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 project='man-pages'><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>Apply settings available only when a certain module is loaded (method one)</title>
 127       <para><filename>/etc/udev/rules.d/99-bridge.rules</filename>:
 128       </para>
 129
 130       <programlisting>ACTION=="add", SUBSYSTEM=="module", KERNEL=="br_netfilter", \
 131       RUN+="/usr/lib/systemd/systemd-sysctl --prefix=/net/bridge"
 132 </programlisting>
 133
 134       <para><filename>/etc/sysctl.d/bridge.conf</filename>:
 135       </para>
 136
 137       <programlisting>net.bridge.bridge-nf-call-ip6tables = 0
 138 net.bridge.bridge-nf-call-iptables = 0
 139 net.bridge.bridge-nf-call-arptables = 0
 140 </programlisting>
 141
 142       <para>This method applies settings when the module is
 143       loaded. Please note that, unless the <filename>br_netfilter</filename>
 144       module is loaded, bridged packets will not be filtered by
 145       Netfilter (starting with kernel 3.18), so simply not loading the
 146       module is sufficient to avoid filtering.</para>
 147     </example>
 148
 149     <example>
 150       <title>Apply settings available only when a certain module is loaded (method two)</title>
 151       <para><filename>/etc/modules-load.d/bridge.conf</filename>:
 152       </para>
 153
 154       <programlisting>br_netfilter</programlisting>
 155
 156       <para><filename>/etc/sysctl.d/bridge.conf</filename>:
 157       </para>
 158
 159       <programlisting>net.bridge.bridge-nf-call-ip6tables = 0
 160 net.bridge.bridge-nf-call-iptables = 0
 161 net.bridge.bridge-nf-call-arptables = 0
 162 </programlisting>
 163
 164       <para>This method forces the module to be always loaded. Please
 165       note that, unless the <filename>br_netfilter</filename> module is
 166       loaded, bridged packets will not be filtered with Netfilter
 167       (starting with kernel 3.18), so simply not loading the module is
 168       sufficient to avoid filtering.</para>
 169     </example>
 170   </refsect1>
 171
 172   <refsect1>
 173     <title>See Also</title>
 174     <para>
 175       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 176       <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 177       <citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 178       <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 179       <citerefentry project='man-pages'><refentrytitle>sysctl.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 180       <citerefentry project='man-pages'><refentrytitle>modprobe</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 181     </para>
 182   </refsect1>
 183
 184 </refentry>