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https://github.com/systemd/systemd-stable.git
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51d8bd3283
Fixes: #32751 (cherry picked from commit 5adc4337996f561df43c617e37ef4b157073b2e6) (cherry picked from commit a6f9c2031666a856f137109e77c856a8e238a59b) (cherry picked from commit b8a62a9f4f399dc09af64642a83f435ade40b2f3) (cherry picked from commit 85e29f7612abed302909d7c0e0db565be0152f5f)
229 lines
11 KiB
XML
229 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 are not accessible,
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<command>systemd</command> will watch for permission changes and notice that conditions are satisfied
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when permissions allow that. </para>
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<para>Note that files whose name starts with a dot (i.e. hidden files) are generally ignored when
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monitoring these paths.</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 paths 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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section <literal>Environment Variables Set or Propagated by the Service Manager</literal> in
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</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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