man/systemd.path.xml

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   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 similarly, 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 paths 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>Environment variables with details on the trigger will be set for triggered units. See the
 212       section <literal>Environment Variables Set or Propagated by the Service Manager</literal> in
 213       <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 214       for more details.</para>
 215       <para>
 216         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 217         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 218         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 219         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 220         <citerefentry project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 221         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 222       </para>
 223   </refsect1>
 224
 225 </refentry>