man/systemd.environment-generator.xml

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