1SYSTEMD.SPECIAL(7) systemd.special SYSTEMD.SPECIAL(7)
2
6 systemd.special - Special systemd units
7
9 basic.target, bluetooth.target, cryptsetup-pre.target,
10 cryptsetup.target, veritysetup-pre.target, veritysetup.target,
11 ctrl-alt-del.target, blockdev@.target, boot-complete.target,
12 default.target, emergency.target, exit.target, final.target,
13 first-boot-complete.target, getty.target, getty-pre.target,
14 graphical.target, halt.target, hibernate.target, hybrid-sleep.target,
15 suspend-then-hibernate.target, initrd.target, initrd-fs.target,
16 initrd-root-device.target, initrd-root-fs.target, initrd-usr-fs.target,
17 kbrequest.target, kexec.target, local-fs-pre.target, local-fs.target,
18 machines.target multi-user.target, network-online.target,
19 network-pre.target, network.target, nss-lookup.target,
20 nss-user-lookup.target, paths.target, poweroff.target, printer.target,
21 reboot.target, remote-cryptsetup.target, remote-veritysetup.target,
22 remote-fs-pre.target, remote-fs.target, rescue.target, rpcbind.target,
23 runlevel2.target, runlevel3.target, runlevel4.target, runlevel5.target,
24 shutdown.target, sigpwr.target, sleep.target, slices.target,
25 smartcard.target, sockets.target, sound.target, suspend.target,
26 swap.target, sysinit.target, system-update.target,
27 system-update-pre.target, time-set.target, time-sync.target,
28 timers.target, umount.target, usb-gadget.target, -.slice, system.slice,
29 user.slice, machine.slice, -.mount, dbus.service, dbus.socket,
30 display-manager.service, init.scope, syslog.socket,
31 system-update-cleanup.service
32
34 A few units are treated specially by systemd. Many of them have special
35 internal semantics and cannot be renamed, while others simply have a
36 standard meaning and should be present on all systems.
37
39 Special System Units
40 -.mount
41 The root mount point, i.e. the mount unit for the / path. This unit
42 is unconditionally active, during the entire time the system is up,
43 as this mount point is where the basic userspace is running from.
44 basic.target
46 A special target unit covering basic boot-up.
47 systemd automatically adds dependency of the type After= for this
49 target unit to all services (except for those with
50 DefaultDependencies=no).
51 Usually, this should pull-in all local mount points plus /var/,
53 /tmp/ and /var/tmp/, swap devices, sockets, timers, path units and
54 other basic initialization necessary for general purpose daemons.
55 The mentioned mount points are special cased to allow them to be
56 remote.
57 This target usually does not pull in any non-target units directly,
59 but rather does so indirectly via other early boot targets. It is
60 instead meant as a synchronization point for late boot services.
61 Refer to bootup(7) for details on the targets involved.
62 boot-complete.target
64 This target is intended as generic synchronization point for
65 services that shall determine or act on whether the boot process
66 completed successfully. Order units that are required to succeed
67 for a boot process to be considered successful before this unit,
68 and add a Requires= dependency from the target unit to them. Order
69 units that shall only run when the boot process is considered
70 successful after the target unit and pull in the target from it,
71 also with Requires=. Note that by default this target unit is not
72 part of the initial boot transaction, but is supposed to be pulled
73 in only if required by units that want to run only on successful
74 boots.
75 See systemd-boot-check-no-failures.service(8) for a service that
77 implements a generic system health check and orders itself before
78 boot-complete.target.
79 See systemd-bless-boot.service(8) for a service that propagates
81 boot success information to the boot loader, and orders itself
82 after boot-complete.target.
83 ctrl-alt-del.target
85 systemd starts this target whenever Control+Alt+Del is pressed on
86 the console. Usually, this should be aliased (symlinked) to
87 reboot.target.
88 cryptsetup.target
90 A target that pulls in setup services for all encrypted block
91 devices.
92 veritysetup.target
94 A target that pulls in setup services for all verity integrity
95 protected block devices.
96 dbus.service
98 A special unit for the D-Bus bus daemon. As soon as this service is
99 fully started up systemd will connect to it and register its
100 service.
101 dbus.socket
103 A special unit for the D-Bus system bus socket. All units with
104 Type=dbus automatically gain a dependency on this unit.
105 default.target
107 The default unit systemd starts at bootup. Usually, this should be
108 aliased (symlinked) to multi-user.target or graphical.target. See
109 bootup(7) for more discussion.
110 The default unit systemd starts at bootup can be overridden with
112 the systemd.unit= kernel command line option, or more conveniently,
113 with the short names like single, rescue, 1, 3, 5, ...; see
114 systemd(1).
115 display-manager.service
117 The display manager service. Usually, this should be aliased
118 (symlinked) to gdm.service or a similar display manager service.
119 emergency.target
121 A special target unit that starts an emergency shell on the main
122 console. This target does not pull in other services or mounts. It
123 is the most minimal version of starting the system in order to
124 acquire an interactive shell; the only processes running are
125 usually just the system manager (PID 1) and the shell process. This
126 unit may be used by specifying emergency on the kernel command
127 line; it is also used when a file system check on a required file
128 system fails and boot-up cannot continue. Compare with
129 rescue.target, which serves a similar purpose, but also starts the
130 most basic services and mounts all file systems.
131 In many ways booting into emergency.target is similar to the effect
133 of booting with "init=/bin/sh" on the kernel command line, except
134 that emergency mode provides you with the full system and service
135 manager, and allows starting individual units in order to continue
136 the boot process in steps.
137 Note that depending on how emergency.target is reached, the root
139 file system might be mounted read-only or read-write (no remounting
140 is done specially for this target). For example, the system may
141 boot with root mounted read-only when ro is used on the kernel
142 command line and remain this way for emergency.target, or the
143 system may transition to emergency.target after the system has been
144 partially booted and disks have already been remounted read-write.
145 exit.target
147 A special service unit for shutting down the system or user service
148 manager. It is equivalent to poweroff.target on non-container
149 systems, and also works in containers.
150 systemd will start this unit when it receives the SIGTERM or SIGINT
152 signal when running as user service daemon.
153 Normally, this (indirectly) pulls in shutdown.target, which in turn
155 should be conflicted by all units that want to be scheduled for
156 shutdown when the service manager starts to exit.
157 final.target
159 A special target unit that is used during the shutdown logic and
160 may be used to pull in late services after all normal services are
161 already terminated and all mounts unmounted.
162 getty.target
164 A special target unit that pulls in statically configured local TTY
165 getty instances.
166 graphical.target
168 A special target unit for setting up a graphical login screen. This
169 pulls in multi-user.target.
170 Units that are needed for graphical logins shall add Wants=
172 dependencies for their unit to this unit (or multi-user.target)
173 during installation. This is best configured via
174 WantedBy=graphical.target in the unit's [Install] section.
175 hibernate.target
177 A special target unit for hibernating the system. This pulls in
178 sleep.target.
179 hybrid-sleep.target
181 A special target unit for hibernating and suspending the system at
182 the same time. This pulls in sleep.target.
183 suspend-then-hibernate.target
185 A special target unit for suspending the system for a period of
186 time, waking it and putting it into hibernate. This pulls in
187 sleep.target.
188 halt.target
190 A special target unit for shutting down and halting the system.
191 Note that this target is distinct from poweroff.target in that it
192 generally really just halts the system rather than powering it
193 down.
194 Applications wanting to halt the system should not start this unit
196 directly, but should instead execute systemctl halt (possibly with
197 the --no-block option) or call systemd(1)'s
198 org.freedesktop.systemd1.Manager.Halt D-Bus method directly.
199 init.scope
201 This scope unit is where the system and service manager (PID 1)
202 itself resides. It is active as long as the system is running.
203 initrd.target
205 This is the default target in the initramfs, similar to
206 default.target in the main system. It is used to mount the real
207 root and transition to it. See bootup(7) for more discussion.
208 initrd-fs.target
210 systemd-fstab-generator(3) automatically adds dependencies of type
211 Before= to sysroot-usr.mount and all mount points found in
212 /etc/fstab that have the x-initrd.mount mount option set and do not
213 have the noauto mount option set. It is also indirectly ordered
214 after sysroot.mount. Thus, once this target is reached the
215 /sysroot/ hierarchy is fully set up, in preparation for the
216 transition to the host OS.
217 initrd-root-device.target
219 A special initrd target unit that is reached when the root
220 filesystem device is available, but before it has been mounted.
221 systemd-fstab-generator(3) and systemd-gpt-auto-generator(3)
222 automatically setup the appropriate dependencies to make this
223 happen.
224 initrd-root-fs.target
226 systemd-fstab-generator(3) automatically adds dependencies of type
227 Before= to the sysroot.mount unit, which is generated from the
228 kernel command line's root= setting (or equivalent).
229 initrd-usr-fs.target
231 systemd-fstab-generator(3) automatically adds dependencies of type
232 Before= to the sysusr-usr.mount unit, which is generated from the
233 kernel command line's usr= switch. Services may order themselves
234 after this target unit in order to run once the /sysusr/ hierarchy
235 becomes available, on systems that come up initially without a root
236 file system, but with an initialized /usr/ and need to access that
237 before setting up the root file system to ultimately switch to. On
238 systems where usr= is not used this target is ordered after
239 sysroot.mount and thus mostly equivalent to initrd-root-fs.target.
240 In effect on any system once this target is reached the file system
241 backing /usr/ is mounted, though possibly at two different
242 locations, either below the /sysusr/ or the /sysroot/ hierarchies.
243 kbrequest.target
245 systemd starts this target whenever Alt+ArrowUp is pressed on the
246 console. Note that any user with physical access to the machine
247 will be able to do this, without authentication, so this should be
248 used carefully.
249 kexec.target
251 A special target unit for shutting down and rebooting the system
252 via kexec.
253 Applications wanting to reboot the system should not start this
255 unit directly, but should instead execute systemctl kexec (possibly
256 with the --no-block option) or call systemd(1)'s
257 org.freedesktop.systemd1.Manager.KExec D-Bus method directly.
258 local-fs.target
260 systemd-fstab-generator(3) automatically adds dependencies of type
261 Before= to all mount units that refer to local mount points for
262 this target unit. In addition, it adds dependencies of type Wants=
263 to this target unit for those mounts listed in /etc/fstab that have
264 the auto mount option set.
265 machines.target
267 A standard target unit for starting all the containers and other
268 virtual machines. See systemd-nspawn@.service for an example.
269 multi-user.target
271 A special target unit for setting up a multi-user system
272 (non-graphical). This is pulled in by graphical.target.
273 Units that are needed for a multi-user system shall add Wants=
275 dependencies for their unit to this unit during installation. This
276 is best configured via WantedBy=multi-user.target in the unit's
277 [Install] section.
278 network-online.target
280 Units that strictly require a configured network connection should
281 pull in network-online.target (via a Wants= type dependency) and
282 order themselves after it. This target unit is intended to pull in
283 a service that delays further execution until the network is
284 sufficiently set up. What precisely this requires is left to the
285 implementation of the network managing service.
286 Note the distinction between this unit and network.target. This
288 unit is an active unit (i.e. pulled in by the consumer rather than
289 the provider of this functionality) and pulls in a service which
290 possibly adds substantial delays to further execution. In contrast,
291 network.target is a passive unit (i.e. pulled in by the provider of
292 the functionality, rather than the consumer) that usually does not
293 delay execution much. Usually, network.target is part of the boot
294 of most systems, while network-online.target is not, except when at
295 least one unit requires it. Also see Running Services After the
296 Network is up[1] for more information.
297 All mount units for remote network file systems automatically pull
299 in this unit, and order themselves after it. Note that networking
300 daemons that simply provide functionality to other hosts (as
301 opposed to consume functionality of other hosts) generally do not
302 need to pull this in.
303 systemd automatically adds dependencies of type Wants= and After=
305 for this target unit to all SysV init script service units with an
306 LSB header referring to the "$network" facility.
307 Note that this unit is only useful during the original system
309 start-up logic. After the system has completed booting up, it will
310 not track the online state of the system anymore. Due to this it
311 cannot be used as a network connection monitor concept, it is
312 purely a one-time system start-up concept.
313 paths.target
315 A special target unit that sets up all path units (see
316 systemd.path(5) for details) that shall be active after boot.
317 It is recommended that path units installed by applications get
319 pulled in via Wants= dependencies from this unit. This is best
320 configured via a WantedBy=paths.target in the path unit's [Install]
321 section.
322 poweroff.target
324 A special target unit for shutting down and powering off the
325 system.
326 Applications wanting to power off the system should not start this
328 unit directly, but should instead execute systemctl poweroff
329 (possibly with the --no-block option) or call systemd-logind(8)'s
330 org.freedesktop.login1.Manager.PowerOff D-Bus method directly.
331 runlevel0.target is an alias for this target unit, for
333 compatibility with SysV.
334 reboot.target
336 A special target unit for shutting down and rebooting the system.
337 Applications wanting to reboot the system should not start this
339 unit directly, but should instead execute systemctl reboot
340 (possibly with the --no-block option) or call systemd-logind(8)'s
341 org.freedesktop.login1.Manager.Reboot D-Bus method directly.
342 runlevel6.target is an alias for this target unit, for
344 compatibility with SysV.
345 remote-cryptsetup.target
347 Similar to cryptsetup.target, but for encrypted devices which are
348 accessed over the network. It is used for crypttab(8) entries
349 marked with _netdev.
350 remote-veritysetup.target
352 Similar to veritysetup.target, but for verity integrity protected
353 devices which are accessed over the network. It is used for
354 veritytab(8) entries marked with _netdev.
355 remote-fs.target
357 Similar to local-fs.target, but for remote mount points.
358 systemd automatically adds dependencies of type After= for this
360 target unit to all SysV init script service units with an LSB
361 header referring to the "$remote_fs" facility.
362 rescue.target
364 A special target unit that pulls in the base system (including
365 system mounts) and spawns a rescue shell. Isolate to this target in
366 order to administer the system in single-user mode with all file
367 systems mounted but with no services running, except for the most
368 basic. Compare with emergency.target, which is much more reduced
369 and does not provide the file systems or most basic services.
370 Compare with multi-user.target, this target could be seen as
371 single-user.target.
372 runlevel1.target is an alias for this target unit, for
374 compatibility with SysV.
375 Use the "systemd.unit=rescue.target" kernel command line option to
377 boot into this mode. A short alias for this kernel command line
378 option is "1", for compatibility with SysV.
379 runlevel2.target, runlevel3.target, runlevel4.target, runlevel5.target
381 These are targets that are called whenever the SysV compatibility
382 code asks for runlevel 2, 3, 4, 5, respectively. It is a good idea
383 to make this an alias for (i.e. symlink to) graphical.target (for
384 runlevel 5) or multi-user.target (the others).
385 shutdown.target
387 A special target unit that terminates the services on system
388 shutdown.
389 Services that shall be terminated on system shutdown shall add
391 Conflicts= and Before= dependencies to this unit for their service
392 unit, which is implicitly done when DefaultDependencies=yes is set
393 (the default).
394 sigpwr.target
396 A special target that is started when systemd receives the SIGPWR
397 process signal, which is normally sent by the kernel or UPS daemons
398 when power fails.
399 sleep.target
401 A special target unit that is pulled in by suspend.target,
402 hibernate.target and hybrid-sleep.target and may be used to hook
403 units into the sleep state logic.
404 slices.target
406 A special target unit that sets up all slice units (see
407 systemd.slice(5) for details) that shall always be active after
408 boot. By default the generic system.slice slice unit as well as the
409 root slice unit -.slice are pulled in and ordered before this unit
410 (see below).
411 Adding slice units to slices.target is generally not necessary.
413 Instead, when some unit that uses Slice= is started, the specified
414 slice will be started automatically. Adding WantedBy=slices.target
415 lines to the [Install] section should only be done for units that
416 need to be always active. In that case care needs to be taken to
417 avoid creating a loop through the automatic dependencies on
418 "parent" slices.
419 sockets.target
421 A special target unit that sets up all socket units (see
422 systemd.socket(5) for details) that shall be active after boot.
423 Services that can be socket-activated shall add Wants= dependencies
425 to this unit for their socket unit during installation. This is
426 best configured via a WantedBy=sockets.target in the socket unit's
427 [Install] section.
428 suspend.target
430 A special target unit for suspending the system. This pulls in
431 sleep.target.
432 swap.target
434 Similar to local-fs.target, but for swap partitions and swap files.
435 sysinit.target
437 systemd automatically adds dependencies of the types Requires= and
438 After= for this target unit to all services (except for those with
439 DefaultDependencies=no).
440 This target pulls in the services required for system
442 initialization. System services pulled in by this target should
443 declare DefaultDependencies=no and specify all their dependencies
444 manually, including access to anything more than a read only root
445 filesystem. For details on the dependencies of this target, refer
446 to bootup(7).
447 syslog.socket
449 The socket unit syslog implementations should listen on. All
450 userspace log messages will be made available on this socket. For
451 more information about syslog integration, please consult the
452 Syslog Interface[2] document.
453 system-update.target, system-update-pre.target,
455 system-update-cleanup.service
456 A special target unit that is used for offline system updates.
457 systemd-system-update-generator(8) will redirect the boot process
458 to this target if /system-update exists. For more information see
459 systemd.offline-updates(7).
460 Updates should happen before the system-update.target is reached,
462 and the services which implement them should cause the machine to
463 reboot. The main units executing the update should order themselves
464 after system-update-pre.target but not pull it in. Services which
465 want to run during system updates only, but before the actual
466 system update is executed should order themselves before this unit
467 and pull it in. As a safety measure, if this does not happen, and
468 /system-update still exists after system-update.target is reached,
469 system-update-cleanup.service will remove this symlink and reboot
470 the machine.
471 timers.target
473 A special target unit that sets up all timer units (see
474 systemd.timer(5) for details) that shall be active after boot.
475 It is recommended that timer units installed by applications get
477 pulled in via Wants= dependencies from this unit. This is best
478 configured via WantedBy=timers.target in the timer unit's [Install]
479 section.
480 umount.target
482 A special target unit that unmounts all mount and automount points
483 on system shutdown.
484 Mounts that shall be unmounted on system shutdown shall add
486 Conflicts dependencies to this unit for their mount unit, which is
487 implicitly done when DefaultDependencies=yes is set (the default).
488 Special System Units for Devices
490 Some target units are automatically pulled in as devices of certain
491 kinds show up in the system. These may be used to automatically
492 activate various services based on the specific type of the available
493 hardware.
494 bluetooth.target
496 This target is started automatically as soon as a Bluetooth
497 controller is plugged in or becomes available at boot.
498 This may be used to pull in Bluetooth management daemons
500 dynamically when Bluetooth hardware is found.
501 printer.target
503 This target is started automatically as soon as a printer is
504 plugged in or becomes available at boot.
505 This may be used to pull in printer management daemons dynamically
507 when printer hardware is found.
508 smartcard.target
510 This target is started automatically as soon as a smartcard
511 controller is plugged in or becomes available at boot.
512 This may be used to pull in smartcard management daemons
514 dynamically when smartcard hardware is found.
515 sound.target
517 This target is started automatically as soon as a sound card is
518 plugged in or becomes available at boot.
519 This may be used to pull in audio management daemons dynamically
521 when audio hardware is found.
522 usb-gadget.target
524 This target is started automatically as soon as a USB Device
525 Controller becomes available at boot.
526 This may be used to pull in usb gadget dynamically when UDC
528 hardware is found.
529 Special Passive System Units
531 A number of special system targets are defined that can be used to
532 properly order boot-up of optional services. These targets are
533 generally not part of the initial boot transaction, unless they are
534 explicitly pulled in by one of the implementing services. Note
535 specifically that these passive target units are generally not pulled
536 in by the consumer of a service, but by the provider of the service.
537 This means: a consuming service should order itself after these targets
538 (as appropriate), but not pull it in. A providing service should order
539 itself before these targets (as appropriate) and pull it in (via a
540 Wants= type dependency).
541 Note that these passive units cannot be started manually, i.e.
543 "systemctl start time-sync.target" will fail with an error. They can
544 only be pulled in by dependency. This is enforced since they exist for
545 ordering purposes only and thus are not useful as only unit within a
546 transaction.
547 blockdev@.target
549 This template unit is used to order mount units and other consumers
550 of block devices after services that synthesize these block
551 devices. In particular, this is intended to be used with storage
552 services (such as systemd-cryptsetup@.service(5)/ systemd-
553 veritysetup@.service(5)) that allocate and manage a virtual block
554 device. Storage services are ordered before an instance of
555 blockdev@.target, and the consumer units after it. The ordering is
556 particularly relevant during shutdown, as it ensures that the mount
557 is deactivated first and the service backing the mount later. The
558 blockdev@.target instance should be pulled in via a Wants=
559 dependency of the storage daemon and thus generally not be part of
560 any transaction unless a storage daemon is used. The instance name
561 for instances of this template unit must be a properly escaped
562 block device node path, e.g. blockdev@dev-mapper-foobar.target for
563 the storage device /dev/mapper/foobar.
564 cryptsetup-pre.target
566 This passive target unit may be pulled in by services that want to
567 run before any encrypted block device is set up. All encrypted
568 block devices are set up after this target has been reached. Since
569 the shutdown order is implicitly the reverse start-up order between
570 units, this target is particularly useful to ensure that a service
571 is shut down only after all encrypted block devices are fully
572 stopped.
573 veritysetup-pre.target
575 This passive target unit may be pulled in by services that want to
576 run before any verity integrity protected block device is set up.
577 All verity integrity protected block devices are set up after this
578 target has been reached. Since the shutdown order is implicitly the
579 reverse start-up order between units, this target is particularly
580 useful to ensure that a service is shut down only after all verity
581 integrity protected block devices are fully stopped.
582 first-boot-complete.target
584 This passive target is intended as a synchronization point for
585 units that need to run once during the first boot. Only after all
586 units ordered before this target have finished, will the machine-
587 id(5) be committed to disk, marking the first boot as completed. If
588 the boot is aborted at any time before that, the next boot will
589 re-run any units with ConditionFirstBoot=yes.
590 getty-pre.target
592 A special passive target unit. Users of this target are expected to
593 pull it in the boot transaction via a dependency (e.g. Wants=).
594 Order your unit before this unit if you want to make use of the
595 console just before getty is started.
596 local-fs-pre.target
598 This target unit is automatically ordered before all local mount
599 points marked with auto (see above). It can be used to execute
600 certain units before all local mounts.
601 network.target
603 This unit is supposed to indicate when network functionality is
604 available, but it is only very weakly defined what that is supposed
605 to mean. However, the following should apply at minimum:
606 • At start-up, any configured synthetic network devices (i.e. not
608 physical ones that require hardware to show up and be probed,
609 but virtual ones like bridge devices and similar which are
610 created programmatically) that do not depend on any underlying
611 hardware should be allocated by the time this target is
612 reached. It is not necessary for these interfaces to also have
613 completed IP level configuration by the time network.target is
614 reached.
615 • At shutdown, a unit that is ordered after network.target will
617 be stopped before the network — to whatever level it might be
618 set up by then — is shut down. It is hence useful when writing
619 service files that require network access on shutdown, which
620 should order themselves after this target, but not pull it in.
621 Also see Running Services After the Network is up[1] for more
622 information.
623 It must emphasized that at start-up there's no guarantee that
625 hardware-based devices have shown up by the time this target is
626 reached, or even acquired complete IP configuration. For that
627 purpose use network-online.target as described above.
628 network-pre.target
630 This passive target unit may be pulled in by services that want to
631 run before any network is set up, for example for the purpose of
632 setting up a firewall. All network management software orders
633 itself after this target, but does not pull it in.
634 nss-lookup.target
636 A target that should be used as synchronization point for all
637 host/network name service lookups. Note that this is independent of
638 UNIX user/group name lookups for which nss-user-lookup.target
639 should be used. All services for which the availability of full
640 host/network name resolution is essential should be ordered after
641 this target, but not pull it in. systemd automatically adds
642 dependencies of type After= for this target unit to all SysV init
643 script service units with an LSB header referring to the "$named"
644 facility.
645 nss-user-lookup.target
647 A target that should be used as synchronization point for all
648 regular UNIX user/group name service lookups. Note that this is
649 independent of host/network name lookups for which
650 nss-lookup.target should be used. All services for which the
651 availability of the full user/group database is essential should be
652 ordered after this target, but not pull it in. All services which
653 provide parts of the user/group database should be ordered before
654 this target, and pull it in. Note that this unit is only relevant
655 for regular users and groups — system users and groups are required
656 to be resolvable during earliest boot already, and hence do not
657 need any special ordering against this target.
658 remote-fs-pre.target
660 This target unit is automatically ordered before all mount point
661 units (see above) and cryptsetup/veritysetup devices marked with
662 the _netdev. It can be used to run certain units before remote
663 encrypted devices and mounts are established. Note that this unit
664 is generally not part of the initial transaction, unless the unit
665 that wants to be ordered before all remote mounts pulls it in via a
666 Wants= type dependency. If the unit wants to be pulled in by the
667 first remote mount showing up, it should use network-online.target
668 (see above).
669 rpcbind.target
671 The portmapper/rpcbind pulls in this target and orders itself
672 before it, to indicate its availability. systemd automatically adds
673 dependencies of type After= for this target unit to all SysV init
674 script service units with an LSB header referring to the "$portmap"
675 facility.
676 time-set.target
678 Services responsible for setting the system clock (CLOCK_REALTIME)
679 from a local source (such as a maintained timestamp file or
680 imprecise real-time clock) should pull in this target and order
681 themselves before it. Services where approximate, roughly monotonic
682 time is desired should be ordered after this unit, but not pull it
683 in.
684 This target does not provide the accuracy guarantees of
686 time-sync.target (see below), however does not depend on remote
687 clock sources to be reachable, i.e. the target is typically not
688 delayed by network problems and similar. Use of this target is
689 recommended for services where approximate clock accuracy and rough
690 monotonicity is desired but activation shall not be delayed for
691 possibly unreliable network communication.
692 The service manager automatically adds dependencies of type After=
694 for this target unit to all timer units with at least one
695 OnCalendar= directive.
696 The systemd-timesyncd.service(8) service is a simple daemon that
698 pulls in this target and orders itself before it. Besides
699 implementing the SNTP network protocol it maintains a timestamp
700 file on disk whose modification time is regularlary updated. At
701 service start-up the local system clock is set from that
702 modification time, ensuring it increases roughly monotonically.
703 Note that ordering a unit after time-set.target only has effect if
705 there's actually a service ordered before it that delays it until
706 the clock is adjusted for rough monotonicity. Otherwise, this
707 target might get reached before the clock is adjusted to be roughly
708 monotonic. Enable systemd-timesyncd.service(8), or an alternative
709 NTP implementation to delay the target.
710 time-sync.target
712 Services indicating completed synchronization of the system clock
713 (CLOCK_REALTIME) to a remote source should pull in this target and
714 order themselves before it. Services where accurate time is
715 essential should be ordered after this unit, but not pull it in.
716 The service manager automatically adds dependencies of type After=
718 for this target unit to all SysV init script service units with an
719 LSB header referring to the "$time" facility, as well to all timer
720 units with at least one OnCalendar= directive.
721 This target provides stricter clock accuracy guarantees than
723 time-set.target (see above), but likely requires network
724 communication and thus introduces unpredictable delays. Services
725 that require clock accuracy and where network communication delays
726 are acceptable should use this target. Services that require a less
727 accurate clock, and only approximate and roughly monotonic clock
728 behaviour should use time-set.target instead.
729 Note that ordering a unit after time-sync.target only has effect if
731 there's actually a service ordered before it that delays it until
732 clock synchronization is reached. Otherwise, this target might get
733 reached before the clock is synchronized to any remote accurate
734 reference clock. When using systemd-timesyncd.service(8), enable
735 systemd-time-wait-sync.service(8) to delay the target; or use an
736 equivalent service for other NTP implementations.
737 Table 1. Comparison
739 ┌───────────────────────────┬────────────────────────────────┐
740 │time-set.target │ time-sync.target │
741 ├───────────────────────────┼────────────────────────────────┤
742 │"quick" to reach │ "slow" to reach │
743 ├───────────────────────────┼────────────────────────────────┤
744 │typically uses local clock │ typically uses remote │
745 │sources, boot process not │ clock sources, inserts │
746 │affected by availability │ dependencies on remote │
747 │of external resources │ resources into boot │
748 │ │ process │
749 ├───────────────────────────┼────────────────────────────────┤
750 │reliable, because local │ unreliable, because │
751 │ │ typically network involved │
752 ├───────────────────────────┼────────────────────────────────┤
753 │typically guarantees an │ typically guarantees an │
754 │approximate and roughly │ accurate clock │
755 │monotonic clock only │ │
756 ├───────────────────────────┼────────────────────────────────┤
757 │implemented by │ implemented by │
758 │systemd-timesyncd.service │ systemd-time-wait-sync.service │
759 └───────────────────────────┴────────────────────────────────┘
760 Special Slice Units
762 There are four ".slice" units which form the basis of the hierarchy for
763 assignment of resources for services, users, and virtual machines or
764 containers. See systemd.slice(7) for details about slice units.
765 -.slice
767 The root slice is the root of the slice hierarchy. It usually does
768 not contain units directly, but may be used to set defaults for the
769 whole tree.
770 system.slice
772 By default, all system services started by systemd are found in
773 this slice.
774 user.slice
776 By default, all user processes and services started on behalf of
777 the user, including the per-user systemd instance are found in this
778 slice. This is pulled in by systemd-logind.service.
779 machine.slice
781 By default, all virtual machines and containers registered with
782 systemd-machined are found in this slice. This is pulled in by
783 systemd-machined.service.
784
786 Special User Units
787 When systemd runs as a user instance, the following special units are
788 available:
789 default.target
791 This is the main target of the user session, started by default.
792 Various services that compose the normal user session should be
793 pulled into this target. In this regard, default.target is similar
794 to multi-user.target in the system instance, but it is a real unit,
795 not an alias.
796 In addition, the following units are available which have definitions
798 similar to their system counterparts: exit.target, shutdown.target,
799 sockets.target, timers.target, paths.target, bluetooth.target,
800 printer.target, smartcard.target, sound.target.
801 Special Passive User Units
803 graphical-session.target
804 This target is active whenever any graphical session is running. It
805 is used to stop user services which only apply to a graphical (X,
806 Wayland, etc.) session when the session is terminated. Such
807 services should have "PartOf=graphical-session.target" in their
808 [Unit] section. A target for a particular session (e. g.
809 gnome-session.target) starts and stops "graphical-session.target"
810 with "BindsTo=graphical-session.target".
811 Which services are started by a session target is determined by the
813 "Wants=" and "Requires=" dependencies. For services that can be
814 enabled independently, symlinks in ".wants/" and ".requires/"
815 should be used, see systemd.unit(5). Those symlinks should either
816 be shipped in packages, or should be added dynamically after
817 installation, for example using "systemctl add-wants", see
818 systemctl(1).
819 Example 1. Nautilus as part of a GNOME session
821 "gnome-session.target" pulls in Nautilus as top-level service:
822 [Unit]
824 Description=User systemd services for GNOME graphical session
825 Wants=nautilus.service
826 BindsTo=graphical-session.target
827 "nautilus.service" gets stopped when the session stops:
829 [Unit]
831 Description=Render the desktop icons with Nautilus
832 PartOf=graphical-session.target
833 [Service]
835 ...
836 graphical-session-pre.target
838 This target contains services which set up the environment or
839 global configuration of a graphical session, such as SSH/GPG agents
840 (which need to export an environment variable into all desktop
841 processes) or migration of obsolete d-conf keys after an OS upgrade
842 (which needs to happen before starting any process that might use
843 them). This target must be started before starting a graphical
844 session like gnome-session.target.
845 xdg-desktop-autostart.target
847 The XDG specification defines a way to autostart applications using
848 XDG desktop files. systemd ships systemd-xdg-autostart-generator(8)
849 for the XDG desktop files in autostart directories. Desktop
850 Environments can opt-in to use this service by adding a Wants=
851 dependency on xdg-desktop-autostart.target.
852 Special User Slice Units
854 There are four ".slice" units which form the basis of the user
855 hierarchy for assignment of resources for user applications and
856 services. See systemd.slice(7) for details about slice units and the
857 documentation about Desktop Environments[3] for further information.
858 -.slice
860 The root slice is the root of the user's slice hierarchy. It
861 usually does not contain units directly, but may be used to set
862 defaults for the whole tree.
863 app.slice
865 By default, all user services and applications managed by systemd
866 are found in this slice. All interactively launched applications
867 like web browsers and text editors as well as non-critical services
868 should be placed into this slice.
869 session.slice
871 All essential services and applications required for the session
872 should use this slice. These are services that either cannot be
873 restarted easily or where latency issues may affect the
874 interactivity of the system and applications. This includes the
875 display server, screen readers and other services such as DBus or
876 XDG portals. Such services should be configured to be part of this
877 slice by adding Slice=session.slice to their unit files.
878 background.slice
880 All services running low-priority background tasks should use this
881 slice. This permits resources to be preferentially assigned to the
882 other slices. Examples include non-interactive tasks like file
883 indexing or backup operations where latency is not important.
884
886 systemd(1), systemd.unit(5), systemd.service(5), systemd.socket(5),
887 systemd.target(5), systemd.slice(5), bootup(7), systemd-fstab-
888 generator(8), user@.service(5)
889
891 1. Running Services After the Network is up
892 https://www.freedesktop.org/wiki/Software/systemd/NetworkTarget
893 2. Syslog Interface
895 https://www.freedesktop.org/wiki/Software/systemd/syslog
896 3. Desktop Environments
898 https://systemd.io/DESKTOP_ENVIRONMENTS
899systemd 249 SYSTEMD.SPECIAL(7)