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7 This file is part of systemd.
9 Copyright 2010 Lennart Poettering
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25 <refentry id="systemd.timer">
27 <title>systemd.timer</title>
28 <productname>systemd</productname>
32 <contrib>Developer</contrib>
33 <firstname>Lennart</firstname>
34 <surname>Poettering</surname>
35 <email>lennart@poettering.net</email>
41 <refentrytitle>systemd.timer</refentrytitle>
42 <manvolnum>5</manvolnum>
46 <refname>systemd.timer</refname>
47 <refpurpose>Timer unit configuration</refpurpose>
51 <para><filename><replaceable>timer</replaceable>.timer</filename></para>
55 <title>Description</title>
57 <para>A unit configuration file whose name ends in
58 <literal>.timer</literal> encodes information about
59 a timer controlled and supervised by systemd, for
60 timer-based activation.</para>
62 <para>This man page lists the configuration options
63 specific to this unit type. See
64 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
65 for the common options of all unit configuration
66 files. The common configuration items are configured
67 in the generic [Unit] and [Install] sections. The
68 timer specific configuration options are configured in
69 the [Timer] section.</para>
71 <para>For each timer file, a matching unit file must
72 exist, describing the unit to activate when the timer
73 elapses. By default, a service by the same name as the
74 timer (except for the suffix) is activated. Example: a
75 timer file <filename>foo.timer</filename> activates a
76 matching service <filename>foo.service</filename>. The
77 unit to activate may be controlled by
78 <varname>Unit=</varname> (see below).</para>
80 <para>Unless <varname>DefaultDependencies=</varname>
81 is set to <option>false</option>, timer units will
82 implicitly have dependencies of type
83 <varname>Conflicts=</varname> and
84 <varname>Before=</varname> on
85 <filename>shutdown.target</filename>. These ensure
86 that timer units are stopped cleanly prior to system
87 shutdown. Only timer units involved with early boot or
88 late system shutdown should disable this
93 <title>Options</title>
95 <para>Timer files must include a [Timer] section,
96 which carries information about the timer it
97 defines. The options specific to the [Timer] section
98 of timer units are the following:</para>
100 <variablelist class='unit-directives'>
102 <term><varname>OnActiveSec=</varname></term>
103 <term><varname>OnBootSec=</varname></term>
104 <term><varname>OnStartupSec=</varname></term>
105 <term><varname>OnUnitActiveSec=</varname></term>
106 <term><varname>OnUnitInactiveSec=</varname></term>
108 <listitem><para>Defines monotonic timers
109 relative to different starting points:
110 <varname>OnActiveSec=</varname> defines a
111 timer relative to the moment the timer
113 activated. <varname>OnBootSec=</varname>
114 defines a timer relative to when the
116 up. <varname>OnStartupSec=</varname>
117 defines a timer relative to when
119 started. <varname>OnUnitActiveSec=</varname>
120 defines a timer relative to when the
121 unit the timer is activating was last
122 activated. <varname>OnUnitInactiveSec=</varname>
123 defines a timer relative to when the
124 unit the timer is activating was last
127 <para>Multiple directives may be
128 combined of the same and of different
129 types. For example, by combining
130 <varname>OnBootSec=</varname> and
131 <varname>OnUnitActiveSec=</varname>, it is
132 possible to define a timer that
133 elapses in regular intervals and
134 activates a specific service each
137 <para>The arguments to the directives
138 are time spans configured in
139 seconds. Example: "OnBootSec=50" means
140 50s after boot-up. The argument may
141 also include time units. Example:
142 "OnBootSec=5h 30min" means 5 hours and
143 30 minutes after boot-up. For details
144 about the syntax of time spans see
145 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
147 <para>If a timer configured with
148 <varname>OnBootSec=</varname> or
149 <varname>OnStartupSec=</varname> is
150 already in the past when the timer
151 unit is activated, it will immediately
152 elapse and the configured unit is
153 started. This is not the case for
154 timers defined in the other
157 <para>These are monotonic timers,
158 independent of wall-clock time and timezones. If the
159 computer is temporarily suspended, the
160 monotonic clock stops too.</para>
162 <para>If the empty string is assigned
163 to any of these options, the list of
164 timers is reset, and all prior
165 assignments will have no
168 <para>Note that timers are not
169 necessarily expired at the precise
170 time configured with these settings,
171 as they are subject to the
172 <varname>AccuracySec=</varname>
173 setting below.</para></listitem>
178 <term><varname>OnCalendar=</varname></term>
180 <listitem><para>Defines realtime
181 (i.e. wallclock) timers with calendar
182 event expressions. See
183 <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
184 for more information on the syntax of
185 calendar event expressions. Otherwise
186 the semantics are similar to
187 <varname>OnActiveSec=</varname> and
188 related settings.</para>
190 <para>Note that timers are not
191 necessarily expired at the precise
192 time configured with this setting,
193 as it is subject to the
194 <varname>AccuracySec=</varname>
195 setting below.</para></listitem>
199 <term><varname>AccuracySec=</varname></term>
201 <listitem><para>Specify the accuracy
202 the timer shall elapse with. Defaults
203 to 1min. The timer is scheduled to
204 expire within a time window starting
205 with the time specified in
206 <varname>OnCalendar=</varname>,
207 <varname>OnActiveSec=</varname>,
208 <varname>OnBootSec=</varname>,
209 <varname>OnStartupSec=</varname>,
210 <varname>OnUnitActiveSec=</varname> or
211 <varname>OnUnitInactiveSec=</varname>
212 and ending the time configured with
213 <varname>AccuracySec=</varname>
214 later. Within this time window the
215 expiry time will be placed at a
216 host-specific, randomized but stable
217 position, that is synchronized between
218 all local timer units. This is done in
219 order to distribute the wake-up time
220 in networked installations, as well as
221 optimizing power consumption to
222 suppress unnecessary CPU wake-ups. To
223 get best accuracy set this option to
224 1us. Note that the timer is still
225 subject to the timer slack configured
227 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
228 <varname>TimerSlackNSec=</varname>
230 <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
231 for details. To optimize power
232 consumption make sure to set this
233 value as high as possible and as low
234 as necessary.</para></listitem>
237 <term><varname>Unit=</varname></term>
239 <listitem><para>The unit to activate
240 when this timer elapses. The argument is a
241 unit name, whose suffix is not
242 <literal>.timer</literal>. If not
243 specified, this value defaults to a
244 service that has the same name as the
245 timer unit, except for the
246 suffix. (See above.) It is recommended
247 that the unit name that is activated
248 and the unit name of the timer unit
249 are named identically, except for the
250 suffix.</para></listitem>
256 <title>See Also</title>
258 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
259 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
260 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
261 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
262 <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
263 <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
264 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
265 <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>