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4<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
5
6<refentry id="systemd.path" xmlns:xi="http://www.w3.org/2001/XInclude">
7  <refentryinfo>
8    <title>systemd.path</title>
9    <productname>systemd</productname>
10  </refentryinfo>
11
12  <refmeta>
13    <refentrytitle>systemd.path</refentrytitle>
14    <manvolnum>5</manvolnum>
15  </refmeta>
16
17  <refnamediv>
18    <refname>systemd.path</refname>
19    <refpurpose>Path unit configuration</refpurpose>
20  </refnamediv>
21
22  <refsynopsisdiv>
23    <para><filename><replaceable>path</replaceable>.path</filename></para>
24  </refsynopsisdiv>
25
26  <refsect1>
27    <title>Description</title>
28
29    <para>A unit configuration file whose name ends in
30    <literal>.path</literal> encodes information about a path
31    monitored by systemd, for path-based activation.</para>
32
33    <para>This man page lists the configuration options specific to
34    this unit type. See
35    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
36    for the common options of all unit configuration files. The common
37    configuration items are configured in the generic [Unit] and
38    [Install] sections. The path specific configuration options are
39    configured in the [Path] section.</para>
40
41    <para>For each path file, a matching unit file must exist,
42    describing the unit to activate when the path changes. By default,
43    a service by the same name as the path (except for the suffix) is
44    activated. Example: a path file <filename>foo.path</filename>
45    activates a matching service <filename>foo.service</filename>. The
46    unit to activate may be controlled by <varname>Unit=</varname>
47    (see below).</para>
48
49    <para>Internally, path units use the
50    <citerefentry project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry>
51    API to monitor file systems. Due to that, it suffers by the same
52    limitations as inotify, and for example cannot be used to monitor
53    files or directories changed by other machines on remote NFS file
54    systems.</para>
55
56    <para>When a service unit triggered by a path unit terminates (regardless whether it exited successfully
57    or failed), monitored paths are checked immediately again, and the service accordingly restarted
58    instantly. As protection against busy looping in this trigger/start cycle, a start rate limit is enforced
59    on the service unit, see <varname>StartLimitIntervalSec=</varname> and
60    <varname>StartLimitBurst=</varname> in
61    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Unlike
62    other service failures, the error condition that the start rate limit is hit is propagated from the
63    service unit to the path unit and causes the path unit to fail as well, thus ending the loop.</para>
64  </refsect1>
65
66  <refsect1>
67    <title>Automatic Dependencies</title>
68
69    <refsect2>
70      <title>Implicit Dependencies</title>
71
72      <para>The following dependencies are implicitly added:</para>
73
74      <itemizedlist>
75        <listitem><para>If a path unit is beneath another mount unit in the file
76        system hierarchy, both a requirement and an ordering dependency
77        between both units are created automatically.</para></listitem>
78
79        <listitem><para>An implicit <varname>Before=</varname> dependency is added
80        between a path unit and the unit it is supposed to activate.</para></listitem>
81      </itemizedlist>
82    </refsect2>
83
84    <refsect2>
85      <title>Default Dependencies</title>
86
87      <para>The following dependencies are added unless <varname>DefaultDependencies=no</varname> is set:</para>
88
89      <itemizedlist>
90        <listitem><para>Path units will automatically have dependencies of type <varname>Before=</varname> on
91        <filename>paths.target</filename>,
92        dependencies of type <varname>After=</varname> and <varname>Requires=</varname> on
93        <filename>sysinit.target</filename>, and have dependencies of type <varname>Conflicts=</varname> and
94        <varname>Before=</varname> on <filename>shutdown.target</filename>. These ensure that path units are terminated
95        cleanly prior to system shutdown. Only path units involved with early boot or late system shutdown should
96        disable <varname>DefaultDependencies=</varname> option.</para></listitem>
97      </itemizedlist>
98
99      <para></para>
100    </refsect2>
101  </refsect1>
102
103  <refsect1>
104    <title>Options</title>
105
106    <para>Path unit files may include [Unit] and [Install] sections, which are described in
107    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
108    </para>
109
110    <para>Path unit files must include a [Path] section, which carries information about the path or paths it
111    monitors. The options specific to the [Path] section of path units are the following:</para>
112
113    <variablelist class='unit-directives'>
114      <varlistentry>
115        <term><varname>PathExists=</varname></term>
116        <term><varname>PathExistsGlob=</varname></term>
117        <term><varname>PathChanged=</varname></term>
118        <term><varname>PathModified=</varname></term>
119        <term><varname>DirectoryNotEmpty=</varname></term>
120
121        <listitem><para>Defines paths to monitor for certain changes:
122        <varname>PathExists=</varname> may be used to watch the mere
123        existence of a file or directory. If the file specified
124        exists, the configured unit is activated.
125        <varname>PathExistsGlob=</varname> works similar, but checks
126        for the existence of at least one file matching the globbing
127        pattern specified. <varname>PathChanged=</varname> may be used
128        to watch a file or directory and activate the configured unit
129        whenever it changes. It is not activated on every write to the
130        watched file but it is activated if the file which was open
131        for writing gets closed. <varname>PathModified=</varname> is
132        similar, but additionally it is activated also on simple
133        writes to the watched file.
134        <varname>DirectoryNotEmpty=</varname> may be used to watch a
135        directory and activate the configured unit whenever it
136        contains at least one file.</para>
137
138        <para>The arguments of these directives must be absolute file
139        system paths.</para>
140
141        <para>Multiple directives may be combined, of the same and of
142        different types, to watch multiple paths. If the empty string
143        is assigned to any of these options, the list of paths to
144        watch is reset, and any prior assignments of these options
145        will not have any effect.</para>
146
147        <para>If a path already exists (in case of
148        <varname>PathExists=</varname> and
149        <varname>PathExistsGlob=</varname>) or a directory already is
150        not empty (in case of <varname>DirectoryNotEmpty=</varname>)
151        at the time the path unit is activated, then the configured
152        unit is immediately activated as well. Something similar does
153        not apply to <varname>PathChanged=</varname> and
154        <varname>PathModified=</varname>.</para>
155
156        <para>If the path itself or any of the containing directories
157        are not accessible, <command>systemd</command> will watch for
158        permission changes and notice that conditions are satisfied
159        when permissions allow that. </para></listitem>
160      </varlistentry>
161      <varlistentry>
162        <term><varname>Unit=</varname></term>
163
164        <listitem><para>The unit to activate when any of the
165        configured paths changes. The argument is a unit name, whose
166        suffix is not <literal>.path</literal>. If not specified, this
167        value defaults to a service that has the same name as the path
168        unit, except for the suffix. (See above.) It is recommended
169        that the unit name that is activated and the unit name of the
170        path unit are named identical, except for the
171        suffix.</para></listitem>
172      </varlistentry>
173      <varlistentry>
174        <term><varname>MakeDirectory=</varname></term>
175
176        <listitem><para>Takes a boolean argument. If true, the
177        directories to watch are created before watching. This option
178        is ignored for <varname>PathExists=</varname> settings.
179        Defaults to <option>false</option>.</para></listitem>
180      </varlistentry>
181      <varlistentry>
182        <term><varname>DirectoryMode=</varname></term>
183
184        <listitem><para>If <varname>MakeDirectory=</varname> is
185        enabled, use the mode specified here to create the directories
186        in question. Takes an access mode in octal notation. Defaults
187        to <option>0755</option>.</para></listitem>
188      </varlistentry>
189      <varlistentry>
190        <term><varname>TriggerLimitIntervalSec=</varname></term>
191        <term><varname>TriggerLimitBurst=</varname></term>
192
193        <listitem><para>Configures a limit on how often this path unit may be activated within a specific
194        time interval. The <varname>TriggerLimitIntervalSec=</varname> may be used to configure the length of
195        the time interval in the usual time units <literal>us</literal>, <literal>ms</literal>,
196        <literal>s</literal>, <literal>min</literal>, <literal>h</literal>, … and defaults to 2s. See
197        <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
198        details on the various time units understood. The <varname>TriggerLimitBurst=</varname> setting takes
199        a positive integer value and specifies the number of permitted activations per time interval, and
200        defaults to 200. Set either to 0 to disable any form of trigger rate limiting. If the limit is hit,
201        the unit is placed into a failure mode, and will not watch the path(s) anymore until restarted. Note
202        that this limit is enforced before the service activation is enqueued.</para></listitem>
203      </varlistentry>
204    </variablelist>
205
206    <xi:include href="systemd.service.xml" xpointer="shared-unit-options" />
207  </refsect1>
208
209  <refsect1>
210      <title>See Also</title>
211      <para>
212        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
213        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
214        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
215        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
216        <citerefentry project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
217        <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
218      </para>
219  </refsect1>
220
221</refentry>
222