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When a service is triggered by a path unit, pass the path unit name and the path that triggered it via env vars to the spawned processes. Note that this is best-effort, as there might be many triggers at the same time, but we only get woken up by one.
226 lines
11 KiB
XML
226 lines
11 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd.path" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>systemd.path</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd.path</refentrytitle>
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<manvolnum>5</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd.path</refname>
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<refpurpose>Path unit configuration</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename><replaceable>path</replaceable>.path</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>A unit configuration file whose name ends in
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<literal>.path</literal> encodes information about a path
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monitored by systemd, for path-based activation.</para>
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<para>This man page lists the configuration options specific to
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this unit type. See
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for the common options of all unit configuration files. The common
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configuration items are configured in the generic [Unit] and
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[Install] sections. The path specific configuration options are
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configured in the [Path] section.</para>
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<para>For each path file, a matching unit file must exist,
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describing the unit to activate when the path changes. By default,
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a service by the same name as the path (except for the suffix) is
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activated. Example: a path file <filename>foo.path</filename>
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activates a matching service <filename>foo.service</filename>. The
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unit to activate may be controlled by <varname>Unit=</varname>
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(see below).</para>
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<para>Internally, path units use the
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<citerefentry project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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API to monitor file systems. Due to that, it suffers by the same
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limitations as inotify, and for example cannot be used to monitor
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files or directories changed by other machines on remote NFS file
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systems.</para>
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<para>When a service unit triggered by a path unit terminates (regardless whether it exited successfully
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or failed), monitored paths are checked immediately again, and the service accordingly restarted
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instantly. As protection against busy looping in this trigger/start cycle, a start rate limit is enforced
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on the service unit, see <varname>StartLimitIntervalSec=</varname> and
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<varname>StartLimitBurst=</varname> in
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Unlike
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other service failures, the error condition that the start rate limit is hit is propagated from the
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service unit to the path unit and causes the path unit to fail as well, thus ending the loop.</para>
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</refsect1>
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<refsect1>
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<title>Automatic Dependencies</title>
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<refsect2>
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<title>Implicit Dependencies</title>
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<para>The following dependencies are implicitly added:</para>
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<itemizedlist>
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<listitem><para>If a path unit is beneath another mount unit in the file
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system hierarchy, both a requirement and an ordering dependency
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between both units are created automatically.</para></listitem>
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<listitem><para>An implicit <varname>Before=</varname> dependency is added
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between a path unit and the unit it is supposed to activate.</para></listitem>
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</itemizedlist>
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</refsect2>
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<refsect2>
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<title>Default Dependencies</title>
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<para>The following dependencies are added unless <varname>DefaultDependencies=no</varname> is set:</para>
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<itemizedlist>
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<listitem><para>Path units will automatically have dependencies of type <varname>Before=</varname> on
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<filename>paths.target</filename>,
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dependencies of type <varname>After=</varname> and <varname>Requires=</varname> on
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<filename>sysinit.target</filename>, and have dependencies of type <varname>Conflicts=</varname> and
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<varname>Before=</varname> on <filename>shutdown.target</filename>. These ensure that path units are terminated
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cleanly prior to system shutdown. Only path units involved with early boot or late system shutdown should
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disable <varname>DefaultDependencies=</varname> option.</para></listitem>
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</itemizedlist>
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<para></para>
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</refsect2>
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</refsect1>
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<refsect1>
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<title>Options</title>
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<para>Path unit files may include [Unit] and [Install] sections, which are described in
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
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</para>
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<para>Path unit files must include a [Path] section, which carries information about the path or paths it
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monitors. The options specific to the [Path] section of path units are the following:</para>
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<variablelist class='unit-directives'>
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<varlistentry>
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<term><varname>PathExists=</varname></term>
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<term><varname>PathExistsGlob=</varname></term>
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<term><varname>PathChanged=</varname></term>
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<term><varname>PathModified=</varname></term>
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<term><varname>DirectoryNotEmpty=</varname></term>
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<listitem><para>Defines paths to monitor for certain changes:
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<varname>PathExists=</varname> may be used to watch the mere
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existence of a file or directory. If the file specified
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exists, the configured unit is activated.
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<varname>PathExistsGlob=</varname> works similarly, but checks
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for the existence of at least one file matching the globbing
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pattern specified. <varname>PathChanged=</varname> may be used
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to watch a file or directory and activate the configured unit
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whenever it changes. It is not activated on every write to the
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watched file but it is activated if the file which was open
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for writing gets closed. <varname>PathModified=</varname> is
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similar, but additionally it is activated also on simple
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writes to the watched file.
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<varname>DirectoryNotEmpty=</varname> may be used to watch a
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directory and activate the configured unit whenever it
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contains at least one file.</para>
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<para>The arguments of these directives must be absolute file
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system paths.</para>
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<para>Multiple directives may be combined, of the same and of
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different types, to watch multiple paths. If the empty string
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is assigned to any of these options, the list of paths to
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watch is reset, and any prior assignments of these options
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will not have any effect.</para>
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<para>If a path already exists (in case of
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<varname>PathExists=</varname> and
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<varname>PathExistsGlob=</varname>) or a directory already is
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not empty (in case of <varname>DirectoryNotEmpty=</varname>)
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at the time the path unit is activated, then the configured
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unit is immediately activated as well. Something similar does
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not apply to <varname>PathChanged=</varname> and
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<varname>PathModified=</varname>.</para>
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<para>If the path itself or any of the containing directories
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are not accessible, <command>systemd</command> will watch for
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permission changes and notice that conditions are satisfied
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when permissions allow that. </para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Unit=</varname></term>
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<listitem><para>The unit to activate when any of the
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configured paths changes. The argument is a unit name, whose
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suffix is not <literal>.path</literal>. If not specified, this
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value defaults to a service that has the same name as the path
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unit, except for the suffix. (See above.) It is recommended
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that the unit name that is activated and the unit name of the
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path unit are named identical, except for the
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suffix.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>MakeDirectory=</varname></term>
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<listitem><para>Takes a boolean argument. If true, the
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directories to watch are created before watching. This option
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is ignored for <varname>PathExists=</varname> settings.
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Defaults to <option>false</option>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>DirectoryMode=</varname></term>
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<listitem><para>If <varname>MakeDirectory=</varname> is
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enabled, use the mode specified here to create the directories
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in question. Takes an access mode in octal notation. Defaults
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to <option>0755</option>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>TriggerLimitIntervalSec=</varname></term>
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<term><varname>TriggerLimitBurst=</varname></term>
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<listitem><para>Configures a limit on how often this path unit may be activated within a specific
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time interval. The <varname>TriggerLimitIntervalSec=</varname> may be used to configure the length of
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the time interval in the usual time units <literal>us</literal>, <literal>ms</literal>,
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<literal>s</literal>, <literal>min</literal>, <literal>h</literal>, … and defaults to 2s. See
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<citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
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details on the various time units understood. The <varname>TriggerLimitBurst=</varname> setting takes
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a positive integer value and specifies the number of permitted activations per time interval, and
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defaults to 200. Set either to 0 to disable any form of trigger rate limiting. If the limit is hit,
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the unit is placed into a failure mode, and will not watch the path(s) anymore until restarted. Note
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that this limit is enforced before the service activation is enqueued.</para></listitem>
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</varlistentry>
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</variablelist>
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<xi:include href="systemd.service.xml" xpointer="shared-unit-options" />
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>Environment variables with details on the trigger will be set for triggered units. See the
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<literal>Environment Variables Set on Triggered Units</literal> section in
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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for more details.</para>
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<para>
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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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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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