systemd.special — Special systemd units
basic.target
,
bluetooth.target
,
cryptsetup-pre.target
,
cryptsetup.target
,
ctrl-alt-del.target
,
default.target
,
emergency.target
,
exit.target
,
final.target
,
getty.target
,
graphical.target
,
halt.target
,
hibernate.target
,
hybrid-sleep.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-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
,
syslog.socket
,
system-update.target
,
time-sync.target
,
timers.target
,
umount.target
,
-.slice
,
system.slice
,
user.slice
,
machine.slice
,
dbus.service
,
dbus.socket
,
display-manager.service
,
system-update-cleanup.service
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.
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 a
request to shut down over D-Bus or a
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
.
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 start this unit.
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.
kbrequest.target
¶systemd starts this target whenever Alt+ArrowUp is
pressed on the console. This is a good candidate to be
aliased (symlinked) to
rescue.target
.
kexec.target
¶A special target unit for shutting down and rebooting the system via kexec.
Applications wanting to reboot the system with kexec should start this unit.
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 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.
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 start this unit.
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 start this unit.
runlevel6.target
is an alias for
this target unit, for compatibility with SysV.
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.
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.
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.
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 user.slice
,
system.slice
, machines.slice
slice units, as well as the root
slice unit -.slice
are 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 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).
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.
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.
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 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 "$named
"
facility.
nss-user-lookup.target
¶A target that should be used as synchronization point
for all user/group name service lookups. Note that this is
independent of host/network name lookups for which
nss-lookup.target
should be used. All
services for which the availability of the full user/group
database is essential should be ordered after this target,
but not pull it in. Note that system users are always
resolvable, and hence do not require any special ordering
against this target.
remote-fs-pre.target
¶This target unit is automatically ordered before all
remote mount point units (see above). It can be used to run
certain units before the remote mounts are established. Note
that this unit is generally not part of the initial
transaction, unless the unit that wants to be ordered before
all remote mounts pulls it in via a
Wants=
type dependency. If the unit wants
to be pulled in by the first remote mount showing up, it
should use network-online.target
(see
above).
rpcbind.target
¶The portmapper/rpcbind pulls in this target and orders
itself before it, to indicate its availability. systemd
automatically adds dependencies of type
After=
for this target unit to all SysV
init script service units with an LSB header referring to
the "$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.
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
.
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
.
There are four ".slice
" units which form
the basis of the hierarchy for assignment of resources for
services, users, and virtual machines or containers.
-.slice
¶The root slice is the root of the 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.
machine.slice
¶By default, all virtual machines and containers registered with systemd-machined are found in this slice.