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, blockdev@.target,
boot-complete.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.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-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
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 SYSTEMS SERVICE MANAGER
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.
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 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.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 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 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)) 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.
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-set.target
Services responsible for setting the system clock 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 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.
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 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 USERS SERVICE MANAGER
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.
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), user@.service(5)
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 245 SYSTEMD.SPECIAL(7)