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 will have an
55 additional After= dependency on time-sync.target to avoid being
56 started before the system clock has been correctly set.
57
59 Timer files must include a [Timer] section, which carries information
60 about the timer it defines. The options specific to the [Timer] section
61 of timer units are the following:
62 OnActiveSec=, OnBootSec=, OnStartupSec=, OnUnitActiveSec=,
64 OnUnitInactiveSec=
65 Defines monotonic timers relative to different starting points:
66 Table 1. Settings and their starting points
68 ┌───────────────────┬────────────────────────────┐
69 │Setting │ Meaning │
70 ├───────────────────┼────────────────────────────┤
71 │OnActiveSec= │ Defines a timer relative │
72 │ │ to the moment the timer │
73 │ │ unit itself is activated. │
74 ├───────────────────┼────────────────────────────┤
75 │OnBootSec= │ Defines a timer relative │
76 │ │ to when the machine was │
77 │ │ booted up. In containers, │
78 │ │ for the system manager │
79 │ │ instance, this is mapped │
80 │ │ to OnStartupSec=, making │
81 │ │ both equivalent. │
82 ├───────────────────┼────────────────────────────┤
83 │OnStartupSec= │ Defines a timer relative │
84 │ │ to when the service │
85 │ │ manager was first started. │
86 │ │ For system timer units │
87 │ │ this is very similar to │
88 │ │ OnBootSec= as the system │
89 │ │ service manager is │
90 │ │ generally started very │
91 │ │ early at boot. It's │
92 │ │ primarily useful when │
93 │ │ configured in units │
94 │ │ running in the per-user │
95 │ │ service manager, as the │
96 │ │ user service manager is │
97 │ │ generally started on first │
98 │ │ login only, not already │
99 │ │ during boot. │
100 ├───────────────────┼────────────────────────────┤
101 │OnUnitActiveSec= │ Defines a timer relative │
102 │ │ to when the unit the timer │
103 │ │ unit is activating was │
104 │ │ last activated. │
105 ├───────────────────┼────────────────────────────┤
106 │OnUnitInactiveSec= │ Defines a timer relative │
107 │ │ to when the unit the timer │
108 │ │ unit is activating was │
109 │ │ last deactivated. │
110 └───────────────────┴────────────────────────────┘
111 Multiple directives may be combined of the same and of different
112 types, in which case the timer unit will trigger whenever any of
113 the specified timer expressions elapse. For example, by combining
114 OnBootSec= and OnUnitActiveSec=, it is possible to define a timer
115 that elapses in regular intervals and activates a specific service
116 each time. Moreover, both monotonic time expressions and
117 OnCalendar= calendar expressions may be combined in the same timer
118 unit.
119 The arguments to the directives are time spans configured in
121 seconds. Example: "OnBootSec=50" means 50s after boot-up. The
122 argument may also include time units. Example: "OnBootSec=5h 30min"
123 means 5 hours and 30 minutes after boot-up. For details about the
124 syntax of time spans, see systemd.time(7).
125 If a timer configured with OnBootSec= or OnStartupSec= is already
127 in the past when the timer unit is activated, it will immediately
128 elapse and the configured unit is started. This is not the case for
129 timers defined in the other directives.
130 These are monotonic timers, independent of wall-clock time and
132 timezones. If the computer is temporarily suspended, the monotonic
133 clock generally pauses, too. Note that if WakeSystem= is used, a
134 different monotonic clock is selected that continues to advance
135 while the system is suspended and thus can be used as the trigger
136 to resume the system.
137 If the empty string is assigned to any of these options, the list
139 of timers is reset (both monotonic timers and OnCalendar= timers,
140 see below), and all prior assignments will have no effect.
141 Note that timers do not necessarily expire at the precise time
143 configured with these settings, as they are subject to the
144 AccuracySec= setting below.
145 OnCalendar=
147 Defines realtime (i.e. wallclock) timers with calendar event
148 expressions. See systemd.time(7) for more information on the syntax
149 of calendar event expressions. Otherwise, the semantics are similar
150 to OnActiveSec= and related settings.
151 Note that timers do not necessarily expire at the precise time
153 configured with this setting, as it is subject to the AccuracySec=
154 setting below.
155 May be specified more than once, in which case the timer unit will
157 trigger whenever any of the specified expressions elapse. Moreover
158 calendar timers and monotonic timers (see above) may be combined
159 within the same timer unit.
160 If the empty string is assigned to any of these options, the list
162 of timers is reset (both OnCalendar= timers and monotonic timers,
163 see above), and all prior assignments will have no effect.
164 AccuracySec=
166 Specify the accuracy the timer shall elapse with. Defaults to 1min.
167 The timer is scheduled to elapse within a time window starting with
168 the time specified in OnCalendar=, OnActiveSec=, OnBootSec=,
169 OnStartupSec=, OnUnitActiveSec= or OnUnitInactiveSec= and ending
170 the time configured with AccuracySec= later. Within this time
171 window, the expiry time will be placed at a host-specific,
172 randomized, but stable position that is synchronized between all
173 local timer units. This is done in order to optimize power
174 consumption to suppress unnecessary CPU wake-ups. To get best
175 accuracy, set this option to 1us. Note that the timer is still
176 subject to the timer slack configured via systemd-system.conf(5)'s
177 TimerSlackNSec= setting. See prctl(2) for details. To optimize
178 power consumption, make sure to set this value as high as possible
179 and as low as necessary.
180 Note that this setting is primarily a power saving option that
182 allows coalescing CPU wake-ups. It should not be confused with
183 RandomizedDelaySec= (see below) which adds a random value to the
184 time the timer shall elapse next and whose purpose is the opposite:
185 to stretch elapsing of timer events over a longer period to reduce
186 workload spikes. For further details and explanations and how both
187 settings play together, see below.
188 RandomizedDelaySec=
190 Delay the timer by a randomly selected, evenly distributed amount
191 of time between 0 and the specified time value. Defaults to 0,
192 indicating that no randomized delay shall be applied. Each timer
193 unit will determine this delay randomly before each iteration, and
194 the delay will simply be added on top of the next determined
195 elapsing time. This is useful to stretch dispatching of similarly
196 configured timer events over a certain amount time, to avoid that
197 they all fire at the same time, possibly resulting in resource
198 congestion. Note the relation to AccuracySec= above: the latter
199 allows the service manager to coalesce timer events within a
200 specified time range in order to minimize wakeups, the former does
201 the opposite: it stretches timer events over a time range, to make
202 it unlikely that they fire simultaneously. If RandomizedDelaySec=
203 and AccuracySec= are used in conjunction, first the randomized
204 delay is added, and then the result is possibly further shifted to
205 coalesce it with other timer events happening on the system. As
206 mentioned above AccuracySec= defaults to 1min and
207 RandomizedDelaySec= to 0, thus encouraging coalescing of timer
208 events. In order to optimally stretch timer events over a certain
209 range of time, make sure to set RandomizedDelaySec= to a higher
210 value, and AccuracySec=1us.
211 OnClockChange=, OnTimezoneChange=
213 These options take boolean arguments. When true, the service unit
214 will be triggered when the system clock (CLOCK_REALTIME) jumps
215 relative to the monotonic clock (CLOCK_MONOTONIC), or when the
216 local system timezone is modified. These options can be used alone
217 or in combination with other timer expressions (see above) within
218 the same timer unit. These options default to false.
219 Unit=
221 The unit to activate when this timer elapses. The argument is a
222 unit name, whose suffix is not ".timer". If not specified, this
223 value defaults to a service that has the same name as the timer
224 unit, except for the suffix. (See above.) It is recommended that
225 the unit name that is activated and the unit name of the timer unit
226 are named identically, except for the suffix.
227 Persistent=
229 Takes a boolean argument. If true, the time when the service unit
230 was last triggered is stored on disk. When the timer is activated,
231 the service unit is triggered immediately if it would have been
232 triggered at least once during the time when the timer was
233 inactive. This is useful to catch up on missed runs of the service
234 when the system was powered down. Note that this setting only has
235 an effect on timers configured with OnCalendar=. Defaults to false.
236 Use systemctl clean --what=state ... on the timer unit to remove
238 the timestamp file maintained by this option from disk. In
239 particular, use this command before uninstalling a timer unit. See
240 systemctl(1) for details.
241 WakeSystem=
243 Takes a boolean argument. If true, an elapsing timer will cause the
244 system to resume from suspend, should it be suspended and if the
245 system supports this. Note that this option will only make sure the
246 system resumes on the appropriate times, it will not take care of
247 suspending it again after any work that is to be done is finished.
248 Defaults to false.
249 Note that this functionality requires privileges and is thus
251 generally only available in the system service manager.
252 Note that behaviour of monotonic clock timers (as configured with
254 OnActiveSec=, OnBootSec=, OnStartupSec=, OnUnitActiveSec=,
255 OnUnitInactiveSec=, see above) is altered depending on this option.
256 If false, a monotonic clock is used that is paused during system
257 suspend (CLOCK_MONOTONIC), if true a different monotonic clock is
258 used that continues advancing during system suspend
259 (CLOCK_BOOTTIME), see clock_getres(2) for details.
260 RemainAfterElapse=
262 Takes a boolean argument. If true, an elapsed timer will stay
263 loaded, and its state remains queryable. If false, an elapsed timer
264 unit that cannot elapse anymore is unloaded. Turning this off is
265 particularly useful for transient timer units that shall disappear
266 after they first elapse. Note that this setting has an effect on
267 repeatedly starting a timer unit that only elapses once: if
268 RemainAfterElapse= is on, it will not be started again, and is
269 guaranteed to elapse only once. However, if RemainAfterElapse= is
270 off, it might be started again if it is already elapsed, and thus
271 be triggered multiple times. Defaults to yes.
272
274 systemd(1), systemctl(1), systemd.unit(5), systemd.service(5),
275 systemd.time(7), systemd.directives(7), systemd-system.conf(5),
276 prctl(2)
277systemd 245 SYSTEMD.TIMER(5)