameters.</para>
  64   </refsect1>
  65
  66   <refsect1>
  67     <title>Configuration Format</title>
  68
  69     <para>The configuration files contain a list of variable
  70     assignments, separated by newlines. Empty lines and lines whose
  71     first non-whitespace character is <literal>#</literal> or
  72     <literal>;</literal> are ignored.</para>
  73
  74     <para>Note that either <literal>/</literal> or
  75     <literal>.</literal> may be used as separators within sysctl
  76     variable names. If the first separator is a slash, remaining
  77     slashes and dots are left intact. If the first separator is a dot,
  78     dots and slashes are interchanged.
  79     <literal>kernel.domainname=foo</literal> and
  80     <literal>kernel/domainname=foo</literal> are equivalent and will
  81     cause <literal>foo</literal> to be written to
  82     <filename>/proc/sys/kernel/domainname</filename>. Either
  83     <literal>net.ipv4.conf.enp3s0/200.forwarding</literal> or
  84     <literal>net/ipv4/conf/enp3s0.200/forwarding</literal> may be used
  85     to refer to
  86     <filename>/proc/sys/net/ipv4/conf/enp3s0.200/forwarding</filename>.
  87     </para>
  88
  89     <para>The settings configured with <filename>sysctl.d</filename>
  90     files will be applied early on boot. The network
  91     interface-specific options will also be applied individually for
  92     each network interface as it shows up in the system. (More
  93     specifically, <filename>net.ipv4.conf.*</filename>,
  94     <filename>net.ipv6.conf.*</filename>,
  95     <filename>net.ipv4.neigh.*</filename> and
  96     <filename>net.ipv6.neigh.*</filename>).</para>
  97
  98     <para>Many sysctl parameters only become available when certain
  99     kernel modules are loaded. Modules are usually loaded on demand,
 100     e.g. when certain hardware is plugged in or network brought up.
 101     This means that
 102     <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 103     which runs during early boot will not configure such parameters if
 104     they become available after it has run. To set such parameters, it
 105     is recommended to add an
 106     <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 107     rule to set those parameters when they become available.
 108     Alternatively, a slightly simpler and less efficient option is to
 109     add the module to
 110     <citerefentry><refentrytitle>modules-load.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 111     causing it to be loaded statically before sysctl settings are
 112     applied (see example below).</para>
 113   </refsect1>
 114
 115   <xi:include href="standard-conf.xml" xpointer="confd" />
 116
 117   <refsect1>
 118     <title>Examples</title>
 119     <example>
 120       <title>Set kernel YP domain name</title>
 121       <para><filename>/etc/sysctl.d/domain-name.conf</filename>:
 122       </para>
 123
 124       <programlisting>kernel.domainname=example.com</programlisting>
 125     </example>
 126
 127     <example>
 128       <title>Apply settings available only when a certain module is loaded (method one)</title>
 129       <para><filename>/etc/udev/rules.d/99-bridge.rules</filename>:
 130       </para>
 131
 132       <programlisting>ACTION=="add", SUBSYSTEM=="module", KERNEL=="br_netfilter", \
 133       RUN+="/usr/lib/systemd/systemd-sysctl --prefix=/net/bridge"
 134 </programlisting>
 135
 136       <para><filename>/etc/sysctl.d/bridge.conf</filename>:
 137       </para>
 138
 139       <programlisting>net.bridge.bridge-nf-call-ip6tables = 0
 140 net.bridge.bridge-nf-call-iptables = 0
 141 net.bridge.bridge-nf-call-arptables = 0
 142 </programlisting>
 143
 144       <para>This method applies settings when the module is
 145       loaded. Please note that, unless the <filename>br_netfilter</filename>
 146       module is loaded, bridged packets will not be filtered by
 147       Netfilter (starting with kernel 3.18), so simply not loading the
 148       module is sufficient to avoid filtering.</para>
 149     </example>
 150
 151     <example>
 152       <title>Apply settings available only when a certain module is loaded (method two)</title>
 153       <para><filename>/etc/modules-load.d/bridge.conf</filename>:
 154       </para>
 155
 156       <programlisting>br_netfilter</programlisting>
 157
 158       <para><filename>/etc/sysctl.d/bridge.conf</filename>:
 159       </para>
 160
 161       <programlisting>net.bridge.bridge-nf-call-ip6tables = 0
 162 net.bridge.bridge-nf-call-iptables = 0
 163 net.bridge.bridge-nf-call-arptables = 0
 164 </programlisting>
 165
 166       <para>This method forces the module to be always loaded. Please
 167       note that, unless the <filename>br_netfilter</filename> module is
 168       loaded, bridged packets will not be filtered with Netfilter
 169       (starting with kernel 3.18), so simply not loading the module is
 170       sufficient to avoid filtering.</para>
 171     </example>
 172   </refsect1>
 173
 174   <refsect1>
 175     <title>See Also</title>
 176     <para>
 177       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 178       <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 179       <citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 180       <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 181       <citerefentry project='man-pages'><refentrytitle>sysctl.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 182       <citerefentry project='man-pages'><refentrytitle>modprobe</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 183     </para>
 184   </refsect1>
 185
 186 </refentry>