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>, timer units will
  82                 implicitly have dependencies of type
  83                 <varname>Conflicts=</varname> and
  84                 <varname>Before=</varname> on
  85                 <filename>shutdown.target</filename>. These ensure
  86                 that timer units are stopped cleanly prior to system
  87                 shutdown. Only timer units involved with early boot or
  88                 late system shutdown should disable this
  89                 option.</para>
  90         </refsect1>
  91
  92         <refsect1>
  93                 <title>Options</title>
  94
  95                 <para>Timer files must include a [Timer] section,
  96                 which carries information about the timer it
  97                 defines. The options specific to the [Timer] section
  98                 of timer units are the following:</para>
  99
 100                 <variablelist class='unit-directives'>
 101                         <varlistentry>
 102                                 <term><varname>OnActiveSec=</varname></term>
 103                                 <term><varname>OnBootSec=</varname></term>
 104                                 <term><varname>OnStartupSec=</varname></term>
 105                                 <term><varname>OnUnitActiveSec=</varname></term>
 106                                 <term><varname>OnUnitInactiveSec=</varname></term>
 107
 108                                 <listitem><para>Defines monotonic timers
 109                                 relative to different starting points:
 110                                 <varname>OnActiveSec=</varname> defines a
 111                                 timer relative to the moment the timer
 112                                 itself is
 113                                 activated. <varname>OnBootSec=</varname>
 114                                 defines a timer relative to when the
 115                                 machine was booted
 116                                 up. <varname>OnStartupSec=</varname>
 117                                 defines a timer relative to when
 118                                 systemd was first
 119                                 started. <varname>OnUnitActiveSec=</varname>
 120                                 defines a timer relative to when the
 121                                 unit the timer is activating was last
 122                                 activated. <varname>OnUnitInactiveSec=</varname>
 123                                 defines a timer relative to when the
 124                                 unit the timer is activating was last
 125                                 deactivated.</para>
 126
 127                                 <para>Multiple directives may be
 128                                 combined of the same and of different
 129                                 types. For example, by combining
 130                                 <varname>OnBootSec=</varname> and
 131                                 <varname>OnUnitActiveSec=</varname>, it is
 132                                 possible to define a timer that
 133                                 elapses in regular intervals and
 134                                 activates a specific service each
 135                                 time.</para>
 136
 137                                 <para>The arguments to the directives
 138                                 are time spans configured in
 139                                 seconds. Example: "OnBootSec=50" means
 140                                 50s after boot-up. The argument may
 141                                 also include time units. Example:
 142                                 "OnBootSec=5h 30min" means 5 hours and
 143                                 30 minutes after boot-up. For details
 144                                 about the syntax of time spans, see
 145                                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 146
 147                                 <para>If a timer configured with
 148                                 <varname>OnBootSec=</varname> or
 149                                 <varname>OnStartupSec=</varname> is
 150                                 already in the past when the timer
 151                                 unit is activated, it will immediately
 152                                 elapse and the configured unit is
 153                                 started. This is not the case for
 154                                 timers defined in the other
 155                                 directives.</para>
 156
 157                                 <para>These are monotonic timers,
 158                                 independent of wall-clock time and timezones. If the
 159                                 computer is temporarily suspended, the
 160                                 monotonic clock stops too.</para>
 161
 162                                 <para>If the empty string is assigned
 163                                 to any of these options, the list of
 164                                 timers is reset, and all prior
 165                                 assignments will have no
 166                                 effect.</para>
 167
 168                                 <para>Note that timers do not
 169                                 necessarily expire at the precise
 170                                 time configured with these settings,
 171                                 as they are subject to the
 172                                 <varname>AccuracySec=</varname>
 173                                 setting below.</para></listitem>
 174
 175                         </varlistentry>
 176
 177                         <varlistentry>
 178                                 <term><varname>OnCalendar=</varname></term>
 179
 180                                 <listitem><para>Defines realtime
 181                                 (i.e. wallclock) timers with calendar
 182                                 event expressions. See
 183                                 <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 184                                 for more information on the syntax of
 185                                 calendar event expressions. Otherwise,
 186                                 the semantics are similar to
 187                                 <varname>OnActiveSec=</varname> and
 188                                 related settings.</para>
 189
 190                                 <para>Note that timers do not
 191                                 necessarily expire at the precise
 192                                 time configured with this setting,
 193                                 as it is subject to the
 194                                 <varname>AccuracySec=</varname>
 195                                 setting below.</para></listitem>
 196                         </varlistentry>
 197
 198                         <varlistentry>
 199                                 <term><varname>AccuracySec=</varname></term>
 200
 201                                 <listitem><para>Specify the accuracy
 202                                 the timer shall elapse with. Defaults
 203                                 to 1min. The timer is scheduled to
 204                                 elapse within a time window starting
 205                                 with the time specified in
 206                                 <varname>OnCalendar=</varname>,
 207                                 <varname>OnActiveSec=</varname>,
 208                                 <varname>OnBootSec=</varname>,
 209                                 <varname>OnStartupSec=</varname>,
 210                                 <varname>OnUnitActiveSec=</varname> or
 211                                 <varname>OnUnitInactiveSec=</varname>
 212                                 and ending the time configured with
 213                                 <varname>AccuracySec=</varname>
 214                                 later. Within this time window, the
 215                                 expiry time will be placed at a
 216                                 host-specific, randomized but stable
 217                                 position, that is synchronized between
 218                                 all local timer units. This is done in
 219                                 order to distribute the wake-up time
 220                                 in networked installations, as well as
 221                                 optimizing power consumption to
 222                                 suppress unnecessary CPU wake-ups. To
 223                                 get best accuracy, set this option to
 224                                 1us. Note that the timer is still
 225                                 subject to the timer slack configured
 226                                 via
 227                                 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
 228                                 <varname>TimerSlackNSec=</varname>
 229                                 setting. See
 230                                 <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 231                                 for details. To optimize power
 232                                 consumption, make sure to set this
 233                                 value as high as possible and as low
 234                                 as necessary.</para></listitem>
 235                         </varlistentry>
 236                         <varlistentry>
 237                                 <term><varname>Unit=</varname></term>
 238
 239                                 <listitem><para>The unit to activate
 240                                 when this timer elapses. The argument is a
 241                                 unit name, whose suffix is not
 242                                 <literal>.timer</literal>. If not
 243                                 specified, this value defaults to a
 244                                 service that has the same name as the
 245                                 timer unit, except for the
 246                                 suffix. (See above.) It is recommended
 247                                 that the unit name that is activated
 248                                 and the unit name of the timer unit
 249                                 are named identically, except for the
 250                                 suffix.</para></listitem>
 251                         </varlistentry>
 252                 </variablelist>
 253         </refsect1>
 254
 255         <refsect1>
 256                   <title>See Also</title>
 257                   <para>
 258                           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 259                           <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 260                           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 261                           <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 262                           <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 263                           <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 264                           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 265                           <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 266                   </para>
 267         </refsect1>
 268
 269 </refentry>