man/standard-conf.xml

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   2 <!DOCTYPE refsection PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3           "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   Copyright 2015 Zbigniew Jędrzejewski-Szmek
   9   Copyright 2014 Josh Triplett
  10 -->
  11
  12 <refsection>
  13   <refsection id='confd'>
  14     <title>Configuration Directories and Precedence</title>
  15
  16     <para>Configuration files are read from directories in
  17     <filename>/etc/</filename>, <filename>/run/</filename>, and
  18     <filename>/usr/lib/</filename>, in order of precedence.
  19     Each configuration file in these configuration directories shall be named in
  20     the style of <filename><replaceable>filename</replaceable>.conf</filename>.
  21     Files in <filename>/etc/</filename> override files with the same name in
  22     <filename>/run/</filename> and <filename>/usr/lib/</filename>. Files in
  23     <filename>/run/</filename> override files with the same name in
  24     <filename>/usr/lib/</filename>.</para>
  25
  26     <para>Packages should install their configuration files in
  27     <filename>/usr/lib/</filename>. Files in <filename>/etc/</filename> are
  28     reserved for the local administrator, who may use this logic to override the
  29     configuration files installed by vendor packages. All configuration files
  30     are sorted by their filename in lexicographic order, regardless of which of
  31     the directories they reside in. If multiple files specify the same option,
  32     the entry in the file with the lexicographically latest name will take
  33     precedence. It is recommended to prefix all filenames with a two-digit number
  34     and a dash, to simplify the ordering of the files.</para>
  35
  36     <para>If the administrator wants to disable a configuration file supplied by
  37     the vendor, the recommended way is to place a symlink to
  38     <filename>/dev/null</filename> in the configuration directory in
  39     <filename>/etc/</filename>, with the same filename as the vendor
  40     configuration file. If the vendor configuration file is included in
  41     the initrd image, the image has to be regenerated.</para>
  42   </refsection>
  43
  44   <refsection id='main-conf'>
  45     <title>Configuration Directories and Precedence</title>
  46
  47     <para>The default configuration is defined during compilation, so a
  48     configuration file is only needed when it is necessary to deviate
  49     from those defaults. By default, the configuration file in
  50     <filename>/etc/systemd/</filename> contains commented out entries
  51     showing the defaults as a guide to the administrator. This file
  52     can be edited to create local overrides.
  53     </para>
  54
  55     <para>When packages need to customize the configuration, they can
  56     install configuration snippets in
  57     <filename>/usr/lib/systemd/*.conf.d/</filename>. Files in
  58     <filename>/etc/</filename> are reserved for the local
  59     administrator, who may use this logic to override the
  60     configuration files installed by vendor packages. The main
  61     configuration file is read before any of the configuration
  62     directories, and has the lowest precedence; entries in a file in
  63     any configuration directory override entries in the single
  64     configuration file. Files in the <filename>*.conf.d/</filename>
  65     configuration subdirectories are sorted by their filename in lexicographic
  66     order, regardless of which of the subdirectories they reside in. When
  67     multiple files specify the same option, for options which accept just a
  68     single value, the entry in the file with the lexicographically latest name
  69     takes precedence. For options which accept a list of values, entries are
  70     collected as they occur in files sorted lexicographically. It is recommended
  71     to prefix all filenames in those subdirectories with a two-digit number and
  72     a dash, to simplify the ordering of the files.</para>
  73
  74     <para>To disable a configuration file supplied by the vendor, the
  75     recommended way is to place a symlink to
  76     <filename>/dev/null</filename> in the configuration directory in
  77     <filename>/etc/</filename>, with the same filename as the vendor
  78     configuration file.</para>
  79   </refsection>
  80 </refsection>