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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
10   the Free Software Foundation; either version 2.1 of the License, or
11   (at your option) any later version.
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16   Lesser General Public License for more details.
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18   You should have received a copy of the GNU Lesser General Public License
19   along with systemd; If not, see <http://www.gnu.org/licenses/>.
20 -->
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>