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 The following dependencies are implicitly added:
38 · Timer units automatically gain a Before= dependency on the service
40 they are supposed to activate.
41
43 Implicit Dependencies
44 There are no implicit dependencies for timer units.
45 Default Dependencies
47 The following dependencies are added unless DefaultDependencies=no is
48 set:
49 · Timer units will automatically have dependencies of type Requires=
51 and After= on sysinit.target, a dependency of type Before= on
52 timers.target, as well as Conflicts= and Before= on shutdown.target
53 to ensure that they are stopped cleanly prior to system shutdown.
54 Only timer units involved with early boot or late system shutdown
55 should disable the DefaultDependencies= option.
56 · Timer units with at least one OnCalendar= directive will have an
58 additional After= dependency on time-sync.target to avoid being
59 started before the system clock has been correctly set.
60
62 Timer files must include a [Timer] section, which carries information
63 about the timer it defines. The options specific to the [Timer] section
64 of timer units are the following:
65 OnActiveSec=, OnBootSec=, OnStartupSec=, OnUnitActiveSec=,
67 OnUnitInactiveSec=
68 Defines monotonic timers relative to different starting points:
69 OnActiveSec= defines a timer relative to the moment the timer
70 itself is activated. OnBootSec= defines a timer relative to when
71 the machine was booted up. OnStartupSec= defines a timer relative
72 to when systemd was first started. OnUnitActiveSec= defines a
73 timer relative to when the unit the timer is activating was last
74 activated. OnUnitInactiveSec= defines a timer relative to when the
75 unit the timer is activating was last deactivated.
76 Multiple directives may be combined of the same and of different
78 types. For example, by combining OnBootSec= and OnUnitActiveSec=,
79 it is possible to define a timer that elapses in regular intervals
80 and activates a specific service each time.
81 The arguments to the directives are time spans configured in
83 seconds. Example: "OnBootSec=50" means 50s after boot-up. The
84 argument may also include time units. Example: "OnBootSec=5h 30min"
85 means 5 hours and 30 minutes after boot-up. For details about the
86 syntax of time spans, see systemd.time(7).
87 If a timer configured with OnBootSec= or OnStartupSec= is already
89 in the past when the timer unit is activated, it will immediately
90 elapse and the configured unit is started. This is not the case for
91 timers defined in the other directives.
92 These are monotonic timers, independent of wall-clock time and
94 timezones. If the computer is temporarily suspended, the monotonic
95 clock stops too.
96 If the empty string is assigned to any of these options, the list
98 of timers is reset, and all prior assignments will have no effect.
99 Note that timers do not necessarily expire at the precise time
101 configured with these settings, as they are subject to the
102 AccuracySec= setting below.
103 OnCalendar=
105 Defines realtime (i.e. wallclock) timers with calendar event
106 expressions. See systemd.time(7) for more information on the syntax
107 of calendar event expressions. Otherwise, the semantics are similar
108 to OnActiveSec= and related settings.
109 Note that timers do not necessarily expire at the precise time
111 configured with this setting, as it is subject to the AccuracySec=
112 setting below.
113 May be specified more than once.
115 AccuracySec=
117 Specify the accuracy the timer shall elapse with. Defaults to 1min.
118 The timer is scheduled to elapse within a time window starting with
119 the time specified in OnCalendar=, OnActiveSec=, OnBootSec=,
120 OnStartupSec=, OnUnitActiveSec= or OnUnitInactiveSec= and ending
121 the time configured with AccuracySec= later. Within this time
122 window, the expiry time will be placed at a host-specific,
123 randomized, but stable position that is synchronized between all
124 local timer units. This is done in order to optimize power
125 consumption to suppress unnecessary CPU wake-ups. To get best
126 accuracy, set this option to 1us. Note that the timer is still
127 subject to the timer slack configured via systemd-system.conf(5)'s
128 TimerSlackNSec= setting. See prctl(2) for details. To optimize
129 power consumption, make sure to set this value as high as possible
130 and as low as necessary.
131 RandomizedDelaySec=
133 Delay the timer by a randomly selected, evenly distributed amount
134 of time between 0 and the specified time value. Defaults to 0,
135 indicating that no randomized delay shall be applied. Each timer
136 unit will determine this delay randomly each time it is started,
137 and the delay will simply be added on top of the next determined
138 elapsing time. This is useful to stretch dispatching of similarly
139 configured timer events over a certain amount time, to avoid that
140 they all fire at the same time, possibly resulting in resource
141 congestion. Note the relation to AccuracySec= above: the latter
142 allows the service manager to coalesce timer events within a
143 specified time range in order to minimize wakeups, the former does
144 the opposite: it stretches timer events over a time range, to make
145 it unlikely that they fire simultaneously. If RandomizedDelaySec=
146 and AccuracySec= are used in conjunction, first the randomized
147 delay is added, and then the result is possibly further shifted to
148 coalesce it with other timer events happening on the system. As
149 mentioned above AccuracySec= defaults to 1min and
150 RandomizedDelaySec= to 0, thus encouraging coalescing of timer
151 events. In order to optimally stretch timer events over a certain
152 range of time, make sure to set RandomizedDelaySec= to a higher
153 value, and AccuracySec=1us.
154 Unit=
156 The unit to activate when this timer elapses. The argument is a
157 unit name, whose suffix is not ".timer". If not specified, this
158 value defaults to a service that has the same name as the timer
159 unit, except for the suffix. (See above.) It is recommended that
160 the unit name that is activated and the unit name of the timer unit
161 are named identically, except for the suffix.
162 Persistent=
164 Takes a boolean argument. If true, the time when the service unit
165 was last triggered is stored on disk. When the timer is activated,
166 the service unit is triggered immediately if it would have been
167 triggered at least once during the time when the timer was
168 inactive. This is useful to catch up on missed runs of the service
169 when the machine was off. Note that this setting only has an effect
170 on timers configured with OnCalendar=. Defaults to false.
171 WakeSystem=
173 Takes a boolean argument. If true, an elapsing timer will cause the
174 system to resume from suspend, should it be suspended and if the
175 system supports this. Note that this option will only make sure the
176 system resumes on the appropriate times, it will not take care of
177 suspending it again after any work that is to be done is finished.
178 Defaults to false.
179 RemainAfterElapse=
181 Takes a boolean argument. If true, an elapsed timer will stay
182 loaded, and its state remains queriable. If false, an elapsed timer
183 unit that cannot elapse anymore is unloaded. Turning this off is
184 particularly useful for transient timer units that shall disappear
185 after they first elapse. Note that this setting has an effect on
186 repeatedly starting a timer unit that only elapses once: if
187 RemainAfterElapse= is on, it will not be started again, and is
188 guaranteed to elapse only once. However, if RemainAfterElapse= is
189 off, it might be started again if it is already elapsed, and thus
190 be triggered multiple times. Defaults to yes.
191
193 systemd(1), systemctl(1), systemd.unit(5), systemd.service(5),
194 systemd.time(7), systemd.directives(7), systemd-system.conf(5),
195 prctl(2)
196systemd 239 SYSTEMD.TIMER(5)