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SYSTEMD.SPECIAL(7) | systemd.special | SYSTEMD.SPECIAL(7) |
NAME¶
systemd.special - Special systemd unitsSYNOPSIS¶
basic.target, bluetooth.target, ctrl-alt-del.target, cryptsetup.target, dbus.service, dbus.socket, default.target, display-manager.service, emergency.target, exit.target, final.target, getty.target, graphical.target, halt.target, hibernate.target, hybrid-sleep.target, initrd-fs.target, kbrequest.target, kexec.target, local-fs.target, local-fs-pre.target, multi-user.target, network.target, network-online.target, nss-lookup.target, nss-user-lookup.target, paths.target, poweroff.target, printer.target, reboot.target, remote-fs.target, remote-fs-pre.target, rescue.target, initrd-root-fs.target, rpcbind.target, runlevel2.target, runlevel3.target, runlevel4.target, runlevel5.target, shutdown.target, sigpwr.target, sleep.target, smartcard.target, sockets.target, sound.target, suspend.target, swap.target, sysinit.target, syslog.socket, syslog.target, system-update.target, time-sync.target, timers.target, umount.targetDESCRIPTION¶
A few units are treated specially by systemd. They have special internal semantics and cannot be renamed.SPECIAL SYSTEM UNITS¶
basic.targetA special target unit covering basic boot-up.
systemd automatically adds dependencies of the types Requires= and
After= for this target unit to all services (except for those with
DefaultDependencies=no).
Usually this should pull-in all mount points, swap devices, sockets, timers, and
path units and other basic initialization necessary for general purpose
daemons.
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 unit is supposed to be used with the kernel
command line option systemd.unit= and has otherwise little use.
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 fround in /etc/fstab that have the auto and
x-initrd.mount 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.
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
$local_fs facility.
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.
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-uer.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 don't 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 for setting up the base
system and a rescue shell.
runlevel1.target is an alias for this target unit, for compatibility with
SysV.
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) multi-user.target (for
runlevel 2) or graphical.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=
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.
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
A special target unit covering early boot-up
scripts.
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.
syslog.target
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 $syslog facility.
system-update.target
A special target unit that is used for
off-line system updates. systemd-system-update-generator(8) will
redirect the boot process to this target if /system-update exists. For more
information see the System Updates Specification[3].
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 umounts 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.targetThis 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. local-fs-pre.targetThis 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. 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.
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. 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.
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).
Again, this target unit is not suitable for pulling in other units, it is
only useful for ordering.
rpcbind.target
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
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: default.target, shutdown.target, sockets.target, timers.target, paths.target, bluetooth.target, printer.target, smartcard.target, sound.target. In addition the following special unit is understood only when systemd runs as service instance: exit.targetA special service unit for shutting down the
user service manager.
Applications wanting to terminate the user service manager should start this
unit. If systemd receives SIGTERM or SIGINT when running as user service
daemon it will start this unit.
Normally, this pulls in shutdown.target which in turn should be conflicted by
all units that want to be shut down on user service manager exit.
SEE ALSO¶
NOTES¶
- 1.
- Running Services After the Network is up
- 2.
- Syslog Interface
- 3.
- System Updates Specification
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