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2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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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 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.
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.
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/>.
24 <refentry id="systemd"
25 xmlns:xi="http://www.w3.org/2001/XInclude">
28 <title>systemd</title>
29 <productname>systemd</productname>
33 <contrib>Developer</contrib>
34 <firstname>Lennart</firstname>
35 <surname>Poettering</surname>
36 <email>lennart@poettering.net</email>
42 <refentrytitle>systemd</refentrytitle>
43 <manvolnum>1</manvolnum>
47 <refname>systemd</refname>
48 <refname>init</refname>
49 <refpurpose>systemd system and service manager</refpurpose>
54 <command>systemd <arg choice="opt" rep="repeat">OPTIONS</arg></command>
57 <command>init <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="req">COMMAND</arg></command>
62 <title>Description</title>
64 <para>systemd is a system and service manager for Linux operating
65 systems. When run as first process on boot (as PID 1), it acts as
66 init system that brings up and maintains userspace
69 <para>For compatibility with SysV, if systemd is called as
70 <command>init</command> and a PID that is not 1, it will execute
71 <command>telinit</command> and pass all command line arguments
72 unmodified. That means <command>init</command> and
73 <command>telinit</command> are mostly equivalent when invoked from
74 normal login sessions. See
75 <citerefentry><refentrytitle>telinit</refentrytitle><manvolnum>8</manvolnum></citerefentry>
76 for more information.</para>
78 <para>When run as a system instance, systemd interprets the
79 configuration file <filename>system.conf</filename> and the files
80 in <filename>system.conf.d</filename> directories; when run as a
81 user instance, systemd interprets the configuration file
82 <filename>user.conf</filename> and the files in
83 <filename>user.conf.d</filename> directories. See
84 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
85 for more information.</para>
89 <title>Options</title>
91 <para>The following options are understood:</para>
95 <term><option>--test</option></term>
97 <listitem><para>Determine startup sequence, dump it and exit.
98 This is an option useful for debugging only.</para></listitem>
101 <term><option>--dump-configuration-items</option></term>
103 <listitem><para>Dump understood unit configuration items. This
104 outputs a terse but complete list of configuration items
105 understood in unit definition files.</para></listitem>
108 <term><option>--unit=</option></term>
110 <listitem><para>Set default unit to activate on startup. If
111 not specified, defaults to
112 <filename>default.target</filename>.</para></listitem>
115 <term><option>--system</option></term>
116 <term><option>--user</option></term>
118 <listitem><para>For <option>--system</option>, tell systemd to
119 run a system instance, even if the process ID is not 1, i.e.
120 systemd is not run as init process. <option>--user</option>
121 does the opposite, running a user instance even if the process
122 ID is 1. Normally it should not be necessary to pass these
123 options, as systemd automatically detects the mode it is
124 started in. These options are hence of little use except for
125 debugging. Note that it is not supported booting and
126 maintaining a full system with systemd running in
127 <option>--system</option> mode, but PID not 1. In practice,
128 passing <option>--system</option> explicitly is only useful in
129 conjunction with <option>--test</option>.</para></listitem>
132 <term><option>--dump-core</option></term>
134 <listitem><para>Dump core on crash. This switch has no effect
135 when run as user instance.</para></listitem>
138 <term><option>--crash-shell</option></term>
140 <listitem><para>Run shell on
141 crash. This switch has no effect when
143 instance.</para></listitem>
146 <term><option>--confirm-spawn</option></term>
148 <listitem><para>Ask for confirmation when spawning processes.
149 This switch has no effect when run as user
150 instance.</para></listitem>
153 <term><option>--show-status=</option></term>
155 <listitem><para>Show terse service status information while
156 booting. This switch has no effect when run as user instance.
157 Takes a boolean argument which may be omitted which is
158 interpreted as <option>true</option>.</para></listitem>
161 <term><option>--log-target=</option></term>
163 <listitem><para>Set log target. Argument must be one of
164 <option>console</option>,
165 <option>journal</option>,
166 <option>kmsg</option>,
167 <option>journal-or-kmsg</option>,
168 <option>null</option>.</para></listitem>
171 <term><option>--log-level=</option></term>
173 <listitem><para>Set log level. As
174 argument this accepts a numerical log
175 level or the well-known <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
176 symbolic names (lowercase):
177 <option>emerg</option>,
178 <option>alert</option>,
179 <option>crit</option>,
180 <option>err</option>,
181 <option>warning</option>,
182 <option>notice</option>,
183 <option>info</option>,
184 <option>debug</option>.</para></listitem>
187 <term><option>--log-color=</option></term>
189 <listitem><para>Highlight important log messages. Argument is
190 a boolean value. If the argument is omitted, it defaults to
191 <option>true</option>.</para></listitem>
194 <term><option>--log-location=</option></term>
196 <listitem><para>Include code location in log messages. This is
197 mostly relevant for debugging purposes. Argument is a boolean
198 value. If the argument is omitted it defaults to
199 <option>true</option>.</para></listitem>
202 <term><option>--default-standard-output=</option></term>
203 <term><option>--default-standard-error=</option></term>
205 <listitem><para>Sets the default output or error output for
206 all services and sockets, respectively. That is, controls the
207 default for <option>StandardOutput=</option> and
208 <option>StandardError=</option> (see
209 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
210 for details). Takes one of
211 <option>inherit</option>,
212 <option>null</option>,
213 <option>tty</option>,
214 <option>journal</option>,
215 <option>journal+console</option>,
216 <option>syslog</option>,
217 <option>syslog+console</option>,
218 <option>kmsg</option>,
219 <option>kmsg+console</option>. If the
221 <option>--default-standard-output=</option> defaults to
222 <option>journal</option> and
223 <option>--default-standard-error=</option> to
224 <option>inherit</option>.</para></listitem>
227 <xi:include href="standard-options.xml" xpointer="help" />
228 <xi:include href="standard-options.xml" xpointer="version" />
233 <title>Concepts</title>
235 <para>systemd provides a dependency system between various
236 entities called "units" of 12 different types. Units encapsulate
237 various objects that are relevant for system boot-up and
238 maintenance. The majority of units are configured in unit
239 configuration files, whose syntax and basic set of options is
241 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
242 however some are created automatically from other configuration,
243 dynamically from system state or programmatically at runtime.
244 Units may be "active" (meaning started, bound, plugged in, ...,
245 depending on the unit type, see below), or "inactive" (meaning
246 stopped, unbound, unplugged, ...), as well as in the process of
247 being activated or deactivated, i.e. between the two states (these
248 states are called "activating", "deactivating"). A special
249 "failed" state is available as well, which is very similar to
250 "inactive" and is entered when the service failed in some way
251 (process returned error code on exit, or crashed, or an operation
252 timed out). If this state is entered, the cause will be logged,
253 for later reference. Note that the various unit types may have a
254 number of additional substates, which are mapped to the five
255 generalized unit states described here.</para>
257 <para>The following unit types are available:</para>
260 <listitem><para>Service units, which start and control daemons
261 and the processes they consist of. For details see
262 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
264 <listitem><para>Socket units, which encapsulate local IPC or
265 network sockets in the system, useful for socket-based
266 activation. For details about socket units see
267 <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
268 for details on socket-based activation and other forms of
270 <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
272 <listitem><para>Target units are useful to group units, or
273 provide well-known synchronization points during boot-up, see
274 <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
276 <listitem><para>Device units expose kernel devices in systemd
277 and may be used to implement device-based activation. For
279 <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
281 <listitem><para>Mount units control mount points in the file
282 system, for details see
283 <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
285 <listitem><para>Automount units provide automount capabilities,
286 for on-demand mounting of file systems as well as parallelized
288 <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
290 <listitem><para>Snapshot units can be used to temporarily save
291 the state of the set of systemd units, which later may be
292 restored by activating the saved snapshot unit. For more
294 <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
296 <listitem><para>Timer units are useful for triggering activation
297 of other units based on timers. You may find details in
298 <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
300 <listitem><para>Swap units are very similar to mount units and
301 encapsulate memory swap partitions or files of the operating
302 system. They are described in
303 <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
305 <listitem><para>Path units may be used to activate other
306 services when file system objects change or are modified. See
307 <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
309 <listitem><para>Slice units may be used to group units which
310 manage system processes (such as service and scope units) in a
311 hierarchical tree for resource management purposes. See
312 <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
314 <listitem><para>Scope units are similar to service units, but
315 manage foreign processes instead of starting them as well. See
316 <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
320 <para>Units are named as their configuration files. Some units
321 have special semantics. A detailed list is available in
322 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
324 <para>systemd knows various kinds of dependencies, including
325 positive and negative requirement dependencies (i.e.
326 <varname>Requires=</varname> and <varname>Conflicts=</varname>) as
327 well as ordering dependencies (<varname>After=</varname> and
328 <varname>Before=</varname>). NB: ordering and requirement
329 dependencies are orthogonal. If only a requirement dependency
330 exists between two units (e.g. <filename>foo.service</filename>
331 requires <filename>bar.service</filename>), but no ordering
332 dependency (e.g. <filename>foo.service</filename> after
333 <filename>bar.service</filename>) and both are requested to start,
334 they will be started in parallel. It is a common pattern that both
335 requirement and ordering dependencies are placed between two
336 units. Also note that the majority of dependencies are implicitly
337 created and maintained by systemd. In most cases, it should be
338 unnecessary to declare additional dependencies manually, however
339 it is possible to do this.</para>
341 <para>Application programs and units (via dependencies) may
342 request state changes of units. In systemd, these requests are
343 encapsulated as 'jobs' and maintained in a job queue. Jobs may
344 succeed or can fail, their execution is ordered based on the
345 ordering dependencies of the units they have been scheduled
348 <para>On boot systemd activates the target unit
349 <filename>default.target</filename> whose job is to activate
350 on-boot services and other on-boot units by pulling them in via
351 dependencies. Usually the unit name is just an alias (symlink) for
352 either <filename>graphical.target</filename> (for fully-featured
353 boots into the UI) or <filename>multi-user.target</filename> (for
354 limited console-only boots for use in embedded or server
355 environments, or similar; a subset of graphical.target). However,
356 it is at the discretion of the administrator to configure it as an
357 alias to any other target unit. See
358 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
359 for details about these target units.</para>
361 <para>Processes systemd spawns are placed in individual Linux
362 control groups named after the unit which they belong to in the
363 private systemd hierarchy. (see <ulink
364 url="https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
365 for more information about control groups, or short "cgroups").
366 systemd uses this to effectively keep track of processes. Control
367 group information is maintained in the kernel, and is accessible
368 via the file system hierarchy (beneath
369 <filename>/sys/fs/cgroup/systemd/</filename>), or in tools such as
370 <citerefentry project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
371 (<command>ps xawf -eo pid,user,cgroup,args</command> is
372 particularly useful to list all processes and the systemd units
373 they belong to.).</para>
375 <para>systemd is compatible with the SysV init system to a large
376 degree: SysV init scripts are supported and simply read as an
377 alternative (though limited) configuration file format. The SysV
378 <filename>/dev/initctl</filename> interface is provided, and
379 compatibility implementations of the various SysV client tools are
380 available. In addition to that, various established Unix
381 functionality such as <filename>/etc/fstab</filename> or the
382 <filename>utmp</filename> database are supported.</para>
384 <para>systemd has a minimal transaction system: if a unit is
385 requested to start up or shut down it will add it and all its
386 dependencies to a temporary transaction. Then, it will verify if
387 the transaction is consistent (i.e. whether the ordering of all
388 units is cycle-free). If it is not, systemd will try to fix it up,
389 and removes non-essential jobs from the transaction that might
390 remove the loop. Also, systemd tries to suppress non-essential
391 jobs in the transaction that would stop a running service. Finally
392 it is checked whether the jobs of the transaction contradict jobs
393 that have already been queued, and optionally the transaction is
394 aborted then. If all worked out and the transaction is consistent
395 and minimized in its impact it is merged with all already
396 outstanding jobs and added to the run queue. Effectively this
397 means that before executing a requested operation, systemd will
398 verify that it makes sense, fixing it if possible, and only
399 failing if it really cannot work.</para>
401 <para>Systemd contains native implementations of various tasks
402 that need to be executed as part of the boot process. For example,
403 it sets the hostname or configures the loopback network device. It
404 also sets up and mounts various API file systems, such as
405 <filename>/sys</filename> or <filename>/proc</filename>.</para>
407 <para>For more information about the concepts and
408 ideas behind systemd, please refer to the
409 <ulink url="http://0pointer.de/blog/projects/systemd.html">Original Design Document</ulink>.</para>
411 <para>Note that some but not all interfaces provided
412 by systemd are covered by the
413 <ulink url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
414 Stability Promise</ulink>.</para>
416 <para>Units may be generated dynamically at boot and system
417 manager reload time, for example based on other configuration
418 files or parameters passed on the kernel command line. For details
420 <ulink url="http://www.freedesktop.org/wiki/Software/systemd/Generators">Generators Specification</ulink>.</para>
422 <para>Systems which invoke systemd in a container or initrd
423 environment should implement the
424 <ulink url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container Interface</ulink> or
425 <ulink url="http://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd Interface</ulink>
426 specifications, respectively.</para>
430 <title>Directories</title>
434 <term>System unit directories</term>
436 <listitem><para>The systemd system manager reads unit
437 configuration from various directories. Packages that want to
438 install unit files shall place them in the directory returned
439 by <command>pkg-config systemd
440 --variable=systemdsystemunitdir</command>. Other directories
441 checked are <filename>/usr/local/lib/systemd/system</filename>
442 and <filename>/usr/lib/systemd/system</filename>. User
443 configuration always takes precedence. <command>pkg-config
444 systemd --variable=systemdsystemconfdir</command> returns the
445 path of the system configuration directory. Packages should
446 alter the content of these directories only with the
447 <command>enable</command> and <command>disable</command>
449 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
450 tool. Full list of directories is provided in
451 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
458 <term>User unit directories</term>
460 <listitem><para>Similar rules apply for the user unit
461 directories. However, here the
462 <ulink url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
463 Base Directory specification</ulink> is followed to find
464 units. Applications should place their unit files in the
465 directory returned by <command>pkg-config systemd
466 --variable=systemduserunitdir</command>. Global configuration
467 is done in the directory reported by <command>pkg-config
468 systemd --variable=systemduserconfdir</command>. The
469 <command>enable</command> and <command>disable</command>
471 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
472 tool can handle both global (i.e. for all users) and private
473 (for one user) enabling/disabling of units. Full list of
474 directories is provided in
475 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
482 <term>SysV init scripts directory</term>
484 <listitem><para>The location of the SysV init script directory
485 varies between distributions. If systemd cannot find a native
486 unit file for a requested service, it will look for a SysV
487 init script of the same name (with the
488 <filename>.service</filename> suffix
489 removed).</para></listitem>
495 <term>SysV runlevel link farm directory</term>
497 <listitem><para>The location of the SysV runlevel link farm
498 directory varies between distributions. systemd will take the
499 link farm into account when figuring out whether a service
500 shall be enabled. Note that a service unit with a native unit
501 configuration file cannot be started by activating it in the
502 SysV runlevel link farm.</para></listitem>
508 <title>Signals</title>
512 <term><constant>SIGTERM</constant></term>
514 <listitem><para>Upon receiving this signal the systemd system
515 manager serializes its state, reexecutes itself and
516 deserializes the saved state again. This is mostly equivalent
517 to <command>systemctl daemon-reexec</command>.</para>
519 <para>systemd user managers will start the
520 <filename>exit.target</filename> unit when this signal is
521 received. This is mostly equivalent to <command>systemctl
522 --user start exit.target</command>.</para></listitem>
526 <term><constant>SIGINT</constant></term>
528 <listitem><para>Upon receiving this signal the systemd system
529 manager will start the
530 <filename>ctrl-alt-del.target</filename> unit. This is mostly
531 equivalent to <command>systemctl start
532 ctl-alt-del.target</command>. If this signal is received more
533 often than 7 times per 2s an immediate reboot is triggered.
534 Note that pressing Ctrl-Alt-Del on the console will trigger
535 this signal. Hence, if a reboot is hanging pressing
536 Ctrl-Alt-Del more than 7 times in 2s is a relatively safe way
537 to trigger an immediate reboot.</para>
539 <para>systemd user managers treat this signal the same way as
540 <constant>SIGTERM</constant>.</para></listitem>
544 <term><constant>SIGWINCH</constant></term>
546 <listitem><para>When this signal is received the systemd
547 system manager will start the
548 <filename>kbrequest.target</filename> unit. This is mostly
549 equivalent to <command>systemctl start
550 kbrequest.target</command>.</para>
552 <para>This signal is ignored by systemd user
553 managers.</para></listitem>
557 <term><constant>SIGPWR</constant></term>
559 <listitem><para>When this signal is received the systemd
560 manager will start the <filename>sigpwr.target</filename>
561 unit. This is mostly equivalent to <command>systemctl start
562 sigpwr.target</command>.</para></listitem>
566 <term><constant>SIGUSR1</constant></term>
568 <listitem><para>When this signal is received the systemd
569 manager will try to reconnect to the D-Bus
570 bus.</para></listitem>
574 <term><constant>SIGUSR2</constant></term>
576 <listitem><para>When this signal is received the systemd
577 manager will log its complete state in human readable form.
578 The data logged is the same as printed by
579 <command>systemd-analyze dump</command>.</para></listitem>
583 <term><constant>SIGHUP</constant></term>
585 <listitem><para>Reloads the complete daemon configuration.
586 This is mostly equivalent to <command>systemctl
587 daemon-reload</command>.</para></listitem>
591 <term><constant>SIGRTMIN+0</constant></term>
593 <listitem><para>Enters default mode, starts the
594 <filename>default.target</filename> unit. This is mostly
595 equivalent to <command>systemctl start
596 default.target</command>.</para></listitem>
600 <term><constant>SIGRTMIN+1</constant></term>
602 <listitem><para>Enters rescue mode, starts the
603 <filename>rescue.target</filename> unit. This is mostly
604 equivalent to <command>systemctl isolate
605 rescue.target</command>.</para></listitem>
609 <term><constant>SIGRTMIN+2</constant></term>
611 <listitem><para>Enters emergency mode, starts the
612 <filename>emergency.service</filename> unit. This is mostly
613 equivalent to <command>systemctl isolate
614 emergency.service</command>.</para></listitem>
618 <term><constant>SIGRTMIN+3</constant></term>
620 <listitem><para>Halts the machine, starts the
621 <filename>halt.target</filename> unit. This is mostly
622 equivalent to <command>systemctl start
623 halt.target</command>.</para></listitem>
627 <term><constant>SIGRTMIN+4</constant></term>
629 <listitem><para>Powers off the machine, starts the
630 <filename>poweroff.target</filename> unit. This is mostly
631 equivalent to <command>systemctl start
632 poweroff.target</command>.</para></listitem>
636 <term><constant>SIGRTMIN+5</constant></term>
638 <listitem><para>Reboots the machine, starts the
639 <filename>reboot.target</filename> unit. This is mostly
640 equivalent to <command>systemctl start
641 reboot.target</command>.</para></listitem>
645 <term><constant>SIGRTMIN+6</constant></term>
647 <listitem><para>Reboots the machine via kexec, starts the
648 <filename>kexec.target</filename> unit. This is mostly
649 equivalent to <command>systemctl start
650 kexec.target</command>.</para></listitem>
654 <term><constant>SIGRTMIN+13</constant></term>
656 <listitem><para>Immediately halts the machine.</para></listitem>
660 <term><constant>SIGRTMIN+14</constant></term>
662 <listitem><para>Immediately powers off the machine.</para></listitem>
666 <term><constant>SIGRTMIN+15</constant></term>
668 <listitem><para>Immediately reboots the machine.</para></listitem>
672 <term><constant>SIGRTMIN+16</constant></term>
674 <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
678 <term><constant>SIGRTMIN+20</constant></term>
680 <listitem><para>Enables display of status messages on the
681 console, as controlled via
682 <varname>systemd.show_status=1</varname> on the kernel command
683 line.</para></listitem>
687 <term><constant>SIGRTMIN+21</constant></term>
689 <listitem><para>Disables display of
690 status messages on the console, as
692 <varname>systemd.show_status=0</varname>
693 on the kernel command
694 line.</para></listitem>
698 <term><constant>SIGRTMIN+22</constant></term>
699 <term><constant>SIGRTMIN+23</constant></term>
701 <listitem><para>Sets the log level to <literal>debug</literal>
702 (or <literal>info</literal> on
703 <constant>SIGRTMIN+23</constant>), as controlled via
704 <varname>systemd.log_level=debug</varname> (or
705 <varname>systemd.log_level=info</varname> on
706 <constant>SIGRTMIN+23</constant>) on the kernel command
707 line.</para></listitem>
711 <term><constant>SIGRTMIN+24</constant></term>
713 <listitem><para>Immediately exits the manager (only available
714 for --user instances).</para></listitem>
718 <term><constant>SIGRTMIN+26</constant></term>
719 <term><constant>SIGRTMIN+27</constant></term>
720 <term><constant>SIGRTMIN+28</constant></term>
722 <listitem><para>Sets the log level to
723 <literal>journal-or-kmsg</literal> (or
724 <literal>console</literal> on
725 <constant>SIGRTMIN+27</constant>, <literal>kmsg</literal> on
726 <constant>SIGRTMIN+28</constant>), as controlled via
727 <varname>systemd.log_target=journal-or-kmsg</varname> (or
728 <varname>systemd.log_target=console</varname> on
729 <constant>SIGRTMIN+27</constant> or
730 <varname>systemd.log_target=kmsg</varname> on
731 <constant>SIGRTMIN+28</constant>) on the kernel command
732 line.</para></listitem>
738 <title>Environment</title>
740 <variablelist class='environment-variables'>
742 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
743 <listitem><para>systemd reads the log level from this
744 environment variable. This can be overridden with
745 <option>--log-level=</option>.</para></listitem>
749 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
750 <listitem><para>systemd reads the log target from this
751 environment variable. This can be overridden with
752 <option>--log-target=</option>.</para></listitem>
756 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
757 <listitem><para>Controls whether systemd highlights important
758 log messages. This can be overridden with
759 <option>--log-color=</option>.</para></listitem>
763 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
764 <listitem><para>Controls whether systemd prints the code
765 location along with log messages. This can be overridden with
766 <option>--log-location=</option>.</para></listitem>
770 <term><varname>$XDG_CONFIG_HOME</varname></term>
771 <term><varname>$XDG_CONFIG_DIRS</varname></term>
772 <term><varname>$XDG_DATA_HOME</varname></term>
773 <term><varname>$XDG_DATA_DIRS</varname></term>
775 <listitem><para>The systemd user manager uses these variables
776 in accordance to the <ulink
777 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
778 Base Directory specification</ulink> to find its
779 configuration.</para></listitem>
783 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
785 <listitem><para>Controls where systemd looks for unit
786 files.</para></listitem>
790 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
792 <listitem><para>Controls where systemd looks for SysV init
793 scripts.</para></listitem>
797 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
799 <listitem><para>Controls where systemd looks for SysV init
800 script runlevel link farms.</para></listitem>
804 <term><varname>$LISTEN_PID</varname></term>
805 <term><varname>$LISTEN_FDS</varname></term>
807 <listitem><para>Set by systemd for supervised processes during
808 socket-based activation. See
809 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
810 for more information. </para></listitem>
814 <term><varname>$NOTIFY_SOCKET</varname></term>
816 <listitem><para>Set by systemd for supervised processes for
817 status and start-up completion notification. See
818 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
819 for more information. </para></listitem>
825 <title>Kernel Command Line</title>
827 <para>When run as system instance systemd parses a number of
828 kernel command line arguments<footnote><para>If run inside a Linux
829 container these arguments may be passed as command line arguments
830 to systemd itself, next to any of the command line options listed
831 in the Options section above. If run outside of Linux containers,
832 these arguments are parsed from <filename>/proc/cmdline</filename>
833 instead.</para></footnote>:</para>
835 <variablelist class='kernel-commandline-options'>
837 <term><varname>systemd.unit=</varname></term>
838 <term><varname>rd.systemd.unit=</varname></term>
840 <listitem><para>Overrides the unit to activate on boot.
841 Defaults to <filename>default.target</filename>. This may be
842 used to temporarily boot into a different boot unit, for
843 example <filename>rescue.target</filename> or
844 <filename>emergency.service</filename>. See
845 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
846 for details about these units. The option prefixed with
847 <literal>rd.</literal> is honored only in the initial RAM disk
848 (initrd), while the one that is not prefixed only in the main
849 system.</para></listitem>
853 <term><varname>systemd.dump_core=</varname></term>
855 <listitem><para>Takes a boolean argument. If
856 <option>true</option>, systemd dumps core when it crashes.
857 Otherwise, no core dump is created. Defaults to
858 <option>true</option>.</para></listitem>
862 <term><varname>systemd.crash_shell=</varname></term>
864 <listitem><para>Takes a boolean argument. If
865 <option>true</option>, systemd spawns a shell when it crashes.
866 Otherwise, no shell is spawned. Defaults to
867 <option>false</option>, for security reasons, as the shell is
868 not protected by any password
869 authentication.</para></listitem>
873 <term><varname>systemd.crash_chvt=</varname></term>
875 <listitem><para>Takes an integer argument. If positive systemd
876 activates the specified virtual terminal when it crashes.
877 Defaults to <constant>-1</constant>.</para></listitem>
881 <term><varname>systemd.confirm_spawn=</varname></term>
883 <listitem><para>Takes a boolean argument. If
884 <option>true</option>, asks for confirmation when spawning
885 processes. Defaults to
886 <option>false</option>.</para></listitem>
890 <term><varname>systemd.show_status=</varname></term>
892 <listitem><para>Takes a boolean argument or the constant
893 <constant>auto</constant>. If <option>true</option>, shows
894 terse service status updates on the console during bootup.
895 <constant>auto</constant> behaves like <option>false</option>
896 until a service fails or there is a significant delay in boot.
897 Defaults to <option>true</option>, unless
898 <option>quiet</option> is passed as kernel command line option
899 in which case it defaults to
900 <constant>auto</constant>.</para></listitem>
904 <term><varname>systemd.log_target=</varname></term>
905 <term><varname>systemd.log_level=</varname></term>
906 <term><varname>systemd.log_color=</varname></term>
907 <term><varname>systemd.log_location=</varname></term>
909 <listitem><para>Controls log output, with the same effect as
910 the <varname>$SYSTEMD_LOG_TARGET</varname>,
911 <varname>$SYSTEMD_LOG_LEVEL</varname>,
912 <varname>$SYSTEMD_LOG_COLOR</varname>,
913 <varname>$SYSTEMD_LOG_LOCATION</varname> environment variables
914 described above.</para></listitem>
918 <term><varname>systemd.default_standard_output=</varname></term>
919 <term><varname>systemd.default_standard_error=</varname></term>
920 <listitem><para>Controls default standard output and error
921 output for services, with the same effect as the
922 <option>--default-standard-output=</option> and
923 <option>--default-standard-error=</option> command line
924 arguments described above, respectively.</para></listitem>
928 <term><varname>systemd.setenv=</varname></term>
930 <listitem><para>Takes a string argument in the form
931 VARIABLE=VALUE. May be used to set default environment
932 variables to add to forked child processes. May be used more
933 than once to set multiple variables.</para></listitem>
937 <term><varname>quiet</varname></term>
939 <listitem><para>Turn off status output at boot, much like
940 <varname>systemd.show_status=false</varname> would. Note that
941 this option is also read by the kernel itself and disables
942 kernel log output. Passing this option hence turns off the
943 usual output from both the system manager and the kernel.
948 <term><varname>debug</varname></term>
950 <listitem><para>Turn on debugging output. This is equivalent
951 to <varname>systemd.log_level=debug</varname>. Note that this
952 option is also read by the kernel itself and enables kernel
953 debug output. Passing this option hence turns on the debug
954 output from both the system manager and the
955 kernel.</para></listitem>
959 <term><varname>emergency</varname></term>
960 <term><varname>-b</varname></term>
962 <listitem><para>Boot into emergency mode. This is equivalent
963 to <varname>systemd.unit=emergency.target</varname> and
964 provided for compatibility reasons and to be easier to
965 type.</para></listitem>
969 <term><varname>rescue</varname></term>
970 <term><varname>single</varname></term>
971 <term><varname>s</varname></term>
972 <term><varname>S</varname></term>
973 <term><varname>1</varname></term>
975 <listitem><para>Boot into rescue mode. This is equivalent to
976 <varname>systemd.unit=rescue.target</varname> and provided for
977 compatibility reasons and to be easier to
978 type.</para></listitem>
982 <term><varname>2</varname></term>
983 <term><varname>3</varname></term>
984 <term><varname>4</varname></term>
985 <term><varname>5</varname></term>
987 <listitem><para>Boot into the specified legacy SysV runlevel.
988 These are equivalent to
989 <varname>systemd.unit=runlevel2.target</varname>,
990 <varname>systemd.unit=runlevel3.target</varname>,
991 <varname>systemd.unit=runlevel4.target</varname>, and
992 <varname>systemd.unit=runlevel5.target</varname>,
993 respectively, and provided for compatibility reasons and to be
994 easier to type.</para></listitem>
998 <term><varname>locale.LANG=</varname></term>
999 <term><varname>locale.LANGUAGE=</varname></term>
1000 <term><varname>locale.LC_CTYPE=</varname></term>
1001 <term><varname>locale.LC_NUMERIC=</varname></term>
1002 <term><varname>locale.LC_TIME=</varname></term>
1003 <term><varname>locale.LC_COLLATE=</varname></term>
1004 <term><varname>locale.LC_MONETARY=</varname></term>
1005 <term><varname>locale.LC_MESSAGES=</varname></term>
1006 <term><varname>locale.LC_PAPER=</varname></term>
1007 <term><varname>locale.LC_NAME=</varname></term>
1008 <term><varname>locale.LC_ADDRESS=</varname></term>
1009 <term><varname>locale.LC_TELEPHONE=</varname></term>
1010 <term><varname>locale.LC_MEASUREMENT=</varname></term>
1011 <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1013 <listitem><para>Set the system locale to use. This overrides
1014 the settings in <filename>/etc/locale.conf</filename>. For
1015 more information see
1016 <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1018 <citerefentry><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1023 <para>For other kernel command line parameters understood by
1024 components of the core OS, please refer to
1025 <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1029 <title>Sockets and FIFOs</title>
1033 <term><filename>/run/systemd/notify</filename></term>
1035 <listitem><para>Daemon status notification socket. This is an
1036 <constant>AF_UNIX</constant> datagram socket and is used to
1037 implement the daemon notification logic as implemented by
1038 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1043 <term><filename>/run/systemd/shutdownd</filename></term>
1045 <listitem><para>Used internally by the
1046 <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1047 tool to implement delayed shutdowns. This is an
1048 <constant>AF_UNIX</constant> datagram
1049 socket.</para></listitem>
1053 <term><filename>/run/systemd/private</filename></term>
1055 <listitem><para>Used internally as communication channel
1057 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1058 and the systemd process. This is an
1059 <constant>AF_UNIX</constant> stream socket. This interface is
1060 private to systemd and should not be used in external
1061 projects.</para></listitem>
1065 <term><filename>/dev/initctl</filename></term>
1067 <listitem><para>Limited compatibility support for the SysV
1068 client interface, as implemented by the
1069 <filename>systemd-initctl.service</filename> unit. This is a
1070 named pipe in the file system. This interface is obsolete and
1071 should not be used in new applications.</para></listitem>
1077 <title>See Also</title>
1079 The <ulink url="http://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>,
1080 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1081 <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1082 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1083 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1084 <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1085 <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1086 <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1087 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1088 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1089 <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1090 <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1091 <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1092 <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>