Provided by: systemd_239-7ubuntu10_amd64 bug

NAME

       systemd.special - Special systemd units

SYNOPSIS

       basic.target, bluetooth.target, cryptsetup-pre.target, cryptsetup.target,
       ctrl-alt-del.target, default.target, emergency.target, exit.target, final.target,
       getty.target, getty-pre.target, graphical.target, halt.target, hibernate.target,
       hybrid-sleep.target, suspend-then-hibernate.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-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-sync.target, timers.target,
       umount.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

       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.

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.

       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.

       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.

           The default unit systemd starts at bootup can be overridden with the systemd.unit=
           kernel command line option.

       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 any 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 is supposed
           to be used with the kernel command line option systemd.unit=; 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.

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

           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.

       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-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 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-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 be active after boot. By default the generic system.slice slice unit, as
           well as the root slice unit -.slice, is pulled in and ordered before this unit (see
           below).

           It's a good idea to add WantedBy=slices.target lines to the "[Install]" section of all
           slices units that may be installed dynamically.

       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.

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.

       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.

       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, with one exception: at
           shutdown, a unit that is ordered after network.target will be stopped before the
           network — to whatever level it might be set up 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. Also see network-online.target 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 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-sync.target
           Services responsible for synchronizing the system clock from a remote source (such as
           NTP client implementations) should pull in this target and order themselves before it.
           All services where correct time is essential should be ordered after this unit, 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 "$time"
           facility.

SPECIAL USER UNITS

       When systemd runs as a user instance, the following special units are available, which
       have similar definitions as their system counterparts: exit.target, default.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.

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

SEE ALSO

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

NOTES

        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