man/sysctl.d.xml

   1 <?xml version="1.0"?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   3 <!--
   4   This file is part of systemd.
   5
   6   Copyright 2011 Lennart Poettering
   7
   8   systemd is free software; you can redistribute it and/or modify it
   9   under the terms of the GNU Lesser General Public License as published by
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  16   Lesser General Public License for more details.
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  21 <refentry id="sysctl.d"
  22           xmlns:xi="http://www.w3.org/2001/XInclude">
  23
  24         <refentryinfo>
  25                 <title>sysctl.d</title>
  26                 <productname>systemd</productname>
  27
  28                 <authorgroup>
  29                         <author>
  30                                 <contrib>Developer</contrib>
  31                                 <firstname>Lennart</firstname>
  32                                 <surname>Poettering</surname>
  33                                 <email>lennart@poettering.net</email>
  34                         </author>
  35                 </authorgroup>
  36         </refentryinfo>
  37
  38         <refmeta>
  39                 <refentrytitle>sysctl.d</refentrytitle>
  40                 <manvolnum>5</manvolnum>
  41         </refmeta>
  42
  43         <refnamediv>
  44                 <refname>sysctl.d</refname>
  45                 <refpurpose>Configure kernel parameters at boot</refpurpose>
  46         </refnamediv>
  47
  48         <refsynopsisdiv>
  49                 <para><filename>/etc/sysctl.d/*.conf</filename></para>
  50                 <para><filename>/run/sysctl.d/*.conf</filename></para>
  51                 <para><filename>/usr/lib/sysctl.d/*.conf</filename></para>
  52         </refsynopsisdiv>
  53
  54         <refsect1>
  55                 <title>Description</title>
  56
  57                 <para>At boot,
  58                 <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  59                 reads configuration files from the above directories
  60                 to configure
  61                 <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  62                 kernel parameters.</para>
  63         </refsect1>
  64
  65         <refsect1>
  66                 <title>Configuration Format</title>
  67
  68                 <para>The configuration files contain a list of
  69                 variable assignments, separated by newlines. Empty
  70                 lines and lines whose first non-whitespace character
  71                 is <literal>#</literal> or <literal>;</literal> are
  72                 ignored.</para>
  73
  74                 <para>Note that either <literal>/</literal> or
  75                 <literal>.</literal> may be used as separators within
  76                 sysctl variable names. If the first separator is a
  77                 slash, remaining slashes and dots are left intact. If
  78                 the first separator is a dot, dots and slashes are
  79                 interchanged. <literal>kernel.domainname=foo</literal>
  80                 and <literal>kernel/domainname=foo</literal> are
  81                 equivalent and will cause <literal>foo</literal> to
  82                 be written to
  83                 <filename>/proc/sys/kernel/domainname</filename>.
  84                 Either
  85                 <literal>net.ipv4.conf.enp3s0/200.forwarding</literal>
  86                 or
  87                 <literal>net/ipv4/conf/enp3s0.200/forwarding</literal>
  88                 may be used to refer to
  89                 <filename>/proc/sys/net/ipv4/conf/enp3s0.200/forwarding</filename>.
  90                 </para>
  91
  92                 <para>The settings configured with
  93                 <filename>sysctl.d</filename> files will be applied
  94                 early on boot. The network interface-specific options
  95                 will also be applied individually for each network
  96                 interface as it shows up in the system. (More
  97                 specifically,
  98                 <filename>net.ipv4.conf.*</filename>,
  99                 <filename>net.ipv6.conf.*</filename>,
 100                 <filename>net.ipv4.neigh.*</filename> and <filename>net.ipv6.neigh.*</filename>).</para>
 101
 102                 <para>Many sysctl parameters only become available
 103                 when certain kernel modules are loaded. Modules are
 104                 usually loaded on demand, e.g. when certain hardware
 105                 is plugged in or network brought up. This means that
 106                 <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> which runs
 107                 during early boot will not configure such parameters
 108                 if they become available after it has run. To
 109                 set such parameters, it is recommended to add
 110                 an <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry> rule to set those parameters when they become
 111                 available. Alternatively, a slightly simpler and
 112                 less efficient option is to add the module to
 113                 <citerefentry><refentrytitle>modules-load.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>, causing it to be loaded statically
 114                 before sysctl settings are applied (see
 115                 example below).</para>
 116         </refsect1>
 117
 118         <xi:include href="standard-conf.xml" xpointer="confd" />
 119
 120         <refsect1>
 121                 <title>Examples</title>
 122                 <example>
 123                         <title>Set kernel YP domain name</title>
 124                         <para><filename>/etc/sysctl.d/domain-name.conf</filename>:
 125                         </para>
 126
 127                         <programlisting>kernel.domainname=example.com</programlisting>
 128                 </example>
 129
 130                 <example>
 131                         <title>Disable packet filter on bridged packets (method one)</title>
 132                         <para><filename>/etc/udev/rules.d/99-bridge.rules</filename>:
 133                         </para>
 134
 135                         <programlisting>ACTION=="add", SUBSYSTEM=="module", KERNEL=="bridge", RUN+="/usr/lib/systemd/systemd-sysctl --prefix=/net/bridge"
 136 </programlisting>
 137
 138                         <para><filename>/etc/sysctl.d/bridge.conf</filename>:
 139                         </para>
 140
 141                         <programlisting>net.bridge.bridge-nf-call-ip6tables = 0
 142 net.bridge.bridge-nf-call-iptables = 0
 143 net.bridge.bridge-nf-call-arptables = 0
 144 </programlisting>
 145                 </example>
 146
 147                 <example>
 148                         <title>Disable packet filter on bridged packets (method two)</title>
 149                         <para><filename>/etc/modules-load.d/bridge.conf</filename>:
 150                         </para>
 151
 152                         <programlisting>bridge</programlisting>
 153
 154                         <para><filename>/etc/sysctl.d/bridge.conf</filename>:
 155                         </para>
 156
 157                         <programlisting>net.bridge.bridge-nf-call-ip6tables = 0
 158 net.bridge.bridge-nf-call-iptables = 0
 159 net.bridge.bridge-nf-call-arptables = 0
 160 </programlisting>
 161                 </example>
 162         </refsect1>
 163
 164         <refsect1>
 165                 <title>See Also</title>
 166                 <para>
 167                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 168                         <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 169                         <citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 170                         <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 171                         <citerefentry><refentrytitle>sysctl.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 172                         <citerefentry><refentrytitle>modprobe</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 173                 </para>
 174         </refsect1>
 175
 176 </refentry>