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514094f9 | 1 | <?xml version='1.0'?> |
3a54a157 | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
0307f791 | 4 | <!-- SPDX-License-Identifier: LGPL-2.1+ --> |
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5 | |
6 | <refentry id="systemd.timer"> | |
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7 | <refentryinfo> |
8 | <title>systemd.timer</title> | |
9 | <productname>systemd</productname> | |
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10 | </refentryinfo> |
11 | ||
12 | <refmeta> | |
13 | <refentrytitle>systemd.timer</refentrytitle> | |
14 | <manvolnum>5</manvolnum> | |
15 | </refmeta> | |
16 | ||
17 | <refnamediv> | |
18 | <refname>systemd.timer</refname> | |
19 | <refpurpose>Timer unit configuration</refpurpose> | |
20 | </refnamediv> | |
21 | ||
22 | <refsynopsisdiv> | |
23 | <para><filename><replaceable>timer</replaceable>.timer</filename></para> | |
24 | </refsynopsisdiv> | |
25 | ||
26 | <refsect1> | |
27 | <title>Description</title> | |
28 | ||
29 | <para>A unit configuration file whose name ends in | |
30 | <literal>.timer</literal> encodes information about a timer | |
31 | controlled and supervised by systemd, for timer-based | |
32 | activation.</para> | |
33 | ||
34 | <para>This man page lists the configuration options specific to | |
35 | this unit type. See | |
36 | <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
37 | for the common options of all unit configuration files. The common | |
38 | configuration items are configured in the generic [Unit] and | |
39 | [Install] sections. The timer specific configuration options are | |
40 | configured in the [Timer] section.</para> | |
41 | ||
42 | <para>For each timer file, a matching unit file must exist, | |
43 | describing the unit to activate when the timer elapses. By | |
44 | default, a service by the same name as the timer (except for the | |
45 | suffix) is activated. Example: a timer file | |
46 | <filename>foo.timer</filename> activates a matching service | |
47 | <filename>foo.service</filename>. The unit to activate may be | |
48 | controlled by <varname>Unit=</varname> (see below).</para> | |
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49 | |
50 | <para>Note that in case the unit to activate is already active at the time the timer elapses it is not restarted, | |
51 | but simply left running. There is no concept of spawning new service instances in this case. Due to this, services | |
595bfe7d | 52 | with <varname>RemainAfterExit=</varname> set (which stay around continuously even after the service's main process |
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53 | exited) are usually not suitable for activation via repetitive timers, as they will only be activated once, and |
54 | then stay around forever.</para> | |
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55 | </refsect1> |
56 | ||
45f09f93 | 57 | <refsect1> |
aed5cb03 | 58 | <title>Automatic Dependencies</title> |
45f09f93 | 59 | |
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60 | <refsect2> |
61 | <title>Implicit Dependencies</title> | |
45f09f93 | 62 | |
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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> | |
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69 | </refsect2> |
70 | ||
71 | <refsect2> | |
72 | <title>Default Dependencies</title> | |
73 | ||
74 | <para>The following dependencies are added unless <varname>DefaultDependencies=no</varname> is set:</para> | |
75 | ||
76 | <itemizedlist> | |
77 | <listitem><para>Timer units will automatically have dependencies of type <varname>Requires=</varname> and | |
78 | <varname>After=</varname> on <filename>sysinit.target</filename>, a dependency of type <varname>Before=</varname> | |
79 | on <filename>timers.target</filename>, as well as <varname>Conflicts=</varname> and <varname>Before=</varname> on | |
80 | <filename>shutdown.target</filename> to ensure that they are stopped cleanly prior to system shutdown. Only timer | |
81 | units involved with early boot or late system shutdown should disable the | |
82 | <varname>DefaultDependencies=</varname> option.</para></listitem> | |
83 | ||
84 | <listitem><para>Timer units | |
85 | with at least one <varname>OnCalendar=</varname> directive will have an additional <varname>After=</varname> | |
86 | dependency on <filename>time-sync.target</filename> to avoid being started before the system clock has been | |
87 | correctly set.</para></listitem> | |
88 | </itemizedlist> | |
89 | </refsect2> | |
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90 | </refsect1> |
91 | ||
92 | <refsect1> | |
93 | <title>Options</title> | |
94 | ||
95 | <para>Timer files must include a [Timer] section, which carries | |
96 | information about the timer it defines. The options specific to | |
97 | the [Timer] section of timer units are the following:</para> | |
98 | ||
99 | <variablelist class='unit-directives'> | |
100 | <varlistentry> | |
101 | <term><varname>OnActiveSec=</varname></term> | |
102 | <term><varname>OnBootSec=</varname></term> | |
103 | <term><varname>OnStartupSec=</varname></term> | |
104 | <term><varname>OnUnitActiveSec=</varname></term> | |
105 | <term><varname>OnUnitInactiveSec=</varname></term> | |
106 | ||
107 | <listitem><para>Defines monotonic timers relative to different | |
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108 | starting points:</para> |
109 | ||
110 | <table> | |
111 | <title>Settings and their starting points</title> | |
112 | ||
113 | <tgroup cols='2'> | |
114 | <thead> | |
115 | <row> | |
116 | <entry>Setting</entry> | |
117 | <entry>Meaning</entry> | |
118 | </row> | |
119 | </thead> | |
120 | <tbody> | |
121 | <row> | |
122 | <entry><varname>OnActiveSec=</varname></entry> | |
123 | <entry>Defines a timer relative to the moment the timer unit itself is activated.</entry> | |
124 | </row> | |
125 | <row> | |
126 | <entry><varname>OnBootSec=</varname></entry> | |
65aeb9d4 | 127 | <entry>Defines a timer relative to when the machine was booted up. In containers, for the system manager instance, this is mapped to <varname>OnStartupSec=</varname>, making both equivalent.</entry> |
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128 | </row> |
129 | <row> | |
130 | <entry><varname>OnStartupSec=</varname></entry> | |
131 | <entry>Defines a timer relative to when the service manager was first started. For system timer units this is very similar to <varname>OnBootSec=</varname> as the system service manager is generally started very early at boot. It's primarily useful when configured in units running in the per-user service manager, as the user service manager is generally started on first login only, not already during boot.</entry> | |
132 | </row> | |
133 | <row> | |
134 | <entry><varname>OnUnitActiveSec=</varname></entry> | |
135 | <entry>Defines a timer relative to when the unit the timer unit is activating was last activated.</entry> | |
136 | </row> | |
137 | <row> | |
138 | <entry><varname>OnUnitInactiveSec=</varname></entry> | |
139 | <entry>Defines a timer relative to when the unit the timer unit is activating was last deactivated.</entry> | |
140 | </row> | |
141 | </tbody> | |
142 | </tgroup> | |
143 | </table> | |
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144 | |
145 | <para>Multiple directives may be combined of the same and of | |
146 | different types. For example, by combining | |
147 | <varname>OnBootSec=</varname> and | |
148 | <varname>OnUnitActiveSec=</varname>, it is possible to define | |
149 | a timer that elapses in regular intervals and activates a | |
150 | specific service each time.</para> | |
151 | ||
152 | <para>The arguments to the directives are time spans | |
153 | configured in seconds. Example: "OnBootSec=50" means 50s after | |
154 | boot-up. The argument may also include time units. Example: | |
155 | "OnBootSec=5h 30min" means 5 hours and 30 minutes after | |
156 | boot-up. For details about the syntax of time spans, see | |
9905e698 | 157 | <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para> |
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158 | |
159 | <para>If a timer configured with <varname>OnBootSec=</varname> | |
160 | or <varname>OnStartupSec=</varname> is already in the past | |
161 | when the timer unit is activated, it will immediately elapse | |
162 | and the configured unit is started. This is not the case for | |
163 | timers defined in the other directives.</para> | |
164 | ||
165 | <para>These are monotonic timers, independent of wall-clock | |
166 | time and timezones. If the computer is temporarily suspended, | |
167 | the monotonic clock stops too.</para> | |
168 | ||
169 | <para>If the empty string is assigned to any of these options, | |
170 | the list of timers is reset, and all prior assignments will | |
171 | have no effect.</para> | |
172 | ||
173 | <para>Note that timers do not necessarily expire at the | |
174 | precise time configured with these settings, as they are | |
175 | subject to the <varname>AccuracySec=</varname> setting | |
176 | below.</para></listitem> | |
177 | ||
178 | </varlistentry> | |
179 | ||
180 | <varlistentry> | |
181 | <term><varname>OnCalendar=</varname></term> | |
182 | ||
183 | <listitem><para>Defines realtime (i.e. wallclock) timers with | |
184 | calendar event expressions. See | |
185 | <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
186 | for more information on the syntax of calendar event | |
187 | expressions. Otherwise, the semantics are similar to | |
188 | <varname>OnActiveSec=</varname> and related settings.</para> | |
189 | ||
190 | <para>Note that timers do not necessarily expire at the | |
191 | precise time configured with this setting, as it is subject to | |
192 | the <varname>AccuracySec=</varname> setting | |
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193 | below.</para> |
194 | ||
195 | <para>May be specified more than once.</para></listitem> | |
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196 | </varlistentry> |
197 | ||
198 | <varlistentry> | |
199 | <term><varname>AccuracySec=</varname></term> | |
200 | ||
201 | <listitem><para>Specify the accuracy the timer shall elapse | |
202 | with. Defaults to 1min. The timer is scheduled to elapse | |
203 | within a time window starting with the time specified in | |
204 | <varname>OnCalendar=</varname>, | |
205 | <varname>OnActiveSec=</varname>, | |
206 | <varname>OnBootSec=</varname>, | |
207 | <varname>OnStartupSec=</varname>, | |
208 | <varname>OnUnitActiveSec=</varname> or | |
209 | <varname>OnUnitInactiveSec=</varname> and ending the time | |
210 | configured with <varname>AccuracySec=</varname> later. Within | |
211 | this time window, the expiry time will be placed at a | |
744c7693 | 212 | host-specific, randomized, but stable position that is |
798d3a52 | 213 | synchronized between all local timer units. This is done in |
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214 | order to optimize power consumption to suppress unnecessary |
215 | CPU wake-ups. To get best accuracy, set this option to | |
216 | 1us. Note that the timer is still subject to the timer slack | |
217 | configured via | |
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218 | <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s |
219 | <varname>TimerSlackNSec=</varname> setting. See | |
220 | <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
221 | for details. To optimize power consumption, make sure to set | |
222 | this value as high as possible and as low as | |
223 | necessary.</para></listitem> | |
224 | </varlistentry> | |
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225 | |
226 | <varlistentry> | |
6f5d7998 | 227 | <term><varname>RandomizedDelaySec=</varname></term> |
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228 | |
229 | <listitem><para>Delay the timer by a randomly selected, evenly | |
230 | distributed amount of time between 0 and the specified time | |
231 | value. Defaults to 0, indicating that no randomized delay | |
232 | shall be applied. Each timer unit will determine this delay | |
3118a4cf | 233 | randomly before each iteration, and the delay will simply be |
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234 | added on top of the next determined elapsing time. This is |
235 | useful to stretch dispatching of similarly configured timer | |
236 | events over a certain amount time, to avoid that they all fire | |
237 | at the same time, possibly resulting in resource | |
238 | congestion. Note the relation to | |
239 | <varname>AccuracySec=</varname> above: the latter allows the | |
240 | service manager to coalesce timer events within a specified | |
241 | time range in order to minimize wakeups, the former does the | |
242 | opposite: it stretches timer events over a time range, to make | |
243 | it unlikely that they fire simultaneously. If | |
6f5d7998 | 244 | <varname>RandomizedDelaySec=</varname> and |
744c7693 | 245 | <varname>AccuracySec=</varname> are used in conjunction, first |
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246 | the randomized delay is added, and then the result is |
247 | possibly further shifted to coalesce it with other timer | |
248 | events happening on the system. As mentioned above | |
744c7693 | 249 | <varname>AccuracySec=</varname> defaults to 1min and |
6f5d7998 | 250 | <varname>RandomizedDelaySec=</varname> to 0, thus encouraging |
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251 | coalescing of timer events. In order to optimally stretch |
252 | timer events over a certain range of time, make sure to set | |
6f5d7998 | 253 | <varname>RandomizedDelaySec=</varname> to a higher value, and |
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254 | <varname>AccuracySec=1us</varname>.</para></listitem> |
255 | </varlistentry> | |
256 | ||
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257 | <varlistentry> |
258 | <term><varname>Unit=</varname></term> | |
259 | ||
260 | <listitem><para>The unit to activate when this timer elapses. | |
261 | The argument is a unit name, whose suffix is not | |
262 | <literal>.timer</literal>. If not specified, this value | |
263 | defaults to a service that has the same name as the timer | |
264 | unit, except for the suffix. (See above.) It is recommended | |
265 | that the unit name that is activated and the unit name of the | |
266 | timer unit are named identically, except for the | |
267 | suffix.</para></listitem> | |
268 | </varlistentry> | |
269 | ||
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270 | <varlistentry> |
271 | <term><varname>Persistent=</varname></term> | |
272 | ||
273 | <listitem><para>Takes a boolean argument. If true, the time | |
274 | when the service unit was last triggered is stored on disk. | |
275 | When the timer is activated, the service unit is triggered | |
276 | immediately if it would have been triggered at least once | |
277 | during the time when the timer was inactive. This is useful to | |
278 | catch up on missed runs of the service when the machine was | |
279 | off. Note that this setting only has an effect on timers | |
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280 | configured with <varname>OnCalendar=</varname>. Defaults |
281 | to <varname>false</varname>. | |
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282 | </para></listitem> |
283 | </varlistentry> | |
284 | ||
285 | <varlistentry> | |
286 | <term><varname>WakeSystem=</varname></term> | |
287 | ||
288 | <listitem><para>Takes a boolean argument. If true, an elapsing | |
289 | timer will cause the system to resume from suspend, should it | |
290 | be suspended and if the system supports this. Note that this | |
291 | option will only make sure the system resumes on the | |
292 | appropriate times, it will not take care of suspending it | |
293 | again after any work that is to be done is finished. Defaults | |
294 | to <varname>false</varname>.</para></listitem> | |
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295 | </varlistentry> |
296 | ||
297 | <varlistentry> | |
70b4f819 | 298 | <term><varname>RemainAfterElapse=</varname></term> |
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299 | |
300 | <listitem><para>Takes a boolean argument. If true, an elapsed | |
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301 | timer will stay loaded, and its state remains queriable. If |
302 | false, an elapsed timer unit that cannot elapse anymore is | |
303 | unloaded. Turning this off is particularly useful for | |
304 | transient timer units that shall disappear after they first | |
305 | elapse. Note that this setting has an effect on repeatedly | |
7f3fdb7f | 306 | starting a timer unit that only elapses once: if |
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307 | <varname>RemainAfterElapse=</varname> is on, it will not be |
308 | started again, and is guaranteed to elapse only once. However, | |
23743744 | 309 | if <varname>RemainAfterElapse=</varname> is off, it might be |
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310 | started again if it is already elapsed, and thus be triggered |
311 | multiple times. Defaults to | |
3e0c30ac | 312 | <varname>yes</varname>.</para></listitem> |
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313 | </varlistentry> |
314 | </variablelist> | |
315 | </refsect1> | |
316 | ||
317 | <refsect1> | |
318 | <title>See Also</title> | |
319 | <para> | |
320 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
321 | <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
322 | <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
323 | <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
324 | <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
325 | <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
326 | <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
327 | <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
328 | </para> | |
329 | </refsect1> | |
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330 | |
331 | </refentry> |