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9   Copyright 2010 Lennart Poettering
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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>