man/sysctl.d.xml

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   6   Copyright 2011 Lennart Poettering
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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 to configure
  60     <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  61     kernel parameters.</para>
  62   </refsect1>
  63
  64   <refsect1>
  65     <title>Configuration Format</title>
  66
  67     <para>The configuration files contain a list of variable
  68     assignments, separated by newlines. Empty lines and lines whose
  69     first non-whitespace character is <literal>#</literal> or
  70     <literal>;</literal> are ignored.</para>
  71
  72     <para>Note that either <literal>/</literal> or
  73     <literal>.</literal> may be used as separators within sysctl
  74     variable names. If the first separator is a slash, remaining
  75     slashes and dots are left intact. If the first separator is a dot,
  76     dots and slashes are interchanged.
  77     <literal>kernel.domainname=foo</literal> and
  78     <literal>kernel/domainname=foo</literal> are equivalent and will
  79     cause <literal>foo</literal> to be written to
  80     <filename>/proc/sys/kernel/domainname</filename>. Either
  81     <literal>net.ipv4.conf.enp3s0/200.forwarding</literal> or
  82     <literal>net/ipv4/conf/enp3s0.200/forwarding</literal> may be used
  83     to refer to
  84     <filename>/proc/sys/net/ipv4/conf/enp3s0.200/forwarding</filename>.
  85     </para>
  86
  87     <para>The settings configured with <filename>sysctl.d</filename>
  88     files will be applied early on boot. The network
  89     interface-specific options will also be applied individually for
  90     each network interface as it shows up in the system. (More
  91     specifically, <filename>net.ipv4.conf.*</filename>,
  92     <filename>net.ipv6.conf.*</filename>,
  93     <filename>net.ipv4.neigh.*</filename> and
  94     <filename>net.ipv6.neigh.*</filename>).</para>
  95
  96     <para>Many sysctl parameters only become available when certain
  97     kernel modules are loaded. Modules are usually loaded on demand,
  98     e.g. when certain hardware is plugged in or network brought up.
  99     This means that
 100     <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 101     which runs during early boot will not configure such parameters if
 102     they become available after it has run. To set such parameters, it
 103     is recommended to add an
 104     <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 105     rule to set those parameters when they become available.
 106     Alternatively, a slightly simpler and less efficient option is to
 107     add the module to
 108     <citerefentry><refentrytitle>modules-load.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 109     causing it to be loaded statically before sysctl settings are
 110     applied (see example below).</para>
 111   </refsect1>
 112
 113   <xi:include href="standard-conf.xml" xpointer="confd" />
 114
 115   <refsect1>
 116     <title>Examples</title>
 117     <example>
 118       <title>Set kernel YP domain name</title>
 119       <para><filename>/etc/sysctl.d/domain-name.conf</filename>:
 120       </para>
 121
 122       <programlisting>kernel.domainname=example.com</programlisting>
 123     </example>
 124
 125     <example>
 126       <title>Disable packet filter on bridged packets (method one)</title>
 127       <para><filename>/etc/udev/rules.d/99-bridge.rules</filename>:
 128       </para>
 129
 130       <programlisting>ACTION=="add", SUBSYSTEM=="module", KERNEL=="bridge", RUN+="/usr/lib/systemd/systemd-sysctl --prefix=/net/bridge"
 131 </programlisting>
 132
 133       <para><filename>/etc/sysctl.d/bridge.conf</filename>:
 134       </para>
 135
 136       <programlisting>net.bridge.bridge-nf-call-ip6tables = 0
 137 net.bridge.bridge-nf-call-iptables = 0
 138 net.bridge.bridge-nf-call-arptables = 0
 139 </programlisting>
 140     </example>
 141
 142     <example>
 143       <title>Disable packet filter on bridged packets (method two)</title>
 144       <para><filename>/etc/modules-load.d/bridge.conf</filename>:
 145       </para>
 146
 147       <programlisting>bridge</programlisting>
 148
 149       <para><filename>/etc/sysctl.d/bridge.conf</filename>:
 150       </para>
 151
 152       <programlisting>net.bridge.bridge-nf-call-ip6tables = 0
 153 net.bridge.bridge-nf-call-iptables = 0
 154 net.bridge.bridge-nf-call-arptables = 0
 155 </programlisting>
 156     </example>
 157   </refsect1>
 158
 159   <refsect1>
 160     <title>See Also</title>
 161     <para>
 162       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 163       <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 164       <citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 165       <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 166       <citerefentry><refentrytitle>sysctl.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 167       <citerefentry><refentrytitle>modprobe</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 168     </para>
 169   </refsect1>
 170
 171 </refentry>