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3 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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9   Copyright 2010 Lennart Poettering
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24
25 <refentry id="systemd.timer">
26         <refentryinfo>
27                 <title>systemd.timer</title>
28                 <productname>systemd</productname>
29
30                 <authorgroup>
31                         <author>
32                                 <contrib>Developer</contrib>
33                                 <firstname>Lennart</firstname>
34                                 <surname>Poettering</surname>
35                                 <email>lennart@poettering.net</email>
36                         </author>
37                 </authorgroup>
38         </refentryinfo>
39
40         <refmeta>
41                 <refentrytitle>systemd.timer</refentrytitle>
42                 <manvolnum>5</manvolnum>
43         </refmeta>
44
45         <refnamediv>
46                 <refname>systemd.timer</refname>
47                 <refpurpose>Timer unit configuration</refpurpose>
48         </refnamediv>
49
50         <refsynopsisdiv>
51                 <para><filename><replaceable>timer</replaceable>.timer</filename></para>
52         </refsynopsisdiv>
53
54         <refsect1>
55                 <title>Description</title>
56
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>
61
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>
70
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>
79
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
89                 option.</para>
90         </refsect1>
91
92         <refsect1>
93                 <title>Options</title>
94
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>
99
100                 <variablelist class='unit-directives'>
101                         <varlistentry>
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>
107
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
112                                 itself is
113                                 activated. <varname>OnBootSec=</varname>
114                                 defines a timer relative to when the
115                                 machine was booted
116                                 up. <varname>OnStartupSec=</varname>
117                                 defines a timer relative to when
118                                 systemd was first
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
125                                 deactivated.</para>
126
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
135                                 time.</para>
136
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>
146
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
155                                 directives.</para>
156
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>
161
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
166                                 effect.</para>
167
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>
174
175                         </varlistentry>
176
177                         <varlistentry>
178                                 <term><varname>OnCalendar=</varname></term>
179
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>
189
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>
196                         </varlistentry>
197
198                         <varlistentry>
199                                 <term><varname>AccuracySec=</varname></term>
200
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
226                                 via
227                                 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
228                                 <varname>TimerSlackNSec=</varname>
229                                 setting. See
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>
235                         </varlistentry>
236                         <varlistentry>
237                                 <term><varname>Unit=</varname></term>
238
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>
251                         </varlistentry>
252                 </variablelist>
253         </refsect1>
254
255         <refsect1>
256                   <title>See Also</title>
257                   <para>
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>
266                   </para>
267         </refsect1>
268
269 </refentry>