systemd.special(7) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | UNITS MANAGED BY THE SYSTEM SERVICE MANAGER | UNITS MANAGED BY THE USER SERVICE MANAGER | SEE ALSO | NOTES | COLOPHON

SYSTEMD.SPECIAL(7)           systemd.special          SYSTEMD.SPECIAL(7)

NAME         top

       systemd.special - Special systemd units

SYNOPSIS         top

       basic.target, bluetooth.target, cryptsetup-pre.target,
       cryptsetup.target, veritysetup-pre.target, veritysetup.target,
       ctrl-alt-del.target, blockdev@.target, boot-complete.target,
       default.target, emergency.target, exit.target, final.target,
       first-boot-complete.target, getty.target, getty-pre.target,
       graphical.target, halt.target, hibernate.target,
       hybrid-sleep.target, suspend-then-hibernate.target,
       initrd.target, initrd-fs.target, initrd-root-device.target,
       initrd-root-fs.target, kbrequest.target, kexec.target,
       local-fs-pre.target, local-fs.target, machines.target
       multi-user.target, network-online.target, network-pre.target,
       network.target, nss-lookup.target, nss-user-lookup.target,
       paths.target, poweroff.target, printer.target, reboot.target,
       remote-cryptsetup.target, remote-veritysetup.target,
       remote-fs-pre.target, remote-fs.target, rescue.target,
       rpcbind.target, runlevel2.target, runlevel3.target,
       runlevel4.target, runlevel5.target, shutdown.target,
       sigpwr.target, sleep.target, slices.target, smartcard.target,
       sockets.target, sound.target, suspend.target, swap.target,
       sysinit.target, system-update.target, system-update-pre.target,
       time-set.target, time-sync.target, timers.target, umount.target,
       usb-gadget.target, -.slice, system.slice, user.slice,
       machine.slice, -.mount, dbus.service, dbus.socket,
       display-manager.service, init.scope, syslog.socket,
       system-update-cleanup.service

DESCRIPTION         top

       A few units are treated specially by systemd. Many of them have
       special internal semantics and cannot be renamed, while others
       simply have a standard meaning and should be present on all
       systems.

UNITS MANAGED BY THE SYSTEM SERVICE MANAGER         top

   Special System Units
       -.mount
           The root mount point, i.e. the mount unit for the / path.
           This unit is unconditionally active, during the entire time
           the system is up, as this mount point is where the basic
           userspace is running from.

       basic.target
           A special target unit covering basic boot-up.

           systemd automatically adds dependency of the type After= for
           this target unit to all services (except for those with
           DefaultDependencies=no).

           Usually, this should pull-in all local mount points plus
           /var/, /tmp/ and /var/tmp/, swap devices, sockets, timers,
           path units and other basic initialization necessary for
           general purpose daemons. The mentioned mount points are
           special cased to allow them to be remote.

           This target usually does not pull in any non-target units
           directly, but rather does so indirectly via other early boot
           targets. It is instead meant as a synchronization point for
           late boot services. Refer to bootup(7) for details on the
           targets involved.

       boot-complete.target
           This target is intended as generic synchronization point for
           services that shall determine or act on whether the boot
           process completed successfully. Order units that are required
           to succeed for a boot process to be considered successful
           before this unit, and add a Requires= dependency from the
           target unit to them. Order units that shall only run when the
           boot process is considered successful after the target unit
           and pull in the target from it, also with Requires=. Note
           that by default this target unit is not part of the initial
           boot transaction, but is supposed to be pulled in only if
           required by units that want to run only on successful boots.

           See systemd-boot-check-no-failures.service(8) for a service
           that implements a generic system health check and orders
           itself before boot-complete.target.

           See systemd-bless-boot.service(8) for a service that
           propagates boot success information to the boot loader, and
           orders itself after boot-complete.target.

       ctrl-alt-del.target
           systemd starts this target whenever Control+Alt+Del is
           pressed on the console. Usually, this should be aliased
           (symlinked) to reboot.target.

       cryptsetup.target
           A target that pulls in setup services for all encrypted block
           devices.

       veritysetup.target
           A target that pulls in setup services for all verity
           integrity protected block devices.

       dbus.service
           A special unit for the D-Bus bus daemon. As soon as this
           service is fully started up systemd will connect to it and
           register its service.

       dbus.socket
           A special unit for the D-Bus system bus socket. All units
           with Type=dbus automatically gain a dependency on this unit.

       default.target
           The default unit systemd starts at bootup. Usually, this
           should be aliased (symlinked) to multi-user.target or
           graphical.target. See bootup(7) for more discussion.

           The default unit systemd starts at bootup can be overridden
           with the systemd.unit= kernel command line option, or more
           conveniently, with the short names like single, rescue, 1, 3,
           5, ...; see systemd(1).

       display-manager.service
           The display manager service. Usually, this should be aliased
           (symlinked) to gdm.service or a similar display manager
           service.

       emergency.target
           A special target unit that starts an emergency shell on the
           main console. This target does not pull in other services or
           mounts. It is the most minimal version of starting the system
           in order to acquire an interactive shell; the only processes
           running are usually just the system manager (PID 1) and the
           shell process. This unit may be used by specifying emergency
           on the kernel command line; it is also used when a file
           system check on a required file system fails and boot-up
           cannot continue. Compare with rescue.target, which serves a
           similar purpose, but also starts the most basic services and
           mounts all file systems.

           In many ways booting into emergency.target is similar to the
           effect of booting with "init=/bin/sh" on the kernel command
           line, except that emergency mode provides you with the full
           system and service manager, and allows starting individual
           units in order to continue the boot process in steps.

           Note that depending on how emergency.target is reached, the
           root file system might be mounted read-only or read-write (no
           remounting is done specially for this target). For example,
           the system may boot with root mounted read-only when ro is
           used on the kernel command line and remain this way for
           emergency.target, or the system may transition to
           emergency.target after the system has been partially booted
           and disks have already been remounted read-write.

       exit.target
           A special service unit for shutting down the system or user
           service manager. It is equivalent to poweroff.target on
           non-container systems, and also works in containers.

           systemd will start this unit when it receives the SIGTERM or
           SIGINT signal when running as user service daemon.

           Normally, this (indirectly) pulls in shutdown.target, which
           in turn should be conflicted by all units that want to be
           scheduled for shutdown when the service manager starts to
           exit.

       final.target
           A special target unit that is used during the shutdown logic
           and may be used to pull in late services after all normal
           services are already terminated and all mounts unmounted.

       getty.target
           A special target unit that pulls in statically configured
           local TTY getty instances.

       graphical.target
           A special target unit for setting up a graphical login
           screen. This pulls in multi-user.target.

           Units that are needed for graphical logins shall add Wants=
           dependencies for their unit to this unit (or
           multi-user.target) during installation. This is best
           configured via WantedBy=graphical.target in the unit's
           [Install] section.

       hibernate.target
           A special target unit for hibernating the system. This pulls
           in sleep.target.

       hybrid-sleep.target
           A special target unit for hibernating and suspending the
           system at the same time. This pulls in sleep.target.

       suspend-then-hibernate.target
           A special target unit for suspending the system for a period
           of time, waking it and putting it into hibernate. This pulls
           in sleep.target.

       halt.target
           A special target unit for shutting down and halting the
           system. Note that this target is distinct from
           poweroff.target in that it generally really just halts the
           system rather than powering it down.

           Applications wanting to halt the system should not start this
           unit directly, but should instead execute systemctl halt
           (possibly with the --no-block option) or call systemd(1)'s
           org.freedesktop.systemd1.Manager.Halt D-Bus method directly.

       init.scope
           This scope unit is where the system and service manager (PID
           1) itself resides. It is active as long as the system is
           running.

       initrd.target
           This is the default target in the initramfs, similar to
           default.target in the main system. It is used to mount the
           real root and transition to it. See bootup(7) for more
           discussion.

       initrd-fs.target
           systemd-fstab-generator(3) automatically adds dependencies of
           type Before= to sysroot-usr.mount and all mount points found
           in /etc/fstab that have x-initrd.mount and not have noauto
           mount options set.

       initrd-root-device.target
           A special initrd target unit that is reached when the root
           filesystem device is available, but before it has been
           mounted.  systemd-fstab-generator(3) and
           systemd-gpt-auto-generator(3) automatically setup the
           appropriate dependencies to make this happen.

       initrd-root-fs.target
           systemd-fstab-generator(3) automatically adds dependencies of
           type Before= to the sysroot.mount unit, which is generated
           from the kernel command line.

       kbrequest.target
           systemd starts this target whenever Alt+ArrowUp is pressed on
           the console. Note that any user with physical access to the
           machine will be able to do this, without authentication, so
           this should be used carefully.

       kexec.target
           A special target unit for shutting down and rebooting the
           system via kexec.

           Applications wanting to reboot the system should not start
           this unit directly, but should instead execute systemctl
           kexec (possibly with the --no-block option) or call
           systemd(1)'s org.freedesktop.systemd1.Manager.KExec D-Bus
           method directly.

       local-fs.target
           systemd-fstab-generator(3) automatically adds dependencies of
           type Before= to all mount units that refer to local mount
           points for this target unit. In addition, it adds
           dependencies of type Wants= to this target unit for those
           mounts listed in /etc/fstab that have the auto mount option
           set.

       machines.target
           A standard target unit for starting all the containers and
           other virtual machines. See systemd-nspawn@.service for an
           example.

       multi-user.target
           A special target unit for setting up a multi-user system
           (non-graphical). This is pulled in by graphical.target.

           Units that are needed for a multi-user system shall add
           Wants= dependencies for their unit to this unit during
           installation. This is best configured via
           WantedBy=multi-user.target in the unit's [Install] section.

       network-online.target
           Units that strictly require a configured network connection
           should pull in network-online.target (via a Wants= type
           dependency) and order themselves after it. This target unit
           is intended to pull in a service that delays further
           execution until the network is sufficiently set up. What
           precisely this requires is left to the implementation of the
           network managing service.

           Note the distinction between this unit and network.target.
           This unit is an active unit (i.e. pulled in by the consumer
           rather than the provider of this functionality) and pulls in
           a service which possibly adds substantial delays to further
           execution. In contrast, network.target is a passive unit
           (i.e. pulled in by the provider of the functionality, rather
           than the consumer) that usually does not delay execution
           much. Usually, network.target is part of the boot of most
           systems, while network-online.target is not, except when at
           least one unit requires it. Also see Running Services After
           the Network is up[1] for more information.

           All mount units for remote network file systems automatically
           pull in this unit, and order themselves after it. Note that
           networking daemons that simply provide functionality to other
           hosts (as opposed to consume functionality of other hosts)
           generally do not need to pull this in.

           systemd automatically adds dependencies of type Wants= and
           After= for this target unit to all SysV init script service
           units with an LSB header referring to the "$network"
           facility.

           Note that this unit is only useful during the original system
           start-up logic. After the system has completed booting up, it
           will not track the online state of the system anymore. Due to
           this it cannot be used as a network connection monitor
           concept, it is purely a one-time system start-up concept.

       paths.target
           A special target unit that sets up all path units (see
           systemd.path(5) for details) that shall be active after boot.

           It is recommended that path units installed by applications
           get pulled in via Wants= dependencies from this unit. This is
           best configured via a WantedBy=paths.target in the path
           unit's [Install] section.

       poweroff.target
           A special target unit for shutting down and powering off the
           system.

           Applications wanting to power off the system should not start
           this unit directly, but should instead execute systemctl
           poweroff (possibly with the --no-block option) or call
           systemd-logind(8)'s org.freedesktop.login1.Manager.PowerOff
           D-Bus method directly.

           runlevel0.target is an alias for this target unit, for
           compatibility with SysV.

       reboot.target
           A special target unit for shutting down and rebooting the
           system.

           Applications wanting to reboot the system should not start
           this unit directly, but should instead execute systemctl
           reboot (possibly with the --no-block option) or call
           systemd-logind(8)'s org.freedesktop.login1.Manager.Reboot
           D-Bus method directly.

           runlevel6.target is an alias for this target unit, for
           compatibility with SysV.

       remote-cryptsetup.target
           Similar to cryptsetup.target, but for encrypted devices which
           are accessed over the network. It is used for crypttab(8)
           entries marked with _netdev.

       remote-veritysetup.target
           Similar to veritysetup.target, but for verity integrity
           protected devices which are accessed over the network. It is
           used for veritytab(8) entries marked with _netdev.

       remote-fs.target
           Similar to local-fs.target, but for remote mount points.

           systemd automatically adds dependencies of type After= for
           this target unit to all SysV init script service units with
           an LSB header referring to the "$remote_fs" facility.

       rescue.target
           A special target unit that pulls in the base system
           (including system mounts) and spawns a rescue shell. Isolate
           to this target in order to administer the system in
           single-user mode with all file systems mounted but with no
           services running, except for the most basic. Compare with
           emergency.target, which is much more reduced and does not
           provide the file systems or most basic services. Compare with
           multi-user.target, this target could be seen as
           single-user.target.

           runlevel1.target is an alias for this target unit, for
           compatibility with SysV.

           Use the "systemd.unit=rescue.target" kernel command line
           option to boot into this mode. A short alias for this kernel
           command line option is "1", for compatibility with SysV.

       runlevel2.target, runlevel3.target, runlevel4.target,
       runlevel5.target
           These are targets that are called whenever the SysV
           compatibility code asks for runlevel 2, 3, 4, 5,
           respectively. It is a good idea to make this an alias for
           (i.e. symlink to) graphical.target (for runlevel 5) or
           multi-user.target (the others).

       shutdown.target
           A special target unit that terminates the services on system
           shutdown.

           Services that shall be terminated on system shutdown shall
           add Conflicts= and Before= dependencies to this unit for
           their service unit, which is implicitly done when
           DefaultDependencies=yes is set (the default).

       sigpwr.target
           A special target that is started when systemd receives the
           SIGPWR process signal, which is normally sent by the kernel
           or UPS daemons when power fails.

       sleep.target
           A special target unit that is pulled in by suspend.target,
           hibernate.target and hybrid-sleep.target and may be used to
           hook units into the sleep state logic.

       slices.target
           A special target unit that sets up all slice units (see
           systemd.slice(5) for details) that shall always be active
           after boot. By default the generic system.slice slice unit as
           well as the root slice unit -.slice are pulled in and ordered
           before this unit (see below).

           Adding slice units to slices.target is generally not
           necessary. Instead, when some unit that uses Slice= is
           started, the specified slice will be started automatically.
           Adding WantedBy=slices.target lines to the [Install] section
           should only be done for units that need to be always active.
           In that case care needs to be taken to avoid creating a loop
           through the automatic dependencies on "parent" slices.

       sockets.target
           A special target unit that sets up all socket units (see
           systemd.socket(5) for details) that shall be active after
           boot.

           Services that can be socket-activated shall add Wants=
           dependencies to this unit for their socket unit during
           installation. This is best configured via a
           WantedBy=sockets.target in the socket unit's [Install]
           section.

       suspend.target
           A special target unit for suspending the system. This pulls
           in sleep.target.

       swap.target
           Similar to local-fs.target, but for swap partitions and swap
           files.

       sysinit.target
           systemd automatically adds dependencies of the types
           Requires= and After= for this target unit to all services
           (except for those with DefaultDependencies=no).

           This target pulls in the services required for system
           initialization. System services pulled in by this target
           should declare DefaultDependencies=no and specify all their
           dependencies manually, including access to anything more than
           a read only root filesystem. For details on the dependencies
           of this target, refer to bootup(7).

       syslog.socket
           The socket unit syslog implementations should listen on. All
           userspace log messages will be made available on this socket.
           For more information about syslog integration, please consult
           the Syslog Interface[2] document.

       system-update.target, system-update-pre.target,
       system-update-cleanup.service
           A special target unit that is used for offline system
           updates.  systemd-system-update-generator(8) will redirect
           the boot process to this target if /system-update exists. For
           more information see systemd.offline-updates(7).

           Updates should happen before the system-update.target is
           reached, and the services which implement them should cause
           the machine to reboot. The main units executing the update
           should order themselves after system-update-pre.target but
           not pull it in. Services which want to run during system
           updates only, but before the actual system update is executed
           should order themselves before this unit and pull it in. As a
           safety measure, if this does not happen, and /system-update
           still exists after system-update.target is reached,
           system-update-cleanup.service will remove this symlink and
           reboot the machine.

       timers.target
           A special target unit that sets up all timer units (see
           systemd.timer(5) for details) that shall be active after
           boot.

           It is recommended that timer units installed by applications
           get pulled in via Wants= dependencies from this unit. This is
           best configured via WantedBy=timers.target in the timer
           unit's [Install] section.

       umount.target
           A special target unit that unmounts all mount and automount
           points on system shutdown.

           Mounts that shall be unmounted on system shutdown shall add
           Conflicts dependencies to this unit for their mount unit,
           which is implicitly done when DefaultDependencies=yes is set
           (the default).

   Special System Units for Devices
       Some target units are automatically pulled in as devices of
       certain kinds show up in the system. These may be used to
       automatically activate various services based on the specific
       type of the available hardware.

       bluetooth.target
           This target is started automatically as soon as a Bluetooth
           controller is plugged in or becomes available at boot.

           This may be used to pull in Bluetooth management daemons
           dynamically when Bluetooth hardware is found.

       printer.target
           This target is started automatically as soon as a printer is
           plugged in or becomes available at boot.

           This may be used to pull in printer management daemons
           dynamically when printer hardware is found.

       smartcard.target
           This target is started automatically as soon as a smartcard
           controller is plugged in or becomes available at boot.

           This may be used to pull in smartcard management daemons
           dynamically when smartcard hardware is found.

       sound.target
           This target is started automatically as soon as a sound card
           is plugged in or becomes available at boot.

           This may be used to pull in audio management daemons
           dynamically when audio hardware is found.

       usb-gadget.target
           This target is started automatically as soon as a USB Device
           Controller becomes available at boot.

           This may be used to pull in usb gadget dynamically when UDC
           hardware is found.

   Special Passive System Units
       A number of special system targets are defined that can be used
       to properly order boot-up of optional services. These targets are
       generally not part of the initial boot transaction, unless they
       are explicitly pulled in by one of the implementing services.
       Note specifically that these passive target units are generally
       not pulled in by the consumer of a service, but by the provider
       of the service. This means: a consuming service should order
       itself after these targets (as appropriate), but not pull it in.
       A providing service should order itself before these targets (as
       appropriate) and pull it in (via a Wants= type dependency).

       Note that these passive units cannot be started manually, i.e.
       "systemctl start time-sync.target" will fail with an error. They
       can only be pulled in by dependency. This is enforced since they
       exist for ordering purposes only and thus are not useful as only
       unit within a transaction.

       blockdev@.target
           This template unit is used to order mount units and other
           consumers of block devices after services that synthesize
           these block devices. In particular, this is intended to be
           used with storage services (such as
           systemd-cryptsetup@.service(5)/
           systemd-veritysetup@.service(5)) that allocate and manage a
           virtual block device. Storage services are ordered before an
           instance of blockdev@.target, and the consumer units after
           it. The ordering is particularly relevant during shutdown, as
           it ensures that the mount is deactivated first and the
           service backing the mount later. The blockdev@.target
           instance should be pulled in via a Wants= dependency of the
           storage daemon and thus generally not be part of any
           transaction unless a storage daemon is used. The instance
           name for instances of this template unit must be a properly
           escaped block device node path, e.g.
           blockdev@dev-mapper-foobar.target for the storage device
           /dev/mapper/foobar.

       cryptsetup-pre.target
           This passive target unit may be pulled in by services that
           want to run before any encrypted block device is set up. All
           encrypted block devices are set up after this target has been
           reached. Since the shutdown order is implicitly the reverse
           start-up order between units, this target is particularly
           useful to ensure that a service is shut down only after all
           encrypted block devices are fully stopped.

       veritysetup-pre.target
           This passive target unit may be pulled in by services that
           want to run before any verity integrity protected block
           device is set up. All verity integrity protected block
           devices are set up after this target has been reached. Since
           the shutdown order is implicitly the reverse start-up order
           between units, this target is particularly useful to ensure
           that a service is shut down only after all verity integrity
           protected block devices are fully stopped.

       first-boot-complete.target
           This passive target is intended as a synchronization point
           for units that need to run once during the first boot. Only
           after all units ordered before this target have finished,
           will the machine-id(5) be committed to disk, marking the
           first boot as completed. If the boot is aborted at any time
           before that, the next boot will re-run any units with
           ConditionFirstBoot=yes.

       getty-pre.target
           A special passive target unit. Users of this target are
           expected to pull it in the boot transaction via a dependency
           (e.g.  Wants=). Order your unit before this unit if you want
           to make use of the console just before getty is started.

       local-fs-pre.target
           This target unit is automatically ordered before all local
           mount points marked with auto (see above). It can be used to
           execute certain units before all local mounts.

       network.target
           This unit is supposed to indicate when network functionality
           is available, but it is only very weakly defined what that is
           supposed to mean. However, the following should apply at
           minimum:

           •   At start-up, any configured synthetic network devices
               (i.e. not physical ones that require hardware to show up
               and be probed, but virtual ones like bridge devices and
               similar which are created programmatically) that do not
               depend on any underlying hardware should be allocated by
               the time this target is reached. It is not necessary for
               these interfaces to also have completed IP level
               configuration by the time network.target is reached.

           •   At shutdown, a unit that is ordered after network.target
               will be stopped before the network — to whatever level it
               might be set up by then — is shut down. It is hence
               useful when writing service files that require network
               access on shutdown, which should order themselves after
               this target, but not pull it in. Also see Running
               Services After the Network is up[1] for more information.

           It must emphasized that at start-up there's no guarantee that
           hardware-based devices have shown up by the time this target
           is reached, or even acquired complete IP configuration. For
           that purpose use network-online.target as described above.

       network-pre.target
           This passive target unit may be pulled in by services that
           want to run before any network is set up, for example for the
           purpose of setting up a firewall. All network management
           software orders itself after this target, but does not pull
           it in.

       nss-lookup.target
           A target that should be used as synchronization point for all
           host/network name service lookups. Note that this is
           independent of UNIX user/group name lookups for which
           nss-user-lookup.target should be used. All services for which
           the availability of full host/network name resolution is
           essential should be ordered after this target, but not pull
           it in. systemd automatically adds dependencies of type After=
           for this target unit to all SysV init script service units
           with an LSB header referring to the "$named" facility.

       nss-user-lookup.target
           A target that should be used as synchronization point for all
           regular UNIX user/group name service lookups. Note that this
           is independent of host/network name lookups for which
           nss-lookup.target should be used. All services for which the
           availability of the full user/group database is essential
           should be ordered after this target, but not pull it in. All
           services which provide parts of the user/group database
           should be ordered before this target, and pull it in. Note
           that this unit is only relevant for regular users and groups
           — system users and groups are required to be resolvable
           during earliest boot already, and hence do not need any
           special ordering against this target.

       remote-fs-pre.target
           This target unit is automatically ordered before all mount
           point units (see above) and cryptsetup/veritysetup devices
           marked with the _netdev. It can be used to run certain units
           before remote encrypted devices and mounts are established.
           Note that this unit is generally not part of the initial
           transaction, unless the unit that wants to be ordered before
           all remote mounts pulls it in via a Wants= type dependency.
           If the unit wants to be pulled in by the first remote mount
           showing up, it should use network-online.target (see above).

       rpcbind.target
           The portmapper/rpcbind pulls in this target and orders itself
           before it, to indicate its availability. systemd
           automatically adds dependencies of type After= for this
           target unit to all SysV init script service units with an LSB
           header referring to the "$portmap" facility.

       time-set.target
           Services responsible for setting the system clock
           (CLOCK_REALTIME) from a local source (such as a maintained
           timestamp file or imprecise real-time clock) should pull in
           this target and order themselves before it. Services where
           approximate, roughly monotonic time is desired should be
           ordered after this unit, but not pull it in.

           This target does not provide the accuracy guarantees of
           time-sync.target (see below), however does not depend on
           remote clock sources to be reachable, i.e. the target is
           typically not delayed by network problems and similar. Use of
           this target is recommended for services where approximate
           clock accuracy and rough monotonicity is desired but
           activation shall not be delayed for possibly unreliable
           network communication.

           The service manager automatically adds dependencies of type
           After= for this target unit to all timer units with at least
           one OnCalendar= directive.

           The systemd-timesyncd.service(8) service is a simple daemon
           that pulls in this target and orders itself before it.
           Besides implementing the SNTP network protocol it maintains a
           timestamp file on disk whose modification time is regularlary
           updated. At service start-up the local system clock is set
           from that modification time, ensuring it increases roughly
           monotonically.

           Note that ordering a unit after time-set.target only has
           effect if there's actually a service ordered before it that
           delays it until the clock is adjusted for rough monotonicity.
           Otherwise, this target might get reached before the clock is
           adjusted to be roughly monotonic. Enable
           systemd-timesyncd.service(8), or an alternative NTP
           implementation to delay the target.

       time-sync.target
           Services indicating completed synchronization of the system
           clock (CLOCK_REALTIME) to a remote source should pull in this
           target and order themselves before it. Services where
           accurate time is essential should be ordered after this unit,
           but not pull it in.

           The service manager automatically adds dependencies of type
           After= for this target unit to all SysV init script service
           units with an LSB header referring to the "$time" facility,
           as well to all timer units with at least one OnCalendar=
           directive.

           This target provides stricter clock accuracy guarantees than
           time-set.target (see above), but likely requires network
           communication and thus introduces unpredictable delays.
           Services that require clock accuracy and where network
           communication delays are acceptable should use this target.
           Services that require a less accurate clock, and only
           approximate and roughly monotonic clock behaviour should use
           time-set.target instead.

           Note that ordering a unit after time-sync.target only has
           effect if there's actually a service ordered before it that
           delays it until clock synchronization is reached. Otherwise,
           this target might get reached before the clock is
           synchronized to any remote accurate reference clock. When
           using systemd-timesyncd.service(8), enable
           systemd-time-wait-sync.service(8) to delay the target; or use
           an equivalent service for other NTP implementations.

           Table 1. Comparison
           ┌──────────────────────────┬────────────────────────────────┐
           │time-set.target           time-sync.target               │
           ├──────────────────────────┼────────────────────────────────┤
           │"quick" to reach          │ "slow" to reach                │
           ├──────────────────────────┼────────────────────────────────┤
           │typically uses local      │ typically uses remote          │
           │clock sources, boot       │ clock sources, inserts         │
           │process not affected by   │ dependencies on remote         │
           │availability of external  │ resources into boot            │
           │resources                 │ process                        │
           ├──────────────────────────┼────────────────────────────────┤
           │reliable, because local   │ unreliable, because            │
           │                          │ typically network              │
           │                          │ involved                       │
           ├──────────────────────────┼────────────────────────────────┤
           │typically guarantees an   │ typically guarantees an        │
           │approximate and roughly   │ accurate clock                 │
           │monotonic clock only      │                                │
           ├──────────────────────────┼────────────────────────────────┤
           │implemented by            │ implemented by                 │
           │systemd-timesyncd.service │ systemd-time-wait-sync.service │
           └──────────────────────────┴────────────────────────────────┘

   Special Slice Units
       There are four ".slice" units which form the basis of the
       hierarchy for assignment of resources for services, users, and
       virtual machines or containers. See systemd.slice(7) for details
       about slice units.

       -.slice
           The root slice is the root of the slice hierarchy. It usually
           does not contain units directly, but may be used to set
           defaults for the whole tree.

       system.slice
           By default, all system services started by systemd are found
           in this slice.

       user.slice
           By default, all user processes and services started on behalf
           of the user, including the per-user systemd instance are
           found in this slice. This is pulled in by
           systemd-logind.service.

       machine.slice
           By default, all virtual machines and containers registered
           with systemd-machined are found in this slice. This is pulled
           in by systemd-machined.service.

UNITS MANAGED BY THE USER SERVICE MANAGER         top

   Special User Units
       When systemd runs as a user instance, the following special units
       are available:

       default.target
           This is the main target of the user session, started by
           default. Various services that compose the normal user
           session should be pulled into this target. In this regard,
           default.target is similar to multi-user.target in the system
           instance, but it is a real unit, not an alias.

       In addition, the following units are available which have
       definitions similar to their system counterparts: exit.target,
       shutdown.target, sockets.target, timers.target, paths.target,
       bluetooth.target, printer.target, smartcard.target, sound.target.

   Special Passive User Units
       graphical-session.target
           This target is active whenever any graphical session is
           running. It is used to stop user services which only apply to
           a graphical (X, Wayland, etc.) session when the session is
           terminated. Such services should have
           "PartOf=graphical-session.target" in their [Unit] section. A
           target for a particular session (e. g.  gnome-session.target)
           starts and stops "graphical-session.target" with
           "BindsTo=graphical-session.target".

           Which services are started by a session target is determined
           by the "Wants=" and "Requires=" dependencies. For services
           that can be enabled independently, symlinks in ".wants/" and
           ".requires/" should be used, see systemd.unit(5). Those
           symlinks should either be shipped in packages, or should be
           added dynamically after installation, for example using
           "systemctl add-wants", see systemctl(1).

           Example 1. Nautilus as part of a GNOME session
           "gnome-session.target" pulls in Nautilus as top-level
           service:

               [Unit]
               Description=User systemd services for GNOME graphical session
               Wants=nautilus.service
               BindsTo=graphical-session.target

           "nautilus.service" gets stopped when the session stops:

               [Unit]
               Description=Render the desktop icons with Nautilus
               PartOf=graphical-session.target

               [Service]
               ...

       graphical-session-pre.target
           This target contains services which set up the environment or
           global configuration of a graphical session, such as SSH/GPG
           agents (which need to export an environment variable into all
           desktop processes) or migration of obsolete d-conf keys after
           an OS upgrade (which needs to happen before starting any
           process that might use them). This target must be started
           before starting a graphical session like
           gnome-session.target.

       xdg-desktop-autostart.target
           The XDG specification defines a way to autostart applications
           using XDG desktop files. systemd ships
           systemd-xdg-autostart-generator(8) for the XDG desktop files
           in autostart directories. Desktop Environments can opt-in to
           use this service by adding a Wants= dependency on
           xdg-desktop-autostart.target.

   Special User Slice Units
       There are four ".slice" units which form the basis of the user
       hierarchy for assignment of resources for user applications and
       services. See systemd.slice(7) for details about slice units and
       the documentation about Desktop Environments[3] for further
       information.

       -.slice
           The root slice is the root of the user's slice hierarchy. It
           usually does not contain units directly, but may be used to
           set defaults for the whole tree.

       app.slice
           By default, all user services and applications managed by
           systemd are found in this slice. All interactively launched
           applications like web browsers and text editors as well as
           non-critical services should be placed into this slice.

       session.slice
           All essential services and applications required for the
           session should use this slice. These are services that either
           cannot be restarted easily or where latency issues may affect
           the interactivity of the system and applications. This
           includes the display server, screen readers and other
           services such as DBus or XDG portals. Such services should be
           configured to be part of this slice by adding
           Slice=session.slice to their unit files.

       background.slice
           All services running low-priority background tasks should use
           this slice. This permits resources to be preferentially
           assigned to the other slices. Examples include
           non-interactive tasks like file indexing or backup operations
           where latency is not important.

SEE ALSO         top

       systemd(1), systemd.unit(5), systemd.service(5),
       systemd.socket(5), systemd.target(5), systemd.slice(5),
       bootup(7), systemd-fstab-generator(8), user@.service(5)

NOTES         top

        1. Running Services After the Network is up
           https://www.freedesktop.org/wiki/Software/systemd/NetworkTarget

        2. Syslog Interface
           https://www.freedesktop.org/wiki/Software/systemd/syslog

        3. Desktop Environments
           https://systemd.io/DESKTOP_ENVIRONMENTS

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have
       a bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2021-04-01.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-04-01.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 248                                           SYSTEMD.SPECIAL(7)

Pages that refer to this page: machinectl(1)systemctl(1)systemd(1)systemd.mount(5)systemd.resource-control(5)systemd.slice(5)systemd.target(5)systemd.timer(5)systemd.unit(5)user@.service(5)bootup(7)daemon(7)systemd.directives(7)systemd.index(7)lvm2-activation-generator(8)systemd-bless-boot.service(8)systemd-boot-check-no-failures.service(8)systemd-halt.service(8)systemd-machined.service(8)systemd-rc-local-generator(8)systemd-suspend.service(8)systemd-system-update-generator(8)systemd-sysv-generator(8)systemd-timesyncd.service(8)systemd-time-wait-sync.service(8)systemd-xdg-autostart-generator(8)