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man: add systemd.environment-generator(7) with two examples
v2: - add example files to EXTRA_DIST v3: - rework for the new scheme where nothing is written to disk v4: - use separate dirs for system and user env generators
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
159
man/systemd.environment-generator.xml
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159
man/systemd.environment-generator.xml
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<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
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<!ENTITY % entities SYSTEM "custom-entities.ent" >
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%entities;
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]>
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<!--
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This file is part of systemd.
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Copyright 2017 Zbigniew Jędrzejewski-Szmek
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="systemd.environment-generator" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>systemd.environment-generator</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Zbigniew</firstname>
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<surname>Jędrzejewski-Szmek</surname>
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<email>zbyszek@in.waw.pl</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd.environment-generator</refentrytitle>
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<manvolnum>7</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd.environment-generator</refname>
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<refpurpose>Systemd environment file generators</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<command>&systemenvgeneratordir;/some-generator</command>
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</cmdsynopsis>
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<cmdsynopsis>
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<command>&userenvgeneratordir;/some-generator</command>
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</cmdsynopsis>
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<para>
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<literallayout><filename>/run/systemd/system-environment-generators/*</filename>
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<filename>/etc/systemd/system-environment-generators/*</filename>
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<filename>/usr/local/lib/systemd/system-environment-generators/*</filename>
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<filename>&systemenvgeneratordir;/*</filename></literallayout>
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</para>
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<para>
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<literallayout><filename>/run/systemd/user-environment-generators/*</filename>
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<filename>/etc/systemd/user-environment-generators/*</filename>
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<filename>/usr/local/lib/systemd/user-environment-generators/*</filename>
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<filename>&userenvgeneratordir;/*</filename></literallayout>
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</para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>Generators are small executables that live in
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<filename>&systemenvgeneratordir;/</filename> and other directories listed above.
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> will
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execute those binaries very early at the startup of each manager and at configuration
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reload time, before running the generators described in
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<citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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and before starting any units. Environment generators can override the environment that the
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manager exports to services and other processes.</para>
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<para>Generators are loaded from a set of paths determined during compilation, as listed
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above. System and user environment generators are loaded from directories with names ending in
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<filename>system-environment-generators/</filename> and
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<filename>user-environment-generators/</filename>, respectively. Generators found in directories
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listed earlier override the ones with the same name in directories lower in the list. A symlink
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to <filename>/dev/null</filename> or an empty file can be used to mask a generator, thereby
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preventing it from running. Please note that the order of the two directories with the highest
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priority is reversed with respect to the unit load path, and generators in
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<filename>/run</filename> overwrite those in <filename>/etc</filename>.</para>
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<para>After installing new generators or updating the configuration, <command>systemctl
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daemon-reload</command> may be executed. This will re-run all generators, updating environment
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configuration. It will be used for any services that are started subsequently.</para>
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<para>Environment file generators are executed similarly to unit file generators described
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in
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<citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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with the following differences:</para>
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<itemizedlist>
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<listitem>
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<para>Generators are executed sequentially in the alphanumerical order of the final
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component of their name. The output of each generator output is immediately parsed and used
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to update the environment for generators that run after that. Thus, later generators can use
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and/or modify the output of earlier generators.</para>
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</listitem>
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<listitem>
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<para>Generators are run by every manager instance, their output can be different for each
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user.</para>
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</listitem>
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</itemizedlist>
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<para>It is recommended to use numerical prefixes for generator names to simplify ordering.</para>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<example>
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<title>A simple generator that extends an environment variable if a directory exists in the file system</title>
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<programlisting># 50-xdg-data-dirs.sh
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<xi:include href="50-xdg-data-dirs.sh" parse="text" /></programlisting>
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</example>
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<example>
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<title>A more complicated generator which reads existing configuration and mutates one variable</title>
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<programlisting># 90-rearrange-path.py
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<xi:include href="90-rearrange-path.py" parse="text" /></programlisting>
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</example>
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<example>
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<title>Debugging a generator</title>
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<programlisting>SYSTEMD_LOG_LEVEL=debug VAR_A=something VAR_B="something else" \
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&systemenvgeneratordir;/path-to-generator
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</programlisting>
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</example>
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</refsect1>
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<refsect1>
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<title>See also</title>
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<para>
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<citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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