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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">
4
5 <!--
6 This file is part of systemd.
7
8 Copyright 2010 Lennart Poettering
9
10 systemd is free software; you can redistribute it and/or modify it
11 under the terms of the GNU Lesser General Public License as published by
12 the Free Software Foundation; either version 2.1 of the License, or
13 (at your option) any later version.
14
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 Lesser General Public License for more details.
19
20 You should have received a copy of the GNU Lesser General Public License
21 along with systemd; If not, see <http://www.gnu.org/licenses/>.
22 -->
23
24 <refentry id="systemd">
25
26 <refentryinfo>
27 <title>systemd</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</refentrytitle>
42 <manvolnum>1</manvolnum>
43 </refmeta>
44
45 <refnamediv>
46 <refname>systemd</refname>
47 <refname>init</refname>
48 <refpurpose>systemd system and service manager</refpurpose>
49 </refnamediv>
50
51 <refsynopsisdiv>
52 <cmdsynopsis>
53 <command>systemd <arg choice="opt" rep="repeat">OPTIONS</arg></command>
54 </cmdsynopsis>
55 <cmdsynopsis>
56 <command>init <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="req">COMMAND</arg></command>
57 </cmdsynopsis>
58 </refsynopsisdiv>
59
60 <refsect1>
61 <title>Description</title>
62
63 <para>systemd is a system and service manager for
64 Linux operating systems. When run as first process on
65 boot (as PID 1), it acts as init system that brings
66 up and maintains userspace services.</para>
67
68 <para>For compatibility with SysV, if systemd is called
69 as <command>init</command> and a PID that is not
70 1, it will execute <command>telinit</command> and pass
71 all command line arguments unmodified. That means
72 <command>init</command> and <command>telinit</command>
73 are mostly equivalent when invoked from normal login sessions. See
74 <citerefentry><refentrytitle>telinit</refentrytitle><manvolnum>8</manvolnum></citerefentry>
75 for more information.</para>
76
77 <para>When run as system instance, systemd interprets
78 the configuration file
79 <filename>system.conf</filename>, otherwise
80 <filename>user.conf</filename>. See
81 <citerefentry><refentrytitle>systemd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
82 for more information.</para>
83 </refsect1>
84
85 <refsect1>
86 <title>Options</title>
87
88 <para>The following options are understood:</para>
89
90 <variablelist>
91 <varlistentry>
92 <term><option>-h</option></term>
93 <term><option>--help</option></term>
94
95 <listitem><para>Prints a short help
96 text and exits.</para></listitem>
97 </varlistentry>
98 <varlistentry>
99 <term><option>--version</option></term>
100
101 <listitem><para>Prints a systemd version
102 identifier and exits.</para></listitem>
103 </varlistentry>
104 <varlistentry>
105 <term><option>--test</option></term>
106
107 <listitem><para>Determine startup
108 sequence, dump it and exit. This is an
109 option useful for debugging
110 only.</para></listitem>
111 </varlistentry>
112 <varlistentry>
113 <term><option>--dump-configuration-items</option></term>
114
115 <listitem><para>Dump understood unit
116 configuration items. This outputs a
117 terse but complete list of
118 configuration items understood in unit
119 definition files.</para></listitem>
120 </varlistentry>
121 <varlistentry>
122 <term><option>--introspect=</option></term>
123
124 <listitem><para>Extract D-Bus
125 interface introspection data. This is
126 mostly useful at install time
127 to generate data suitable for the
128 D-Bus interfaces
129 repository. Optionally the interface
130 name for the introspection data may be
131 specified. If omitted, the
132 introspection data for all interfaces
133 is dumped.</para></listitem>
134 </varlistentry>
135 <varlistentry>
136 <term><option>--unit=</option></term>
137
138 <listitem><para>Set default unit to
139 activate on startup. If not specified
140 defaults to
141 <filename>default.target</filename>.</para></listitem>
142 </varlistentry>
143 <varlistentry>
144 <term><option>--system</option></term>
145 <term><option>--user</option></term>
146
147 <listitem><para>For <option>--system</option>,
148 tell systemd to run a
149 system instance, even if the process ID is
150 not 1, i.e. systemd is not run as init process.
151 <option>--user</option> does the opposite,
152 running a user instance even if the process
153 ID is 1.
154 Normally it should not be necessary to
155 pass these options, as systemd
156 automatically detects the mode it is
157 started in. These options are hence of
158 little use except for debugging. Note
159 that it is not supported booting and
160 maintaining a full system with systemd
161 running in <option>--system</option>
162 mode, but PID not 1. In practice,
163 passing <option>--system</option> explicitly is
164 only useful in conjunction with
165 <option>--test</option>.</para></listitem>
166 </varlistentry>
167 <varlistentry>
168 <term><option>--dump-core</option></term>
169
170 <listitem><para>Dump core on
171 crash. This switch has no effect when
172 run as user
173 instance.</para></listitem>
174 </varlistentry>
175 <varlistentry>
176 <term><option>--crash-shell</option></term>
177
178 <listitem><para>Run shell on
179 crash. This switch has no effect when
180 run as user
181 instance.</para></listitem>
182 </varlistentry>
183 <varlistentry>
184 <term><option>--confirm-spawn</option></term>
185
186 <listitem><para>Ask for confirmation
187 when spawning processes. This switch
188 has no effect when run as user
189 instance.</para></listitem>
190 </varlistentry>
191 <varlistentry>
192 <term><option>--show-status=</option></term>
193
194 <listitem><para>Show terse service
195 status information while booting. This
196 switch has no effect when run as user
197 instance. Takes a boolean argument
198 which may be omitted which is
199 interpreted as
200 <option>true</option>.</para></listitem>
201 </varlistentry>
202 <varlistentry>
203 <term><option>--log-target=</option></term>
204
205 <listitem><para>Set log
206 target. Argument must be one of
207 <option>console</option>,
208 <option>journal</option>,
209 <option>syslog</option>,
210 <option>kmsg</option>,
211 <option>journal-or-kmsg</option>,
212 <option>syslog-or-kmsg</option>,
213 <option>null</option>.</para></listitem>
214 </varlistentry>
215 <varlistentry>
216 <term><option>--log-level=</option></term>
217
218 <listitem><para>Set log level. As
219 argument this accepts a numerical log
220 level or the well-known <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
221 symbolic names (lowercase):
222 <option>emerg</option>,
223 <option>alert</option>,
224 <option>crit</option>,
225 <option>err</option>,
226 <option>warning</option>,
227 <option>notice</option>,
228 <option>info</option>,
229 <option>debug</option>.</para></listitem>
230 </varlistentry>
231 <varlistentry>
232 <term><option>--log-color=</option></term>
233
234 <listitem><para>Highlight important
235 log messages. Argument is a boolean
236 value. If the argument is omitted it
237 defaults to
238 <option>true</option>.</para></listitem>
239 </varlistentry>
240 <varlistentry>
241 <term><option>--log-location=</option></term>
242
243 <listitem><para>Include code location
244 in log messages. This is mostly
245 relevant for debugging
246 purposes. Argument is a boolean
247 value. If the argument is omitted
248 it defaults to
249 <option>true</option>.</para></listitem>
250 </varlistentry>
251 <varlistentry>
252 <term><option>--default-standard-output=</option></term>
253 <term><option>--default-standard-error=</option></term>
254
255 <listitem><para>Sets the default
256 output or error output for all
257 services and sockets, respectively. That is, controls
258 the default for
259 <option>StandardOutput=</option>
260 and <option>StandardError=</option>
261 (see
262 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
263 for details). Takes one of
264 <option>inherit</option>,
265 <option>null</option>,
266 <option>tty</option>,
267 <option>journal</option>,
268 <option>journal+console</option>,
269 <option>syslog</option>,
270 <option>syslog+console</option>,
271 <option>kmsg</option>,
272 <option>kmsg+console</option>. If the
273 argument is omitted
274 <option>--default-standard-output=</option>
275 defaults to <option>journal</option>
276 and
277 <option>--default-standard-error=</option>
278 to
279 <option>inherit</option>.</para></listitem>
280 </varlistentry>
281 </variablelist>
282 </refsect1>
283
284 <refsect1>
285 <title>Concepts</title>
286
287 <para>systemd provides a dependency system between
288 various entities called "units". Units encapsulate
289 various objects that are relevant for system boot-up
290 and maintenance. The majority of units are configured
291 in unit configuration files, whose syntax and basic
292 set of options is described in
293 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
294 however some are created automatically from other
295 configuration or dynamically from system state. Units
296 may be 'active' (meaning started, bound, plugged in,
297 ... depending on the unit type, see below), or
298 'inactive' (meaning stopped, unbound, unplugged, ...),
299 as well as in the process of being activated or
300 deactivated, i.e. between the two states (these states
301 are called 'activating', 'deactivating'). A special
302 'failed' state is available as well which is very
303 similar to 'inactive' and is entered when the service
304 failed in some way (process returned error code on
305 exit, or crashed, or an operation timed out). If this
306 state is entered the cause will be logged, for later
307 reference. Note that the various unit types may have a
308 number of additional substates, which are mapped to
309 the five generalized unit states described
310 here.</para>
311
312 <para>The following unit types are available:</para>
313
314 <orderedlist>
315 <listitem><para>Service units, which control
316 daemons and the processes they consist of. For
317 details see
318 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
319
320 <listitem><para>Socket units, which
321 encapsulate local IPC or network sockets in
322 the system, useful for socket-based
323 activation. For details about socket units see
324 <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
325 for details on socket-based activation and
326 other forms of activation, see
327 <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
328
329 <listitem><para>Target units are useful to
330 group units, or provide well-known
331 synchronization points during boot-up, see
332 <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
333
334 <listitem><para>Device units expose kernel
335 devices in systemd and may be used to
336 implement device-based activation. For details
337 see
338 <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
339
340 <listitem><para>Mount units control mount
341 points in the file system, for details see
342 <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
343
344 <listitem><para>Automount units provide
345 automount capabilities, for on-demand mounting
346 of file systems as well as parallelized
347 boot-up. See
348 <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
349
350 <listitem><para>Snapshot units can be used to
351 temporarily save the state of the set of
352 systemd units, which later may be restored by
353 activating the saved snapshot unit. For more
354 information see
355 <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
356
357 <listitem><para>Timer units are useful for
358 triggering activation of other units based on
359 timers. You may find details in
360 <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
361
362 <listitem><para>Swap units are very similar to
363 mount units and encapsulate memory swap
364 partitions or files of the operating
365 system. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
366
367 <listitem><para>Path units may be used
368 to activate other services when file system
369 objects change or are modified. See
370 <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
371
372 </orderedlist>
373
374 <para>Units are named as their configuration
375 files. Some units have special semantics. A detailed
376 list is available in
377 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
378
379 <para>systemd knows various kinds of dependencies,
380 including positive and negative requirement
381 dependencies (i.e. <varname>Requires=</varname> and
382 <varname>Conflicts=</varname>) as well as ordering
383 dependencies (<varname>After=</varname> and
384 <varname>Before=</varname>). NB: ordering and
385 requirement dependencies are orthogonal. If only a
386 requirement dependency exists between two units
387 (e.g. <filename>foo.service</filename> requires
388 <filename>bar.service</filename>), but no ordering
389 dependency (e.g. <filename>foo.service</filename>
390 after <filename>bar.service</filename>) and both are
391 requested to start, they will be started in
392 parallel. It is a common pattern that both requirement
393 and ordering dependencies are placed between two
394 units. Also note that the majority of dependencies are
395 implicitly created and maintained by systemd. In most
396 cases it should be unnecessary to declare additional
397 dependencies manually, however it is possible to do
398 this.</para>
399
400 <para>Application programs and units (via
401 dependencies) may request state changes of units. In
402 systemd, these requests are encapsulated as 'jobs' and
403 maintained in a job queue. Jobs may succeed or can
404 fail, their execution is ordered based on the ordering
405 dependencies of the units they have been scheduled
406 for.</para>
407
408 <para>On boot systemd activates the target unit
409 <filename>default.target</filename> whose job is to
410 activate on-boot services and other on-boot units by
411 pulling them in via dependencies. Usually the unit
412 name is just an alias (symlink) for either
413 <filename>graphical.target</filename> (for
414 fully-featured boots into the UI) or
415 <filename>multi-user.target</filename> (for limited
416 console-only boots for use in embedded or server
417 environments, or similar; a subset of
418 graphical.target). However it is at the discretion of
419 the administrator to configure it as an alias to any
420 other target unit. See
421 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
422 for details about these target units.</para>
423
424 <para>Processes systemd spawns are placed in
425 individual Linux control groups named after the unit
426 which they belong to in the private systemd
427 hierarchy. (see <ulink
428 url="http://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
429 for more information about control groups, or short
430 "cgroups"). systemd uses this to effectively keep
431 track of processes. Control group information is
432 maintained in the kernel, and is accessible via the
433 file system hierarchy (beneath
434 <filename>/sys/fs/cgroup/systemd/</filename>), or in tools
435 such as
436 <citerefentry><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
437 (<command>ps xawf -eo pid,user,cgroup,args</command>
438 is particularly useful to list all processes and the
439 systemd units they belong to.).</para>
440
441 <para>systemd is compatible with the SysV init system
442 to a large degree: SysV init scripts are supported and
443 simply read as an alternative (though limited)
444 configuration file format. The SysV
445 <filename>/dev/initctl</filename> interface is
446 provided, and compatibility implementations of the
447 various SysV client tools are available. In addition to
448 that, various established Unix functionality such as
449 <filename>/etc/fstab</filename> or the
450 <filename>utmp</filename> database are
451 supported.</para>
452
453 <para>systemd has a minimal transaction system: if a
454 unit is requested to start up or shut down it will add
455 it and all its dependencies to a temporary
456 transaction. Then, it will verify if the transaction
457 is consistent (i.e. whether the ordering of all units
458 is cycle-free). If it is not, systemd will try to fix
459 it up, and removes non-essential jobs from the
460 transaction that might remove the loop. Also, systemd
461 tries to suppress non-essential jobs in the
462 transaction that would stop a running service. Finally
463 it is checked whether the jobs of the transaction
464 contradict jobs that have already been queued, and
465 optionally the transaction is aborted then. If all
466 worked out and the transaction is consistent and
467 minimized in its impact it is merged with all already
468 outstanding jobs and added to the run
469 queue. Effectively this means that before executing a
470 requested operation, systemd will verify that it makes
471 sense, fixing it if possible, and only failing if it
472 really cannot work.</para>
473
474 <para>Systemd contains native implementations of
475 various tasks that need to be executed as part of the
476 boot process. For example, it sets the host name or
477 configures the loopback network device. It also sets
478 up and mounts various API file systems, such as
479 <filename>/sys</filename> or
480 <filename>/proc</filename>.</para>
481
482 <para>For more information about the concepts and
483 ideas behind systemd please refer to the <ulink
484 url="http://0pointer.de/blog/projects/systemd.html">Original
485 Design Document</ulink>.</para>
486
487 <para>Note that some but not all interfaces provided
488 by systemd are covered by the <ulink
489 url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
490 Stability Promise</ulink>.</para>
491
492 <para>Units may be generated dynamically at boot and
493 system manager reload time, for example based on other
494 configuration files or parameters passed on the kernel
495 command line. For details see the <ulink
496 url="http://www.freedesktop.org/wiki/Software/systemd/Generators">Generators
497 Specification</ulink>.</para>
498
499 <para>Systems which invoke systemd in a container
500 or initrd environment should implement the
501 <ulink
502 url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container
503 Interface</ulink> or <ulink
504 url="http://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd
505 Interface</ulink> specifications, respectively.</para>
506 </refsect1>
507
508 <refsect1>
509 <title>Directories</title>
510
511 <variablelist>
512 <varlistentry>
513 <term>System unit directories</term>
514
515 <listitem><para>The systemd system
516 manager reads unit configuration from
517 various directories. Packages that
518 want to install unit files shall place
519 them in the directory returned by
520 <command>pkg-config systemd
521 --variable=systemdsystemunitdir</command>. Other
522 directories checked are
523 <filename>/usr/local/lib/systemd/system</filename>
524 and
525 <filename>/usr/lib/systemd/system</filename>. User
526 configuration always takes
527 precedence. <command>pkg-config
528 systemd
529 --variable=systemdsystemconfdir</command>
530 returns the path of the system
531 configuration directory. Packages
532 should alter the content of these
533 directories only with the
534 <command>enable</command> and
535 <command>disable</command> commands of
536 the
537 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
538 tool.</para></listitem>
539 </varlistentry>
540 </variablelist>
541
542 <variablelist>
543 <varlistentry>
544 <term>User unit directories</term>
545
546 <listitem><para>Similar rules apply
547 for the user unit
548 directories. However, here the <ulink
549 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
550 Base Directory specification</ulink>
551 is followed to find
552 units. Applications should place their
553 unit files in the directory returned
554 by <command>pkg-config systemd
555 --variable=systemduserunitdir</command>. Global
556 configuration is done in the directory
557 reported by <command>pkg-config
558 systemd
559 --variable=systemduserconfdir</command>. The
560 <command>enable</command> and
561 <command>disable</command> commands of
562 the
563 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
564 tool can handle both global (i.e. for
565 all users) and private (for one user)
566 enabling/disabling of
567 units.</para></listitem>
568 </varlistentry>
569 </variablelist>
570
571 <variablelist>
572 <varlistentry>
573 <term>SysV init scripts directory</term>
574
575 <listitem><para>The location of the
576 SysV init script directory varies
577 between distributions. If systemd
578 cannot find a native unit file for a
579 requested service, it will look for a
580 SysV init script of the same name
581 (with the
582 <filename>.service</filename> suffix
583 removed).</para></listitem>
584 </varlistentry>
585 </variablelist>
586
587 <variablelist>
588 <varlistentry>
589 <term>SysV runlevel link farm directory</term>
590
591 <listitem><para>The location of the
592 SysV runlevel link farm directory
593 varies between distributions. systemd
594 will take the link farm into account
595 when figuring out whether a service
596 shall be enabled. Note that a service
597 unit with a native unit configuration
598 file cannot be started by activating it
599 in the SysV runlevel link
600 farm.</para></listitem>
601 </varlistentry>
602 </variablelist>
603 </refsect1>
604
605 <refsect1>
606 <title>Signals</title>
607
608 <variablelist>
609 <varlistentry>
610 <term>SIGTERM</term>
611
612 <listitem><para>Upon receiving this
613 signal the systemd system manager
614 serializes its state, reexecutes
615 itself and deserializes the saved
616 state again. This is mostly equivalent
617 to <command>systemctl
618 daemon-reexec</command>.</para>
619
620 <para>systemd user managers will
621 start the
622 <filename>exit.target</filename> unit
623 when this signal is received. This is
624 mostly equivalent to
625 <command>systemctl --user start
626 exit.target</command>.</para></listitem>
627 </varlistentry>
628
629 <varlistentry>
630 <term>SIGINT</term>
631
632 <listitem><para>Upon receiving this
633 signal the systemd system manager will
634 start the
635 <filename>ctrl-alt-del.target</filename> unit. This
636 is mostly equivalent to
637 <command>systemctl start
638 ctl-alt-del.target</command>.</para>
639
640 <para>systemd user managers
641 treat this signal the same way as
642 SIGTERM.</para></listitem>
643 </varlistentry>
644
645 <varlistentry>
646 <term>SIGWINCH</term>
647
648 <listitem><para>When this signal is
649 received the systemd system manager
650 will start the
651 <filename>kbrequest.target</filename>
652 unit. This is mostly equivalent to
653 <command>systemctl start
654 kbrequest.target</command>.</para>
655
656 <para>This signal is ignored by
657 systemd user
658 managers.</para></listitem>
659 </varlistentry>
660
661 <varlistentry>
662 <term>SIGPWR</term>
663
664 <listitem><para>When this signal is
665 received the systemd manager
666 will start the
667 <filename>sigpwr.target</filename>
668 unit. This is mostly equivalent to
669 <command>systemctl start
670 sigpwr.target</command>.</para></listitem>
671 </varlistentry>
672
673 <varlistentry>
674 <term>SIGUSR1</term>
675
676 <listitem><para>When this signal is
677 received the systemd manager will try
678 to reconnect to the D-Bus
679 bus.</para></listitem>
680 </varlistentry>
681
682 <varlistentry>
683 <term>SIGUSR2</term>
684
685 <listitem><para>When this signal is
686 received the systemd manager will log
687 its complete state in human readable
688 form. The data logged is the same as
689 printed by <command>systemctl
690 dump</command>.</para></listitem>
691 </varlistentry>
692
693 <varlistentry>
694 <term>SIGHUP</term>
695
696 <listitem><para>Reloads the complete
697 daemon configuration. This is mostly
698 equivalent to <command>systemctl
699 daemon-reload</command>.</para></listitem>
700 </varlistentry>
701
702 <varlistentry>
703 <term>SIGRTMIN+0</term>
704
705 <listitem><para>Enters default mode, starts the
706 <filename>default.target</filename>
707 unit. This is mostly equivalent to
708 <command>systemctl start
709 default.target</command>.</para></listitem>
710 </varlistentry>
711
712 <varlistentry>
713 <term>SIGRTMIN+1</term>
714
715 <listitem><para>Enters rescue mode,
716 starts the
717 <filename>rescue.target</filename>
718 unit. This is mostly equivalent to
719 <command>systemctl isolate
720 rescue.target</command>.</para></listitem>
721 </varlistentry>
722
723 <varlistentry>
724 <term>SIGRTMIN+2</term>
725
726 <listitem><para>Enters emergency mode,
727 starts the
728 <filename>emergency.service</filename>
729 unit. This is mostly equivalent to
730 <command>systemctl isolate
731 emergency.service</command>.</para></listitem>
732 </varlistentry>
733
734 <varlistentry>
735 <term>SIGRTMIN+3</term>
736
737 <listitem><para>Halts the machine,
738 starts the
739 <filename>halt.target</filename>
740 unit. This is mostly equivalent to
741 <command>systemctl start
742 halt.target</command>.</para></listitem>
743 </varlistentry>
744
745 <varlistentry>
746 <term>SIGRTMIN+4</term>
747
748 <listitem><para>Powers off the machine,
749 starts the
750 <filename>poweroff.target</filename>
751 unit. This is mostly equivalent to
752 <command>systemctl start
753 poweroff.target</command>.</para></listitem>
754 </varlistentry>
755
756 <varlistentry>
757 <term>SIGRTMIN+5</term>
758
759 <listitem><para>Reboots the machine,
760 starts the
761 <filename>reboot.target</filename>
762 unit. This is mostly equivalent to
763 <command>systemctl start
764 reboot.target</command>.</para></listitem>
765 </varlistentry>
766
767 <varlistentry>
768 <term>SIGRTMIN+6</term>
769
770 <listitem><para>Reboots the machine via kexec,
771 starts the
772 <filename>kexec.target</filename>
773 unit. This is mostly equivalent to
774 <command>systemctl start
775 kexec.target</command>.</para></listitem>
776 </varlistentry>
777
778 <varlistentry>
779 <term>SIGRTMIN+13</term>
780
781 <listitem><para>Immediately halts the machine.</para></listitem>
782 </varlistentry>
783
784 <varlistentry>
785 <term>SIGRTMIN+14</term>
786
787 <listitem><para>Immediately powers off the machine.</para></listitem>
788 </varlistentry>
789
790 <varlistentry>
791 <term>SIGRTMIN+15</term>
792
793 <listitem><para>Immediately reboots the machine.</para></listitem>
794 </varlistentry>
795
796 <varlistentry>
797 <term>SIGRTMIN+16</term>
798
799 <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
800 </varlistentry>
801
802 <varlistentry>
803 <term>SIGRTMIN+20</term>
804
805 <listitem><para>Enables display of
806 status messages on the console, as
807 controlled via
808 <varname>systemd.show_status=1</varname>
809 on the kernel command
810 line.</para></listitem>
811 </varlistentry>
812
813 <varlistentry>
814 <term>SIGRTMIN+21</term>
815
816 <listitem><para>Disables display of
817 status messages on the console, as
818 controlled via
819 <varname>systemd.show_status=0</varname>
820 on the kernel command
821 line.</para></listitem>
822 </varlistentry>
823
824 <varlistentry>
825 <term>SIGRTMIN+22</term>
826 <term>SIGRTMIN+23</term>
827
828 <listitem><para>Sets the log level to
829 <literal>debug</literal>
830 (or <literal>info</literal> on
831 <literal>SIGRTMIN+23</literal>), as
832 controlled via
833 <varname>systemd.log_level=debug</varname>
834 (or <varname>systemd.log_level=info</varname>
835 on <literal>SIGRTMIN+23</literal>) on
836 the kernel command
837 line.</para></listitem>
838 </varlistentry>
839
840 <varlistentry>
841 <term>SIGRTMIN+24</term>
842
843 <listitem><para>Immediately exits the
844 manager (only available for --user
845 instances).</para></listitem>
846 </varlistentry>
847
848 <varlistentry>
849 <term>SIGRTMIN+26</term>
850 <term>SIGRTMIN+27</term>
851 <term>SIGRTMIN+28</term>
852 <term>SIGRTMIN+29</term>
853
854 <listitem><para>Sets the log level to
855 <literal>journal-or-kmsg</literal>
856 (or <literal>console</literal> on
857 <literal>SIGRTMIN+27</literal>,
858 <literal>kmsg</literal> on
859 <literal>SIGRTMIN+28</literal>,
860 or <literal>syslog-or-kmsg</literal>
861 on <literal>SIGRTMIN+29</literal>), as
862 controlled via
863 <varname>systemd.log_target=journal-or-kmsg</varname>
864 (or <varname>systemd.log_target=console</varname>
865 on <literal>SIGRTMIN+27</literal>,
866 <varname>systemd.log_target=kmsg</varname>
867 on <literal>SIGRTMIN+28</literal>,
868 or
869 <varname>systemd.log_target=syslog-or-kmsg</varname>
870 on <literal>SIGRTMIN+29</literal>) on
871 the kernel command
872 line.</para></listitem>
873 </varlistentry>
874 </variablelist>
875 </refsect1>
876
877 <refsect1>
878 <title>Environment</title>
879
880 <variablelist class='environment-variables'>
881 <varlistentry>
882 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
883 <listitem><para>systemd reads the
884 log level from this environment
885 variable. This can be overridden with
886 <option>--log-level=</option>.</para></listitem>
887 </varlistentry>
888
889 <varlistentry>
890 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
891 <listitem><para>systemd reads the
892 log target from this environment
893 variable. This can be overridden with
894 <option>--log-target=</option>.</para></listitem>
895 </varlistentry>
896
897 <varlistentry>
898 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
899 <listitem><para>Controls whether
900 systemd highlights important log
901 messages. This can be overridden with
902 <option>--log-color=</option>.</para></listitem>
903 </varlistentry>
904
905 <varlistentry>
906 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
907 <listitem><para>Controls whether
908 systemd prints the code location along
909 with log messages. This can be
910 overridden with
911 <option>--log-location=</option>.</para></listitem>
912 </varlistentry>
913
914 <varlistentry>
915 <term><varname>$XDG_CONFIG_HOME</varname></term>
916 <term><varname>$XDG_CONFIG_DIRS</varname></term>
917 <term><varname>$XDG_DATA_HOME</varname></term>
918 <term><varname>$XDG_DATA_DIRS</varname></term>
919
920 <listitem><para>The systemd user
921 manager uses these variables in
922 accordance to the <ulink
923 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
924 Base Directory specification</ulink>
925 to find its configuration.</para></listitem>
926 </varlistentry>
927
928 <varlistentry>
929 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
930
931 <listitem><para>Controls where systemd
932 looks for unit
933 files.</para></listitem>
934 </varlistentry>
935
936 <varlistentry>
937 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
938
939 <listitem><para>Controls where systemd
940 looks for SysV init scripts.</para></listitem>
941 </varlistentry>
942
943 <varlistentry>
944 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
945
946 <listitem><para>Controls where systemd
947 looks for SysV init script runlevel link
948 farms.</para></listitem>
949 </varlistentry>
950
951 <varlistentry>
952 <term><varname>$LISTEN_PID</varname></term>
953 <term><varname>$LISTEN_FDS</varname></term>
954
955 <listitem><para>Set by systemd for
956 supervised processes during
957 socket-based activation. See
958 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
959 for more information.
960 </para></listitem>
961 </varlistentry>
962
963 <varlistentry>
964 <term><varname>$NOTIFY_SOCKET</varname></term>
965
966 <listitem><para>Set by systemd for
967 supervised processes for status and
968 start-up completion notification. See
969 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
970 for more information.
971 </para></listitem>
972 </varlistentry>
973 </variablelist>
974 </refsect1>
975
976 <refsect1>
977 <title>Kernel Command Line</title>
978
979 <para>When run as system instance systemd parses a
980 number of kernel command line
981 arguments<footnote><para>If run inside a Linux
982 container these arguments may be passed as command
983 line arguments to systemd itself, next to any of the
984 command line options listed in the Options section
985 above. If run outside of Linux containers, these
986 arguments are parsed from
987 <filename>/proc/cmdline</filename>
988 instead.</para></footnote>:</para>
989
990 <variablelist class='kernel-commandline-directives'>
991 <varlistentry>
992 <term><varname>systemd.unit=</varname></term>
993 <term><varname>rd.systemd.unit=</varname></term>
994
995 <listitem><para>Overrides the unit to
996 activate on boot. Defaults to
997 <filename>default.target</filename>. This
998 may be used to temporarily boot into a
999 different boot unit, for example
1000 <filename>rescue.target</filename> or
1001 <filename>emergency.service</filename>. See
1002 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1003 for details about these units. The
1004 option prefixed with
1005 <literal>rd.</literal> is honored
1006 only in the initial RAM disk (initrd),
1007 while the one that isn't prefixed only
1008 in the main system.</para></listitem>
1009 </varlistentry>
1010
1011 <varlistentry>
1012 <term><varname>systemd.dump_core=</varname></term>
1013
1014 <listitem><para>Takes a boolean
1015 argument. If <option>true</option>
1016 systemd dumps core when it
1017 crashes. Otherwise no core dump is
1018 created. Defaults to
1019 <option>true</option>.</para></listitem>
1020 </varlistentry>
1021
1022 <varlistentry>
1023 <term><varname>systemd.crash_shell=</varname></term>
1024
1025 <listitem><para>Takes a boolean
1026 argument. If <option>true</option>
1027 systemd spawns a shell when it
1028 crashes. Otherwise no shell is
1029 spawned. Defaults to
1030 <option>false</option>, for security
1031 reasons, as the shell is not protected
1032 by any password
1033 authentication.</para></listitem>
1034 </varlistentry>
1035
1036 <varlistentry>
1037 <term><varname>systemd.crash_chvt=</varname></term>
1038
1039 <listitem><para>Takes an integer
1040 argument. If positive systemd
1041 activates the specified virtual
1042 terminal when it crashes. Defaults to
1043 <literal>-1</literal>.</para></listitem>
1044 </varlistentry>
1045
1046 <varlistentry>
1047 <term><varname>systemd.confirm_spawn=</varname></term>
1048
1049 <listitem><para>Takes a boolean
1050 argument. If <option>true</option>
1051 asks for confirmation when spawning
1052 processes. Defaults to
1053 <option>false</option>.</para></listitem>
1054 </varlistentry>
1055
1056 <varlistentry>
1057 <term><varname>systemd.show_status=</varname></term>
1058
1059 <listitem><para>Takes a boolean
1060 argument. If <option>true</option>
1061 shows terse service status updates on
1062 the console during bootup. Defaults to
1063 <option>true</option>, unless
1064 <option>quiet</option> is passed as
1065 kernel command line option in which
1066 case it defaults to
1067 <option>false</option>.</para></listitem>
1068 </varlistentry>
1069
1070 <varlistentry>
1071 <term><varname>systemd.log_target=</varname></term>
1072 <term><varname>systemd.log_level=</varname></term>
1073 <term><varname>systemd.log_color=</varname></term>
1074 <term><varname>systemd.log_location=</varname></term>
1075
1076 <listitem><para>Controls log output,
1077 with the same effect as the
1078 <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
1079 environment variables described above.</para></listitem>
1080 </varlistentry>
1081
1082 <varlistentry>
1083 <term><varname>systemd.default_standard_output=</varname></term>
1084 <term><varname>systemd.default_standard_error=</varname></term>
1085 <listitem><para>Controls default
1086 standard output and error output for
1087 services, with the same effect as the
1088 <option>--default-standard-output=</option>
1089 and <option>--default-standard-error=</option>
1090 command line arguments described
1091 above, respectively.</para></listitem>
1092 </varlistentry>
1093
1094 <varlistentry>
1095 <term><varname>systemd.setenv=</varname></term>
1096
1097 <listitem><para>Takes a string
1098 argument in the form
1099 VARIABLE=VALUE. May be used to set
1100 environment variables for the init
1101 process and all its children at boot
1102 time. May be used more than once to
1103 set multiple variables. If the equal
1104 sign and variable are missing it unsets
1105 an environment variable which might be
1106 passed in from the initial ram
1107 disk.</para></listitem>
1108 </varlistentry>
1109
1110 <varlistentry>
1111 <term><varname>quiet</varname></term>
1112
1113 <listitem><para>If passed turns off
1114 status output at boot, much like
1115 <varname>systemd.show_status=false</varname>
1116 would. Note that this option is also
1117 read by the kernel itself and disables
1118 kernel log output to the
1119 kernel. Passing this option hence
1120 turns off the usual output from both
1121 the system manager and the
1122 kernel.</para></listitem>
1123 </varlistentry>
1124
1125 <varlistentry>
1126 <term><varname>emergency</varname></term>
1127
1128 <listitem><para>Boot into emergency
1129 mode. This is equivalent to
1130 <varname>systemd.unit=emergency.target</varname>
1131 and provided for compatibility
1132 reasons and to be easier to type.</para></listitem>
1133 </varlistentry>
1134
1135 <varlistentry>
1136 <term><varname>single</varname></term>
1137 <term><varname>s</varname></term>
1138 <term><varname>S</varname></term>
1139 <term><varname>1</varname></term>
1140
1141 <listitem><para>Boot into rescue
1142 mode. This is equivalent to
1143 <varname>systemd.unit=rescue.target</varname>
1144 and provided for compatibility reasons
1145 and to be easier to
1146 type.</para></listitem>
1147 </varlistentry>
1148
1149 <varlistentry>
1150 <term><varname>2</varname></term>
1151 <term><varname>3</varname></term>
1152 <term><varname>4</varname></term>
1153 <term><varname>5</varname></term>
1154
1155 <listitem><para>Boot into the
1156 specified legacy SysV runlevel. These
1157 are equivalent to
1158 <varname>systemd.unit=runlevel2.target</varname>,
1159 <varname>systemd.unit=runlevel3.target</varname>,
1160 <varname>systemd.unit=runlevel4.target</varname>,
1161 and <varname>systemd.unit=runlevel5.target</varname>, respectively,
1162 and provided for compatibility reasons
1163 and to be easier to
1164 type.</para></listitem>
1165 </varlistentry>
1166
1167 <varlistentry>
1168 <term><varname>locale.LANG=</varname></term>
1169 <term><varname>locale.LANGUAGE=</varname></term>
1170 <term><varname>locale.LC_CTYPE=</varname></term>
1171 <term><varname>locale.LC_NUMERIC=</varname></term>
1172 <term><varname>locale.LC_TIME=</varname></term>
1173 <term><varname>locale.LC_COLLATE=</varname></term>
1174 <term><varname>locale.LC_MONETARY=</varname></term>
1175 <term><varname>locale.LC_MESSAGES=</varname></term>
1176 <term><varname>locale.LC_PAPER=</varname></term>
1177 <term><varname>locale.LC_NAME=</varname></term>
1178 <term><varname>locale.LC_ADDRESS=</varname></term>
1179 <term><varname>locale.LC_TELEPHONE=</varname></term>
1180 <term><varname>locale.LC_MEASUREMENT=</varname></term>
1181 <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1182
1183 <listitem><para>Set the system locale
1184 to use. This overrides the settings in
1185 <filename>/etc/locale.conf</filename>. For
1186 more information see
1187 <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1188 and
1189 <citerefentry><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1190 </para></listitem>
1191 </varlistentry>
1192 </variablelist>
1193
1194 <para>For other kernel command line parameters
1195 understood by components of the core OS, please refer
1196 to
1197 <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1198 </refsect1>
1199
1200 <refsect1>
1201 <title>Sockets and FIFOs</title>
1202
1203 <variablelist>
1204 <varlistentry>
1205 <term><filename>/run/systemd/notify</filename></term>
1206
1207 <listitem><para>Daemon status
1208 notification socket. This is an
1209 AF_UNIX datagram socket and is used to
1210 implement the daemon notification
1211 logic as implemented by
1212 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1213
1214 </varlistentry>
1215
1216 <varlistentry>
1217 <term><filename>/run/systemd/shutdownd</filename></term>
1218
1219 <listitem><para>Used internally by the
1220 <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1221 tool to implement delayed
1222 shutdowns. This is an AF_UNIX datagram
1223 socket.</para></listitem>
1224 </varlistentry>
1225
1226 <varlistentry>
1227 <term><filename>/run/systemd/private</filename></term>
1228
1229 <listitem><para>Used internally as
1230 communication channel between
1231 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1232 and the systemd process. This is an
1233 AF_UNIX stream socket. This interface
1234 is private to systemd and should not
1235 be used in external
1236 projects.</para></listitem>
1237 </varlistentry>
1238
1239 <varlistentry>
1240 <term><filename>/dev/initctl</filename></term>
1241
1242 <listitem><para>Limited compatibility
1243 support for the SysV client interface,
1244 as implemented by the
1245 <filename>systemd-initctl.service</filename>
1246 unit. This is a named pipe in the file
1247 system. This interface is obsolete and
1248 should not be used in new
1249 applications.</para></listitem>
1250 </varlistentry>
1251 </variablelist>
1252 </refsect1>
1253
1254 <refsect1>
1255 <title>See Also</title>
1256 <para>
1257 <citerefentry><refentrytitle>systemd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1258 <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1259 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1260 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1261 <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1262 <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1263 <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1264 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1265 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1266 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1267 <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1268 <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1269 <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1270 </para>
1271 </refsect1>
1272
1273 </refentry>
Unnamed repository; edit this file 'description' to name the repository.