1SYSTEMD.TIMER(5) systemd.timer SYSTEMD.TIMER(5)
2
6 systemd.timer - Timer unit configuration
7
9 timer.timer
10
12 A unit configuration file whose name ends in ".timer" encodes
13 information about a timer controlled and supervised by systemd, for
14 timer-based activation.
15 This man page lists the configuration options specific to this unit
17 type. See systemd.unit(5) for the common options of all unit
18 configuration files. The common configuration items are configured in
19 the generic [Unit] and [Install] sections. The timer specific
20 configuration options are configured in the [Timer] section.
21 For each timer file, a matching unit file must exist, describing the
23 unit to activate when the timer elapses. By default, a service by the
24 same name as the timer (except for the suffix) is activated. Example: a
25 timer file foo.timer activates a matching service foo.service. The unit
26 to activate may be controlled by Unit= (see below).
27 Note that in case the unit to activate is already active at the time
29 the timer elapses it is not restarted, but simply left running. There
30 is no concept of spawning new service instances in this case. Due to
31 this, services with RemainAfterExit= set (which stay around
32 continuously even after the service's main process exited) are usually
33 not suitable for activation via repetitive timers, as they will only be
34 activated once, and then stay around forever.
35
37 Implicit Dependencies
38 The following dependencies are implicitly added:
39 • Timer units automatically gain a Before= dependency on the service
41 they are supposed to activate.
42 Default Dependencies
44 The following dependencies are added unless DefaultDependencies=no is
45 set:
46 • Timer units will automatically have dependencies of type Requires=
48 and After= on sysinit.target, a dependency of type Before= on
49 timers.target, as well as Conflicts= and Before= on shutdown.target
50 to ensure that they are stopped cleanly prior to system shutdown.
51 Only timer units involved with early boot or late system shutdown
52 should disable the DefaultDependencies= option.
53 • Timer units with at least one OnCalendar= directive acquire a pair
55 of additional After= dependencies on time-set.target and
56 time-sync.target, in order to avoid being started before the system
57 clock has been correctly set. See systemd.special(7) for details on
58 these two targets.
59
61 Timer unit files may include [Unit] and [Install] sections, which are
62 described in systemd.unit(5).
63 Timer unit files must include a [Timer] section, which carries
65 information about the timer it defines. The options specific to the
66 [Timer] section of timer units are the following:
67 OnActiveSec=, OnBootSec=, OnStartupSec=, OnUnitActiveSec=,
69 OnUnitInactiveSec=
70 Defines monotonic timers relative to different starting points:
71 Table 1. Settings and their starting points
73 ┌───────────────────┬────────────────────────────┐
74 │Setting │ Meaning │
75 ├───────────────────┼────────────────────────────┤
76 │OnActiveSec= │ Defines a timer relative │
77 │ │ to the moment the timer │
78 │ │ unit itself is activated. │
79 ├───────────────────┼────────────────────────────┤
80 │OnBootSec= │ Defines a timer relative │
81 │ │ to when the machine was │
82 │ │ booted up. In containers, │
83 │ │ for the system manager │
84 │ │ instance, this is mapped │
85 │ │ to OnStartupSec=, making │
86 │ │ both equivalent. │
87 ├───────────────────┼────────────────────────────┤
88 │OnStartupSec= │ Defines a timer relative │
89 │ │ to when the service │
90 │ │ manager was first started. │
91 │ │ For system timer units │
92 │ │ this is very similar to │
93 │ │ OnBootSec= as the system │
94 │ │ service manager is │
95 │ │ generally started very │
96 │ │ early at boot. It's │
97 │ │ primarily useful when │
98 │ │ configured in units │
99 │ │ running in the per-user │
100 │ │ service manager, as the │
101 │ │ user service manager is │
102 │ │ generally started on first │
103 │ │ login only, not already │
104 │ │ during boot. │
105 ├───────────────────┼────────────────────────────┤
106 │OnUnitActiveSec= │ Defines a timer relative │
107 │ │ to when the unit the timer │
108 │ │ unit is activating was │
109 │ │ last activated. │
110 ├───────────────────┼────────────────────────────┤
111 │OnUnitInactiveSec= │ Defines a timer relative │
112 │ │ to when the unit the timer │
113 │ │ unit is activating was │
114 │ │ last deactivated. │
115 └───────────────────┴────────────────────────────┘
116 Multiple directives may be combined of the same and of different
117 types, in which case the timer unit will trigger whenever any of
118 the specified timer expressions elapse. For example, by combining
119 OnBootSec= and OnUnitActiveSec=, it is possible to define a timer
120 that elapses in regular intervals and activates a specific service
121 each time. Moreover, both monotonic time expressions and
122 OnCalendar= calendar expressions may be combined in the same timer
123 unit.
124 The arguments to the directives are time spans configured in
126 seconds. Example: "OnBootSec=50" means 50s after boot-up. The
127 argument may also include time units. Example: "OnBootSec=5h 30min"
128 means 5 hours and 30 minutes after boot-up. For details about the
129 syntax of time spans, see systemd.time(7).
130 If a timer configured with OnBootSec= or OnStartupSec= is already
132 in the past when the timer unit is activated, it will immediately
133 elapse and the configured unit is started. This is not the case for
134 timers defined in the other directives.
135 These are monotonic timers, independent of wall-clock time and
137 timezones. If the computer is temporarily suspended, the monotonic
138 clock generally pauses, too. Note that if WakeSystem= is used, a
139 different monotonic clock is selected that continues to advance
140 while the system is suspended and thus can be used as the trigger
141 to resume the system.
142 If the empty string is assigned to any of these options, the list
144 of timers is reset (both monotonic timers and OnCalendar= timers,
145 see below), and all prior assignments will have no effect.
146 Note that timers do not necessarily expire at the precise time
148 configured with these settings, as they are subject to the
149 AccuracySec= setting below.
150 OnCalendar=
152 Defines realtime (i.e. wallclock) timers with calendar event
153 expressions. See systemd.time(7) for more information on the syntax
154 of calendar event expressions. Otherwise, the semantics are similar
155 to OnActiveSec= and related settings.
156 Note that timers do not necessarily expire at the precise time
158 configured with this setting, as it is subject to the AccuracySec=
159 setting below.
160 May be specified more than once, in which case the timer unit will
162 trigger whenever any of the specified expressions elapse. Moreover
163 calendar timers and monotonic timers (see above) may be combined
164 within the same timer unit.
165 If the empty string is assigned to any of these options, the list
167 of timers is reset (both OnCalendar= timers and monotonic timers,
168 see above), and all prior assignments will have no effect.
169 Note that calendar timers might be triggered at unexpected times if
171 the system's realtime clock is not set correctly. Specifically, on
172 systems that lack a battery-buffered Realtime Clock (RTC) it might
173 be wise to enable systemd-time-wait-sync.service to ensure the
174 clock is adjusted to a network time source before the timer event
175 is set up. Timer units with at least one OnCalendar= expression are
176 automatically ordered after time-sync.target, which
177 systemd-time-wait-sync.service is ordered before.
178 When a system is temporarily put to sleep (i.e. system suspend or
180 hibernation) the realtime clock does not pause. When a calendar
181 timer elapses while the system is sleeping it will not be acted on
182 immediately, but once the system is later resumed it will catch up
183 and process all timers that triggered while the system was
184 sleeping. Note that if a calendar timer elapsed more than once
185 while the system was continuously sleeping the timer will only
186 result in a single service activation. If WakeSystem= (see below)
187 is enabled a calendar time event elapsing while the system is
188 suspended will cause the system to wake up (under the condition the
189 system's hardware supports time-triggered wake-up functionality).
190 AccuracySec=
192 Specify the accuracy the timer shall elapse with. Defaults to 1min.
193 The timer is scheduled to elapse within a time window starting with
194 the time specified in OnCalendar=, OnActiveSec=, OnBootSec=,
195 OnStartupSec=, OnUnitActiveSec= or OnUnitInactiveSec= and ending
196 the time configured with AccuracySec= later. Within this time
197 window, the expiry time will be placed at a host-specific,
198 randomized, but stable position that is synchronized between all
199 local timer units. This is done in order to optimize power
200 consumption to suppress unnecessary CPU wake-ups. To get best
201 accuracy, set this option to 1us. Note that the timer is still
202 subject to the timer slack configured via systemd-system.conf(5)'s
203 TimerSlackNSec= setting. See prctl(2) for details. To optimize
204 power consumption, make sure to set this value as high as possible
205 and as low as necessary.
206 Note that this setting is primarily a power saving option that
208 allows coalescing CPU wake-ups. It should not be confused with
209 RandomizedDelaySec= (see below) which adds a random value to the
210 time the timer shall elapse next and whose purpose is the opposite:
211 to stretch elapsing of timer events over a longer period to reduce
212 workload spikes. For further details and explanations and how both
213 settings play together, see below.
214 RandomizedDelaySec=
216 Delay the timer by a randomly selected, evenly distributed amount
217 of time between 0 and the specified time value. Defaults to 0,
218 indicating that no randomized delay shall be applied. Each timer
219 unit will determine this delay randomly before each iteration, and
220 the delay will simply be added on top of the next determined
221 elapsing time, unless modified with FixedRandomDelay=, see below.
222 This setting is useful to stretch dispatching of similarly
224 configured timer events over a certain time interval, to prevent
225 them from firing all at the same time, possibly resulting in
226 resource congestion.
227 Note the relation to AccuracySec= above: the latter allows the
229 service manager to coalesce timer events within a specified time
230 range in order to minimize wakeups, while this setting does the
231 opposite: it stretches timer events over an interval, to make it
232 unlikely that they fire simultaneously. If RandomizedDelaySec= and
233 AccuracySec= are used in conjunction, first the randomized delay is
234 added, and then the result is possibly further shifted to coalesce
235 it with other timer events happening on the system. As mentioned
236 above AccuracySec= defaults to 1 minute and RandomizedDelaySec= to
237 0, thus encouraging coalescing of timer events. In order to
238 optimally stretch timer events over a certain range of time, set
239 AccuracySec=1us and RandomizedDelaySec= to some higher value.
240 FixedRandomDelay=
242 Takes a boolean argument. When enabled, the randomized offset
243 specified by RandomizedDelaySec= is reused for all firings of the
244 same timer. For a given timer unit, the offset depends on the
245 machine ID, user identifier and timer name, which means that it is
246 stable between restarts of the manager. This effectively creates a
247 fixed offset for an individual timer, reducing the jitter in
248 firings of this timer, while still avoiding firing at the same time
249 as other similarly configured timers.
250 This setting has no effect if RandomizedDelaySec= is set to 0.
252 Defaults to false.
253 OnClockChange=, OnTimezoneChange=
255 These options take boolean arguments. When true, the service unit
256 will be triggered when the system clock (CLOCK_REALTIME) jumps
257 relative to the monotonic clock (CLOCK_MONOTONIC), or when the
258 local system timezone is modified. These options can be used alone
259 or in combination with other timer expressions (see above) within
260 the same timer unit. These options default to false.
261 Unit=
263 The unit to activate when this timer elapses. The argument is a
264 unit name, whose suffix is not ".timer". If not specified, this
265 value defaults to a service that has the same name as the timer
266 unit, except for the suffix. (See above.) It is recommended that
267 the unit name that is activated and the unit name of the timer unit
268 are named identically, except for the suffix.
269 Persistent=
271 Takes a boolean argument. If true, the time when the service unit
272 was last triggered is stored on disk. When the timer is activated,
273 the service unit is triggered immediately if it would have been
274 triggered at least once during the time when the timer was
275 inactive. Such triggering is nonetheless subject to the delay
276 imposed by RandomizedDelaySec=. This is useful to catch up on
277 missed runs of the service when the system was powered down. Note
278 that this setting only has an effect on timers configured with
279 OnCalendar=. Defaults to false.
280 Use systemctl clean --what=state ... on the timer unit to remove
282 the timestamp file maintained by this option from disk. In
283 particular, use this command before uninstalling a timer unit. See
284 systemctl(1) for details.
285 WakeSystem=
287 Takes a boolean argument. If true, an elapsing timer will cause the
288 system to resume from suspend, should it be suspended and if the
289 system supports this. Note that this option will only make sure the
290 system resumes on the appropriate times, it will not take care of
291 suspending it again after any work that is to be done is finished.
292 Defaults to false.
293 Note that this functionality requires privileges and is thus
295 generally only available in the system service manager.
296 Note that behaviour of monotonic clock timers (as configured with
298 OnActiveSec=, OnBootSec=, OnStartupSec=, OnUnitActiveSec=,
299 OnUnitInactiveSec=, see above) is altered depending on this option.
300 If false, a monotonic clock is used that is paused during system
301 suspend (CLOCK_MONOTONIC), if true a different monotonic clock is
302 used that continues advancing during system suspend
303 (CLOCK_BOOTTIME), see clock_getres(2) for details.
304 RemainAfterElapse=
306 Takes a boolean argument. If true, a timer will stay loaded, and
307 its state remains queryable even after it elapsed and the
308 associated unit (as configured with Unit=, see above) deactivated
309 again. If false, an elapsed timer unit that cannot elapse anymore
310 is unloaded once its associated unit deactivated again. Turning
311 this off is particularly useful for transient timer units. Note
312 that this setting has an effect when repeatedly starting a timer
313 unit: if RemainAfterElapse= is on, starting the timer a second time
314 has no effect. However, if RemainAfterElapse= is off and the timer
315 unit was already unloaded, it can be started again, and thus the
316 service can be triggered multiple times. Defaults to true.
317 Check systemd.unit(5), systemd.exec(5), and systemd.kill(5) for more
319 settings.
320
322 Environment variables with details on the trigger will be set for
323 triggered units. See the "Environment Variables Set or Propagated by
324 the Service Manager" section in systemd.exec(5) for more details.
325 systemd(1), systemctl(1), systemd.unit(5), systemd.service(5),
327 systemd.time(7), systemd.directives(7), systemd-system.conf(5),
328 prctl(2)
329systemd 254 SYSTEMD.TIMER(5)