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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="systemd.path" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>systemd.path</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>systemd.path</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd.path</refname>
<refpurpose>Path unit configuration</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename><replaceable>path</replaceable>.path</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>A unit configuration file whose name ends in
<literal>.path</literal> encodes information about a path
monitored by systemd, for path-based activation.</para>
<para>This man page lists the configuration options specific to
this unit type. See
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for the common options of all unit configuration files. The common
configuration items are configured in the generic [Unit] and
[Install] sections. The path specific configuration options are
configured in the [Path] section.</para>
<para>For each path file, a matching unit file must exist,
describing the unit to activate when the path changes. By default,
a service by the same name as the path (except for the suffix) is
activated. Example: a path file <filename>foo.path</filename>
activates a matching service <filename>foo.service</filename>. The
unit to activate may be controlled by <varname>Unit=</varname>
(see below).</para>
<para>Internally, path units use the
<citerefentry project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry>
API to monitor file systems. Due to that, it suffers by the same
limitations as inotify, and for example cannot be used to monitor
files or directories changed by other machines on remote NFS file
systems.</para>
<para>When a service unit triggered by a path unit terminates (regardless whether it exited successfully
or failed), monitored paths are checked immediately again, and the service accordingly restarted
instantly. As protection against busy looping in this trigger/start cycle, a start rate limit is enforced
on the service unit, see <varname>StartLimitIntervalSec=</varname> and
<varname>StartLimitBurst=</varname> in
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Unlike
other service failures, the error condition that the start rate limit is hit is propagated from the
service unit to the path unit and causes the path unit to fail as well, thus ending the loop.</para>
</refsect1>
<refsect1>
<title>Automatic Dependencies</title>
<refsect2>
<title>Implicit Dependencies</title>
<para>The following dependencies are implicitly added:</para>
<itemizedlist>
<listitem><para>If a path unit is beneath another mount unit in the file
system hierarchy, both a requirement and an ordering dependency
between both units are created automatically.</para></listitem>
<listitem><para>An implicit <varname>Before=</varname> dependency is added
between a path unit and the unit it is supposed to activate.</para></listitem>
</itemizedlist>
</refsect2>
<refsect2>
<title>Default Dependencies</title>
<para>The following dependencies are added unless <varname>DefaultDependencies=no</varname> is set:</para>
<itemizedlist>
<listitem><para>Path units will automatically have dependencies of type <varname>Before=</varname> on
<filename>paths.target</filename>,
dependencies of type <varname>After=</varname> and <varname>Requires=</varname> on
<filename>sysinit.target</filename>, and have dependencies of type <varname>Conflicts=</varname> and
<varname>Before=</varname> on <filename>shutdown.target</filename>. These ensure that path units are terminated
cleanly prior to system shutdown. Only path units involved with early boot or late system shutdown should
disable <varname>DefaultDependencies=</varname> option.</para></listitem>
</itemizedlist>
<para></para>
</refsect2>
</refsect1>
<refsect1>
<title>Options</title>
<para>Path unit files may include [Unit] and [Install] sections, which are described in
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para>
<para>Path unit files must include a [Path] section, which carries information about the path or paths it
monitors. The options specific to the [Path] section of path units are the following:</para>
<variablelist class='unit-directives'>
<varlistentry>
<term><varname>PathExists=</varname></term>
<term><varname>PathExistsGlob=</varname></term>
<term><varname>PathChanged=</varname></term>
<term><varname>PathModified=</varname></term>
<term><varname>DirectoryNotEmpty=</varname></term>
<listitem><para>Defines paths to monitor for certain changes:
<varname>PathExists=</varname> may be used to watch the mere
existence of a file or directory. If the file specified
exists, the configured unit is activated.
<varname>PathExistsGlob=</varname> works similarly, but checks
for the existence of at least one file matching the globbing
pattern specified. <varname>PathChanged=</varname> may be used
to watch a file or directory and activate the configured unit
whenever it changes. It is not activated on every write to the
watched file but it is activated if the file which was open
for writing gets closed. <varname>PathModified=</varname> is
similar, but additionally it is activated also on simple
writes to the watched file.
<varname>DirectoryNotEmpty=</varname> may be used to watch a
directory and activate the configured unit whenever it
contains at least one file.</para>
<para>The arguments of these directives must be absolute file
system paths.</para>
<para>Multiple directives may be combined, of the same and of
different types, to watch multiple paths. If the empty string
is assigned to any of these options, the list of paths to
watch is reset, and any prior assignments of these options
will not have any effect.</para>
<para>If a path already exists (in case of
<varname>PathExists=</varname> and
<varname>PathExistsGlob=</varname>) or a directory already is
not empty (in case of <varname>DirectoryNotEmpty=</varname>)
at the time the path unit is activated, then the configured
unit is immediately activated as well. Something similar does
not apply to <varname>PathChanged=</varname> and
<varname>PathModified=</varname>.</para>
<para>If the path itself or any of the containing directories
are not accessible, <command>systemd</command> will watch for
permission changes and notice that conditions are satisfied
when permissions allow that. </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Unit=</varname></term>
<listitem><para>The unit to activate when any of the
configured paths changes. The argument is a unit name, whose
suffix is not <literal>.path</literal>. If not specified, this
value defaults to a service that has the same name as the path
unit, except for the suffix. (See above.) It is recommended
that the unit name that is activated and the unit name of the
path unit are named identical, except for the
suffix.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>MakeDirectory=</varname></term>
<listitem><para>Takes a boolean argument. If true, the
directories to watch are created before watching. This option
is ignored for <varname>PathExists=</varname> settings.
Defaults to <option>false</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>DirectoryMode=</varname></term>
<listitem><para>If <varname>MakeDirectory=</varname> is
enabled, use the mode specified here to create the directories
in question. Takes an access mode in octal notation. Defaults
to <option>0755</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TriggerLimitIntervalSec=</varname></term>
<term><varname>TriggerLimitBurst=</varname></term>
<listitem><para>Configures a limit on how often this path unit may be activated within a specific
time interval. The <varname>TriggerLimitIntervalSec=</varname> may be used to configure the length of
the time interval in the usual time units <literal>us</literal>, <literal>ms</literal>,
<literal>s</literal>, <literal>min</literal>, <literal>h</literal>, … and defaults to 2s. See
<citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
details on the various time units understood. The <varname>TriggerLimitBurst=</varname> setting takes
a positive integer value and specifies the number of permitted activations per time interval, and
defaults to 200. Set either to 0 to disable any form of trigger rate limiting. If the limit is hit,
the unit is placed into a failure mode, and will not watch the paths anymore until restarted. Note
that this limit is enforced before the service activation is enqueued.</para>
<xi:include href="version-info.xml" xpointer="v250"/></listitem>
</varlistentry>
</variablelist>
<xi:include href="systemd.service.xml" xpointer="shared-unit-options" />
</refsect1>
<refsect1>
<title>See Also</title>
<para>Environment variables with details on the trigger will be set for triggered units. See the
section <literal>Environment Variables Set or Propagated by the Service Manager</literal> in
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for more details.</para>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
|
