1 <?xml version='
1.0'
?> <!--*-nxml-*-->
2 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.2//EN"
3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
6 This file is part of systemd.
8 Copyright 2010 Lennart Poettering
10 systemd is free software; you can redistribute it and/or modify it
11 under the terms of the GNU General Public License as published by
12 the Free Software Foundation; either version 2 of the License, or
13 (at your option) any later version.
15 systemd is distributed in the hope that it will be useful, but
16 WITHOUT ANY WARRANTY; without even the implied warranty of
17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
18 General Public License for more details.
20 You should have received a copy of the GNU General Public License
21 along with systemd; If not, see <http://www.gnu.org/licenses/>.
24 <refentry id=
"systemd.unit">
27 <title>systemd.unit
</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.unit
</refentrytitle>
42 <manvolnum>5</manvolnum>
46 <refname>systemd.unit
</refname>
47 <refpurpose>systemd unit configuration files
</refpurpose>
51 <para><filename>systemd.service
</filename>,
52 <filename>systemd.socket
</filename>,
53 <filename>systemd.device
</filename>,
54 <filename>systemd.mount
</filename>,
55 <filename>systemd.automount
</filename>,
56 <filename>systemd.swap
</filename>,
57 <filename>systemd.target
</filename>,
58 <filename>systemd.path
</filename>,
59 <filename>systemd.timer
</filename>,
60 <filename>systemd.snapshot
</filename></para>
64 <title>Description
</title>
66 <para>A unit configuration file encodes information
67 about a service, a socket, a device, a mount point, an
68 automount point, a swap file or partition, a start-up
69 target, a file system path or a timer controlled and
71 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>. The
72 syntax is inspired by
<ulink
73 url=
"http://standards.freedesktop.org/desktop-entry-spec/latest/">XDG
74 Desktop Entry Specification
</ulink> <filename>.desktop
</filename> files, which are in turn
75 inspired by Microsoft Windows
76 <filename>.ini
</filename> files.
</para>
78 <para>This man pages lists the common configuration
79 options of all the unit types. These options need to
80 be configured in the [Unit] resp. [Install]
81 section of the unit files.
</para>
83 <para>In addition to the generic [Unit] and [Install]
84 sections described here, each unit should have a
85 type-specific section, e.g. [Service] for a service
86 unit. See the respective man pages for more
89 <para>Unit files may contain additional options on top
90 of those listed here. If systemd encounters an unknown
91 option it will write a warning log message but
92 continue loading the unit. If an option is prefixed
93 with
<option>X-
</option> it is ignored completely by
94 systemd. Applications may use this to include
95 additional information in the unit files.
</para>
97 <para>Boolean arguments used in unit files can be
98 written in various formats. For positive settings the
99 strings
<option>1</option>,
<option>yes
</option>,
100 <option>true
</option> and
<option>on
</option> are
101 equivalent. For negative settings the strings
102 <option>0</option>,
<option>no
</option>,
103 <option>false
</option> and
<option>off
</option> are
106 <para>Time span values encoded in unit files can be
107 written in various formats. A stand-alone number
108 specifies a time in seconds. If suffixed with a time
109 unit, the unit is honored. A concatenation of
110 multiple values with units is supported, in which case
111 the values are added up. Example:
"50" refers to
50
112 seconds;
"2min 200ms" refers to
2 minutes plus
200
113 milliseconds, i.e.
120200ms. The following time units
114 are understood: s, min, h, d, w, ms, us.
</para>
116 <para>Empty lines and lines starting with # or ; are
117 ignored. This may be used for commenting. Lines ending
118 in a backslash are concatenated with the following
119 line while reading and the backslash is replaced by a
120 space character. This may be used to wrap long lines.
</para>
122 <para>If a line starts with
<option>.include
</option>
123 followed by a file name, the specified file will be
124 read as if its contents were listed in place of the
125 <option>.include
</option> directive.
</para>
127 <para>Along with a unit file
128 <filename>foo.service
</filename> a directory
129 <filename>foo.service.wants/
</filename> may exist. All
130 units symlinked from such a directory are implicitly
131 added as dependencies of type
132 <varname>Wanted=
</varname> to the unit. This is useful
133 to hook units into the start-up of other units,
134 without having to modify their unit configuration
135 files. For details about the semantics of
136 <varname>Wanted=
</varname> see below. The preferred
137 way to create symlinks in the
138 <filename>.wants/
</filename> directory of a service is
139 with the
<command>enable
</command> command of the
140 <citerefentry><refentrytitle>systemctl
</refentrytitle><manvolnum>1</manvolnum></citerefentry>
141 tool which reads information from the [Install]
142 section of unit files. (See below.)
</para>
144 <para>Note that while systemd offers a flexible
145 dependency system between units it is recommended to
146 use this functionality only sparsely and instead rely
147 on techniques such as bus-based or socket-based
148 activation which makes dependencies implicit, which
149 both results in a simpler and more flexible
152 <para>Some unit names reflect paths existing in the
153 file system name space. Example: a device unit
154 <filename>dev-sda.device
</filename> refers to a device
155 with the device node
<filename>/dev/sda
</filename> in
156 the file system namespace. If this applies a special
157 way to escape the path name is used, so that the
158 result is usable as part of a file name. Basically,
159 given a path,
"/" is replaced by
"-", and all
160 unprintable characters and the
"-" are replaced by
161 C-style
"\x20" escapes. The root directory
"/" is
162 encoded as single dash, while otherwise the initial
163 and ending
"/" is removed from all paths during
164 transformation. This escaping is reversible.
</para>
166 <para>Optionally, units may be instantiated from a
167 template file at runtime. This allows creation of
168 multiple units from a single configuration file. If
169 systemd looks for a unit configuration file it will
170 first search for the literal unit name in the
171 filesystem. If that yields no success and the unit
172 name contains an @ character, systemd will look for a
173 unit template that shares the same name but with the
174 instance string (i.e. the part between the @ character
175 and the suffix) removed. Example: if a service
176 <filename>getty@tty3.service
</filename> is requested
177 and no file by that name is found, systemd will look
178 for
<filename>getty@.service
</filename> and
179 instantiate a service from that configuration file if
180 it is found. To refer to the instance string from
181 within the configuration file you may use the special
182 <literal>%i
</literal> specifier in many of the
183 configuration options. Other specifiers that may be
184 used are
<literal>%n
</literal>,
<literal>%N
</literal>,
185 <literal>%p
</literal>,
<literal>%P
</literal>,
186 <literal>%I
</literal> and
<literal>%f
</literal>, for
187 the full unit name, the unescaped unit name, the
188 prefix name, the unescaped prefix name, the unescaped
189 instance name and the unescaped filename,
190 respectively. The unescaped filename is either the
191 unescaped instance name (if set) with / prepended (if
192 necessary), or the prefix name similarly prepended
193 with /. The prefix name here refers to the string
194 before the @, i.e.
"getty" in the example above, where
195 "tty3" is the instance name.
</para>
197 <para>If a unit file is empty (i.e. has the file size
198 0) or is symlinked to
<filename>/dev/null
</filename>
199 its configuration will not be loaded and it appears
200 with a load state of
<literal>masked
</literal>, and
201 cannot be activated. Use this as an effective way to
202 fully disable a unit, making it impossible to start it
203 even manually.
</para>
205 <para>The unit file format is covered by the
207 url=
"http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
208 Stability Promise
</ulink>.
</para>
212 <title>Options
</title>
214 <para>Unit file may include a [Unit] section, which
215 carries generic information about the unit that is not
216 dependent on the type of unit:
</para>
220 <term><varname>Names=
</varname></term>
222 <listitem><para>Additional names for
223 this unit. The names listed here must
224 have the same suffix (i.e. type) as
225 the unit file name. This option may be
226 specified more than once, in which
227 case all listed names are used. Note
228 that this option is different from the
229 <varname>Alias=
</varname> option from
230 the [Install] section mentioned
231 below. See below for details.
</para>
236 <term><varname>Description=
</varname></term>
237 <listitem><para>A free-form string
238 describing the unit. This is intended
239 for use in UIs to show descriptive
240 information along with the unit
241 name.
</para></listitem>
245 <term><varname>Requires=
</varname></term>
247 <listitem><para>Configures requirement
248 dependencies on other units. If this
249 unit gets activated, the units listed
250 here will be activated as well. If one
251 of the other units gets deactivated or
252 its activation fails, this unit will
253 be deactivated. This option may be
254 specified more than once, in which
255 case requirement dependencies for all
256 listed names are created. Note that
257 requirement dependencies do not
258 influence the order in which services
259 are started or stopped. This has to be
260 configured independently with the
261 <varname>After=
</varname> or
262 <varname>Before=
</varname> options. If
264 <filename>foo.service
</filename>
266 <filename>bar.service
</filename> as
268 <varname>Requires=
</varname> and no
269 ordering is configured with
270 <varname>After=
</varname> or
271 <varname>Before=
</varname>, then both
272 units will be started simultaneously
273 and without any delay between them if
274 <filename>foo.service
</filename> is
275 activated. Often it is a better choice
276 to use
<varname>Wants=
</varname>
278 <varname>Requires=
</varname> in order
279 to achieve a system that is more
280 robust when dealing with failing
281 services.
</para></listitem>
285 <term><varname>RequiresOverridable=
</varname></term>
287 <listitem><para>Similar to
288 <varname>Requires=
</varname>.
289 Dependencies listed in
290 <varname>RequiresOverridable=
</varname>
291 which cannot be fulfilled or fail to
292 start are ignored if the startup was
293 explicitly requested by the user. If
294 the start-up was pulled in indirectly
295 by some dependency or automatic
296 start-up of units that is not
297 requested by the user this dependency
298 must be fulfilled and otherwise the
299 transaction fails. Hence, this option
300 may be used to configure dependencies
301 that are normally honored unless the
302 user explicitly starts up the unit, in
303 which case whether they failed or not
304 is irrelevant.
</para></listitem>
308 <term><varname>Requisite=
</varname></term>
309 <term><varname>RequisiteOverridable=
</varname></term>
311 <listitem><para>Similar to
312 <varname>Requires=
</varname>
313 resp.
<varname>RequiresOverridable=
</varname>. However,
314 if a unit listed here is not started
315 already it will not be started and the
317 immediately.
</para></listitem>
321 <term><varname>Wants=
</varname></term>
323 <listitem><para>A weaker version of
324 <varname>Requires=
</varname>. A unit
325 listed in this option will be started
326 if the configuring unit is. However,
327 if the listed unit fails to start up
328 or cannot be added to the transaction
329 this has no impact on the validity of
330 the transaction as a whole. This is
331 the recommended way to hook start-up
332 of one unit to the start-up of another
333 unit. Note that dependencies of this
334 type may also be configured outside of
335 the unit configuration file by
336 adding a symlink to a
337 <filename>.wants/
</filename> directory
338 accompanying the unit file. For
339 details see above.
</para></listitem>
343 <term><varname>BindTo=
</varname></term>
345 <listitem><para>Configures requirement
346 dependencies, very similar in style to
347 <varname>Requires=
</varname>, however
348 in addition to this behaviour it also
349 declares that this unit is stopped
350 when any of the units listed suddenly
351 disappears. Units can suddenly,
352 unexpectedly disappear if a service
353 terminates on its own choice, a device
354 is unplugged or a mount point
355 unmounted without involvement of
356 systemd.
</para></listitem>
360 <term><varname>Conflicts=
</varname></term>
362 <listitem><para>Configures negative
363 requirement dependencies. If a unit
365 <varname>Conflicts=
</varname> setting
366 on another unit, starting the former
367 will stop the latter and vice
368 versa. Note that this setting is
369 independent of and orthogonal to the
370 <varname>After=
</varname> and
371 <varname>Before=
</varname> ordering
374 <para>If a unit A that conflicts with
375 a unit B is scheduled to be started at
376 the same time as B, the transaction
377 will either fail (in case both are
378 required part of the transaction) or
379 be modified to be fixed (in case one
380 or both jobs are not a required part
381 of the transaction). In the latter
382 case the job that is not the required
383 will be removed, or in case both are
384 not required the unit that conflicts
385 will be started and the unit that is
387 stopped.
</para></listitem>
391 <term><varname>Before=
</varname></term>
392 <term><varname>After=
</varname></term>
394 <listitem><para>Configures ordering
395 dependencies between units. If a unit
396 <filename>foo.service
</filename>
398 <option>Before=bar.service
</option>
399 and both units are being started,
400 <filename>bar.service
</filename>'s
401 start-up is delayed until
402 <filename>foo.service
</filename> is
403 started up. Note that this setting is
404 independent of and orthogonal to the
405 requirement dependencies as configured
406 by
<varname>Requires=
</varname>. It is
407 a common pattern to include a unit
409 <varname>After=
</varname> and
410 <varname>Requires=
</varname> option in
411 which case the unit listed will be
412 started before the unit that is
413 configured with these options. This
414 option may be specified more than
415 once, in which case ordering
416 dependencies for all listed names are
417 created.
<varname>After=
</varname> is
419 <varname>Before=
</varname>, i.e. while
420 <varname>After=
</varname> ensures that
421 the configured unit is started after
422 the listed unit finished starting up,
423 <varname>Before=
</varname> ensures the
424 opposite, i.e. that the configured
425 unit is fully started up before the
426 listed unit is started. Note that when
427 two units with an ordering dependency
428 between them are shut down, the
429 inverse of the start-up order is
430 applied. i.e. if a unit is configured
431 with
<varname>After=
</varname> on
432 another unit, the former is stopped
433 before the latter if both are shut
434 down. If one unit with an ordering
435 dependency on another unit is shut
436 down while the latter is started up,
437 the shut down is ordered before the
438 start-up regardless whether the
439 ordering dependency is actually of
440 type
<varname>After=
</varname> or
441 <varname>Before=
</varname>. If two
442 units have no ordering dependencies
443 between them they are shut down
444 resp. started up simultaneously, and
446 place.
</para></listitem>
450 <term><varname>OnFailure=
</varname></term>
452 <listitem><para>Lists one or more
453 units that are activated when this
455 '
<literal>failed
</literal>'
456 state.
</para></listitem>
460 <term><varname>StopWhenUnneeded=
</varname></term>
462 <listitem><para>Takes a boolean
463 argument. If
<option>true
</option>
464 this unit will be stopped when it is
465 no longer used. Note that in order to
466 minimize the work to be executed,
467 systemd will not stop units by default
468 unless they are conflicting with other
469 units, or the user explicitly
470 requested their shut down. If this
471 option is set, a unit will be
472 automatically cleaned up if no other
473 active unit requires it. Defaults to
474 <option>false
</option>.
</para></listitem>
478 <term><varname>RefuseManualStart=
</varname></term>
479 <term><varname>RefuseManualStop=
</varname></term>
481 <listitem><para>Takes a boolean
482 argument. If
<option>true
</option>
483 this unit can only be activated
484 (resp. deactivated) indirectly. In
485 this case explicit start-up
486 (resp. termination) requested by the
487 user is denied, however if it is
488 started (resp. stopped) as a
489 dependency of another unit, start-up
490 (resp. termination) will succeed. This
491 is mostly a safety feature to ensure
492 that the user does not accidentally
493 activate units that are not intended
494 to be activated explicitly, and not
495 accidentally deactivate units that are
496 not intended to be deactivated.
497 These options default to
498 <option>false
</option>.
</para></listitem>
502 <term><varname>AllowIsolate=
</varname></term>
504 <listitem><para>Takes a boolean
505 argument. If
<option>true
</option>
506 this unit may be used with the
507 <command>systemctl isolate
</command>
508 command. Otherwise this will be
509 refused. It probably is a good idea to
510 leave this disabled except for target
511 units that shall be used similar to
512 runlevels in SysV init systems, just
513 as a precaution to avoid unusable
514 system states. This option defaults to
515 <option>false
</option>.
</para></listitem>
519 <term><varname>DefaultDependencies=
</varname></term>
521 <listitem><para>Takes a boolean
522 argument. If
<option>true
</option>
523 (the default), a few default
524 dependencies will implicitly be
525 created for the unit. The actual
526 dependencies created depend on the
527 unit type. For example, for service
528 units, these dependencies ensure that
529 the service is started only after
530 basic system initialization is
531 completed and is properly terminated on
532 system shutdown. See the respective
533 man pages for details. Generally, only
534 services involved with early boot or
535 late shutdown should set this option
536 to
<option>false
</option>. It is
537 highly recommended to leave this
538 option enabled for the majority of
539 common units. If set to
540 <option>false
</option> this option
541 does not disable all implicit
542 dependencies, just non-essential
543 ones.
</para></listitem>
547 <term><varname>JobTimeoutSec=
</varname></term>
549 <listitem><para>When clients are
550 waiting for a job of this unit to
551 complete, time out after the specified
552 time. If this time limit is reached
553 the job will be cancelled, the unit
554 however will not change state or even
555 enter the '
<literal>failed
</literal>'
556 mode. This value defaults to
0 (job
557 timeouts disabled), except for device
558 units. NB: this timeout is independent
559 from any unit-specific timeout (for
560 example, the timeout set with
561 <varname>Timeout=
</varname> in service
562 units) as the job timeout has no
563 effect on the unit itself, only on the
564 job that might be pending for it. Or
565 in other words: unit-specific timeouts
566 are useful to abort unit state
567 changes, and revert them. The job
568 timeout set with this option however
569 is useful to abort only the job
570 waiting for the unit state to
571 change.
</para></listitem>
575 <term><varname>ConditionPathExists=
</varname></term>
576 <term><varname>ConditionDirectoryNotEmpty=
</varname></term>
577 <term><varname>ConditionKernelCommandLine=
</varname></term>
578 <term><varname>ConditionNull=
</varname></term>
580 <listitem><para>Before starting a unit
581 verify that the specified condition is
583 <varname>ConditionPathExists=
</varname>
584 a file existance condition can be
585 checked before a unit is started. If
586 the specified absolute path name does
587 not exist startup of a unit will not
588 actually happen, however the unit is
589 still useful for ordering purposes in
590 this case. The condition is checked at
591 the time the queued start job is to be
592 executed. If the absolute path name
594 <varname>ConditionPathExists=
</varname>
595 is prefixed with an exclamation mark
596 (!), the test is negated, and the unit
597 only started if the path does not
598 exist.
<varname>ConditionDirectoryNotEmpty=
</varname>
600 <varname>ConditionPathExists=
</varname>
601 but verifies whether a cetrain path is
602 exists and is a non-empty
604 <varname>ConditionKernelCommandLine=
</varname>
605 may be used to check whether a
606 specific kernel command line option is
607 set (or if prefixed with the
608 exclamation mark unset). The argument
609 must either be a single word, or an
610 assignment (i.e. two words, seperated
611 by the equality sign). In the former
612 case the kernel command line is
613 searched for the word appearing as is,
614 or as left hand side of an
615 assignment. In the latter case the
616 exact assignment is looked for with
617 right and left hand side
619 <varname>ConditionNull=
</varname> may
620 be used to add a constant condition
621 check value to the unit. It takes a
622 boolean argument. If set to
623 <varname>false
</varname> the condition
624 will always fail, otherwise
625 succeed. If multiple conditions are
626 specified the unit will be executed
627 iff at least one of them applies
628 (i.e. a logical OR is
629 applied).
</para></listitem>
633 <para>Unit file may include a [Install] section, which
634 carries installation information for the unit. This
635 section is not interpreted by
636 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>
637 during runtime. It is used exclusively by the
638 <command>enable
</command> and
639 <command>disable
</command> commands of the
640 <citerefentry><refentrytitle>systemctl
</refentrytitle><manvolnum>1</manvolnum></citerefentry>
641 tool during installation of a unit:
</para>
645 <term><varname>Alias=
</varname></term>
647 <listitem><para>Additional names this
648 unit shall be installed under. The
649 names listed here must have the same
650 suffix (i.e. type) as the unit file
651 name. This option may be specified
652 more than once, in which case all
653 listed names are used. At installation
655 <command>systemctl enable
</command>
656 will create symlinks from these names
657 to the unit file name. Note that this
658 is different from the
659 <varname>Names=
</varname> option from
660 the [Unit] section mentioned above:
662 <varname>Names=
</varname> apply
663 unconditionally if the unit is
664 loaded. The names from
665 <varname>Alias=
</varname> apply only
666 if the unit has actually been
668 <command>systemctl enable
</command>
669 command. Also, if systemd searches for a
670 unit, it will discover symlinked alias
671 names as configured with
672 <varname>Alias=
</varname>, but not
673 names configured with
674 <varname>Names=
</varname> only. It is
675 a common pattern to list a name in
676 both options. In this case, a unit
677 will be active under all names if
678 installed, but also if not installed
679 but requested explicitly under its
680 main name.
</para></listitem>
684 <term><varname>WantedBy=
</varname></term>
686 <listitem><para>Installs a symlink in
687 the
<filename>.wants/
</filename>
688 subdirectory for a unit. This has the
689 effect that when the listed unit name
690 is activated the unit listing it is
692 too.
<command>WantedBy=foo.service
</command>
694 <filename>bar.service
</filename> is
696 <command>Alias=foo.service.wants/bar.service
</command>
697 in the same file.
</para></listitem>
701 <term><varname>Also=
</varname></term>
703 <listitem><para>Additional units to
704 install when this unit is
705 installed. If the user requests
706 installation of a unit with this
708 <command>systemctl enable
</command>
709 will automatically install units
710 listed in this option as
711 well.
</para></listitem>
718 <title>See Also
</title>
720 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
721 <citerefentry><refentrytitle>systemctl
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
722 <citerefentry><refentrytitle>systemd.special
</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
723 <citerefentry><refentrytitle>systemd.service
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
724 <citerefentry><refentrytitle>systemd.socket
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
725 <citerefentry><refentrytitle>systemd.device
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
726 <citerefentry><refentrytitle>systemd.mount
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
727 <citerefentry><refentrytitle>systemd.automount
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
728 <citerefentry><refentrytitle>systemd.swap
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
729 <citerefentry><refentrytitle>systemd.target
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
730 <citerefentry><refentrytitle>systemd.path
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
731 <citerefentry><refentrytitle>systemd.timer
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
732 <citerefentry><refentrytitle>systemd.snapshot
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
projects / thirdparty / systemd.git / blob