man/systemd.environment-generator.xml

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