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 pauses, too.
134 If the empty string is assigned to any of these options, the list
136 of timers is reset (both monotonic timers and OnCalendar= timers,
137 see below), and all prior assignments will have no effect.
138 Note that timers do not necessarily expire at the precise time
140 configured with these settings, as they are subject to the
141 AccuracySec= setting below.
142 OnCalendar=
144 Defines realtime (i.e. wallclock) timers with calendar event
145 expressions. See systemd.time(7) for more information on the syntax
146 of calendar event expressions. Otherwise, the semantics are similar
147 to OnActiveSec= and related settings.
148 Note that timers do not necessarily expire at the precise time
150 configured with this setting, as it is subject to the AccuracySec=
151 setting below.
152 May be specified more than once, in which case the timer unit will
154 trigger whenever any of the specified expressions elapse. Moreover
155 calendar timers and monotonic timers (see above) may be combined
156 within the same timer unit.
157 If the empty string is assigned to any of these options, the list
159 of timers is reset (both OnCalendar= timers and monotonic timers,
160 see above), and all prior assignments will have no effect.
161 AccuracySec=
163 Specify the accuracy the timer shall elapse with. Defaults to 1min.
164 The timer is scheduled to elapse within a time window starting with
165 the time specified in OnCalendar=, OnActiveSec=, OnBootSec=,
166 OnStartupSec=, OnUnitActiveSec= or OnUnitInactiveSec= and ending
167 the time configured with AccuracySec= later. Within this time
168 window, the expiry time will be placed at a host-specific,
169 randomized, but stable position that is synchronized between all
170 local timer units. This is done in order to optimize power
171 consumption to suppress unnecessary CPU wake-ups. To get best
172 accuracy, set this option to 1us. Note that the timer is still
173 subject to the timer slack configured via systemd-system.conf(5)'s
174 TimerSlackNSec= setting. See prctl(2) for details. To optimize
175 power consumption, make sure to set this value as high as possible
176 and as low as necessary.
177 RandomizedDelaySec=
179 Delay the timer by a randomly selected, evenly distributed amount
180 of time between 0 and the specified time value. Defaults to 0,
181 indicating that no randomized delay shall be applied. Each timer
182 unit will determine this delay randomly before each iteration, and
183 the delay will simply be added on top of the next determined
184 elapsing time. This is useful to stretch dispatching of similarly
185 configured timer events over a certain amount time, to avoid that
186 they all fire at the same time, possibly resulting in resource
187 congestion. Note the relation to AccuracySec= above: the latter
188 allows the service manager to coalesce timer events within a
189 specified time range in order to minimize wakeups, the former does
190 the opposite: it stretches timer events over a time range, to make
191 it unlikely that they fire simultaneously. If RandomizedDelaySec=
192 and AccuracySec= are used in conjunction, first the randomized
193 delay is added, and then the result is possibly further shifted to
194 coalesce it with other timer events happening on the system. As
195 mentioned above AccuracySec= defaults to 1min and
196 RandomizedDelaySec= to 0, thus encouraging coalescing of timer
197 events. In order to optimally stretch timer events over a certain
198 range of time, make sure to set RandomizedDelaySec= to a higher
199 value, and AccuracySec=1us.
200 OnClockChange=, OnTimezoneChange=
202 These options take boolean arguments. When true, the service unit
203 will be triggered when the system clock (CLOCK_REALTIME) jumps
204 relative to the monotonic clock (CLOCK_MONOTONIC), or when the
205 local system timezone is modified. These options can be used alone
206 or in combination with other timer expressions (see above) within
207 the same timer unit. These options default to false.
208 Unit=
210 The unit to activate when this timer elapses. The argument is a
211 unit name, whose suffix is not ".timer". If not specified, this
212 value defaults to a service that has the same name as the timer
213 unit, except for the suffix. (See above.) It is recommended that
214 the unit name that is activated and the unit name of the timer unit
215 are named identically, except for the suffix.
216 Persistent=
218 Takes a boolean argument. If true, the time when the service unit
219 was last triggered is stored on disk. When the timer is activated,
220 the service unit is triggered immediately if it would have been
221 triggered at least once during the time when the timer was
222 inactive. This is useful to catch up on missed runs of the service
223 when the system was powered down. Note that this setting only has
224 an effect on timers configured with OnCalendar=. Defaults to false.
225 Use systemctl clean --what=state ... on the timer unit to remove
227 the timestamp file maintained by this option from disk. In
228 particular, use this command before uninstalling a timer unit. See
229 systemctl(1) for details.
230 WakeSystem=
232 Takes a boolean argument. If true, an elapsing timer will cause the
233 system to resume from suspend, should it be suspended and if the
234 system supports this. Note that this option will only make sure the
235 system resumes on the appropriate times, it will not take care of
236 suspending it again after any work that is to be done is finished.
237 Defaults to false.
238 Note that this functionality requires privileges and is thus
240 generally only available in the system service manager.
241 RemainAfterElapse=
243 Takes a boolean argument. If true, an elapsed timer will stay
244 loaded, and its state remains queryable. If false, an elapsed timer
245 unit that cannot elapse anymore is unloaded. Turning this off is
246 particularly useful for transient timer units that shall disappear
247 after they first elapse. Note that this setting has an effect on
248 repeatedly starting a timer unit that only elapses once: if
249 RemainAfterElapse= is on, it will not be started again, and is
250 guaranteed to elapse only once. However, if RemainAfterElapse= is
251 off, it might be started again if it is already elapsed, and thus
252 be triggered multiple times. Defaults to yes.
253
255 systemd(1), systemctl(1), systemd.unit(5), systemd.service(5),
256 systemd.time(7), systemd.directives(7), systemd-system.conf(5),
257 prctl(2)
258systemd 243 SYSTEMD.TIMER(5)