SYSTEMD.SPECIAL(7) systemd.special SYSTEMD.SPECIAL(7)
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, 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.
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 reboot 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-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. 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.
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 "$network" facility.
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
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 "$named" facility.
nss-user-lookup.target
A target that should be used as synchronization point for all user/group name service lookups. Note that this is independent of
host/network name lookups for which nss-lookup.target should be used. All services for which the availability of the full user/group
database is essential should be ordered after this target, but not pull it in. Note that system users are always resolvable, and hence
do not require any special ordering against this target.
remote-fs-pre.target
This target unit is automatically ordered before all mount point units (see above) and cryptsetup devices marked with the _netdev. It
can be used to run certain units before remote encrypted devices and mounts are established. Note that this unit is generally not part
of the initial transaction, unless the unit that wants to be ordered before all remote mounts pulls it in via a Wants= type dependency.
If the unit wants to be pulled in by the first remote mount showing up, it should use network-online.target (see above).
rpcbind.target
The portmapper/rpcbind pulls in this target and orders itself before it, to indicate its availability. systemd automatically adds
dependencies of type After= for this target unit to all SysV init script service units with an LSB header referring to the "$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
systemd 237 SYSTEMD.SPECIAL(7)