man/standard-conf.xml

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