man/systemd.timer.xml

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  24
  25 <refentry id="systemd.timer">
  26         <refentryinfo>
  27                 <title>systemd.timer</title>
  28                 <productname>systemd</productname>
  29
  30                 <authorgroup>
  31                         <author>
  32                                 <contrib>Developer</contrib>
  33                                 <firstname>Lennart</firstname>
  34                                 <surname>Poettering</surname>
  35                                 <email>lennart@poettering.net</email>
  36                         </author>
  37                 </authorgroup>
  38         </refentryinfo>
  39
  40         <refmeta>
  41                 <refentrytitle>systemd.timer</refentrytitle>
  42                 <manvolnum>5</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>systemd.timer</refname>
  47                 <refpurpose>Timer unit configuration</refpurpose>
  48         </refnamediv>
  49
  50         <refsynopsisdiv>
  51                 <para><filename><replaceable>timer</replaceable>.timer</filename></para>
  52         </refsynopsisdiv>
  53
  54         <refsect1>
  55                 <title>Description</title>
  56
  57                 <para>A unit configuration file whose name ends in
  58                 <literal>.timer</literal> encodes information about
  59                 a timer controlled and supervised by systemd, for
  60                 timer-based activation.</para>
  61
  62                 <para>This man page lists the configuration options
  63                 specific to this unit type. See
  64                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  65                 for the common options of all unit configuration
  66                 files. The common configuration items are configured
  67                 in the generic [Unit] and [Install] sections. The
  68                 timer specific configuration options are configured in
  69                 the [Timer] section.</para>
  70
  71                 <para>For each timer file, a matching unit file must
  72                 exist, describing the unit to activate when the timer
  73                 elapses. By default, a service by the same name as the
  74                 timer (except for the suffix) is activated. Example: a
  75                 timer file <filename>foo.timer</filename> activates a
  76                 matching service <filename>foo.service</filename>. The
  77                 unit to activate may be controlled by
  78                 <varname>Unit=</varname> (see below).</para>
  79
  80                 <para>Unless <varname>DefaultDependencies=</varname>
  81                 is set to <option>false</option>, all timer units will
  82                 implicitly have dependencies of type
  83                 <varname>Conflicts=</varname> and
  84                 <varname>Before=</varname> on
  85                 <filename>shutdown.target</filename> to ensure that
  86                 they are stopped cleanly prior to system shutdown.
  87                 Timer units with at least one
  88                 <varname>OnCalendar=</varname> directive will have an
  89                 additional <varname>After=</varname> dependency on
  90                 <filename>timer-sync.target</filename> to avoid
  91                 being started before the system clock has been
  92                 correctly set. Only timer units involved with early
  93                 boot or late system shutdown should disable the
  94                 <varname>DefaultDependencies=</varname> option.</para>
  95         </refsect1>
  96
  97         <refsect1>
  98                 <title>Options</title>
  99
 100                 <para>Timer files must include a [Timer] section,
 101                 which carries information about the timer it
 102                 defines. The options specific to the [Timer] section
 103                 of timer units are the following:</para>
 104
 105                 <variablelist class='unit-directives'>
 106                         <varlistentry>
 107                                 <term><varname>OnActiveSec=</varname></term>
 108                                 <term><varname>OnBootSec=</varname></term>
 109                                 <term><varname>OnStartupSec=</varname></term>
 110                                 <term><varname>OnUnitActiveSec=</varname></term>
 111                                 <term><varname>OnUnitInactiveSec=</varname></term>
 112
 113                                 <listitem><para>Defines monotonic timers
 114                                 relative to different starting points:
 115                                 <varname>OnActiveSec=</varname> defines a
 116                                 timer relative to the moment the timer
 117                                 itself is
 118                                 activated. <varname>OnBootSec=</varname>
 119                                 defines a timer relative to when the
 120                                 machine was booted
 121                                 up. <varname>OnStartupSec=</varname>
 122                                 defines a timer relative to when
 123                                 systemd was first
 124                                 started. <varname>OnUnitActiveSec=</varname>
 125                                 defines a timer relative to when the
 126                                 unit the timer is activating was last
 127                                 activated. <varname>OnUnitInactiveSec=</varname>
 128                                 defines a timer relative to when the
 129                                 unit the timer is activating was last
 130                                 deactivated.</para>
 131
 132                                 <para>Multiple directives may be
 133                                 combined of the same and of different
 134                                 types. For example, by combining
 135                                 <varname>OnBootSec=</varname> and
 136                                 <varname>OnUnitActiveSec=</varname>, it is
 137                                 possible to define a timer that
 138                                 elapses in regular intervals and
 139                                 activates a specific service each
 140                                 time.</para>
 141
 142                                 <para>The arguments to the directives
 143                                 are time spans configured in
 144                                 seconds. Example: "OnBootSec=50" means
 145                                 50s after boot-up. The argument may
 146                                 also include time units. Example:
 147                                 "OnBootSec=5h 30min" means 5 hours and
 148                                 30 minutes after boot-up. For details
 149                                 about the syntax of time spans, see
 150                                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 151
 152                                 <para>If a timer configured with
 153                                 <varname>OnBootSec=</varname> or
 154                                 <varname>OnStartupSec=</varname> is
 155                                 already in the past when the timer
 156                                 unit is activated, it will immediately
 157                                 elapse and the configured unit is
 158                                 started. This is not the case for
 159                                 timers defined in the other
 160                                 directives.</para>
 161
 162                                 <para>These are monotonic timers,
 163                                 independent of wall-clock time and timezones. If the
 164                                 computer is temporarily suspended, the
 165                                 monotonic clock stops too.</para>
 166
 167                                 <para>If the empty string is assigned
 168                                 to any of these options, the list of
 169                                 timers is reset, and all prior
 170                                 assignments will have no
 171                                 effect.</para>
 172
 173                                 <para>Note that timers do not
 174                                 necessarily expire at the precise
 175                                 time configured with these settings,
 176                                 as they are subject to the
 177                                 <varname>AccuracySec=</varname>
 178                                 setting below.</para></listitem>
 179
 180                         </varlistentry>
 181
 182                         <varlistentry>
 183                                 <term><varname>OnCalendar=</varname></term>
 184
 185                                 <listitem><para>Defines realtime
 186                                 (i.e. wallclock) timers with calendar
 187                                 event expressions. See
 188                                 <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 189                                 for more information on the syntax of
 190                                 calendar event expressions. Otherwise,
 191                                 the semantics are similar to
 192                                 <varname>OnActiveSec=</varname> and
 193                                 related settings.</para>
 194
 195                                 <para>Note that timers do not
 196                                 necessarily expire at the precise
 197                                 time configured with this setting,
 198                                 as it is subject to the
 199                                 <varname>AccuracySec=</varname>
 200                                 setting below.</para></listitem>
 201                         </varlistentry>
 202
 203                         <varlistentry>
 204                                 <term><varname>AccuracySec=</varname></term>
 205
 206                                 <listitem><para>Specify the accuracy
 207                                 the timer shall elapse with. Defaults
 208                                 to 1min. The timer is scheduled to
 209                                 elapse within a time window starting
 210                                 with the time specified in
 211                                 <varname>OnCalendar=</varname>,
 212                                 <varname>OnActiveSec=</varname>,
 213                                 <varname>OnBootSec=</varname>,
 214                                 <varname>OnStartupSec=</varname>,
 215                                 <varname>OnUnitActiveSec=</varname> or
 216                                 <varname>OnUnitInactiveSec=</varname>
 217                                 and ending the time configured with
 218                                 <varname>AccuracySec=</varname>
 219                                 later. Within this time window, the
 220                                 expiry time will be placed at a
 221                                 host-specific, randomized but stable
 222                                 position that is synchronized between
 223                                 all local timer units. This is done in
 224                                 order to distribute the wake-up time
 225                                 in networked installations, as well as
 226                                 optimizing power consumption to
 227                                 suppress unnecessary CPU wake-ups. To
 228                                 get best accuracy, set this option to
 229                                 1us. Note that the timer is still
 230                                 subject to the timer slack configured
 231                                 via
 232                                 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
 233                                 <varname>TimerSlackNSec=</varname>
 234                                 setting. See
 235                                 <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 236                                 for details. To optimize power
 237                                 consumption, make sure to set this
 238                                 value as high as possible and as low
 239                                 as necessary.</para></listitem>
 240                         </varlistentry>
 241                         <varlistentry>
 242                                 <term><varname>Unit=</varname></term>
 243
 244                                 <listitem><para>The unit to activate
 245                                 when this timer elapses. The argument is a
 246                                 unit name, whose suffix is not
 247                                 <literal>.timer</literal>. If not
 248                                 specified, this value defaults to a
 249                                 service that has the same name as the
 250                                 timer unit, except for the
 251                                 suffix. (See above.) It is recommended
 252                                 that the unit name that is activated
 253                                 and the unit name of the timer unit
 254                                 are named identically, except for the
 255                                 suffix.</para></listitem>
 256                         </varlistentry>
 257
 258
 259                         <varlistentry>
 260                                 <term><varname>Persistent=</varname></term>
 261
 262                                 <listitem><para>Takes a boolean
 263                                 argument. If true, the time when the
 264                                 service unit was last triggered is
 265                                 stored on disk. When the timer is
 266                                 activated, the service unit is
 267                                 triggered immediately if it would have
 268                                 been triggered at least once during
 269                                 the time when the timer was inactive.
 270                                 This is useful to catch up on missed
 271                                 runs of the service when the machine
 272                                 was off. Note that this setting only
 273                                 has an effect on timers configured
 274                                 with <varname>OnCalendar=</varname>.
 275                                 </para></listitem>
 276                         </varlistentry>
 277
 278                         <varlistentry>
 279                                 <term><varname>WakeSystem=</varname></term>
 280
 281                                 <listitem><para>Takes a boolean
 282                                 argument. If true, an elapsing timer
 283                                 will cause the system to resume from
 284                                 suspend, should it be suspended and if
 285                                 the system supports this. Note that
 286                                 this option will only make sure the
 287                                 system resumes on the appropriate
 288                                 times, it will not take care of
 289                                 suspending it again after any work
 290                                 that is to be done is
 291                                 finished. Defaults to
 292                                 <varname>false</varname>.</para></listitem>
 293                         </varlistentry>
 294                 </variablelist>
 295         </refsect1>
 296
 297         <refsect1>
 298                   <title>See Also</title>
 299                   <para>
 300                           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 301                           <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 302                           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 303                           <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 304                           <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 305                           <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 306                           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 307                           <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 308                   </para>
 309         </refsect1>
 310
 311 </refentry>