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12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
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4 | |
5 | <!-- | |
572eb058 | 6 | SPDX-License-Identifier: LGPL-2.1+ |
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7 | --> |
8 | ||
9 | <refentry id="systemd.timer"> | |
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10 | <refentryinfo> |
11 | <title>systemd.timer</title> | |
12 | <productname>systemd</productname> | |
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13 | </refentryinfo> |
14 | ||
15 | <refmeta> | |
16 | <refentrytitle>systemd.timer</refentrytitle> | |
17 | <manvolnum>5</manvolnum> | |
18 | </refmeta> | |
19 | ||
20 | <refnamediv> | |
21 | <refname>systemd.timer</refname> | |
22 | <refpurpose>Timer unit configuration</refpurpose> | |
23 | </refnamediv> | |
24 | ||
25 | <refsynopsisdiv> | |
26 | <para><filename><replaceable>timer</replaceable>.timer</filename></para> | |
27 | </refsynopsisdiv> | |
28 | ||
29 | <refsect1> | |
30 | <title>Description</title> | |
31 | ||
32 | <para>A unit configuration file whose name ends in | |
33 | <literal>.timer</literal> encodes information about a timer | |
34 | controlled and supervised by systemd, for timer-based | |
35 | activation.</para> | |
36 | ||
37 | <para>This man page lists the configuration options specific to | |
38 | this unit type. See | |
39 | <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
40 | for the common options of all unit configuration files. The common | |
41 | configuration items are configured in the generic [Unit] and | |
42 | [Install] sections. The timer specific configuration options are | |
43 | configured in the [Timer] section.</para> | |
44 | ||
45 | <para>For each timer file, a matching unit file must exist, | |
46 | describing the unit to activate when the timer elapses. By | |
47 | default, a service by the same name as the timer (except for the | |
48 | suffix) is activated. Example: a timer file | |
49 | <filename>foo.timer</filename> activates a matching service | |
50 | <filename>foo.service</filename>. The unit to activate may be | |
51 | controlled by <varname>Unit=</varname> (see below).</para> | |
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52 | |
53 | <para>Note that in case the unit to activate is already active at the time the timer elapses it is not restarted, | |
54 | but simply left running. There is no concept of spawning new service instances in this case. Due to this, services | |
595bfe7d | 55 | with <varname>RemainAfterExit=</varname> set (which stay around continuously even after the service's main process |
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56 | exited) are usually not suitable for activation via repetitive timers, as they will only be activated once, and |
57 | then stay around forever.</para> | |
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58 | </refsect1> |
59 | ||
60 | <refsect1> | |
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61 | <title>Implicit Dependencies</title> |
62 | ||
63 | <para>The following dependencies are implicitly added:</para> | |
64 | ||
65 | <itemizedlist> | |
66 | <listitem><para>Timer units automatically gain a <varname>Before=</varname> | |
67 | dependency on the service they are supposed to activate.</para></listitem> | |
68 | </itemizedlist> | |
69 | </refsect1> | |
70 | ||
71 | <refsect1> | |
aed5cb03 | 72 | <title>Automatic Dependencies</title> |
45f09f93 | 73 | |
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74 | <refsect2> |
75 | <title>Implicit Dependencies</title> | |
45f09f93 | 76 | |
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77 | <para>There are no implicit dependencies for timer units.</para> |
78 | </refsect2> | |
79 | ||
80 | <refsect2> | |
81 | <title>Default Dependencies</title> | |
82 | ||
83 | <para>The following dependencies are added unless <varname>DefaultDependencies=no</varname> is set:</para> | |
84 | ||
85 | <itemizedlist> | |
86 | <listitem><para>Timer units will automatically have dependencies of type <varname>Requires=</varname> and | |
87 | <varname>After=</varname> on <filename>sysinit.target</filename>, a dependency of type <varname>Before=</varname> | |
88 | on <filename>timers.target</filename>, as well as <varname>Conflicts=</varname> and <varname>Before=</varname> on | |
89 | <filename>shutdown.target</filename> to ensure that they are stopped cleanly prior to system shutdown. Only timer | |
90 | units involved with early boot or late system shutdown should disable the | |
91 | <varname>DefaultDependencies=</varname> option.</para></listitem> | |
92 | ||
93 | <listitem><para>Timer units | |
94 | with at least one <varname>OnCalendar=</varname> directive will have an additional <varname>After=</varname> | |
95 | dependency on <filename>time-sync.target</filename> to avoid being started before the system clock has been | |
96 | correctly set.</para></listitem> | |
97 | </itemizedlist> | |
98 | </refsect2> | |
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99 | </refsect1> |
100 | ||
101 | <refsect1> | |
102 | <title>Options</title> | |
103 | ||
104 | <para>Timer files must include a [Timer] section, which carries | |
105 | information about the timer it defines. The options specific to | |
106 | the [Timer] section of timer units are the following:</para> | |
107 | ||
108 | <variablelist class='unit-directives'> | |
109 | <varlistentry> | |
110 | <term><varname>OnActiveSec=</varname></term> | |
111 | <term><varname>OnBootSec=</varname></term> | |
112 | <term><varname>OnStartupSec=</varname></term> | |
113 | <term><varname>OnUnitActiveSec=</varname></term> | |
114 | <term><varname>OnUnitInactiveSec=</varname></term> | |
115 | ||
116 | <listitem><para>Defines monotonic timers relative to different | |
117 | starting points: <varname>OnActiveSec=</varname> defines a | |
118 | timer relative to the moment the timer itself is activated. | |
119 | <varname>OnBootSec=</varname> defines a timer relative to when | |
120 | the machine was booted up. <varname>OnStartupSec=</varname> | |
121 | defines a timer relative to when systemd was first started. | |
122 | <varname>OnUnitActiveSec=</varname> defines a timer relative | |
123 | to when the unit the timer is activating was last activated. | |
124 | <varname>OnUnitInactiveSec=</varname> defines a timer relative | |
125 | to when the unit the timer is activating was last | |
126 | deactivated.</para> | |
127 | ||
128 | <para>Multiple directives may be combined of the same and of | |
129 | different types. For example, by combining | |
130 | <varname>OnBootSec=</varname> and | |
131 | <varname>OnUnitActiveSec=</varname>, it is possible to define | |
132 | a timer that elapses in regular intervals and activates a | |
133 | specific service each time.</para> | |
134 | ||
135 | <para>The arguments to the directives are time spans | |
136 | configured in seconds. Example: "OnBootSec=50" means 50s after | |
137 | boot-up. The argument may also include time units. Example: | |
138 | "OnBootSec=5h 30min" means 5 hours and 30 minutes after | |
139 | boot-up. For details about the syntax of time spans, see | |
9905e698 | 140 | <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para> |
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141 | |
142 | <para>If a timer configured with <varname>OnBootSec=</varname> | |
143 | or <varname>OnStartupSec=</varname> is already in the past | |
144 | when the timer unit is activated, it will immediately elapse | |
145 | and the configured unit is started. This is not the case for | |
146 | timers defined in the other directives.</para> | |
147 | ||
148 | <para>These are monotonic timers, independent of wall-clock | |
149 | time and timezones. If the computer is temporarily suspended, | |
150 | the monotonic clock stops too.</para> | |
151 | ||
152 | <para>If the empty string is assigned to any of these options, | |
153 | the list of timers is reset, and all prior assignments will | |
154 | have no effect.</para> | |
155 | ||
156 | <para>Note that timers do not necessarily expire at the | |
157 | precise time configured with these settings, as they are | |
158 | subject to the <varname>AccuracySec=</varname> setting | |
159 | below.</para></listitem> | |
160 | ||
161 | </varlistentry> | |
162 | ||
163 | <varlistentry> | |
164 | <term><varname>OnCalendar=</varname></term> | |
165 | ||
166 | <listitem><para>Defines realtime (i.e. wallclock) timers with | |
167 | calendar event expressions. See | |
168 | <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
169 | for more information on the syntax of calendar event | |
170 | expressions. Otherwise, the semantics are similar to | |
171 | <varname>OnActiveSec=</varname> and related settings.</para> | |
172 | ||
173 | <para>Note that timers do not necessarily expire at the | |
174 | precise time configured with this setting, as it is subject to | |
175 | the <varname>AccuracySec=</varname> setting | |
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176 | below.</para> |
177 | ||
178 | <para>May be specified more than once.</para></listitem> | |
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179 | </varlistentry> |
180 | ||
181 | <varlistentry> | |
182 | <term><varname>AccuracySec=</varname></term> | |
183 | ||
184 | <listitem><para>Specify the accuracy the timer shall elapse | |
185 | with. Defaults to 1min. The timer is scheduled to elapse | |
186 | within a time window starting with the time specified in | |
187 | <varname>OnCalendar=</varname>, | |
188 | <varname>OnActiveSec=</varname>, | |
189 | <varname>OnBootSec=</varname>, | |
190 | <varname>OnStartupSec=</varname>, | |
191 | <varname>OnUnitActiveSec=</varname> or | |
192 | <varname>OnUnitInactiveSec=</varname> and ending the time | |
193 | configured with <varname>AccuracySec=</varname> later. Within | |
194 | this time window, the expiry time will be placed at a | |
744c7693 | 195 | host-specific, randomized, but stable position that is |
798d3a52 | 196 | synchronized between all local timer units. This is done in |
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197 | order to optimize power consumption to suppress unnecessary |
198 | CPU wake-ups. To get best accuracy, set this option to | |
199 | 1us. Note that the timer is still subject to the timer slack | |
200 | configured via | |
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201 | <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s |
202 | <varname>TimerSlackNSec=</varname> setting. See | |
203 | <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
204 | for details. To optimize power consumption, make sure to set | |
205 | this value as high as possible and as low as | |
206 | necessary.</para></listitem> | |
207 | </varlistentry> | |
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208 | |
209 | <varlistentry> | |
6f5d7998 | 210 | <term><varname>RandomizedDelaySec=</varname></term> |
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211 | |
212 | <listitem><para>Delay the timer by a randomly selected, evenly | |
213 | distributed amount of time between 0 and the specified time | |
214 | value. Defaults to 0, indicating that no randomized delay | |
215 | shall be applied. Each timer unit will determine this delay | |
216 | randomly each time it is started, and the delay will simply be | |
217 | added on top of the next determined elapsing time. This is | |
218 | useful to stretch dispatching of similarly configured timer | |
219 | events over a certain amount time, to avoid that they all fire | |
220 | at the same time, possibly resulting in resource | |
221 | congestion. Note the relation to | |
222 | <varname>AccuracySec=</varname> above: the latter allows the | |
223 | service manager to coalesce timer events within a specified | |
224 | time range in order to minimize wakeups, the former does the | |
225 | opposite: it stretches timer events over a time range, to make | |
226 | it unlikely that they fire simultaneously. If | |
6f5d7998 | 227 | <varname>RandomizedDelaySec=</varname> and |
744c7693 | 228 | <varname>AccuracySec=</varname> are used in conjunction, first |
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229 | the randomized delay is added, and then the result is |
230 | possibly further shifted to coalesce it with other timer | |
231 | events happening on the system. As mentioned above | |
744c7693 | 232 | <varname>AccuracySec=</varname> defaults to 1min and |
6f5d7998 | 233 | <varname>RandomizedDelaySec=</varname> to 0, thus encouraging |
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234 | coalescing of timer events. In order to optimally stretch |
235 | timer events over a certain range of time, make sure to set | |
6f5d7998 | 236 | <varname>RandomizedDelaySec=</varname> to a higher value, and |
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237 | <varname>AccuracySec=1us</varname>.</para></listitem> |
238 | </varlistentry> | |
239 | ||
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240 | <varlistentry> |
241 | <term><varname>Unit=</varname></term> | |
242 | ||
243 | <listitem><para>The unit to activate when this timer elapses. | |
244 | The argument is a unit name, whose suffix is not | |
245 | <literal>.timer</literal>. If not specified, this value | |
246 | defaults to a service that has the same name as the timer | |
247 | unit, except for the suffix. (See above.) It is recommended | |
248 | that the unit name that is activated and the unit name of the | |
249 | timer unit are named identically, except for the | |
250 | suffix.</para></listitem> | |
251 | </varlistentry> | |
252 | ||
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253 | <varlistentry> |
254 | <term><varname>Persistent=</varname></term> | |
255 | ||
256 | <listitem><para>Takes a boolean argument. If true, the time | |
257 | when the service unit was last triggered is stored on disk. | |
258 | When the timer is activated, the service unit is triggered | |
259 | immediately if it would have been triggered at least once | |
260 | during the time when the timer was inactive. This is useful to | |
261 | catch up on missed runs of the service when the machine was | |
262 | off. Note that this setting only has an effect on timers | |
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263 | configured with <varname>OnCalendar=</varname>. Defaults |
264 | to <varname>false</varname>. | |
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265 | </para></listitem> |
266 | </varlistentry> | |
267 | ||
268 | <varlistentry> | |
269 | <term><varname>WakeSystem=</varname></term> | |
270 | ||
271 | <listitem><para>Takes a boolean argument. If true, an elapsing | |
272 | timer will cause the system to resume from suspend, should it | |
273 | be suspended and if the system supports this. Note that this | |
274 | option will only make sure the system resumes on the | |
275 | appropriate times, it will not take care of suspending it | |
276 | again after any work that is to be done is finished. Defaults | |
277 | to <varname>false</varname>.</para></listitem> | |
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278 | </varlistentry> |
279 | ||
280 | <varlistentry> | |
70b4f819 | 281 | <term><varname>RemainAfterElapse=</varname></term> |
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282 | |
283 | <listitem><para>Takes a boolean argument. If true, an elapsed | |
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284 | timer will stay loaded, and its state remains queriable. If |
285 | false, an elapsed timer unit that cannot elapse anymore is | |
286 | unloaded. Turning this off is particularly useful for | |
287 | transient timer units that shall disappear after they first | |
288 | elapse. Note that this setting has an effect on repeatedly | |
7f3fdb7f | 289 | starting a timer unit that only elapses once: if |
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290 | <varname>RemainAfterElapse=</varname> is on, it will not be |
291 | started again, and is guaranteed to elapse only once. However, | |
23743744 | 292 | if <varname>RemainAfterElapse=</varname> is off, it might be |
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293 | started again if it is already elapsed, and thus be triggered |
294 | multiple times. Defaults to | |
3e0c30ac | 295 | <varname>yes</varname>.</para></listitem> |
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296 | </varlistentry> |
297 | </variablelist> | |
298 | </refsect1> | |
299 | ||
300 | <refsect1> | |
301 | <title>See Also</title> | |
302 | <para> | |
303 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
304 | <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
305 | <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
306 | <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
307 | <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
308 | <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
309 | <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
310 | <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
311 | </para> | |
312 | </refsect1> | |
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313 | |
314 | </refentry> |