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, factory-reset.target,
13 final.target, first-boot-complete.target, getty.target,
14 getty-pre.target, graphical.target, halt.target, hibernate.target,
15 hybrid-sleep.target, suspend-then-hibernate.target, initrd.target,
16 initrd-fs.target, initrd-root-device.target, initrd-root-fs.target,
17 initrd-usr-fs.target, integritysetup-pre.target, integritysetup.target,
18 kbrequest.target, kexec.target, local-fs-pre.target, local-fs.target,
19 machines.target multi-user.target, network-online.target,
20 network-pre.target, network.target, nss-lookup.target,
21 nss-user-lookup.target, paths.target, poweroff.target, printer.target,
22 reboot.target, remote-cryptsetup.target, remote-veritysetup.target,
23 remote-fs-pre.target, remote-fs.target, rescue.target, rpcbind.target,
24 runlevel2.target, runlevel3.target, runlevel4.target, runlevel5.target,
25 shutdown.target, sigpwr.target, sleep.target, slices.target,
26 smartcard.target, sockets.target, sound.target, suspend.target,
27 swap.target, sysinit.target, system-update.target,
28 system-update-pre.target, time-set.target, time-sync.target,
29 timers.target, umount.target, usb-gadget.target, -.slice, system.slice,
30 user.slice, machine.slice, -.mount, dbus.service, dbus.socket,
31 display-manager.service, init.scope, syslog.socket,
32 system-update-cleanup.service
33
35 A few units are treated specially by systemd. Many of them have special
36 internal semantics and cannot be renamed, while others simply have a
37 standard meaning and should be present on all systems.
38
40 Special System Units
41 -.mount
42 The root mount point, i.e. the mount unit for the / path. This unit
43 is unconditionally active, during the entire time the system is up,
44 as this mount point is where the basic userspace is running from.
45 basic.target
47 A special target unit covering basic boot-up.
48 systemd automatically adds dependency of the type After= for this
50 target unit to all services (except for those with
51 DefaultDependencies=no).
52 Usually, this should pull-in all local mount points plus /var/,
54 /tmp/ and /var/tmp/, swap devices, sockets, timers, path units and
55 other basic initialization necessary for general purpose daemons.
56 The mentioned mount points are special cased to allow them to be
57 remote.
58 This target usually does not pull in any non-target units directly,
60 but rather does so indirectly via other early boot targets. It is
61 instead meant as a synchronization point for late boot services.
62 Refer to bootup(7) for details on the targets involved.
63 boot-complete.target
65 This target is intended as generic synchronization point for
66 services that shall determine or act on whether the boot process
67 completed successfully. Order units that are required to succeed
68 for a boot process to be considered successful before this unit,
69 and add a Requires= dependency from the target unit to them. Order
70 units that shall only run when the boot process is considered
71 successful after the target unit and pull in the target from it,
72 also with Requires=. Note that by default this target unit is not
73 part of the initial boot transaction, but is supposed to be pulled
74 in only if required by units that want to run only on successful
75 boots.
76 See systemd-boot-check-no-failures.service(8) for a service that
78 implements a generic system health check and orders itself before
79 boot-complete.target.
80 See systemd-bless-boot.service(8) for a service that propagates
82 boot success information to the boot loader, and orders itself
83 after boot-complete.target.
84 ctrl-alt-del.target
86 systemd starts this target whenever Control+Alt+Del is pressed on
87 the console. Usually, this should be aliased (symlinked) to
88 reboot.target.
89 cryptsetup.target
91 A target that pulls in setup services for all encrypted block
92 devices.
93 veritysetup.target
95 A target that pulls in setup services for all verity integrity
96 protected block devices.
97 dbus.service
99 A special unit for the D-Bus bus daemon. As soon as this service is
100 fully started up systemd will connect to it and register its
101 service.
102 dbus.socket
104 A special unit for the D-Bus system bus socket. All units with
105 Type=dbus automatically gain a dependency on this unit.
106 default.target
108 The default unit systemd starts at bootup. Usually, this should be
109 aliased (symlinked) to multi-user.target or graphical.target. See
110 bootup(7) for more discussion.
111 The default unit systemd starts at bootup can be overridden with
113 the systemd.unit= kernel command line option, or more conveniently,
114 with the short names like single, rescue, 1, 3, 5, ...; see
115 systemd(1).
116 display-manager.service
118 The display manager service. Usually, this should be aliased
119 (symlinked) to gdm.service or a similar display manager service.
120 emergency.target
122 A special target unit that starts an emergency shell on the main
123 console. This target does not pull in other services or mounts. It
124 is the most minimal version of starting the system in order to
125 acquire an interactive shell; the only processes running are
126 usually just the system manager (PID 1) and the shell process. This
127 unit may be used by specifying emergency on the kernel command
128 line; it is also used when a file system check on a required file
129 system fails and boot-up cannot continue. Compare with
130 rescue.target, which serves a similar purpose, but also starts the
131 most basic services and mounts all file systems.
132 In many ways booting into emergency.target is similar to the effect
134 of booting with "init=/bin/sh" on the kernel command line, except
135 that emergency mode provides you with the full system and service
136 manager, and allows starting individual units in order to continue
137 the boot process in steps.
138 Note that depending on how emergency.target is reached, the root
140 file system might be mounted read-only or read-write (no remounting
141 is done specially for this target). For example, the system may
142 boot with root mounted read-only when ro is used on the kernel
143 command line and remain this way for emergency.target, or the
144 system may transition to emergency.target after the system has been
145 partially booted and disks have already been remounted read-write.
146 exit.target
148 A special service unit for shutting down the system or user service
149 manager. It is equivalent to poweroff.target on non-container
150 systems, and also works in containers.
151 systemd will start this unit when it receives the SIGTERM or SIGINT
153 signal when running as user service daemon.
154 Normally, this (indirectly) pulls in shutdown.target, which in turn
156 should be conflicted by all units that want to be scheduled for
157 shutdown when the service manager starts to exit.
158 factory-reset.target
160 A special target to trigger a factory reset.
161 final.target
163 A special target unit that is used during the shutdown logic and
164 may be used to pull in late services after all normal services are
165 already terminated and all mounts unmounted.
166 getty.target
168 A special target unit that pulls in statically configured local TTY
169 getty instances.
170 graphical.target
172 A special target unit for setting up a graphical login screen. This
173 pulls in multi-user.target.
174 Units that are needed for graphical logins shall add Wants=
176 dependencies for their unit to this unit (or multi-user.target)
177 during installation. This is best configured via
178 WantedBy=graphical.target in the unit's [Install] section.
179 hibernate.target
181 A special target unit for hibernating the system. This pulls in
182 sleep.target.
183 hybrid-sleep.target
185 A special target unit for hibernating and suspending the system at
186 the same time. This pulls in sleep.target.
187 suspend-then-hibernate.target
189 A special target unit for suspending the system for a period of
190 time, waking it and putting it into hibernate. This pulls in
191 sleep.target.
192 halt.target
194 A special target unit for shutting down and halting the system.
195 Note that this target is distinct from poweroff.target in that it
196 generally really just halts the system rather than powering it
197 down.
198 Applications wanting to halt the system should not start this unit
200 directly, but should instead execute systemctl halt (possibly with
201 the --no-block option) or call systemd(1)'s
202 org.freedesktop.systemd1.Manager.Halt D-Bus method directly.
203 init.scope
205 This scope unit is where the system and service manager (PID 1)
206 itself resides. It is active as long as the system is running.
207 initrd.target
209 This is the default target in the initramfs, similar to
210 default.target in the main system. It is used to mount the real
211 root and transition to it. See bootup(7) for more discussion.
212 initrd-fs.target
214 systemd-fstab-generator(3) automatically adds dependencies of type
215 Before= to sysroot-usr.mount and all mount points found in
216 /etc/fstab that have the x-initrd.mount mount option set and do not
217 have the noauto mount option set. It is also indirectly ordered
218 after sysroot.mount. Thus, once this target is reached the
219 /sysroot/ hierarchy is fully set up, in preparation for the
220 transition to the host OS.
221 initrd-root-device.target
223 A special initrd target unit that is reached when the root
224 filesystem device is available, but before it has been mounted.
225 systemd-fstab-generator(3) and systemd-gpt-auto-generator(3)
226 automatically setup the appropriate dependencies to make this
227 happen.
228 initrd-root-fs.target
230 systemd-fstab-generator(3) automatically adds dependencies of type
231 Before= to the sysroot.mount unit, which is generated from the
232 kernel command line's root= setting (or equivalent).
233 initrd-usr-fs.target
235 systemd-fstab-generator(3) automatically adds dependencies of type
236 Before= to the sysusr-usr.mount unit, which is generated from the
237 kernel command line's usr= switch. Services may order themselves
238 after this target unit in order to run once the /sysusr/ hierarchy
239 becomes available, on systems that come up initially without a root
240 file system, but with an initialized /usr/ and need to access that
241 before setting up the root file system to ultimately switch to. On
242 systems where usr= is not used this target is ordered after
243 sysroot.mount and thus mostly equivalent to initrd-root-fs.target.
244 In effect on any system once this target is reached the file system
245 backing /usr/ is mounted, though possibly at two different
246 locations, either below the /sysusr/ or the /sysroot/ hierarchies.
247 kbrequest.target
249 systemd starts this target whenever Alt+ArrowUp is pressed on the
250 console. Note that any user with physical access to the machine
251 will be able to do this, without authentication, so this should be
252 used carefully.
253 kexec.target
255 A special target unit for shutting down and rebooting the system
256 via kexec.
257 Applications wanting to reboot the system should not start this
259 unit directly, but should instead execute systemctl kexec (possibly
260 with the --no-block option) or call systemd(1)'s
261 org.freedesktop.systemd1.Manager.KExec D-Bus method directly.
262 local-fs.target
264 systemd-fstab-generator(3) automatically adds dependencies of type
265 Before= to all mount units that refer to local mount points for
266 this target unit. In addition, it adds dependencies of type Wants=
267 to this target unit for those mounts listed in /etc/fstab that have
268 the auto mount option set.
269 machines.target
271 A standard target unit for starting all the containers and other
272 virtual machines. See systemd-nspawn@.service for an example.
273 multi-user.target
275 A special target unit for setting up a multi-user system
276 (non-graphical). This is pulled in by graphical.target.
277 Units that are needed for a multi-user system shall add Wants=
279 dependencies for their unit to this unit during installation. This
280 is best configured via WantedBy=multi-user.target in the unit's
281 [Install] section.
282 network-online.target
284 Units that strictly require a configured network connection should
285 pull in network-online.target (via a Wants= type dependency) and
286 order themselves after it. This target unit is intended to pull in
287 a service that delays further execution until the network is
288 sufficiently set up. What precisely this requires is left to the
289 implementation of the network managing service.
290 Note the distinction between this unit and network.target. This
292 unit is an active unit (i.e. pulled in by the consumer rather than
293 the provider of this functionality) and pulls in a service which
294 possibly adds substantial delays to further execution. In contrast,
295 network.target is a passive unit (i.e. pulled in by the provider of
296 the functionality, rather than the consumer) that usually does not
297 delay execution much. Usually, network.target is part of the boot
298 of most systems, while network-online.target is not, except when at
299 least one unit requires it. Also see Running Services After the
300 Network is up[1] for more information.
301 All mount units for remote network file systems automatically pull
303 in this unit, and order themselves after it. Note that networking
304 daemons that simply provide functionality to other hosts (as
305 opposed to consume functionality of other hosts) generally do not
306 need to pull this in.
307 systemd automatically adds dependencies of type Wants= and After=
309 for this target unit to all SysV init script service units with an
310 LSB header referring to the "$network" facility.
311 Note that this unit is only useful during the original system
313 start-up logic. After the system has completed booting up, it will
314 not track the online state of the system anymore. Due to this it
315 cannot be used as a network connection monitor concept, it is
316 purely a one-time system start-up concept.
317 paths.target
319 A special target unit that sets up all path units (see
320 systemd.path(5) for details) that shall be active after boot.
321 It is recommended that path units installed by applications get
323 pulled in via Wants= dependencies from this unit. This is best
324 configured via a WantedBy=paths.target in the path unit's [Install]
325 section.
326 poweroff.target
328 A special target unit for shutting down and powering off the
329 system.
330 Applications wanting to power off the system should not start this
332 unit directly, but should instead execute systemctl poweroff
333 (possibly with the --no-block option) or call systemd-logind(8)'s
334 org.freedesktop.login1.Manager.PowerOff D-Bus method directly.
335 runlevel0.target is an alias for this target unit, for
337 compatibility with SysV.
338 reboot.target
340 A special target unit for shutting down and rebooting the system.
341 Applications wanting to reboot the system should not start this
343 unit directly, but should instead execute systemctl reboot
344 (possibly with the --no-block option) or call systemd-logind(8)'s
345 org.freedesktop.login1.Manager.Reboot D-Bus method directly.
346 runlevel6.target is an alias for this target unit, for
348 compatibility with SysV.
349 remote-cryptsetup.target
351 Similar to cryptsetup.target, but for encrypted devices which are
352 accessed over the network. It is used for crypttab(8) entries
353 marked with _netdev.
354 remote-veritysetup.target
356 Similar to veritysetup.target, but for verity integrity protected
357 devices which are accessed over the network. It is used for
358 veritytab(8) entries marked with _netdev.
359 remote-fs.target
361 Similar to local-fs.target, but for remote mount points.
362 systemd automatically adds dependencies of type After= for this
364 target unit to all SysV init script service units with an LSB
365 header referring to the "$remote_fs" facility.
366 rescue.target
368 A special target unit that pulls in the base system (including
369 system mounts) and spawns a rescue shell. Isolate to this target in
370 order to administer the system in single-user mode with all file
371 systems mounted but with no services running, except for the most
372 basic. Compare with emergency.target, which is much more reduced
373 and does not provide the file systems or most basic services.
374 Compare with multi-user.target, this target could be seen as
375 single-user.target.
376 runlevel1.target is an alias for this target unit, for
378 compatibility with SysV.
379 Use the "systemd.unit=rescue.target" kernel command line option to
381 boot into this mode. A short alias for this kernel command line
382 option is "1", for compatibility with SysV.
383 runlevel2.target, runlevel3.target, runlevel4.target, runlevel5.target
385 These are targets that are called whenever the SysV compatibility
386 code asks for runlevel 2, 3, 4, 5, respectively. It is a good idea
387 to make this an alias for (i.e. symlink to) graphical.target (for
388 runlevel 5) or multi-user.target (the others).
389 shutdown.target
391 A special target unit that terminates the services on system
392 shutdown.
393 Services that shall be terminated on system shutdown shall add
395 Conflicts= and Before= dependencies to this unit for their service
396 unit, which is implicitly done when DefaultDependencies=yes is set
397 (the default).
398 sigpwr.target
400 A special target that is started when systemd receives the SIGPWR
401 process signal, which is normally sent by the kernel or UPS daemons
402 when power fails.
403 sleep.target
405 A special target unit that is pulled in by suspend.target,
406 hibernate.target and hybrid-sleep.target and may be used to hook
407 units into the sleep state logic.
408 slices.target
410 A special target unit that sets up all slice units (see
411 systemd.slice(5) for details) that shall always be active after
412 boot. By default the generic system.slice slice unit as well as the
413 root slice unit -.slice are pulled in and ordered before this unit
414 (see below).
415 Adding slice units to slices.target is generally not necessary.
417 Instead, when some unit that uses Slice= is started, the specified
418 slice will be started automatically. Adding WantedBy=slices.target
419 lines to the [Install] section should only be done for units that
420 need to be always active. In that case care needs to be taken to
421 avoid creating a loop through the automatic dependencies on
422 "parent" slices.
423 sockets.target
425 A special target unit that sets up all socket units (see
426 systemd.socket(5) for details) that shall be active after boot.
427 Services that can be socket-activated shall add Wants= dependencies
429 to this unit for their socket unit during installation. This is
430 best configured via a WantedBy=sockets.target in the socket unit's
431 [Install] section.
432 suspend.target
434 A special target unit for suspending the system. This pulls in
435 sleep.target.
436 swap.target
438 Similar to local-fs.target, but for swap partitions and swap files.
439 sysinit.target
441 systemd automatically adds dependencies of the types Requires= and
442 After= for this target unit to all services (except for those with
443 DefaultDependencies=no).
444 This target pulls in the services required for system
446 initialization. System services pulled in by this target should
447 declare DefaultDependencies=no and specify all their dependencies
448 manually, including access to anything more than a read only root
449 filesystem. For details on the dependencies of this target, refer
450 to bootup(7).
451 syslog.socket
453 The socket unit syslog implementations should listen on. All
454 userspace log messages will be made available on this socket. For
455 more information about syslog integration, please consult the
456 Syslog Interface[2] document.
457 system-update.target, system-update-pre.target,
459 system-update-cleanup.service
460 A special target unit that is used for offline system updates.
461 systemd-system-update-generator(8) will redirect the boot process
462 to this target if /system-update exists. For more information see
463 systemd.offline-updates(7).
464 Updates should happen before the system-update.target is reached,
466 and the services which implement them should cause the machine to
467 reboot. The main units executing the update should order themselves
468 after system-update-pre.target but not pull it in. Services which
469 want to run during system updates only, but before the actual
470 system update is executed should order themselves before this unit
471 and pull it in. As a safety measure, if this does not happen, and
472 /system-update still exists after system-update.target is reached,
473 system-update-cleanup.service will remove this symlink and reboot
474 the machine.
475 timers.target
477 A special target unit that sets up all timer units (see
478 systemd.timer(5) for details) that shall be active after boot.
479 It is recommended that timer units installed by applications get
481 pulled in via Wants= dependencies from this unit. This is best
482 configured via WantedBy=timers.target in the timer unit's [Install]
483 section.
484 umount.target
486 A special target unit that unmounts all mount and automount points
487 on system shutdown.
488 Mounts that shall be unmounted on system shutdown shall add
490 Conflicts dependencies to this unit for their mount unit, which is
491 implicitly done when DefaultDependencies=yes is set (the default).
492 Special System Units for Devices
494 Some target units are automatically pulled in as devices of certain
495 kinds show up in the system. These may be used to automatically
496 activate various services based on the specific type of the available
497 hardware.
498 bluetooth.target
500 This target is started automatically as soon as a Bluetooth
501 controller is plugged in or becomes available at boot.
502 This may be used to pull in Bluetooth management daemons
504 dynamically when Bluetooth hardware is found.
505 printer.target
507 This target is started automatically as soon as a printer is
508 plugged in or becomes available at boot.
509 This may be used to pull in printer management daemons dynamically
511 when printer hardware is found.
512 smartcard.target
514 This target is started automatically as soon as a smartcard
515 controller is plugged in or becomes available at boot.
516 This may be used to pull in smartcard management daemons
518 dynamically when smartcard hardware is found.
519 sound.target
521 This target is started automatically as soon as a sound card is
522 plugged in or becomes available at boot.
523 This may be used to pull in audio management daemons dynamically
525 when audio hardware is found.
526 usb-gadget.target
528 This target is started automatically as soon as a USB Device
529 Controller becomes available at boot.
530 This may be used to pull in usb gadget dynamically when UDC
532 hardware is found.
533 Special Passive System Units
535 A number of special system targets are defined that can be used to
536 properly order boot-up of optional services. These targets are
537 generally not part of the initial boot transaction, unless they are
538 explicitly pulled in by one of the implementing services. Note
539 specifically that these passive target units are generally not pulled
540 in by the consumer of a service, but by the provider of the service.
541 This means: a consuming service should order itself after these targets
542 (as appropriate), but not pull it in. A providing service should order
543 itself before these targets (as appropriate) and pull it in (via a
544 Wants= type dependency).
545 Note that these passive units cannot be started manually, i.e.
547 "systemctl start time-sync.target" will fail with an error. They can
548 only be pulled in by dependency. This is enforced since they exist for
549 ordering purposes only and thus are not useful as only unit within a
550 transaction.
551 blockdev@.target
553 This template unit is used to order mount units and other consumers
554 of block devices after services that synthesize these block
555 devices. In particular, this is intended to be used with storage
556 services (such as systemd-cryptsetup@.service(5)/ systemd-
557 veritysetup@.service(5)) that allocate and manage a virtual block
558 device. Storage services are ordered before an instance of
559 blockdev@.target, and the consumer units after it. The ordering is
560 particularly relevant during shutdown, as it ensures that the mount
561 is deactivated first and the service backing the mount later. The
562 blockdev@.target instance should be pulled in via a Wants=
563 dependency of the storage daemon and thus generally not be part of
564 any transaction unless a storage daemon is used. The instance name
565 for instances of this template unit must be a properly escaped
566 block device node path, e.g. blockdev@dev-mapper-foobar.target for
567 the storage device /dev/mapper/foobar.
568 cryptsetup-pre.target
570 This passive target unit may be pulled in by services that want to
571 run before any encrypted block device is set up. All encrypted
572 block devices are set up after this target has been reached. Since
573 the shutdown order is implicitly the reverse start-up order between
574 units, this target is particularly useful to ensure that a service
575 is shut down only after all encrypted block devices are fully
576 stopped.
577 veritysetup-pre.target
579 This passive target unit may be pulled in by services that want to
580 run before any verity integrity protected block device is set up.
581 All verity integrity protected block devices are set up after this
582 target has been reached. Since the shutdown order is implicitly the
583 reverse start-up order between units, this target is particularly
584 useful to ensure that a service is shut down only after all verity
585 integrity protected block devices are fully stopped.
586 first-boot-complete.target
588 This passive target is intended as a synchronization point for
589 units that need to run once during the first boot. Only after all
590 units ordered before this target have finished, will the machine-
591 id(5) be committed to disk, marking the first boot as completed. If
592 the boot is aborted at any time before that, the next boot will
593 re-run any units with ConditionFirstBoot=yes.
594 getty-pre.target
596 A special passive target unit. Users of this target are expected to
597 pull it in the boot transaction via a dependency (e.g. Wants=).
598 Order your unit before this unit if you want to make use of the
599 console just before getty is started.
600 local-fs-pre.target
602 This target unit is automatically ordered before all local mount
603 points marked with auto (see above). It can be used to execute
604 certain units before all local mounts.
605 network.target
607 This unit is supposed to indicate when network functionality is
608 available, but it is only very weakly defined what that is supposed
609 to mean. However, the following should apply at minimum:
610 • At start-up, any configured synthetic network devices (i.e. not
612 physical ones that require hardware to show up and be probed,
613 but virtual ones like bridge devices and similar which are
614 created programmatically) that do not depend on any underlying
615 hardware should be allocated by the time this target is
616 reached. It is not necessary for these interfaces to also have
617 completed IP level configuration by the time network.target is
618 reached.
619 • At shutdown, a unit that is ordered after network.target will
621 be stopped before the network — to whatever level it might be
622 set up by then — is shut down. It is hence useful when writing
623 service files that require network access on shutdown, which
624 should order themselves after this target, but not pull it in.
625 Also see Running Services After the Network is up[1] for more
626 information.
627 It must emphasized that at start-up there's no guarantee that
629 hardware-based devices have shown up by the time this target is
630 reached, or even acquired complete IP configuration. For that
631 purpose use network-online.target as described above.
632 network-pre.target
634 This passive target unit may be pulled in by services that want to
635 run before any network is set up, for example for the purpose of
636 setting up a firewall. All network management software orders
637 itself after this target, but does not pull it in.
638 nss-lookup.target
640 A target that should be used as synchronization point for all
641 host/network name service lookups. Note that this is independent of
642 UNIX user/group name lookups for which nss-user-lookup.target
643 should be used. All services for which the availability of full
644 host/network name resolution is essential should be ordered after
645 this target, but not pull it in. systemd automatically adds
646 dependencies of type After= for this target unit to all SysV init
647 script service units with an LSB header referring to the "$named"
648 facility.
649 nss-user-lookup.target
651 A target that should be used as synchronization point for all
652 regular UNIX user/group name service lookups. Note that this is
653 independent of host/network name lookups for which
654 nss-lookup.target should be used. All services for which the
655 availability of the full user/group database is essential should be
656 ordered after this target, but not pull it in. All services which
657 provide parts of the user/group database should be ordered before
658 this target, and pull it in. Note that this unit is only relevant
659 for regular users and groups — system users and groups are required
660 to be resolvable during earliest boot already, and hence do not
661 need any special ordering against this target.
662 remote-fs-pre.target
664 This target unit is automatically ordered before all mount point
665 units (see above) and cryptsetup/veritysetup devices marked with
666 the _netdev. It can be used to run certain units before remote
667 encrypted devices and mounts are established. Note that this unit
668 is generally not part of the initial transaction, unless the unit
669 that wants to be ordered before all remote mounts pulls it in via a
670 Wants= type dependency. If the unit wants to be pulled in by the
671 first remote mount showing up, it should use network-online.target
672 (see above).
673 rpcbind.target
675 The portmapper/rpcbind pulls in this target and orders itself
676 before it, to indicate its availability. systemd automatically adds
677 dependencies of type After= for this target unit to all SysV init
678 script service units with an LSB header referring to the "$portmap"
679 facility.
680 time-set.target
682 Services responsible for setting the system clock (CLOCK_REALTIME)
683 from a local source (such as a maintained timestamp file or
684 imprecise real-time clock) should pull in this target and order
685 themselves before it. Services where approximate, roughly monotonic
686 time is desired should be ordered after this unit, but not pull it
687 in.
688 This target does not provide the accuracy guarantees of
690 time-sync.target (see below), however does not depend on remote
691 clock sources to be reachable, i.e. the target is typically not
692 delayed by network problems and similar. Use of this target is
693 recommended for services where approximate clock accuracy and rough
694 monotonicity is desired but activation shall not be delayed for
695 possibly unreliable network communication.
696 The service manager automatically adds dependencies of type After=
698 for this target unit to all timer units with at least one
699 OnCalendar= directive.
700 The systemd-timesyncd.service(8) service is a simple daemon that
702 pulls in this target and orders itself before it. Besides
703 implementing the SNTP network protocol it maintains a timestamp
704 file on disk whose modification time is regularlary updated. At
705 service start-up the local system clock is set from that
706 modification time, ensuring it increases roughly monotonically.
707 Note that ordering a unit after time-set.target only has effect if
709 there's actually a service ordered before it that delays it until
710 the clock is adjusted for rough monotonicity. Otherwise, this
711 target might get reached before the clock is adjusted to be roughly
712 monotonic. Enable systemd-timesyncd.service(8), or an alternative
713 NTP implementation to delay the target.
714 time-sync.target
716 Services indicating completed synchronization of the system clock
717 (CLOCK_REALTIME) to a remote source should pull in this target and
718 order themselves before it. Services where accurate time is
719 essential should be ordered after this unit, but not pull it in.
720 The service manager automatically adds dependencies of type After=
722 for this target unit to all SysV init script service units with an
723 LSB header referring to the "$time" facility, as well to all timer
724 units with at least one OnCalendar= directive.
725 This target provides stricter clock accuracy guarantees than
727 time-set.target (see above), but likely requires network
728 communication and thus introduces unpredictable delays. Services
729 that require clock accuracy and where network communication delays
730 are acceptable should use this target. Services that require a less
731 accurate clock, and only approximate and roughly monotonic clock
732 behaviour should use time-set.target instead.
733 Note that ordering a unit after time-sync.target only has effect if
735 there's actually a service ordered before it that delays it until
736 clock synchronization is reached. Otherwise, this target might get
737 reached before the clock is synchronized to any remote accurate
738 reference clock. When using systemd-timesyncd.service(8), enable
739 systemd-time-wait-sync.service(8) to delay the target; or use an
740 equivalent service for other NTP implementations.
741 Table 1. Comparison
743 ┌───────────────────────────┬────────────────────────────────┐
744 │time-set.target │ time-sync.target │
745 ├───────────────────────────┼────────────────────────────────┤
746 │"quick" to reach │ "slow" to reach │
747 ├───────────────────────────┼────────────────────────────────┤
748 │typically uses local clock │ typically uses remote │
749 │sources, boot process not │ clock sources, inserts │
750 │affected by availability │ dependencies on remote │
751 │of external resources │ resources into boot │
752 │ │ process │
753 ├───────────────────────────┼────────────────────────────────┤
754 │reliable, because local │ unreliable, because │
755 │ │ typically network involved │
756 ├───────────────────────────┼────────────────────────────────┤
757 │typically guarantees an │ typically guarantees an │
758 │approximate and roughly │ accurate clock │
759 │monotonic clock only │ │
760 ├───────────────────────────┼────────────────────────────────┤
761 │implemented by │ implemented by │
762 │systemd-timesyncd.service │ systemd-time-wait-sync.service │
763 └───────────────────────────┴────────────────────────────────┘
764 Special Slice Units
766 There are four ".slice" units which form the basis of the hierarchy for
767 assignment of resources for services, users, and virtual machines or
768 containers. See systemd.slice(7) for details about slice units.
769 -.slice
771 The root slice is the root of the slice hierarchy. It usually does
772 not contain units directly, but may be used to set defaults for the
773 whole tree.
774 system.slice
776 By default, all system services started by systemd are found in
777 this slice.
778 user.slice
780 By default, all user processes and services started on behalf of
781 the user, including the per-user systemd instance are found in this
782 slice. This is pulled in by systemd-logind.service.
783 machine.slice
785 By default, all virtual machines and containers registered with
786 systemd-machined are found in this slice. This is pulled in by
787 systemd-machined.service.
788
790 Special User Units
791 When systemd runs as a user instance, the following special units are
792 available:
793 default.target
795 This is the main target of the user session, started by default.
796 Various services that compose the normal user session should be
797 pulled into this target. In this regard, default.target is similar
798 to multi-user.target in the system instance, but it is a real unit,
799 not an alias.
800 In addition, the following units are available which have definitions
802 similar to their system counterparts: exit.target, shutdown.target,
803 sockets.target, timers.target, paths.target, bluetooth.target,
804 printer.target, smartcard.target, sound.target.
805 Special Passive User Units
807 graphical-session.target
808 This target is active whenever any graphical session is running. It
809 is used to stop user services which only apply to a graphical (X,
810 Wayland, etc.) session when the session is terminated. Such
811 services should have "PartOf=graphical-session.target" in their
812 [Unit] section. A target for a particular session (e. g.
813 gnome-session.target) starts and stops "graphical-session.target"
814 with "BindsTo=graphical-session.target".
815 Which services are started by a session target is determined by the
817 "Wants=" and "Requires=" dependencies. For services that can be
818 enabled independently, symlinks in ".wants/" and ".requires/"
819 should be used, see systemd.unit(5). Those symlinks should either
820 be shipped in packages, or should be added dynamically after
821 installation, for example using "systemctl add-wants", see
822 systemctl(1).
823 Example 1. Nautilus as part of a GNOME session
825 "gnome-session.target" pulls in Nautilus as top-level service:
826 [Unit]
828 Description=User systemd services for GNOME graphical session
829 Wants=nautilus.service
830 BindsTo=graphical-session.target
831 "nautilus.service" gets stopped when the session stops:
833 [Unit]
835 Description=Render the desktop icons with Nautilus
836 PartOf=graphical-session.target
837 [Service]
839 ...
840 graphical-session-pre.target
842 This target contains services which set up the environment or
843 global configuration of a graphical session, such as SSH/GPG agents
844 (which need to export an environment variable into all desktop
845 processes) or migration of obsolete d-conf keys after an OS upgrade
846 (which needs to happen before starting any process that might use
847 them). This target must be started before starting a graphical
848 session like gnome-session.target.
849 xdg-desktop-autostart.target
851 The XDG specification defines a way to autostart applications using
852 XDG desktop files. systemd ships systemd-xdg-autostart-generator(8)
853 for the XDG desktop files in autostart directories. Desktop
854 Environments can opt-in to use this service by adding a Wants=
855 dependency on xdg-desktop-autostart.target.
856 Special User Slice Units
858 There are four ".slice" units which form the basis of the user
859 hierarchy for assignment of resources for user applications and
860 services. See systemd.slice(7) for details about slice units and the
861 documentation about Desktop Environments[3] for further information.
862 -.slice
864 The root slice is the root of the user's slice hierarchy. It
865 usually does not contain units directly, but may be used to set
866 defaults for the whole tree.
867 app.slice
869 By default, all user services and applications managed by systemd
870 are found in this slice. All interactively launched applications
871 like web browsers and text editors as well as non-critical services
872 should be placed into this slice.
873 session.slice
875 All essential services and applications required for the session
876 should use this slice. These are services that either cannot be
877 restarted easily or where latency issues may affect the
878 interactivity of the system and applications. This includes the
879 display server, screen readers and other services such as DBus or
880 XDG portals. Such services should be configured to be part of this
881 slice by adding Slice=session.slice to their unit files.
882 background.slice
884 All services running low-priority background tasks should use this
885 slice. This permits resources to be preferentially assigned to the
886 other slices. Examples include non-interactive tasks like file
887 indexing or backup operations where latency is not important.
888
890 systemd(1), systemd.unit(5), systemd.service(5), systemd.socket(5),
891 systemd.target(5), systemd.slice(5), bootup(7), systemd-fstab-
892 generator(8), user@.service(5)
893
895 1. Running Services After the Network is up
896 https://www.freedesktop.org/wiki/Software/systemd/NetworkTarget
897 2. Syslog Interface
899 https://www.freedesktop.org/wiki/Software/systemd/syslog
900 3. Desktop Environments
902 https://systemd.io/DESKTOP_ENVIRONMENTS
903systemd 251 SYSTEMD.SPECIAL(7)