1 <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
6 SPDX-License-Identifier: LGPL-2.1+
10 xmlns:xi="http://www.w3.org/2001/XInclude">
13 <title>elogind</title>
14 <productname>elogind</productname>
18 <refentrytitle>elogind</refentrytitle>
19 <!-- 0 /// elogind is in section 8
20 <manvolnum>1</manvolnum>
22 <manvolnum>8</manvolnum>
27 <!-- 0 /// Well, elogind isn't that much...
28 <refname>systemd</refname>
29 <refname>init</refname>
30 <refpurpose>systemd system and service manager</refpurpose>
32 <refname>elogind</refname>
33 <refpurpose>Login manager</refpurpose>
38 <!-- 0 /// elogind has a different synopsis of course...
40 <command>/usr/lib/systemd/systemd</command>
41 <arg choice="opt" rep="repeat">OPTIONS</arg>
44 <command>init</command>
45 <arg choice="opt" rep="repeat">OPTIONS</arg>
46 <arg choice="req">COMMAND</arg>
50 <command>elogind</command>
51 <arg choice="opt" rep="repeat">OPTIONS</arg>
52 <arg choice="req">COMMAND</arg>
58 <title>Description</title>
60 <!-- 0 /// elogind does not need that much explanation.
61 <para>systemd is a system and service manager for Linux operating
62 systems. When run as first process on boot (as PID 1), it acts as
63 init system that brings up and maintains userspace
66 <para>For compatibility with SysV, if systemd is called as
67 <command>init</command> and a PID that is not 1, it will execute
68 <command>telinit</command> and pass all command line arguments
69 unmodified. That means <command>init</command> and
70 <command>telinit</command> are mostly equivalent when invoked from
71 normal login sessions. See
72 <citerefentry><refentrytitle>telinit</refentrytitle><manvolnum>8</manvolnum></citerefentry>
73 for more information.</para>
75 <para>When run as a system instance, systemd interprets the
76 configuration file <filename>system.conf</filename> and the files
77 in <filename>system.conf.d</filename> directories; when run as a
78 user instance, systemd interprets the configuration file
79 <filename>user.conf</filename> and the files in
80 <filename>user.conf.d</filename> directories. See
81 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
82 for more information.</para>
84 <para><command>elogind</command> is a system service that
85 manages user logins. It is responsible for:</para>
88 <listitem><para>Keeping track of users and sessions, their
89 processes and their idle state</para></listitem>
91 <listitem><para>Providing PolicyKit-based access for users to
92 operations such as system shutdown or sleep</para></listitem>
94 <listitem><para>Implementing a shutdown/sleep inhibition logic
95 for applications</para></listitem>
97 <listitem><para>Handling of power/sleep hardware
98 keys</para></listitem>
100 <listitem><para>Multi-seat management</para></listitem>
102 <listitem><para>Session switch management</para></listitem>
104 <listitem><para>Device access management for
105 users</para></listitem>
109 <para>User sessions are registered in elogind via the
110 <citerefentry><refentrytitle>pam_elogind</refentrytitle><manvolnum>8</manvolnum></citerefentry>
114 <citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
115 for information about the configuration of this service.</para>
118 url="http://www.freedesktop.org/wiki/Software/systemd/multiseat">Multi-Seat
119 on Linux</ulink> for an introduction into basic concepts of logind
120 such as users, sessions and seats.</para>
123 url="http://www.freedesktop.org/wiki/Software/systemd/logind">
124 logind D-Bus API Documentation</ulink> for information about the
125 APIs <filename>logind</filename> provides.</para>
127 <para>For more information on the inhibition logic see the <ulink
128 url="http://www.freedesktop.org/wiki/Software/systemd/inhibit">Inhibitor
129 Lock Developer Documentation</ulink>.</para>
134 <title>Options</title>
136 <para>The following options are understood:</para>
139 <!-- 0 /// This list is much shorter with elogind of course.
141 <term><option>--test</option></term>
143 <listitem><para>Determine startup sequence, dump it and exit.
144 This is an option useful for debugging only.</para></listitem>
147 <term><option>--dump-configuration-items</option></term>
149 <listitem><para>Dump understood unit configuration items. This
150 outputs a terse but complete list of configuration items
151 understood in unit definition files.</para></listitem>
154 <term><option>--dump-bus-properties</option></term>
156 <listitem><para>Dump exposed bus properties. This outputs
157 a terse but complete list of properties exposed to dbus.
161 <term><option>--unit=</option></term>
163 <listitem><para>Set default unit to activate on startup. If
164 not specified, defaults to
165 <filename>default.target</filename>.</para></listitem>
168 <term><option>--system</option></term>
169 <term><option>--user</option></term>
171 <listitem><para>For <option>--system</option>, tell systemd to
172 run a system instance, even if the process ID is not 1, i.e.
173 systemd is not run as init process. <option>--user</option>
174 does the opposite, running a user instance even if the process
175 ID is 1. Normally, it should not be necessary to pass these
176 options, as systemd automatically detects the mode it is
177 started in. These options are hence of little use except for
178 debugging. Note that it is not supported booting and
179 maintaining a full system with systemd running in
180 <option>--system</option> mode, but PID not 1. In practice,
181 passing <option>--system</option> explicitly is only useful in
182 conjunction with <option>--test</option>.</para></listitem>
185 <term><option>--dump-core</option></term>
187 <listitem><para>Enable core dumping on crash. This switch has
188 no effect when running as user instance. This setting may also
189 be enabled during boot on the kernel command line via the
190 <varname>systemd.dump_core=</varname> option, see
191 below.</para></listitem>
195 <term><option>--crash-vt=</option><replaceable>VT</replaceable></term>
197 <listitem><para>Switch to a specific virtual console (VT) on
198 crash. Takes a positive integer in the range 1–63, or a
199 boolean argument. If an integer is passed, selects which VT to
200 switch to. If <constant>yes</constant>, the VT kernel messages
201 are written to is selected. If <constant>no</constant>, no VT
202 switch is attempted. This switch has no effect when running as
203 user instance. This setting may also be enabled during boot,
204 on the kernel command line via the
205 <varname>systemd.crash_vt=</varname> option, see
207 <!-- FIXME: there is no crash_vt command line option? -->
208 <!-- 0 /// elogind check_tree.pl can not mangle closed comments.
209 below.</para></listitem>
213 <term><option>--crash-shell</option></term>
215 <listitem><para>Run a shell on crash. This switch has no
216 effect when running as user instance. This setting may also be
217 enabled during boot, on the kernel command line via the
218 <varname>systemd.crash_shell=</varname> option, see
219 below.</para></listitem>
223 <term><option>--crash-reboot</option></term>
225 <listitem><para>Automatically reboot the system on crash. This
226 switch has no effect when running as user instance. This
227 setting may also be enabled during boot, on the kernel command
228 line via the <varname>systemd.crash_reboot=</varname> option,
229 see below.</para></listitem>
233 <term><option>--confirm-spawn</option></term>
235 <listitem><para>Ask for confirmation when spawning processes.
236 This switch has no effect when run as user
237 instance.</para></listitem>
240 <term><option>--show-status=</option></term>
242 <listitem><para>Takes a boolean argument or the special value <constant>auto</constant>. If on, terse unit
243 status information is shown on the console during boot-up and shutdown. If off, no such status information is
244 shown. If set to <constant>auto</constant> behavior is similar to off, except that it is automatically switched
245 to on, as soon as the first unit failure or significant boot delay is encountered. This switch has no effect
246 when invoked as user instance. If specified, overrides both the kernel command line setting
247 <varname>systemd.show_status=</varname> (see below) and the configuration file option
248 <option>ShowStatus=</option>, see
249 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
252 <term><option>--log-target=</option></term>
254 <listitem><para>Set log target. Argument must be one of
255 <option>console</option>,
256 <option>journal</option>,
257 <option>kmsg</option>,
258 <option>journal-or-kmsg</option>,
259 <option>null</option>.</para></listitem>
262 <term><option>--log-level=</option></term>
264 <listitem><para>Set log level. As
265 argument this accepts a numerical log
266 level or the well-known <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
267 symbolic names (lowercase):
268 <option>emerg</option>,
269 <option>alert</option>,
270 <option>crit</option>,
271 <option>err</option>,
272 <option>warning</option>,
273 <option>notice</option>,
274 <option>info</option>,
275 <option>debug</option>.</para></listitem>
278 <term><option>--log-color=</option></term>
280 <listitem><para>Highlight important log messages. Argument is
281 a boolean value. If the argument is omitted, it defaults to
282 <option>true</option>.</para></listitem>
285 <term><option>--log-location=</option></term>
287 <listitem><para>Include code location in log messages. This is
288 mostly relevant for debugging purposes. Argument is a boolean
289 value. If the argument is omitted it defaults to
290 <option>true</option>.</para></listitem>
293 <term><option>--default-standard-output=</option></term>
294 <term><option>--default-standard-error=</option></term>
296 <listitem><para>Sets the default output or error output for
297 all services and sockets, respectively. That is, controls the
298 default for <option>StandardOutput=</option> and
299 <option>StandardError=</option> (see
300 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
301 for details). Takes one of
302 <option>inherit</option>,
303 <option>null</option>,
304 <option>tty</option>,
305 <option>journal</option>,
306 <option>journal+console</option>,
307 <option>syslog</option>,
308 <option>syslog+console</option>,
309 <option>kmsg</option>,
310 <option>kmsg+console</option>. If the
312 <option>--default-standard-output=</option> defaults to
313 <option>journal</option> and
314 <option>--default-standard-error=</option> to
315 <option>inherit</option>.</para></listitem>
319 <term><option>--machine-id=</option></term>
321 <listitem><para>Override the machine-id set on the hard drive,
322 useful for network booting or for containers. May not be set
323 to all zeros.</para></listitem>
327 <term><option>--service-watchdogs=</option></term>
329 <listitem><para>Globally enable/disable all service watchdog timeouts and emergency
330 actions. This setting may also be specified during boot, on the kernel
331 command line via the <varname>systemd.service_watchdogs=</varname>
332 option, see below. Defaults to enabled.</para></listitem>
335 <xi:include href="standard-options.xml" xpointer="help" />
336 <xi:include href="standard-options.xml" xpointer="version" />
339 <term><option>-D</option></term>
340 <term><option>--daemon</option></term>
342 <listitem><para>Daemonize elogind by double-forking
343 into background.</para></listitem>
347 <term><option>-h</option></term>
348 <term><option>--help</option></term>
350 <listitem><para>Show the helpt text and exit.</para></listitem>
356 <!-- 0 /// The whole concpets section is unneeded in elogind
358 <title>Concepts</title>
360 <para>systemd provides a dependency system between various
361 entities called "units" of 11 different types. Units encapsulate
362 various objects that are relevant for system boot-up and
363 maintenance. The majority of units are configured in unit
364 configuration files, whose syntax and basic set of options is
366 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
367 however some are created automatically from other configuration,
368 dynamically from system state or programmatically at runtime.
369 Units may be "active" (meaning started, bound, plugged in, …,
370 depending on the unit type, see below), or "inactive" (meaning
371 stopped, unbound, unplugged, …), as well as in the process of
372 being activated or deactivated, i.e. between the two states (these
373 states are called "activating", "deactivating"). A special
374 "failed" state is available as well, which is very similar to
375 "inactive" and is entered when the service failed in some way
376 (process returned error code on exit, or crashed, an operation
377 timed out, or after too many restarts). If this state is entered,
378 the cause will be logged, for later reference. Note that the
379 various unit types may have a number of additional substates,
380 which are mapped to the five generalized unit states described
383 <para>The following unit types are available:</para>
386 <listitem><para>Service units, which start and control daemons
387 and the processes they consist of. For details, see
388 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
390 <listitem><para>Socket units, which encapsulate local IPC or
391 network sockets in the system, useful for socket-based
392 activation. For details about socket units, see
393 <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
394 for details on socket-based activation and other forms of
396 <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
398 <listitem><para>Target units are useful to group units, or
399 provide well-known synchronization points during boot-up, see
400 <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
402 <listitem><para>Device units expose kernel devices in systemd
403 and may be used to implement device-based activation. For
405 <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
407 <listitem><para>Mount units control mount points in the file
408 system, for details see
409 <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
411 <listitem><para>Automount units provide automount capabilities,
412 for on-demand mounting of file systems as well as parallelized
414 <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
416 <listitem><para>Timer units are useful for triggering activation
417 of other units based on timers. You may find details in
418 <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
420 <listitem><para>Swap units are very similar to mount units and
421 encapsulate memory swap partitions or files of the operating
422 system. They are described in
423 <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
425 <listitem><para>Path units may be used to activate other
426 services when file system objects change or are modified. See
427 <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
429 <listitem><para>Slice units may be used to group units which
430 manage system processes (such as service and scope units) in a
431 hierarchical tree for resource management purposes. See
432 <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
434 <listitem><para>Scope units are similar to service units, but
435 manage foreign processes instead of starting them as well. See
436 <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
440 <para>Units are named as their configuration files. Some units
441 have special semantics. A detailed list is available in
442 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
444 <para>systemd knows various kinds of dependencies, including
445 positive and negative requirement dependencies (i.e.
446 <varname>Requires=</varname> and <varname>Conflicts=</varname>) as
447 well as ordering dependencies (<varname>After=</varname> and
448 <varname>Before=</varname>). NB: ordering and requirement
449 dependencies are orthogonal. If only a requirement dependency
450 exists between two units (e.g. <filename>foo.service</filename>
451 requires <filename>bar.service</filename>), but no ordering
452 dependency (e.g. <filename>foo.service</filename> after
453 <filename>bar.service</filename>) and both are requested to start,
454 they will be started in parallel. It is a common pattern that both
455 requirement and ordering dependencies are placed between two
456 units. Also note that the majority of dependencies are implicitly
457 created and maintained by systemd. In most cases, it should be
458 unnecessary to declare additional dependencies manually, however
459 it is possible to do this.</para>
461 <para>Application programs and units (via dependencies) may
462 request state changes of units. In systemd, these requests are
463 encapsulated as 'jobs' and maintained in a job queue. Jobs may
464 succeed or can fail, their execution is ordered based on the
465 ordering dependencies of the units they have been scheduled
468 <para>On boot systemd activates the target unit
469 <filename>default.target</filename> whose job is to activate
470 on-boot services and other on-boot units by pulling them in via
471 dependencies. Usually, the unit name is just an alias (symlink) for
472 either <filename>graphical.target</filename> (for fully-featured
473 boots into the UI) or <filename>multi-user.target</filename> (for
474 limited console-only boots for use in embedded or server
475 environments, or similar; a subset of graphical.target). However,
476 it is at the discretion of the administrator to configure it as an
477 alias to any other target unit. See
478 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
479 for details about these target units.</para>
481 <para>Processes systemd spawns are placed in individual Linux
482 control groups named after the unit which they belong to in the
483 private systemd hierarchy. (see <ulink
484 url="https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt">cgroups.txt</ulink>
485 for more information about control groups, or short "cgroups").
486 systemd uses this to effectively keep track of processes. Control
487 group information is maintained in the kernel, and is accessible
488 via the file system hierarchy (beneath
489 <filename>/sys/fs/cgroup/systemd/</filename>), or in tools such as
490 <citerefentry project='man-pages'><refentrytitle>systemd-cgls</refentrytitle><manvolnum>1</manvolnum></citerefentry>
492 <citerefentry project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
493 (<command>ps xawf -eo pid,user,cgroup,args</command> is
494 particularly useful to list all processes and the systemd units
495 they belong to.).</para>
497 <para>systemd is compatible with the SysV init system to a large
498 degree: SysV init scripts are supported and simply read as an
499 alternative (though limited) configuration file format. The SysV
500 <filename>/dev/initctl</filename> interface is provided, and
501 compatibility implementations of the various SysV client tools are
502 available. In addition to that, various established Unix
503 functionality such as <filename>/etc/fstab</filename> or the
504 <filename>utmp</filename> database are supported.</para>
506 <para>systemd has a minimal transaction system: if a unit is
507 requested to start up or shut down it will add it and all its
508 dependencies to a temporary transaction. Then, it will verify if
509 the transaction is consistent (i.e. whether the ordering of all
510 units is cycle-free). If it is not, systemd will try to fix it up,
511 and removes non-essential jobs from the transaction that might
512 remove the loop. Also, systemd tries to suppress non-essential
513 jobs in the transaction that would stop a running service. Finally
514 it is checked whether the jobs of the transaction contradict jobs
515 that have already been queued, and optionally the transaction is
516 aborted then. If all worked out and the transaction is consistent
517 and minimized in its impact it is merged with all already
518 outstanding jobs and added to the run queue. Effectively this
519 means that before executing a requested operation, systemd will
520 verify that it makes sense, fixing it if possible, and only
521 failing if it really cannot work.</para>
523 <para>systemd contains native implementations of various tasks
524 that need to be executed as part of the boot process. For example,
525 it sets the hostname or configures the loopback network device. It
526 also sets up and mounts various API file systems, such as
527 <filename>/sys</filename> or <filename>/proc</filename>.</para>
529 <para>For more information about the concepts and
530 ideas behind systemd, please refer to the
531 <ulink url="http://0pointer.de/blog/projects/systemd.html">Original Design Document</ulink>.</para>
533 <para>Note that some but not all interfaces provided
534 by systemd are covered by the
535 <ulink url="https://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
536 Stability Promise</ulink>.</para>
538 <para>Units may be generated dynamically at boot and system
539 manager reload time, for example based on other configuration
540 files or parameters passed on the kernel command line. For details, see
541 <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
543 <para>Systems which invoke systemd in a container or initrd
544 environment should implement the
545 <ulink url="https://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container Interface</ulink> or
546 <ulink url="https://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd Interface</ulink>
547 specifications, respectively.</para>
551 <!-- 0 /// The whole directories section is unneeded in elogind
553 <title>Directories</title>
557 <term>System unit directories</term>
559 <listitem><para>The systemd system manager reads unit
560 configuration from various directories. Packages that want to
561 install unit files shall place them in the directory returned
562 by <command>pkg-config systemd
563 --variable=systemdsystemunitdir</command>. Other directories
564 checked are <filename>/usr/local/lib/systemd/system</filename>
565 and <filename>/usr/lib/systemd/system</filename>. User
566 configuration always takes precedence. <command>pkg-config
567 systemd --variable=systemdsystemconfdir</command> returns the
568 path of the system configuration directory. Packages should
569 alter the content of these directories only with the
570 <command>enable</command> and <command>disable</command>
572 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
573 tool. Full list of directories is provided in
574 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
581 <term>User unit directories</term>
583 <listitem><para>Similar rules apply for the user unit
584 directories. However, here the
585 <ulink url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
586 Base Directory specification</ulink> is followed to find
587 units. Applications should place their unit files in the
588 directory returned by <command>pkg-config systemd
589 --variable=systemduserunitdir</command>. Global configuration
590 is done in the directory reported by <command>pkg-config
591 systemd --variable=systemduserconfdir</command>. The
592 <command>enable</command> and <command>disable</command>
594 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
595 tool can handle both global (i.e. for all users) and private
596 (for one user) enabling/disabling of units. Full list of
597 directories is provided in
598 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
605 <term>SysV init scripts directory</term>
607 <listitem><para>The location of the SysV init script directory
608 varies between distributions. If systemd cannot find a native
609 unit file for a requested service, it will look for a SysV
610 init script of the same name (with the
611 <filename>.service</filename> suffix
612 removed).</para></listitem>
618 <term>SysV runlevel link farm directory</term>
620 <listitem><para>The location of the SysV runlevel link farm
621 directory varies between distributions. systemd will take the
622 link farm into account when figuring out whether a service
623 shall be enabled. Note that a service unit with a native unit
624 configuration file cannot be started by activating it in the
625 SysV runlevel link farm.</para></listitem>
631 <!-- 0 /// The whole Signals section is unneeded in elogind
633 <title>Signals</title>
637 <term><constant>SIGTERM</constant></term>
639 <listitem><para>Upon receiving this signal the systemd system
640 manager serializes its state, reexecutes itself and
641 deserializes the saved state again. This is mostly equivalent
642 to <command>systemctl daemon-reexec</command>.</para>
644 <para>systemd user managers will start the
645 <filename>exit.target</filename> unit when this signal is
646 received. This is mostly equivalent to <command>systemctl
647 --user start exit.target
648 --job-mode=replace-irreversible</command>.</para></listitem>
652 <term><constant>SIGINT</constant></term>
654 <listitem><para>Upon receiving this signal the systemd system
655 manager will start the
656 <filename>ctrl-alt-del.target</filename> unit. This is mostly
657 equivalent to <command>systemctl start ctrl-alt-del.target
658 --job-mode=replace-irreversible</command>. If this signal is
659 received more than 7 times per 2s, an immediate reboot is
660 triggered. Note that pressing Ctrl-Alt-Del on the console
661 will trigger this signal. Hence, if a reboot is hanging,
662 pressing Ctrl-Alt-Del more than 7 times in 2s is a relatively
663 safe way to trigger an immediate reboot.</para>
665 <para>systemd user managers treat this signal the same way as
666 <constant>SIGTERM</constant>.</para></listitem>
670 <term><constant>SIGWINCH</constant></term>
672 <listitem><para>When this signal is received the systemd
673 system manager will start the
674 <filename>kbrequest.target</filename> unit. This is mostly
675 equivalent to <command>systemctl start
676 kbrequest.target</command>.</para>
678 <para>This signal is ignored by systemd user
679 managers.</para></listitem>
683 <term><constant>SIGPWR</constant></term>
685 <listitem><para>When this signal is received the systemd
686 manager will start the <filename>sigpwr.target</filename>
687 unit. This is mostly equivalent to <command>systemctl start
688 sigpwr.target</command>.</para></listitem>
692 <term><constant>SIGUSR1</constant></term>
694 <listitem><para>When this signal is received the systemd
695 manager will try to reconnect to the D-Bus
696 bus.</para></listitem>
700 <term><constant>SIGUSR2</constant></term>
702 <listitem><para>When this signal is received the systemd
703 manager will log its complete state in human-readable form.
704 The data logged is the same as printed by
705 <command>systemd-analyze dump</command>.</para></listitem>
709 <term><constant>SIGHUP</constant></term>
711 <listitem><para>Reloads the complete daemon configuration.
712 This is mostly equivalent to <command>systemctl
713 daemon-reload</command>.</para></listitem>
717 <term><constant>SIGRTMIN+0</constant></term>
719 <listitem><para>Enters default mode, starts the
720 <filename>default.target</filename> unit. This is mostly
721 equivalent to <command>systemctl isolate
722 default.target</command>.</para></listitem>
726 <term><constant>SIGRTMIN+1</constant></term>
728 <listitem><para>Enters rescue mode, starts the
729 <filename>rescue.target</filename> unit. This is mostly
730 equivalent to <command>systemctl isolate
731 rescue.target</command>.</para></listitem>
735 <term><constant>SIGRTMIN+2</constant></term>
737 <listitem><para>Enters emergency mode, starts the
738 <filename>emergency.service</filename> unit. This is mostly
739 equivalent to <command>systemctl isolate
740 emergency.service</command>.</para></listitem>
744 <term><constant>SIGRTMIN+3</constant></term>
746 <listitem><para>Halts the machine, starts the
747 <filename>halt.target</filename> unit. This is mostly
748 equivalent to <command>systemctl start halt.target
749 --job-mode=replace-irreversible</command>.</para>
754 <term><constant>SIGRTMIN+4</constant></term>
756 <listitem><para>Powers off the machine, starts the
757 <filename>poweroff.target</filename> unit. This is mostly
758 equivalent to <command>systemctl start poweroff.target
759 --job-mode=replace-irreversible</command>.</para>
764 <term><constant>SIGRTMIN+5</constant></term>
766 <listitem><para>Reboots the machine, starts the
767 <filename>reboot.target</filename> unit. This is mostly
768 equivalent to <command>systemctl start reboot.target
769 --job-mode=replace-irreversible</command>.</para>
774 <term><constant>SIGRTMIN+6</constant></term>
776 <listitem><para>Reboots the machine via kexec, starts the
777 <filename>kexec.target</filename> unit. This is mostly
778 equivalent to <command>systemctl start kexec.target
779 --job-mode=replace-irreversible</command>.</para>
784 <term><constant>SIGRTMIN+13</constant></term>
786 <listitem><para>Immediately halts the machine.</para></listitem>
790 <term><constant>SIGRTMIN+14</constant></term>
792 <listitem><para>Immediately powers off the machine.</para></listitem>
796 <term><constant>SIGRTMIN+15</constant></term>
798 <listitem><para>Immediately reboots the machine.</para></listitem>
802 <term><constant>SIGRTMIN+16</constant></term>
804 <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
808 <term><constant>SIGRTMIN+20</constant></term>
810 <listitem><para>Enables display of status messages on the
811 console, as controlled via
812 <varname>systemd.show_status=1</varname> on the kernel command
813 line.</para></listitem>
817 <term><constant>SIGRTMIN+21</constant></term>
819 <listitem><para>Disables display of
820 status messages on the console, as
822 <varname>systemd.show_status=0</varname>
823 on the kernel command
824 line.</para></listitem>
828 <term><constant>SIGRTMIN+22</constant></term>
830 <listitem><para>Sets the service manager's log level to <literal>debug</literal>, in a fashion equivalent to
831 <varname>systemd.log_level=debug</varname> on the kernel command line.</para></listitem>
835 <term><constant>SIGRTMIN+23</constant></term>
837 <listitem><para>Restores the log level to its configured value. The configured value is derived from – in order
838 of priority – the value specified with <varname>systemd.log-level=</varname> on the kernel command line, or the
839 value specified with <option>LogLevel=</option> in the configuration file, or the built-in default of
840 <literal>info</literal>.</para></listitem>
844 <term><constant>SIGRTMIN+24</constant></term>
846 <listitem><para>Immediately exits the manager (only available
847 for --user instances).</para></listitem>
851 <term><constant>SIGRTMIN+26</constant></term>
853 <listitem><para>Restores the log target to its configured value. The configured value is derived from – in
854 order of priority – the value specified with <varname>systemd.log-target=</varname> on the kernel command line,
855 or the value specified with <option>LogTarget=</option> in the configuration file, or the built-in
856 default.</para></listitem>
860 <term><constant>SIGRTMIN+27</constant></term>
861 <term><constant>SIGRTMIN+28</constant></term>
863 <listitem><para>Sets the log target to <literal>console</literal> on <constant>SIGRTMIN+27</constant> (or
864 <literal>kmsg</literal> on <constant>SIGRTMIN+28</constant>), in a fashion equivalent to
865 <varname>systemd.log_target=console</varname> (or <varname>systemd.log_target=kmsg</varname> on
866 <constant>SIGRTMIN+28</constant>) on the kernel command line.</para></listitem>
872 <!-- 0 /// The whole environment section is unneeded in elogind
874 <title>Environment</title>
876 <variablelist class='environment-variables'>
878 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
879 <listitem><para>systemd reads the log level from this
880 environment variable. This can be overridden with
881 <option>--log-level=</option>.</para></listitem>
885 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
886 <listitem><para>systemd reads the log target from this
887 environment variable. This can be overridden with
888 <option>--log-target=</option>.</para></listitem>
892 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
893 <listitem><para>Controls whether systemd highlights important
894 log messages. This can be overridden with
895 <option>--log-color=</option>.</para></listitem>
899 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
900 <listitem><para>Controls whether systemd prints the code
901 location along with log messages. This can be overridden with
902 <option>--log-location=</option>.</para></listitem>
906 <term><varname>$XDG_CONFIG_HOME</varname></term>
907 <term><varname>$XDG_CONFIG_DIRS</varname></term>
908 <term><varname>$XDG_DATA_HOME</varname></term>
909 <term><varname>$XDG_DATA_DIRS</varname></term>
911 <listitem><para>The systemd user manager uses these variables
912 in accordance to the <ulink
913 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
914 Base Directory specification</ulink> to find its
915 configuration.</para></listitem>
919 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
921 <listitem><para>Controls where systemd looks for unit
922 files.</para></listitem>
926 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
928 <listitem><para>Controls where systemd looks for SysV init
929 scripts.</para></listitem>
933 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
935 <listitem><para>Controls where systemd looks for SysV init
936 script runlevel link farms.</para></listitem>
940 <term><varname>$SYSTEMD_COLORS</varname></term>
942 <listitem><para>The value must be a boolean. Controls whether colorized output should be
943 generated. This can be specified to override the decision that <command>systemd</command>
944 makes based on <varname>$TERM</varname> and what the console is connected to.</para>
949 <term><varname>$SYSTEMD_URLIFY</varname></term>
951 <listitem><para>The value must be a boolean. Controls whether clickable links should be generated in the output
952 for terminal emulators supporting this. This can be specified to override the decision that
953 <command>systemd</command> makes based on <varname>$TERM</varname> and other conditions.</para>
958 <term><varname>$LISTEN_PID</varname></term>
959 <term><varname>$LISTEN_FDS</varname></term>
960 <term><varname>$LISTEN_FDNAMES</varname></term>
962 <listitem><para>Set by systemd for supervised processes during
963 socket-based activation. See
964 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
965 for more information.</para></listitem>
969 <term><varname>$NOTIFY_SOCKET</varname></term>
971 <listitem><para>Set by systemd for supervised processes for
972 status and start-up completion notification. See
973 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
974 for more information.</para></listitem>
980 <!-- 0 /// The whole kernel section is unneeded in elogind
982 <title>Kernel Command Line</title>
984 <para>When run as system instance systemd parses a number of
985 kernel command line arguments<footnote><para>If run inside a Linux
986 container these arguments may be passed as command line arguments
987 to systemd itself, next to any of the command line options listed
988 in the Options section above. If run outside of Linux containers,
989 these arguments are parsed from <filename>/proc/cmdline</filename>
990 instead.</para></footnote>:</para>
992 <variablelist class='kernel-commandline-options'>
994 <term><varname>systemd.unit=</varname></term>
995 <term><varname>rd.systemd.unit=</varname></term>
997 <listitem><para>Overrides the unit to activate on boot.
998 Defaults to <filename>default.target</filename>. This may be
999 used to temporarily boot into a different boot unit, for
1000 example <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 option prefixed with
1004 <literal>rd.</literal> is honored only in the initial RAM disk
1005 (initrd), while the one that is not prefixed only in the main
1006 system.</para></listitem>
1010 <term><varname>systemd.dump_core</varname></term>
1012 <listitem><para>Takes a boolean argument or enables the option if specified
1013 without an argument. If enabled, the systemd manager (PID 1) dumps core when
1014 it crashes. Otherwise, no core dump is created. Defaults to enabled.</para>
1019 <term><varname>systemd.crash_chvt</varname></term>
1021 <listitem><para>Takes a positive integer, or a boolean argument. Can be also
1022 specified without an argument, with the same effect as a positive boolean. If
1023 a positive integer (in the range 1–63) is specified, the system manager (PID
1024 1) will activate the specified virtual terminal (VT) when it
1025 crashes. Defaults to disabled, meaning that no such switch is attempted. If
1026 set to enabled, the VT the kernel messages are written to is selected.
1031 <term><varname>systemd.crash_shell</varname></term>
1033 <listitem><para>Takes a boolean argument or enables the option if specified
1034 without an argument. If enabled, the system manager (PID 1) spawns a shell
1035 when it crashes, after a 10s delay. Otherwise, no shell is spawned. Defaults
1036 to disabled, for security reasons, as the shell is not protected by password
1037 authentication.</para></listitem>
1041 <term><varname>systemd.crash_reboot</varname></term>
1043 <listitem><para>Takes a boolean argument or enables the option if specified
1044 without an argument. If enabled, the system manager (PID 1) will reboot the
1045 machine automatically when it crashes, after a 10s delay. Otherwise, the
1046 system will hang indefinitely. Defaults to disabled, in order to avoid a
1047 reboot loop. If combined with <varname>systemd.crash_shell</varname>, the
1048 system is rebooted after the shell exits.</para></listitem>
1052 <term><varname>systemd.confirm_spawn</varname></term>
1054 <listitem><para>Takes a boolean argument or a path to the virtual console
1055 where the confirmation messages should be emitted. Can be also specified
1056 without an argument, with the same effect as a positive boolean. If enabled,
1057 the system manager (PID 1) asks for confirmation when spawning processes
1058 using <option>/dev/console</option>. If a path or a console name (such as
1059 <literal>ttyS0</literal>) is provided, the virtual console pointed to by this
1060 path or described by the give name will be used instead. Defaults to disabled.
1065 <term><varname>systemd.service_watchdogs=</varname></term>
1067 <listitem><para>Takes a boolean argument. If disabled, all service runtime
1068 watchdogs (<option>WatchdogSec=</option>) and emergency actions (e.g.
1069 <option>OnFailure=</option> or <option>StartLimitAction=</option>) are
1070 ignored by the system manager (PID 1); see
1071 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
1072 Defaults to enabled, i.e. watchdogs and failure actions are processed
1073 normally. The hardware watchdog is not affected by this
1074 option.</para></listitem>
1078 <term><varname>systemd.show_status</varname></term>
1080 <listitem><para>Takes a boolean argument or the constant
1081 <constant>auto</constant>. Can be also specified without an argument, with
1082 the same effect as a positive boolean. If enabled, the systemd manager (PID
1083 1) shows terse service status updates on the console during bootup.
1084 <constant>auto</constant> behaves like <option>false</option> until a unit
1085 fails or there is a significant delay in boot. Defaults to enabled, unless
1086 <option>quiet</option> is passed as kernel command line option, in which case
1087 it defaults to <constant>auto</constant>. If specified overrides the system
1088 manager configuration file option <option>ShowStatus=</option>, see
1089 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
1090 However, the process command line option <option>--show-status=</option>
1091 takes precedence over both this kernel command line option and the
1092 configuration file option.</para></listitem>
1096 <term><varname>systemd.log_target=</varname></term>
1097 <term><varname>systemd.log_level=</varname></term>
1098 <term><varname>systemd.log_location=</varname></term>
1099 <term><varname>systemd.log_color</varname></term>
1101 <listitem><para>Controls log output, with the same effect as the
1102 <varname>$SYSTEMD_LOG_TARGET</varname>,
1103 <varname>$SYSTEMD_LOG_LEVEL</varname>,
1104 <varname>$SYSTEMD_LOG_LOCATION</varname>,
1105 <varname>$SYSTEMD_LOG_COLOR</varname> environment variables described above.
1106 <varname>systemd.log_color</varname> can be specified without an argument,
1107 with the same effect as a positive boolean.</para></listitem>
1111 <term><varname>systemd.default_standard_output=</varname></term>
1112 <term><varname>systemd.default_standard_error=</varname></term>
1113 <listitem><para>Controls default standard output and error
1114 output for services, with the same effect as the
1115 <option>--default-standard-output=</option> and
1116 <option>--default-standard-error=</option> command line
1117 arguments described above, respectively.</para></listitem>
1121 <term><varname>systemd.setenv=</varname></term>
1123 <listitem><para>Takes a string argument in the form
1124 VARIABLE=VALUE. May be used to set default environment
1125 variables to add to forked child processes. May be used more
1126 than once to set multiple variables.</para></listitem>
1130 <term><varname>systemd.machine_id=</varname></term>
1132 <listitem><para>Takes a 32 character hex value to be
1133 used for setting the machine-id. Intended mostly for
1134 network booting where the same machine-id is desired
1135 for every boot.</para></listitem>
1139 <term><varname>systemd.unified_cgroup_hierarchy</varname></term>
1141 <listitem><para>When specified without an argument or with a true argument,
1142 enables the usage of
1143 <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">unified cgroup hierarchy</ulink>
1144 (a.k.a. cgroups-v2). When specified with a false argument, fall back to
1145 hybrid or full legacy cgroup hierarchy.</para>
1147 <para>If this option is not specified, the default behaviour is determined
1148 during compilation (the <option>--with-default-hierarchy=</option>
1149 option). If the kernel does not support unified cgroup hierarchy, the legacy
1150 hierarchy will be used even if this option is specified.</para>
1155 <term><varname>systemd.legacy_systemd_cgroup_controller</varname></term>
1157 <listitem><para>Takes effect if the full unified cgroup hierarchy is not used
1158 (see previous option). When specified without an argument or with a true
1159 argument, disables the use of "hybrid" cgroup hierarchy (i.e. a cgroups-v2
1160 tree used for systemd, and
1161 <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v1/">legacy
1162 cgroup hierarchy</ulink>, a.k.a. cgroups-v1, for other controllers), and
1163 forces a full "legacy" mode. When specified with a false argument, enables
1164 the use of "hybrid" hierarchy.</para>
1166 <para>If this option is not specified, the default behaviour is determined
1167 during compilation (the <option>--with-default-hierarchy=</option>
1168 option). If the kernel does not support unified cgroup hierarchy, the legacy
1169 hierarchy will be used even if this option is specified.</para>
1174 <term><varname>quiet</varname></term>
1176 <listitem><para>Turn off status output at boot, much like
1177 <varname>systemd.show_status=false</varname> would. Note that
1178 this option is also read by the kernel itself and disables
1179 kernel log output. Passing this option hence turns off the
1180 usual output from both the system manager and the kernel.
1185 <term><varname>debug</varname></term>
1187 <listitem><para>Turn on debugging output. This is equivalent
1188 to <varname>systemd.log_level=debug</varname>. Note that this
1189 option is also read by the kernel itself and enables kernel
1190 debug output. Passing this option hence turns on the debug
1191 output from both the system manager and the
1192 kernel.</para></listitem>
1196 <term><varname>emergency</varname></term>
1197 <term><varname>rd.emergency</varname></term>
1198 <term><varname>-b</varname></term>
1200 <listitem><para>Boot into emergency mode. This is equivalent
1201 to <varname>systemd.unit=emergency.target</varname> or
1202 <varname>rd.systemd.unit=emergency.target</varname>, respectively, and
1203 provided for compatibility reasons and to be easier to type.</para></listitem>
1207 <term><varname>rescue</varname></term>
1208 <term><varname>rd.rescue</varname></term>
1209 <term><varname>single</varname></term>
1210 <term><varname>s</varname></term>
1211 <term><varname>S</varname></term>
1212 <term><varname>1</varname></term>
1214 <listitem><para>Boot into rescue mode. This is equivalent to
1215 <varname>systemd.unit=rescue.target</varname> or
1216 <varname>rd.systemd.unit=rescue.target</varname>, respectively, and
1217 provided for compatibility reasons and to be easier to type.</para></listitem>
1221 <term><varname>2</varname></term>
1222 <term><varname>3</varname></term>
1223 <term><varname>4</varname></term>
1224 <term><varname>5</varname></term>
1226 <listitem><para>Boot into the specified legacy SysV runlevel.
1227 These are equivalent to
1228 <varname>systemd.unit=runlevel2.target</varname>,
1229 <varname>systemd.unit=runlevel3.target</varname>,
1230 <varname>systemd.unit=runlevel4.target</varname>, and
1231 <varname>systemd.unit=runlevel5.target</varname>,
1232 respectively, and provided for compatibility reasons and to be
1233 easier to type.</para></listitem>
1237 <term><varname>locale.LANG=</varname></term>
1238 <term><varname>locale.LANGUAGE=</varname></term>
1239 <term><varname>locale.LC_CTYPE=</varname></term>
1240 <term><varname>locale.LC_NUMERIC=</varname></term>
1241 <term><varname>locale.LC_TIME=</varname></term>
1242 <term><varname>locale.LC_COLLATE=</varname></term>
1243 <term><varname>locale.LC_MONETARY=</varname></term>
1244 <term><varname>locale.LC_MESSAGES=</varname></term>
1245 <term><varname>locale.LC_PAPER=</varname></term>
1246 <term><varname>locale.LC_NAME=</varname></term>
1247 <term><varname>locale.LC_ADDRESS=</varname></term>
1248 <term><varname>locale.LC_TELEPHONE=</varname></term>
1249 <term><varname>locale.LC_MEASUREMENT=</varname></term>
1250 <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1252 <listitem><para>Set the system locale to use. This overrides
1253 the settings in <filename>/etc/locale.conf</filename>. For
1254 more information, see
1255 <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1257 <citerefentry project='man-pages'><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1262 <para>For other kernel command line parameters understood by
1263 components of the core OS, please refer to
1264 <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1268 <!-- 0 /// The whole sockets section is unneeded in elogind
1270 <title>Sockets and FIFOs</title>
1274 <term><filename>/run/systemd/notify</filename></term>
1276 <listitem><para>Daemon status notification socket. This is an
1277 <constant>AF_UNIX</constant> datagram socket and is used to
1278 implement the daemon notification logic as implemented by
1279 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1284 <term><filename>/run/systemd/private</filename></term>
1286 <listitem><para>Used internally as communication channel
1288 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1289 and the systemd process. This is an
1290 <constant>AF_UNIX</constant> stream socket. This interface is
1291 private to systemd and should not be used in external
1292 projects.</para></listitem>
1296 <term><filename>/dev/initctl</filename></term>
1298 <listitem><para>Limited compatibility support for the SysV
1299 client interface, as implemented by the
1300 <filename>systemd-initctl.service</filename> unit. This is a
1301 named pipe in the file system. This interface is obsolete and
1302 should not be used in new applications.</para></listitem>
1309 <title>See Also</title>
1311 <!-- 0 /// elogind does not have that much to see also...
1312 The <ulink url="https://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>,
1313 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1314 <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1315 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1316 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1317 <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1318 <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1319 <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1320 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1321 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1322 <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1323 <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1324 <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1325 <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1327 The <ulink url="https://github.com/elogind/elogind/">elogind Homepage</ulink>,
1328 <citerefentry><refentrytitle>loginctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1329 <citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1330 <citerefentry><refentrytitle>pam_elogind</refentrytitle><manvolnum>8</manvolnum></citerefentry>