man/systemd.environment-generator.xml

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   8 <!--
   9   SPDX-License-Identifier: LGPL-2.1+
  10
  11   This file is part of systemd.
  12
  13   Copyright 2017 Zbigniew Jędrzejewski-Szmek
  14 -->
  15
  16 <refentry id="systemd.environment-generator" conditional='ENABLE_ENVIRONMENT_D'
  17     xmlns:xi="http://www.w3.org/2001/XInclude">
  18   <refentryinfo>
  19     <title>systemd.environment-generator</title>
  20     <productname>systemd</productname>
  21
  22     <authorgroup>
  23       <author>
  24         <contrib>Developer</contrib>
  25         <firstname>Zbigniew</firstname>
  26         <surname>Jędrzejewski-Szmek</surname>
  27         <email>zbyszek@in.waw.pl</email>
  28       </author>
  29     </authorgroup>
  30   </refentryinfo>
  31
  32   <refmeta>
  33     <refentrytitle>systemd.environment-generator</refentrytitle>
  34     <manvolnum>7</manvolnum>
  35   </refmeta>
  36
  37   <refnamediv>
  38     <refname>systemd.environment-generator</refname>
  39     <refpurpose>systemd environment file generators</refpurpose>
  40   </refnamediv>
  41
  42   <refsynopsisdiv>
  43     <cmdsynopsis>
  44       <command>&systemenvgeneratordir;/some-generator</command>
  45     </cmdsynopsis>
  46     <cmdsynopsis>
  47       <command>&userenvgeneratordir;/some-generator</command>
  48     </cmdsynopsis>
  49
  50     <para>
  51       <literallayout><filename>/run/systemd/system-environment-generators/*</filename>
  52 <filename>/etc/systemd/system-environment-generators/*</filename>
  53 <filename>/usr/local/lib/systemd/system-environment-generators/*</filename>
  54 <filename>&systemenvgeneratordir;/*</filename></literallayout>
  55     </para>
  56
  57     <para>
  58       <literallayout><filename>/run/systemd/user-environment-generators/*</filename>
  59 <filename>/etc/systemd/user-environment-generators/*</filename>
  60 <filename>/usr/local/lib/systemd/user-environment-generators/*</filename>
  61 <filename>&userenvgeneratordir;/*</filename></literallayout>
  62     </para>
  63   </refsynopsisdiv>
  64
  65   <refsect1>
  66     <title>Description</title>
  67     <para>Generators are small executables that live in
  68     <filename>&systemenvgeneratordir;/</filename> and other directories listed above.
  69     <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> will
  70     execute those binaries very early at the startup of each manager and at configuration
  71     reload time, before running the generators described in
  72     <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  73     and before starting any units. Environment generators can override the environment that the
  74     manager exports to services and other processes.</para>
  75
  76     <para>Generators are loaded from a set of paths determined during compilation, as listed
  77     above. System and user environment generators are loaded from directories with names ending in
  78     <filename>system-environment-generators/</filename> and
  79     <filename>user-environment-generators/</filename>, respectively. Generators found in directories
  80     listed earlier override the ones with the same name in directories lower in the list. A symlink
  81     to <filename>/dev/null</filename> or an empty file can be used to mask a generator, thereby
  82     preventing it from running. Please note that the order of the two directories with the highest
  83     priority is reversed with respect to the unit load path, and generators in
  84     <filename>/run</filename> overwrite those in <filename>/etc</filename>.</para>
  85
  86     <para>After installing new generators or updating the configuration, <command>systemctl
  87     daemon-reload</command> may be executed. This will re-run all generators, updating environment
  88     configuration. It will be used for any services that are started subsequently.</para>
  89
  90     <para>Environment file generators are executed similarly to unit file generators described
  91     in
  92     <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
  93     with the following differences:</para>
  94
  95     <itemizedlist>
  96       <listitem>
  97         <para>Generators are executed sequentially in the alphanumerical order of the final
  98         component of their name. The output of each generator output is immediately parsed and used
  99         to update the environment for generators that run after that. Thus, later generators can use
 100         and/or modify the output of earlier generators.</para>
 101       </listitem>
 102
 103       <listitem>
 104         <para>Generators are run by every manager instance, their output can be different for each
 105         user.</para>
 106       </listitem>
 107     </itemizedlist>
 108
 109     <para>It is recommended to use numerical prefixes for generator names to simplify ordering.</para>
 110   </refsect1>
 111
 112   <refsect1>
 113     <title>Examples</title>
 114
 115     <example>
 116       <title>A simple generator that extends an environment variable if a directory exists in the file system</title>
 117
 118       <programlisting># 50-xdg-data-dirs.sh
 119
 120 <xi:include href="50-xdg-data-dirs.sh" parse="text" /></programlisting>
 121     </example>
 122
 123     <example>
 124       <title>A more complicated generator which reads existing configuration and mutates one variable</title>
 125
 126       <programlisting># 90-rearrange-path.py
 127
 128 <xi:include href="90-rearrange-path.py" parse="text" /></programlisting>
 129     </example>
 130
 131     <example>
 132       <title>Debugging a generator</title>
 133
 134       <programlisting>SYSTEMD_LOG_LEVEL=debug VAR_A=something VAR_B="something else" \
 135 &systemenvgeneratordir;/path-to-generator
 136 </programlisting>
 137     </example>
 138   </refsect1>
 139
 140   <refsect1>
 141     <title>See also</title>
 142
 143     <para>
 144       <citerefentry><refentrytitle>systemd-environment-d-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 145       <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 146       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 147       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 148     </para>
 149   </refsect1>
 150 </refentry>