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