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db2df898 | 1 | <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*--> |
663996b3 | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" |
e735f4d4 | 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 | |
11 | ||
12 | systemd is free software; you can redistribute it and/or modify it | |
13 | under the terms of the GNU Lesser General Public License as published by | |
14 | the Free Software Foundation; either version 2.1 of the License, or | |
15 | (at your option) any later version. | |
16 | ||
17 | systemd is distributed in the hope that it will be useful, but | |
18 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
19 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
20 | Lesser General Public License for more details. | |
21 | ||
22 | You should have received a copy of the GNU Lesser General Public License | |
23 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
24 | --> | |
25 | ||
26 | <refentry id="systemd.timer"> | |
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27 | <refentryinfo> |
28 | <title>systemd.timer</title> | |
29 | <productname>systemd</productname> | |
30 | ||
31 | <authorgroup> | |
32 | <author> | |
33 | <contrib>Developer</contrib> | |
34 | <firstname>Lennart</firstname> | |
35 | <surname>Poettering</surname> | |
36 | <email>lennart@poettering.net</email> | |
37 | </author> | |
38 | </authorgroup> | |
39 | </refentryinfo> | |
40 | ||
41 | <refmeta> | |
42 | <refentrytitle>systemd.timer</refentrytitle> | |
43 | <manvolnum>5</manvolnum> | |
44 | </refmeta> | |
45 | ||
46 | <refnamediv> | |
47 | <refname>systemd.timer</refname> | |
48 | <refpurpose>Timer unit configuration</refpurpose> | |
49 | </refnamediv> | |
50 | ||
51 | <refsynopsisdiv> | |
52 | <para><filename><replaceable>timer</replaceable>.timer</filename></para> | |
53 | </refsynopsisdiv> | |
54 | ||
55 | <refsect1> | |
56 | <title>Description</title> | |
57 | ||
58 | <para>A unit configuration file whose name ends in | |
59 | <literal>.timer</literal> encodes information about a timer | |
60 | controlled and supervised by systemd, for timer-based | |
61 | activation.</para> | |
62 | ||
63 | <para>This man page lists the configuration options specific to | |
64 | this unit type. See | |
65 | <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
66 | for the common options of all unit configuration files. The common | |
67 | configuration items are configured in the generic [Unit] and | |
68 | [Install] sections. The timer specific configuration options are | |
69 | configured in the [Timer] section.</para> | |
70 | ||
71 | <para>For each timer file, a matching unit file must exist, | |
72 | describing the unit to activate when the timer elapses. By | |
73 | default, a service by the same name as the timer (except for the | |
74 | suffix) is activated. Example: a timer file | |
75 | <filename>foo.timer</filename> activates a matching service | |
76 | <filename>foo.service</filename>. The unit to activate may be | |
77 | controlled by <varname>Unit=</varname> (see below).</para> | |
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78 | |
79 | <para>Note that in case the unit to activate is already active at the time the timer elapses it is not restarted, | |
80 | but simply left running. There is no concept of spawning new service instances in this case. Due to this, services | |
5a920b42 | 81 | with <varname>RemainAfterExit=</varname> set (which stay around continuously even after the service's main process |
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82 | exited) are usually not suitable for activation via repetitive timers, as they will only be activated once, and |
83 | then stay around forever.</para> | |
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84 | </refsect1> |
85 | ||
86 | <refsect1> | |
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87 | <title>Implicit Dependencies</title> |
88 | ||
89 | <para>The following dependencies are implicitly added:</para> | |
90 | ||
91 | <itemizedlist> | |
92 | <listitem><para>Timer units automatically gain a <varname>Before=</varname> | |
93 | dependency on the service they are supposed to activate.</para></listitem> | |
94 | </itemizedlist> | |
95 | </refsect1> | |
96 | ||
97 | <refsect1> | |
98 | <title>Default Dependencies</title> | |
99 | ||
100 | <para>The following dependencies are added unless <varname>DefaultDependencies=no</varname> is set:</para> | |
101 | ||
102 | <itemizedlist> | |
103 | <listitem><para>Timer units will automatically have dependencies of type <varname>Requires=</varname> and | |
104 | <varname>After=</varname> on <filename>sysinit.target</filename>, a dependency of type <varname>Before=</varname> | |
105 | on <filename>timers.target</filename>, as well as <varname>Conflicts=</varname> and <varname>Before=</varname> on | |
106 | <filename>shutdown.target</filename> to ensure that they are stopped cleanly prior to system shutdown. Only timer | |
107 | units involved with early boot or late system shutdown should disable the | |
108 | <varname>DefaultDependencies=</varname> option.</para></listitem> | |
109 | ||
110 | <listitem><para>Timer units | |
111 | with at least one <varname>OnCalendar=</varname> directive will have an additional <varname>After=</varname> | |
112 | dependency on <filename>time-sync.target</filename> to avoid being started before the system clock has been | |
113 | correctly set.</para></listitem> | |
114 | </itemizedlist> | |
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115 | </refsect1> |
116 | ||
117 | <refsect1> | |
118 | <title>Options</title> | |
119 | ||
120 | <para>Timer files must include a [Timer] section, which carries | |
121 | information about the timer it defines. The options specific to | |
122 | the [Timer] section of timer units are the following:</para> | |
123 | ||
124 | <variablelist class='unit-directives'> | |
125 | <varlistentry> | |
126 | <term><varname>OnActiveSec=</varname></term> | |
127 | <term><varname>OnBootSec=</varname></term> | |
128 | <term><varname>OnStartupSec=</varname></term> | |
129 | <term><varname>OnUnitActiveSec=</varname></term> | |
130 | <term><varname>OnUnitInactiveSec=</varname></term> | |
131 | ||
132 | <listitem><para>Defines monotonic timers relative to different | |
133 | starting points: <varname>OnActiveSec=</varname> defines a | |
134 | timer relative to the moment the timer itself is activated. | |
135 | <varname>OnBootSec=</varname> defines a timer relative to when | |
136 | the machine was booted up. <varname>OnStartupSec=</varname> | |
137 | defines a timer relative to when systemd was first started. | |
138 | <varname>OnUnitActiveSec=</varname> defines a timer relative | |
139 | to when the unit the timer is activating was last activated. | |
140 | <varname>OnUnitInactiveSec=</varname> defines a timer relative | |
141 | to when the unit the timer is activating was last | |
142 | deactivated.</para> | |
143 | ||
144 | <para>Multiple directives may be combined of the same and of | |
145 | different types. For example, by combining | |
146 | <varname>OnBootSec=</varname> and | |
147 | <varname>OnUnitActiveSec=</varname>, it is possible to define | |
148 | a timer that elapses in regular intervals and activates a | |
149 | specific service each time.</para> | |
150 | ||
151 | <para>The arguments to the directives are time spans | |
152 | configured in seconds. Example: "OnBootSec=50" means 50s after | |
153 | boot-up. The argument may also include time units. Example: | |
154 | "OnBootSec=5h 30min" means 5 hours and 30 minutes after | |
155 | boot-up. For details about the syntax of time spans, see | |
db2df898 | 156 | <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para> |
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157 | |
158 | <para>If a timer configured with <varname>OnBootSec=</varname> | |
159 | or <varname>OnStartupSec=</varname> is already in the past | |
160 | when the timer unit is activated, it will immediately elapse | |
161 | and the configured unit is started. This is not the case for | |
162 | timers defined in the other directives.</para> | |
163 | ||
164 | <para>These are monotonic timers, independent of wall-clock | |
165 | time and timezones. If the computer is temporarily suspended, | |
166 | the monotonic clock stops too.</para> | |
167 | ||
168 | <para>If the empty string is assigned to any of these options, | |
169 | the list of timers is reset, and all prior assignments will | |
170 | have no effect.</para> | |
171 | ||
172 | <para>Note that timers do not necessarily expire at the | |
173 | precise time configured with these settings, as they are | |
174 | subject to the <varname>AccuracySec=</varname> setting | |
175 | below.</para></listitem> | |
176 | ||
177 | </varlistentry> | |
178 | ||
179 | <varlistentry> | |
180 | <term><varname>OnCalendar=</varname></term> | |
181 | ||
182 | <listitem><para>Defines realtime (i.e. wallclock) timers with | |
183 | calendar event expressions. See | |
184 | <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
185 | for more information on the syntax of calendar event | |
186 | expressions. Otherwise, the semantics are similar to | |
187 | <varname>OnActiveSec=</varname> and related settings.</para> | |
188 | ||
189 | <para>Note that timers do not necessarily expire at the | |
190 | precise time configured with this setting, as it is subject to | |
191 | the <varname>AccuracySec=</varname> setting | |
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192 | below.</para> |
193 | ||
194 | <para>May be specified more than once.</para></listitem> | |
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195 | </varlistentry> |
196 | ||
197 | <varlistentry> | |
198 | <term><varname>AccuracySec=</varname></term> | |
199 | ||
200 | <listitem><para>Specify the accuracy the timer shall elapse | |
201 | with. Defaults to 1min. The timer is scheduled to elapse | |
202 | within a time window starting with the time specified in | |
203 | <varname>OnCalendar=</varname>, | |
204 | <varname>OnActiveSec=</varname>, | |
205 | <varname>OnBootSec=</varname>, | |
206 | <varname>OnStartupSec=</varname>, | |
207 | <varname>OnUnitActiveSec=</varname> or | |
208 | <varname>OnUnitInactiveSec=</varname> and ending the time | |
209 | configured with <varname>AccuracySec=</varname> later. Within | |
210 | this time window, the expiry time will be placed at a | |
4c89c718 | 211 | host-specific, randomized, but stable position that is |
e735f4d4 | 212 | synchronized between all local timer units. This is done in |
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213 | order to optimize power consumption to suppress unnecessary |
214 | CPU wake-ups. To get best accuracy, set this option to | |
215 | 1us. Note that the timer is still subject to the timer slack | |
216 | configured via | |
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217 | <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s |
218 | <varname>TimerSlackNSec=</varname> setting. See | |
219 | <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
220 | for details. To optimize power consumption, make sure to set | |
221 | this value as high as possible and as low as | |
222 | necessary.</para></listitem> | |
223 | </varlistentry> | |
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224 | |
225 | <varlistentry> | |
226 | <term><varname>RandomizedDelaySec=</varname></term> | |
227 | ||
228 | <listitem><para>Delay the timer by a randomly selected, evenly | |
229 | distributed amount of time between 0 and the specified time | |
230 | value. Defaults to 0, indicating that no randomized delay | |
231 | shall be applied. Each timer unit will determine this delay | |
232 | randomly each time it is started, and the delay will simply be | |
233 | added on top of the next determined elapsing time. This is | |
234 | useful to stretch dispatching of similarly configured timer | |
235 | events over a certain amount time, to avoid that they all fire | |
236 | at the same time, possibly resulting in resource | |
237 | congestion. Note the relation to | |
238 | <varname>AccuracySec=</varname> above: the latter allows the | |
239 | service manager to coalesce timer events within a specified | |
240 | time range in order to minimize wakeups, the former does the | |
241 | opposite: it stretches timer events over a time range, to make | |
242 | it unlikely that they fire simultaneously. If | |
243 | <varname>RandomizedDelaySec=</varname> and | |
244 | <varname>AccuracySec=</varname> are used in conjunction, first | |
245 | the randomized delay is added, and then the result is | |
246 | possibly further shifted to coalesce it with other timer | |
247 | events happening on the system. As mentioned above | |
248 | <varname>AccuracySec=</varname> defaults to 1min and | |
249 | <varname>RandomizedDelaySec=</varname> to 0, thus encouraging | |
250 | coalescing of timer events. In order to optimally stretch | |
251 | timer events over a certain range of time, make sure to set | |
252 | <varname>RandomizedDelaySec=</varname> to a higher value, and | |
253 | <varname>AccuracySec=1us</varname>.</para></listitem> | |
254 | </varlistentry> | |
255 | ||
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256 | <varlistentry> |
257 | <term><varname>Unit=</varname></term> | |
258 | ||
259 | <listitem><para>The unit to activate when this timer elapses. | |
260 | The argument is a unit name, whose suffix is not | |
261 | <literal>.timer</literal>. If not specified, this value | |
262 | defaults to a service that has the same name as the timer | |
263 | unit, except for the suffix. (See above.) It is recommended | |
264 | that the unit name that is activated and the unit name of the | |
265 | timer unit are named identically, except for the | |
266 | suffix.</para></listitem> | |
267 | </varlistentry> | |
268 | ||
269 | ||
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> | |
4c89c718 | 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 | |
306 | starting a timer unit that only elapses once: if | |
307 | <varname>RemainAfterElapse=</varname> is on, it will not be | |
308 | started again, and is guaranteed to elapse only once. However, | |
aa27b158 | 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 | |
db2df898 | 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> |