1SYSTEMD(1) systemd SYSTEMD(1)
2
6 systemd, init - systemd system and service manager
7
9 systemd [OPTIONS...]
10 init [OPTIONS...] {COMMAND}
12
14 systemd is a system and service manager for Linux operating systems.
15 When run as first process on boot (as PID 1), it acts as init system
16 that brings up and maintains userspace services.
17 For compatibility with SysV, if systemd is called as init and a PID
19 that is not 1, it will execute telinit and pass all command line
20 arguments unmodified. That means init and telinit are mostly equivalent
21 when invoked from normal login sessions. See telinit(8) for more
22 information.
23 When run as a system instance, systemd interprets the configuration
25 file system.conf and the files in system.conf.d directories. See
26 systemd-system.conf(5) for more information.
27
29 The following options are understood:
30 --test
32 Determine startup sequence, dump it and exit. This is an option
33 useful for debugging only.
34 --dump-configuration-items
36 Dump understood unit configuration items. This outputs a terse but
37 complete list of configuration items understood in unit definition
38 files.
39 --unit=
41 Set default unit to activate on startup. If not specified, defaults
42 to default.target.
43 --system
45 --system, tell systemd to run a system instance, even if the
46 process ID is not 1, i.e. systemd is not run as init process.
47 Normally it should not be necessary to pass this options, as
48 systemd automatically detects the mode it is started in. This
49 option is hence of little use except for debugging. Note that it is
50 not supported booting and maintaining a full system with systemd
51 running in --system mode, but PID not 1. In practice, passing
52 --system explicitly is only useful in conjunction with --test.
53 --dump-core
55 Dump core on crash.
56 --crash-shell
58 Run shell on crash.
59 --confirm-spawn
61 Ask for confirmation when spawning processes.
62 --show-status=
64 Show terse service status information while booting. Takes a
65 boolean argument which may be omitted which is interpreted as true.
66 --log-target=
68 Set log target. Argument must be one of console, journal, kmsg,
69 journal-or-kmsg, null.
70 --log-level=
72 Set log level. As argument this accepts a numerical log level or
73 the well-known syslog(3) symbolic names (lowercase): emerg, alert,
74 crit, err, warning, notice, info, debug.
75 --log-color=
77 Highlight important log messages. Argument is a boolean value. If
78 the argument is omitted, it defaults to true.
79 --log-location=
81 Include code location in log messages. This is mostly relevant for
82 debugging purposes. Argument is a boolean value. If the argument is
83 omitted it defaults to true.
84 --default-standard-output=, --default-standard-error=
86 Sets the default output or error output for all services and
87 sockets, respectively. That is, controls the default for
88 StandardOutput= and StandardError= (see systemd.exec(5) for
89 details). Takes one of inherit, null, tty, journal,
90 journal+console, syslog, syslog+console, kmsg, kmsg+console. If the
91 argument is omitted --default-standard-output= defaults to journal
92 and --default-standard-error= to inherit.
93 -h, --help
95 Print a short help text and exit.
96 --version
98 Print a short version string and exit.
99
101 systemd provides a dependency system between various entities called
102 "units" of 12 different types. Units encapsulate various objects that
103 are relevant for system boot-up and maintenance. The majority of units
104 are configured in unit configuration files, whose syntax and basic set
105 of options is described in systemd.unit(5), however some are created
106 automatically from other configuration, dynamically from system state
107 or programmatically at runtime. Units may be "active" (meaning started,
108 bound, plugged in, ..., depending on the unit type, see below), or
109 "inactive" (meaning stopped, unbound, unplugged, ...), as well as in
110 the process of being activated or deactivated, i.e. between the two
111 states (these states are called "activating", "deactivating"). A
112 special "failed" state is available as well, which is very similar to
113 "inactive" and is entered when the service failed in some way (process
114 returned error code on exit, or crashed, or an operation timed out). If
115 this state is entered, the cause will be logged, for later reference.
116 Note that the various unit types may have a number of additional
117 substates, which are mapped to the five generalized unit states
118 described here.
119 The following unit types are available:
121 1. Service units, which start and control daemons and the processes
123 they consist of. For details see systemd.service(5).
124 2. Socket units, which encapsulate local IPC or network sockets in the
126 system, useful for socket-based activation. For details about
127 socket units see systemd.socket(5), for details on socket-based
128 activation and other forms of activation, see daemon(7).
129 3. Target units are useful to group units, or provide well-known
131 synchronization points during boot-up, see systemd.target(5).
132 4. Device units expose kernel devices in systemd and may be used to
134 implement device-based activation. For details see
135 systemd.device(5).
136 5. Mount units control mount points in the file system, for details
138 see systemd.mount(5).
139 6. Automount units provide automount capabilities, for on-demand
141 mounting of file systems as well as parallelized boot-up. See
142 systemd.automount(5).
143 7. Snapshot units can be used to temporarily save the state of the set
145 of systemd units, which later may be restored by activating the
146 saved snapshot unit. For more information see systemd.snapshot(5).
147 8. Timer units are useful for triggering activation of other units
149 based on timers. You may find details in systemd.timer(5).
150 9. Swap units are very similar to mount units and encapsulate memory
152 swap partitions or files of the operating system. They are
153 described in systemd.swap(5).
154 10. Path units may be used to activate other services when file system
156 objects change or are modified. See systemd.path(5).
157 11. Slice units may be used to group units which manage system
159 processes (such as service and scope units) in a hierarchical tree
160 for resource management purposes. See systemd.slice(5).
161 12. Scope units are similar to service units, but manage foreign
163 processes instead of starting them as well. See systemd.scope(5).
164 Units are named as their configuration files. Some units have special
166 semantics. A detailed list is available in systemd.special(7).
167 systemd knows various kinds of dependencies, including positive and
169 negative requirement dependencies (i.e. Requires= and Conflicts=) as
170 well as ordering dependencies (After= and Before=). NB: ordering and
171 requirement dependencies are orthogonal. If only a requirement
172 dependency exists between two units (e.g. foo.service requires
173 bar.service), but no ordering dependency (e.g. foo.service after
174 bar.service) and both are requested to start, they will be started in
175 parallel. It is a common pattern that both requirement and ordering
176 dependencies are placed between two units. Also note that the majority
177 of dependencies are implicitly created and maintained by systemd. In
178 most cases, it should be unnecessary to declare additional dependencies
179 manually, however it is possible to do this.
180 Application programs and units (via dependencies) may request state
182 changes of units. In systemd, these requests are encapsulated as 'jobs'
183 and maintained in a job queue. Jobs may succeed or can fail, their
184 execution is ordered based on the ordering dependencies of the units
185 they have been scheduled for.
186 On boot systemd activates the target unit default.target whose job is
188 to activate on-boot services and other on-boot units by pulling them in
189 via dependencies. Usually the unit name is just an alias (symlink) for
190 either graphical.target (for fully-featured boots into the UI) or
191 multi-user.target (for limited console-only boots for use in embedded
192 or server environments, or similar; a subset of graphical.target).
193 However, it is at the discretion of the administrator to configure it
194 as an alias to any other target unit. See systemd.special(7) for
195 details about these target units.
196 Processes systemd spawns are placed in individual Linux control groups
198 named after the unit which they belong to in the private systemd
199 hierarchy. (see cgroups.txt[1] for more information about control
200 groups, or short "cgroups"). systemd uses this to effectively keep
201 track of processes. Control group information is maintained in the
202 kernel, and is accessible via the file system hierarchy (beneath
203 /sys/fs/cgroup/systemd/), or in tools such as ps(1) (ps xawf -eo
204 pid,user,cgroup,args is particularly useful to list all processes and
205 the systemd units they belong to.).
206 systemd is compatible with the SysV init system to a large degree: SysV
208 init scripts are supported and simply read as an alternative (though
209 limited) configuration file format. The SysV /dev/initctl interface is
210 provided, and compatibility implementations of the various SysV client
211 tools are available. In addition to that, various established Unix
212 functionality such as /etc/fstab or the utmp database are supported.
213 systemd has a minimal transaction system: if a unit is requested to
215 start up or shut down it will add it and all its dependencies to a
216 temporary transaction. Then, it will verify if the transaction is
217 consistent (i.e. whether the ordering of all units is cycle-free). If
218 it is not, systemd will try to fix it up, and removes non-essential
219 jobs from the transaction that might remove the loop. Also, systemd
220 tries to suppress non-essential jobs in the transaction that would stop
221 a running service. Finally it is checked whether the jobs of the
222 transaction contradict jobs that have already been queued, and
223 optionally the transaction is aborted then. If all worked out and the
224 transaction is consistent and minimized in its impact it is merged with
225 all already outstanding jobs and added to the run queue. Effectively
226 this means that before executing a requested operation, systemd will
227 verify that it makes sense, fixing it if possible, and only failing if
228 it really cannot work.
229 Systemd contains native implementations of various tasks that need to
231 be executed as part of the boot process. For example, it sets the
232 hostname or configures the loopback network device. It also sets up and
233 mounts various API file systems, such as /sys or /proc.
234 For more information about the concepts and ideas behind systemd,
236 please refer to the Original Design Document[2].
237 Note that some but not all interfaces provided by systemd are covered
239 by the Interface Stability Promise[3].
240 Units may be generated dynamically at boot and system manager reload
242 time, for example based on other configuration files or parameters
243 passed on the kernel command line. For details see
244 systemd.generator(7).
245 Systems which invoke systemd in a container or initrd environment
247 should implement the Container Interface[4] or initrd Interface[5]
248 specifications, respectively.
249
251 System unit directories
252 The systemd system manager reads unit configuration from various
253 directories. Packages that want to install unit files shall place
254 them in the directory returned by pkg-config systemd
255 --variable=systemdsystemunitdir. Other directories checked are
256 /usr/local/lib/systemd/system and /usr/lib/systemd/system. User
257 configuration always takes precedence. pkg-config systemd
258 --variable=systemdsystemconfdir returns the path of the system
259 configuration directory. Packages should alter the content of these
260 directories only with the enable and disable commands of the
261 systemctl(1) tool. Full list of directories is provided in
262 systemd.unit(5).
263 SysV init scripts directory
265 The location of the SysV init script directory varies between
266 distributions. If systemd cannot find a native unit file for a
267 requested service, it will look for a SysV init script of the same
268 name (with the .service suffix removed).
269 SysV runlevel link farm directory
271 The location of the SysV runlevel link farm directory varies
272 between distributions. systemd will take the link farm into account
273 when figuring out whether a service shall be enabled. Note that a
274 service unit with a native unit configuration file cannot be
275 started by activating it in the SysV runlevel link farm.
276
278 SIGTERM
279 Upon receiving this signal the systemd system manager serializes
280 its state, reexecutes itself and deserializes the saved state
281 again. This is mostly equivalent to systemctl daemon-reexec.
282 SIGINT
284 Upon receiving this signal the systemd system manager will start
285 the ctrl-alt-del.target unit. This is mostly equivalent to
286 systemctl start ctl-alt-del.target. If this signal is received more
287 often than 7 times per 2s an immediate reboot is triggered. Note
288 that pressing Ctrl-Alt-Del on the console will trigger this signal.
289 Hence, if a reboot is hanging pressing Ctrl-Alt-Del more than 7
290 times in 2s is a relatively safe way to trigger an immediate
291 reboot.
292 systemd user managers treat this signal the same way as SIGTERM.
294 SIGWINCH
296 When this signal is received the systemd system manager will start
297 the kbrequest.target unit. This is mostly equivalent to systemctl
298 start kbrequest.target.
299 This signal is ignored by systemd user managers.
301 SIGPWR
303 When this signal is received the systemd manager will start the
304 sigpwr.target unit. This is mostly equivalent to systemctl start
305 sigpwr.target.
306 SIGUSR1
308 When this signal is received the systemd manager will try to
309 reconnect to the D-Bus bus.
310 SIGUSR2
312 When this signal is received the systemd manager will log its
313 complete state in human readable form. The data logged is the same
314 as printed by systemd-analyze dump.
315 SIGHUP
317 Reloads the complete daemon configuration. This is mostly
318 equivalent to systemctl daemon-reload.
319 SIGRTMIN+0
321 Enters default mode, starts the default.target unit. This is mostly
322 equivalent to systemctl start default.target.
323 SIGRTMIN+1
325 Enters rescue mode, starts the rescue.target unit. This is mostly
326 equivalent to systemctl isolate rescue.target.
327 SIGRTMIN+2
329 Enters emergency mode, starts the emergency.service unit. This is
330 mostly equivalent to systemctl isolate emergency.service.
331 SIGRTMIN+3
333 Halts the machine, starts the halt.target unit. This is mostly
334 equivalent to systemctl start halt.target.
335 SIGRTMIN+4
337 Powers off the machine, starts the poweroff.target unit. This is
338 mostly equivalent to systemctl start poweroff.target.
339 SIGRTMIN+5
341 Reboots the machine, starts the reboot.target unit. This is mostly
342 equivalent to systemctl start reboot.target.
343 SIGRTMIN+6
345 Reboots the machine via kexec, starts the kexec.target unit. This
346 is mostly equivalent to systemctl start kexec.target.
347 SIGRTMIN+13
349 Immediately halts the machine.
350 SIGRTMIN+14
352 Immediately powers off the machine.
353 SIGRTMIN+15
355 Immediately reboots the machine.
356 SIGRTMIN+16
358 Immediately reboots the machine with kexec.
359 SIGRTMIN+20
361 Enables display of status messages on the console, as controlled
362 via systemd.show_status=1 on the kernel command line.
363 SIGRTMIN+21
365 Disables display of status messages on the console, as controlled
366 via systemd.show_status=0 on the kernel command line.
367 SIGRTMIN+22, SIGRTMIN+23
369 Sets the log level to "debug" (or "info" on SIGRTMIN+23), as
370 controlled via systemd.log_level=debug (or systemd.log_level=info
371 on SIGRTMIN+23) on the kernel command line.
372 SIGRTMIN+26, SIGRTMIN+27, SIGRTMIN+28
374 Sets the log level to "journal-or-kmsg" (or "console" on
375 SIGRTMIN+27, "kmsg" on SIGRTMIN+28), as controlled via
376 systemd.log_target=journal-or-kmsg (or systemd.log_target=console
377 on SIGRTMIN+27 or systemd.log_target=kmsg on SIGRTMIN+28) on the
378 kernel command line.
379
381 $SYSTEMD_LOG_LEVEL
382 systemd reads the log level from this environment variable. This
383 can be overridden with --log-level=.
384 $SYSTEMD_LOG_TARGET
386 systemd reads the log target from this environment variable. This
387 can be overridden with --log-target=.
388 $SYSTEMD_LOG_COLOR
390 Controls whether systemd highlights important log messages. This
391 can be overridden with --log-color=.
392 $SYSTEMD_LOG_LOCATION
394 Controls whether systemd prints the code location along with log
395 messages. This can be overridden with --log-location=.
396 $XDG_CONFIG_HOME, $XDG_CONFIG_DIRS, $XDG_DATA_HOME, $XDG_DATA_DIRS
398 The systemd user manager uses these variables in accordance to the
399 XDG Base Directory specification[6] to find its configuration.
400 $SYSTEMD_UNIT_PATH
402 Controls where systemd looks for unit files.
403 $SYSTEMD_SYSVINIT_PATH
405 Controls where systemd looks for SysV init scripts.
406 $SYSTEMD_SYSVRCND_PATH
408 Controls where systemd looks for SysV init script runlevel link
409 farms.
410 $SYSTEMD_COLORS
412 Controls whether colorized output should be generated.
413 $LISTEN_PID, $LISTEN_FDS
415 Set by systemd for supervised processes during socket-based
416 activation. See sd_listen_fds(3) for more information.
417 $NOTIFY_SOCKET
419 Set by systemd for supervised processes for status and start-up
420 completion notification. See sd_notify(3) for more information.
421
423 When run as system instance systemd parses a number of kernel command
424 line arguments[7]:
425 systemd.unit=, rd.systemd.unit=
427 Overrides the unit to activate on boot. Defaults to default.target.
428 This may be used to temporarily boot into a different boot unit,
429 for example rescue.target or emergency.service. See
430 systemd.special(7) for details about these units. The option
431 prefixed with "rd." is honored only in the initial RAM disk
432 (initrd), while the one that is not prefixed only in the main
433 system.
434 systemd.dump_core=
436 Takes a boolean argument. If true, systemd dumps core when it
437 crashes. Otherwise, no core dump is created. Defaults to true.
438 systemd.crash_shell=
440 Takes a boolean argument. If true, systemd spawns a shell when it
441 crashes. Otherwise, no shell is spawned. Defaults to false, for
442 security reasons, as the shell is not protected by any password
443 authentication.
444 systemd.crash_chvt=
446 Takes an integer argument. If positive systemd activates the
447 specified virtual terminal when it crashes. Defaults to -1.
448 systemd.confirm_spawn=
450 Takes a boolean argument. If true, asks for confirmation when
451 spawning processes. Defaults to false.
452 systemd.show_status=
454 Takes a boolean argument or the constant auto. If true, shows terse
455 service status updates on the console during bootup. auto behaves
456 like false until a service fails or there is a significant delay in
457 boot. Defaults to true, unless quiet is passed as kernel command
458 line option in which case it defaults to auto.
459 systemd.log_target=, systemd.log_level=, systemd.log_color=,
461 systemd.log_location=
462 Controls log output, with the same effect as the
463 $SYSTEMD_LOG_TARGET, $SYSTEMD_LOG_LEVEL, $SYSTEMD_LOG_COLOR,
464 $SYSTEMD_LOG_LOCATION environment variables described above.
465 systemd.default_standard_output=, systemd.default_standard_error=
467 Controls default standard output and error output for services,
468 with the same effect as the --default-standard-output= and
469 --default-standard-error= command line arguments described above,
470 respectively.
471 systemd.setenv=
473 Takes a string argument in the form VARIABLE=VALUE. May be used to
474 set default environment variables to add to forked child processes.
475 May be used more than once to set multiple variables.
476 quiet
478 Turn off status output at boot, much like systemd.show_status=false
479 would. Note that this option is also read by the kernel itself and
480 disables kernel log output. Passing this option hence turns off the
481 usual output from both the system manager and the kernel.
482 debug
484 Turn on debugging output. This is equivalent to
485 systemd.log_level=debug. Note that this option is also read by the
486 kernel itself and enables kernel debug output. Passing this option
487 hence turns on the debug output from both the system manager and
488 the kernel.
489 emergency, -b
491 Boot into emergency mode. This is equivalent to
492 systemd.unit=emergency.target and provided for compatibility
493 reasons and to be easier to type.
494 rescue, single, s, S, 1
496 Boot into rescue mode. This is equivalent to
497 systemd.unit=rescue.target and provided for compatibility reasons
498 and to be easier to type.
499 2, 3, 4, 5
501 Boot into the specified legacy SysV runlevel. These are equivalent
502 to systemd.unit=runlevel2.target, systemd.unit=runlevel3.target,
503 systemd.unit=runlevel4.target, and systemd.unit=runlevel5.target,
504 respectively, and provided for compatibility reasons and to be
505 easier to type.
506 locale.LANG=, locale.LANGUAGE=, locale.LC_CTYPE=, locale.LC_NUMERIC=,
508 locale.LC_TIME=, locale.LC_COLLATE=, locale.LC_MONETARY=,
509 locale.LC_MESSAGES=, locale.LC_PAPER=, locale.LC_NAME=,
510 locale.LC_ADDRESS=, locale.LC_TELEPHONE=, locale.LC_MEASUREMENT=,
511 locale.LC_IDENTIFICATION=
512 Set the system locale to use. This overrides the settings in
513 /etc/locale.conf. For more information see locale.conf(5) and
514 locale(7).
515 For other kernel command line parameters understood by components of
517 the core OS, please refer to kernel-command-line(7).
518
520 /run/systemd/notify
521 Daemon status notification socket. This is an AF_UNIX datagram
522 socket and is used to implement the daemon notification logic as
523 implemented by sd_notify(3).
524 /run/systemd/shutdownd
526 Used internally by the shutdown(8) tool to implement delayed
527 shutdowns. This is an AF_UNIX datagram socket.
528 /run/systemd/private
530 Used internally as communication channel between systemctl(1) and
531 the systemd process. This is an AF_UNIX stream socket. This
532 interface is private to systemd and should not be used in external
533 projects.
534 /dev/initctl
536 Limited compatibility support for the SysV client interface, as
537 implemented by the systemd-initctl.service unit. This is a named
538 pipe in the file system. This interface is obsolete and should not
539 be used in new applications.
540
542 The systemd Homepage[8], systemd-system.conf(5), locale.conf(5),
543 systemctl(1), journalctl(1), systemd-notify(1), daemon(7), sd-
544 daemon(3), systemd.unit(5), systemd.special(5), pkg-config(1), kernel-
545 command-line(7), bootup(7), systemd.directives(7)
546
548 1. cgroups.txt
549 https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt
550 2. Original Design Document
552 http://0pointer.de/blog/projects/systemd.html
553 3. Interface Stability Promise
555 http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise
556 4. Container Interface
558 http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface
559 5. initrd Interface
561 http://www.freedesktop.org/wiki/Software/systemd/InitrdInterface
562 6. XDG Base Directory specification
564 http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
565 7. If run inside a Linux container these arguments may be passed as
567 command line arguments to systemd itself, next to any of the
568 command line options listed in the Options section above. If run
569 outside of Linux containers, these arguments are parsed from
570 /proc/cmdline instead.
571 8. systemd Homepage
573 http://www.freedesktop.org/wiki/Software/systemd/
574systemd 219 SYSTEMD(1)