chiark / gitweb /
timesyncd: make sure to reread /etc/resolv.conf when we try the next NTP server
[elogind.git] / man / sysctl.d.xml
1 <?xml version="1.0"?>
2 <!--*-nxml-*-->
3 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4 <!--
5   This file is part of systemd.
6
7   Copyright 2011 Lennart Poettering
8
9   systemd is free software; you can redistribute it and/or modify it
10   under the terms of the GNU Lesser General Public License as published by
11   the Free Software Foundation; either version 2.1 of the License, or
12   (at your option) any later version.
13
14   systemd is distributed in the hope that it will be useful, but
15   WITHOUT ANY WARRANTY; without even the implied warranty of
16   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17   Lesser General Public License for more details.
18
19   You should have received a copy of the GNU Lesser General Public License
20   along with systemd; If not, see <http://www.gnu.org/licenses/>.
21 -->
22 <refentry id="sysctl.d">
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>Each configuration file shall be named in the
93                 style of <filename><replaceable>program</replaceable>.conf</filename>.
94                 Files in <filename>/etc/</filename> override files
95                 with the same name in <filename>/usr/lib/</filename>
96                 and <filename>/run/</filename>.  Files in
97                 <filename>/run/</filename> override files with the same
98                 name in <filename>/usr/lib/</filename>. Packages
99                 should install their configuration files in
100                 <filename>/usr/lib/</filename>. Files in
101                 <filename>/etc/</filename> are reserved for the local
102                 administrator, who may use this logic to override the
103                 configuration files installed by vendor packages. All
104                 configuration files are sorted by their filename in
105                 lexicographic order, regardless of which of the
106                 directories they reside in. If multiple files specify the
107                 same variable name, the entry in the file with the
108                 lexicographically latest name will be applied. It is
109                 recommended to prefix all filenames with a two-digit
110                 number and a dash, to simplify the ordering of the
111                 files.</para>
112
113                 <para>If the administrator wants to disable a
114                 configuration file supplied by the vendor, the
115                 recommended way is to place a symlink to
116                 <filename>/dev/null</filename> in
117                 <filename>/etc/sysctl.d/</filename> bearing the
118                 same filename.</para>
119
120                 <para>The settings configured with
121                 <filename>sysctl.d</filename> files will be applied
122                 early on boot. The network interface-specific options
123                 will also be applied individually for each network
124                 interface as it shows up in the system. (More
125                 specifically,
126                 <filename>net.ipv4.conf.*</filename>,
127                 <filename>net.ipv6.conf.*</filename>,
128                 <filename>net.ipv4.neigh.*</filename> and <filename>net.ipv6.neigh.*</filename>)</para>
129         </refsect1>
130
131         <refsect1>
132                 <title>Example</title>
133                 <example>
134                         <title>/etc/sysctl.d/domain-name.conf example:</title>
135
136                         <programlisting># Set kernel YP domain name
137 kernel.domainname=example.com</programlisting>
138                 </example>
139         </refsect1>
140
141         <refsect1>
142                 <title>See Also</title>
143                 <para>
144                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
145                         <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
146                         <citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
147                         <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
148                         <citerefentry><refentrytitle>sysctl.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
149                 </para>
150         </refsect1>
151
152 </refentry>