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12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
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4 | |
5 | <!-- | |
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6 | SPDX-License-Identifier: LGPL-2.1+ |
7 | ||
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8 | This file is part of systemd. |
9 | ||
10 | Copyright 2010 Lennart Poettering | |
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11 | --> |
12 | ||
13 | <refentry id="systemd.timer"> | |
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14 | <refentryinfo> |
15 | <title>systemd.timer</title> | |
16 | <productname>systemd</productname> | |
17 | ||
18 | <authorgroup> | |
19 | <author> | |
20 | <contrib>Developer</contrib> | |
21 | <firstname>Lennart</firstname> | |
22 | <surname>Poettering</surname> | |
23 | <email>lennart@poettering.net</email> | |
24 | </author> | |
25 | </authorgroup> | |
26 | </refentryinfo> | |
27 | ||
28 | <refmeta> | |
29 | <refentrytitle>systemd.timer</refentrytitle> | |
30 | <manvolnum>5</manvolnum> | |
31 | </refmeta> | |
32 | ||
33 | <refnamediv> | |
34 | <refname>systemd.timer</refname> | |
35 | <refpurpose>Timer unit configuration</refpurpose> | |
36 | </refnamediv> | |
37 | ||
38 | <refsynopsisdiv> | |
39 | <para><filename><replaceable>timer</replaceable>.timer</filename></para> | |
40 | </refsynopsisdiv> | |
41 | ||
42 | <refsect1> | |
43 | <title>Description</title> | |
44 | ||
45 | <para>A unit configuration file whose name ends in | |
46 | <literal>.timer</literal> encodes information about a timer | |
47 | controlled and supervised by systemd, for timer-based | |
48 | activation.</para> | |
49 | ||
50 | <para>This man page lists the configuration options specific to | |
51 | this unit type. See | |
52 | <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
53 | for the common options of all unit configuration files. The common | |
54 | configuration items are configured in the generic [Unit] and | |
55 | [Install] sections. The timer specific configuration options are | |
56 | configured in the [Timer] section.</para> | |
57 | ||
58 | <para>For each timer file, a matching unit file must exist, | |
59 | describing the unit to activate when the timer elapses. By | |
60 | default, a service by the same name as the timer (except for the | |
61 | suffix) is activated. Example: a timer file | |
62 | <filename>foo.timer</filename> activates a matching service | |
63 | <filename>foo.service</filename>. The unit to activate may be | |
64 | controlled by <varname>Unit=</varname> (see below).</para> | |
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65 | |
66 | <para>Note that in case the unit to activate is already active at the time the timer elapses it is not restarted, | |
67 | but simply left running. There is no concept of spawning new service instances in this case. Due to this, services | |
595bfe7d | 68 | with <varname>RemainAfterExit=</varname> set (which stay around continuously even after the service's main process |
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69 | exited) are usually not suitable for activation via repetitive timers, as they will only be activated once, and |
70 | then stay around forever.</para> | |
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71 | </refsect1> |
72 | ||
73 | <refsect1> | |
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74 | <title>Implicit Dependencies</title> |
75 | ||
76 | <para>The following dependencies are implicitly added:</para> | |
77 | ||
78 | <itemizedlist> | |
79 | <listitem><para>Timer units automatically gain a <varname>Before=</varname> | |
80 | dependency on the service they are supposed to activate.</para></listitem> | |
81 | </itemizedlist> | |
82 | </refsect1> | |
83 | ||
84 | <refsect1> | |
85 | <title>Default Dependencies</title> | |
86 | ||
87 | <para>The following dependencies are added unless <varname>DefaultDependencies=no</varname> is set:</para> | |
88 | ||
89 | <itemizedlist> | |
90 | <listitem><para>Timer units will automatically have dependencies of type <varname>Requires=</varname> and | |
91 | <varname>After=</varname> on <filename>sysinit.target</filename>, a dependency of type <varname>Before=</varname> | |
92 | on <filename>timers.target</filename>, as well as <varname>Conflicts=</varname> and <varname>Before=</varname> on | |
93 | <filename>shutdown.target</filename> to ensure that they are stopped cleanly prior to system shutdown. Only timer | |
94 | units involved with early boot or late system shutdown should disable the | |
95 | <varname>DefaultDependencies=</varname> option.</para></listitem> | |
96 | ||
97 | <listitem><para>Timer units | |
98 | with at least one <varname>OnCalendar=</varname> directive will have an additional <varname>After=</varname> | |
99 | dependency on <filename>time-sync.target</filename> to avoid being started before the system clock has been | |
100 | correctly set.</para></listitem> | |
101 | </itemizedlist> | |
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102 | </refsect1> |
103 | ||
104 | <refsect1> | |
105 | <title>Options</title> | |
106 | ||
107 | <para>Timer files must include a [Timer] section, which carries | |
108 | information about the timer it defines. The options specific to | |
109 | the [Timer] section of timer units are the following:</para> | |
110 | ||
111 | <variablelist class='unit-directives'> | |
112 | <varlistentry> | |
113 | <term><varname>OnActiveSec=</varname></term> | |
114 | <term><varname>OnBootSec=</varname></term> | |
115 | <term><varname>OnStartupSec=</varname></term> | |
116 | <term><varname>OnUnitActiveSec=</varname></term> | |
117 | <term><varname>OnUnitInactiveSec=</varname></term> | |
118 | ||
119 | <listitem><para>Defines monotonic timers relative to different | |
120 | starting points: <varname>OnActiveSec=</varname> defines a | |
121 | timer relative to the moment the timer itself is activated. | |
122 | <varname>OnBootSec=</varname> defines a timer relative to when | |
123 | the machine was booted up. <varname>OnStartupSec=</varname> | |
124 | defines a timer relative to when systemd was first started. | |
125 | <varname>OnUnitActiveSec=</varname> defines a timer relative | |
126 | to when the unit the timer is activating was last activated. | |
127 | <varname>OnUnitInactiveSec=</varname> defines a timer relative | |
128 | to when the unit the timer is activating was last | |
129 | deactivated.</para> | |
130 | ||
131 | <para>Multiple directives may be combined of the same and of | |
132 | different types. For example, by combining | |
133 | <varname>OnBootSec=</varname> and | |
134 | <varname>OnUnitActiveSec=</varname>, it is possible to define | |
135 | a timer that elapses in regular intervals and activates a | |
136 | specific service each time.</para> | |
137 | ||
138 | <para>The arguments to the directives are time spans | |
139 | configured in seconds. Example: "OnBootSec=50" means 50s after | |
140 | boot-up. The argument may also include time units. Example: | |
141 | "OnBootSec=5h 30min" means 5 hours and 30 minutes after | |
142 | boot-up. For details about the syntax of time spans, see | |
9905e698 | 143 | <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para> |
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144 | |
145 | <para>If a timer configured with <varname>OnBootSec=</varname> | |
146 | or <varname>OnStartupSec=</varname> is already in the past | |
147 | when the timer unit is activated, it will immediately elapse | |
148 | and the configured unit is started. This is not the case for | |
149 | timers defined in the other directives.</para> | |
150 | ||
151 | <para>These are monotonic timers, independent of wall-clock | |
152 | time and timezones. If the computer is temporarily suspended, | |
153 | the monotonic clock stops too.</para> | |
154 | ||
155 | <para>If the empty string is assigned to any of these options, | |
156 | the list of timers is reset, and all prior assignments will | |
157 | have no effect.</para> | |
158 | ||
159 | <para>Note that timers do not necessarily expire at the | |
160 | precise time configured with these settings, as they are | |
161 | subject to the <varname>AccuracySec=</varname> setting | |
162 | below.</para></listitem> | |
163 | ||
164 | </varlistentry> | |
165 | ||
166 | <varlistentry> | |
167 | <term><varname>OnCalendar=</varname></term> | |
168 | ||
169 | <listitem><para>Defines realtime (i.e. wallclock) timers with | |
170 | calendar event expressions. See | |
171 | <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
172 | for more information on the syntax of calendar event | |
173 | expressions. Otherwise, the semantics are similar to | |
174 | <varname>OnActiveSec=</varname> and related settings.</para> | |
175 | ||
176 | <para>Note that timers do not necessarily expire at the | |
177 | precise time configured with this setting, as it is subject to | |
178 | the <varname>AccuracySec=</varname> setting | |
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179 | below.</para> |
180 | ||
181 | <para>May be specified more than once.</para></listitem> | |
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182 | </varlistentry> |
183 | ||
184 | <varlistentry> | |
185 | <term><varname>AccuracySec=</varname></term> | |
186 | ||
187 | <listitem><para>Specify the accuracy the timer shall elapse | |
188 | with. Defaults to 1min. The timer is scheduled to elapse | |
189 | within a time window starting with the time specified in | |
190 | <varname>OnCalendar=</varname>, | |
191 | <varname>OnActiveSec=</varname>, | |
192 | <varname>OnBootSec=</varname>, | |
193 | <varname>OnStartupSec=</varname>, | |
194 | <varname>OnUnitActiveSec=</varname> or | |
195 | <varname>OnUnitInactiveSec=</varname> and ending the time | |
196 | configured with <varname>AccuracySec=</varname> later. Within | |
197 | this time window, the expiry time will be placed at a | |
744c7693 | 198 | host-specific, randomized, but stable position that is |
798d3a52 | 199 | synchronized between all local timer units. This is done in |
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200 | order to optimize power consumption to suppress unnecessary |
201 | CPU wake-ups. To get best accuracy, set this option to | |
202 | 1us. Note that the timer is still subject to the timer slack | |
203 | configured via | |
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204 | <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s |
205 | <varname>TimerSlackNSec=</varname> setting. See | |
206 | <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
207 | for details. To optimize power consumption, make sure to set | |
208 | this value as high as possible and as low as | |
209 | necessary.</para></listitem> | |
210 | </varlistentry> | |
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211 | |
212 | <varlistentry> | |
6f5d7998 | 213 | <term><varname>RandomizedDelaySec=</varname></term> |
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214 | |
215 | <listitem><para>Delay the timer by a randomly selected, evenly | |
216 | distributed amount of time between 0 and the specified time | |
217 | value. Defaults to 0, indicating that no randomized delay | |
218 | shall be applied. Each timer unit will determine this delay | |
219 | randomly each time it is started, and the delay will simply be | |
220 | added on top of the next determined elapsing time. This is | |
221 | useful to stretch dispatching of similarly configured timer | |
222 | events over a certain amount time, to avoid that they all fire | |
223 | at the same time, possibly resulting in resource | |
224 | congestion. Note the relation to | |
225 | <varname>AccuracySec=</varname> above: the latter allows the | |
226 | service manager to coalesce timer events within a specified | |
227 | time range in order to minimize wakeups, the former does the | |
228 | opposite: it stretches timer events over a time range, to make | |
229 | it unlikely that they fire simultaneously. If | |
6f5d7998 | 230 | <varname>RandomizedDelaySec=</varname> and |
744c7693 | 231 | <varname>AccuracySec=</varname> are used in conjunction, first |
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232 | the randomized delay is added, and then the result is |
233 | possibly further shifted to coalesce it with other timer | |
234 | events happening on the system. As mentioned above | |
744c7693 | 235 | <varname>AccuracySec=</varname> defaults to 1min and |
6f5d7998 | 236 | <varname>RandomizedDelaySec=</varname> to 0, thus encouraging |
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237 | coalescing of timer events. In order to optimally stretch |
238 | timer events over a certain range of time, make sure to set | |
6f5d7998 | 239 | <varname>RandomizedDelaySec=</varname> to a higher value, and |
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240 | <varname>AccuracySec=1us</varname>.</para></listitem> |
241 | </varlistentry> | |
242 | ||
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243 | <varlistentry> |
244 | <term><varname>Unit=</varname></term> | |
245 | ||
246 | <listitem><para>The unit to activate when this timer elapses. | |
247 | The argument is a unit name, whose suffix is not | |
248 | <literal>.timer</literal>. If not specified, this value | |
249 | defaults to a service that has the same name as the timer | |
250 | unit, except for the suffix. (See above.) It is recommended | |
251 | that the unit name that is activated and the unit name of the | |
252 | timer unit are named identically, except for the | |
253 | suffix.</para></listitem> | |
254 | </varlistentry> | |
255 | ||
256 | ||
257 | <varlistentry> | |
258 | <term><varname>Persistent=</varname></term> | |
259 | ||
260 | <listitem><para>Takes a boolean argument. If true, the time | |
261 | when the service unit was last triggered is stored on disk. | |
262 | When the timer is activated, the service unit is triggered | |
263 | immediately if it would have been triggered at least once | |
264 | during the time when the timer was inactive. This is useful to | |
265 | catch up on missed runs of the service when the machine was | |
266 | off. Note that this setting only has an effect on timers | |
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267 | configured with <varname>OnCalendar=</varname>. Defaults |
268 | to <varname>false</varname>. | |
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269 | </para></listitem> |
270 | </varlistentry> | |
271 | ||
272 | <varlistentry> | |
273 | <term><varname>WakeSystem=</varname></term> | |
274 | ||
275 | <listitem><para>Takes a boolean argument. If true, an elapsing | |
276 | timer will cause the system to resume from suspend, should it | |
277 | be suspended and if the system supports this. Note that this | |
278 | option will only make sure the system resumes on the | |
279 | appropriate times, it will not take care of suspending it | |
280 | again after any work that is to be done is finished. Defaults | |
281 | to <varname>false</varname>.</para></listitem> | |
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282 | </varlistentry> |
283 | ||
284 | <varlistentry> | |
70b4f819 | 285 | <term><varname>RemainAfterElapse=</varname></term> |
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286 | |
287 | <listitem><para>Takes a boolean argument. If true, an elapsed | |
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288 | timer will stay loaded, and its state remains queriable. If |
289 | false, an elapsed timer unit that cannot elapse anymore is | |
290 | unloaded. Turning this off is particularly useful for | |
291 | transient timer units that shall disappear after they first | |
292 | elapse. Note that this setting has an effect on repeatedly | |
7f3fdb7f | 293 | starting a timer unit that only elapses once: if |
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294 | <varname>RemainAfterElapse=</varname> is on, it will not be |
295 | started again, and is guaranteed to elapse only once. However, | |
23743744 | 296 | if <varname>RemainAfterElapse=</varname> is off, it might be |
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297 | started again if it is already elapsed, and thus be triggered |
298 | multiple times. Defaults to | |
3e0c30ac | 299 | <varname>yes</varname>.</para></listitem> |
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300 | </varlistentry> |
301 | </variablelist> | |
302 | </refsect1> | |
303 | ||
304 | <refsect1> | |
305 | <title>See Also</title> | |
306 | <para> | |
307 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
308 | <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
309 | <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
310 | <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
311 | <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
312 | <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
313 | <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
314 | <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
315 | </para> | |
316 | </refsect1> | |
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317 | |
318 | </refentry> |