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91 lines
6.0 KiB
XML
91 lines
6.0 KiB
XML
<?xml version="1.0"?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1-or-later
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Copyright © 2014 Josh Triplett
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-->
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<refentry>
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<refnamediv>
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<refname/>
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<refpurpose/>
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</refnamediv>
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<refsect1 id='confd'>
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<title>Configuration Directories and Precedence</title>
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<para>Configuration files are read from directories in <filename>/etc/</filename>,
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<filename>/run/</filename>, <filename>/usr/local/lib/</filename>, and <filename>/usr/lib/</filename>, in
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order of precedence, as listed in the SYNOPSIS section above. Files must have the
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<literal>.conf</literal> extension. Files in <filename>/etc/</filename> override files with the same name
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in <filename>/run/</filename>, <filename>/usr/local/lib/</filename>, and
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<filename>/usr/lib/</filename>. Files in <filename>/run/</filename> override files with the same name
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under <filename>/usr/</filename>.</para>
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<para>All configuration files are sorted by their filename in lexicographic order, regardless of which of
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the directories they reside in. If multiple files specify the same option, the entry in the file with the
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lexicographically latest name will take precedence. Thus, the configuration in a certain file may either
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be replaced completely (by placing a file with the same name in a directory with higher priority), or
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individual settings might be changed (by specifying additional settings in a file with a different name
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that is ordered later).</para>
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<para>Packages should install their configuration files in <filename>/usr/lib/</filename> (distribution
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packages) or <filename>/usr/local/lib/</filename> (local installs). Files in <filename>/etc/</filename>
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are reserved for the local administrator, who may use this logic to override the configuration files
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installed by vendor packages. It is recommended to prefix all filenames with a two-digit number and a
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dash, to simplify the ordering of the files. It is recommended to use the range 10-40 for configuration
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files in <filename>/usr/</filename> and the range 60-90 for configuration files in
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<filename>/etc/</filename> and <filename>/run/</filename>, to make sure that local and transient
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configuration files will always take priority over configuration files shipped by the OS vendor.</para>
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<para>If the administrator wants to disable a configuration file supplied by the vendor, the recommended
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way is to place a symlink to <filename>/dev/null</filename> in the configuration directory in
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<filename>/etc/</filename>, with the same filename as the vendor configuration file. If the vendor
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configuration file is included in the initrd image, the image has to be regenerated.</para>
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</refsect1>
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<refsect1 id='main-conf'>
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<title>Configuration Directories and Precedence</title>
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<para>The default configuration is set during compilation, so configuration is only needed when it is
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necessary to deviate from those defaults. The main configuration file is loaded from one of the
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listed directories in order of priority, only the first file found is used:
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<filename>/etc/systemd/</filename>,
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<filename>/run/systemd/</filename>,
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<filename>/usr/local/lib/systemd/</filename>,
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<filename>/usr/lib/systemd/</filename>.
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The vendor version of the file contains commented out entries showing the defaults as a guide to the
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administrator. Local overrides can also be created by creating drop-ins, as described below. The main
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configuration file can also be edited for this purpose (or a copy in <filename>/etc/</filename> if it's
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shipped under <filename>/usr/</filename>), however using drop-ins for local configuration is recommended
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over modifications to the main configuration file.</para>
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<para>In addition to the main configuration file, drop-in configuration snippets are read from
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<filename>/usr/lib/systemd/*.conf.d/</filename>, <filename>/usr/local/lib/systemd/*.conf.d/</filename>,
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and <filename>/etc/systemd/*.conf.d/</filename>. Those drop-ins have higher precedence and override the
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main configuration file. Files in the <filename>*.conf.d/</filename> configuration subdirectories are
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sorted by their filename in lexicographic order, regardless of in which of the subdirectories they
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reside. When multiple files specify the same option, for options which accept just a single value, the
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entry in the file sorted last takes precedence, and for options which accept a list of values, entries
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are collected as they occur in the sorted files.</para>
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<para>When packages need to customize the configuration, they can install drop-ins under
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<filename>/usr/</filename>. Files in <filename>/etc/</filename> are reserved for the local administrator,
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who may use this logic to override the configuration files installed by vendor packages. Drop-ins have to
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be used to override package drop-ins, since the main configuration file has lower precedence. It is
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recommended to prefix all filenames in those subdirectories with a two-digit number and a dash, to
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simplify the ordering of the files. This also defines a concept of drop-in priorities to allow
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OS vendors to ship drop-ins within a specific range lower than the range used by users. This should
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lower the risk of package drop-ins overriding accidentally drop-ins defined by users. It is recommended
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to use the range 10-40 for drop-ins in <filename>/usr/</filename> and the range 60-90 for drop-ins in
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<filename>/etc/</filename> and <filename>/run/</filename>, to make sure that local and transient drop-ins
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take priority over drop-ins shipped by the OS vendor.</para>
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<para>To disable a configuration file supplied by the vendor, the recommended way is to place a symlink
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to <filename>/dev/null</filename> in the configuration directory in <filename>/etc/</filename>, with the
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same filename as the vendor configuration file.</para>
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</refsect1>
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</refentry>
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