| SYSTEMD.SPECIAL(7) | systemd.special | SYSTEMD.SPECIAL(7) |
.SH "NAME" systemd.special - Special systemd units
.SH "SYNOPSIS"
basic.target, bluetooth.target, cryptsetup-pre.target, cryptsetup.target, veritysetup-pre.target, veritysetup.target, ctrl-alt-del.target, blockdev@.target, boot-complete.target, default.target, emergency.target, exit.target, factory-reset.target, factory-reset-now.target, final.target, first-boot-complete.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, initrd-usr-fs.target, integritysetup-pre.target, integritysetup.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-integritysetup.target, remote-veritysetup.target, remote-fs-pre.target, remote-fs.target, rescue.target, rpcbind.target, shutdown.target, sigpwr.target, sleep.target, slices.target, smartcard.target, sockets.target, soft-reboot.target, sound.target, ssh-access.target, storage-target-mode.target, suspend.target, swap.target, sysinit.target, system-update.target, system-update-pre.target, time-set.target, time-sync.target, timers.target, tpm2.target, umount.target, usb-gadget.target, -.slice, capsule.slice, machine.slice, system.slice, user.slice, -.mount, dbus.service, dbus.socket, display-manager.service, init.scope, syslog.socket, system-update-cleanup.service
.SH "DESCRIPTION"
.PP 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.
.SH "UNITS MANAGED BY THE SYSTEM SERVICE MANAGER"
.SS "Special System Units"
.PP -.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.
Added in version 235.
.RE
.PP 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.
.RE
.PP 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.
Added in version 240.
.RE
.PP 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.
.RE
.PP cryptsetup.target
A target that pulls in setup services for all encrypted block devices.
.RE
.PP veritysetup.target
A target that pulls in setup services for all verity integrity protected
block devices.
Added in version 248.
.RE
.PP 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.
.RE
.PP dbus.socket
A special unit for the D-Bus system bus socket. All units with
Type=dbus automatically gain a dependency on this unit.
.RE
.PP 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).
If default.target is not present on disk and no unit was requested on the
kernel command line, the default set at compile time will be used
(graphical.target).
If the default unit or one of the fallbacks cannot be started, systemd starts
rescue.target.
For typical unit files please set WantedBy= to a regular target (like
multi-user.target or graphical.target), instead of default.target, since
such a service will also be run on special boots like on system update,
emergency boot...
.RE
.PP display-manager.service
The display manager service. Usually, this should be aliased (symlinked) to
gdm.service or a similar display manager service.
.RE
.PP emergency.target
A special target unit that starts an emergency shell on the main console.
This target does not pull in other 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 may be used by specifying
emergency on the kernel command line; 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.
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.
Note that depending on how emergency.target is reached, the root file system
might be mounted read-only or read-write (no remounting is done specially
for this target). For example, the system may boot with root mounted
read-only when ro is used on the kernel command line and remain this
way for emergency.target, or the system may transition to emergency.target
after the system has been partially booted and disks have already been
remounted read-write.
.RE
.PP 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.
Added in version 186.
.RE
.PP factory-reset.target
A special target to request a factory reset operation. This will typically
persistently store a request flag for the next boot and then reboot in order
to reset the system to factory state.
See Factory Reset[1] for more information.
Added in version 250.
.RE
.PP factory-reset-now.target
A special target that is started on boots that shall execute a factory reset.
It may be used to pull in additional services that shall be invoked during a
factory reset operation. It also acts as ordering barrier: once the target
is reached the factory reset state is marked as "completed".
See Factory Reset[1] for more information.
Added in version 258.
.RE
.PP 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.
.RE
.PP getty.target
A special target unit that pulls in statically configured local TTY getty
instances.
.RE
.PP 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.
.RE
.PP hibernate.target
A special target unit for hibernating the system. This pulls in
sleep.target.
.RE
.PP hybrid-sleep.target
A special target unit for hibernating and suspending the system at the same
time. This pulls in sleep.target.
Added in version 196.
.RE
.PP 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.
Added in version 239.
.RE
.PP 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.
.RE
.PP imports.target
A target unit that pulls in all disk image download jobs to execute on system
boot. This is used by systemd-import-generator(8).
Added in version 258.
.RE
.PP 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.
Added in version 235.
.RE
.PP initrd.target
This is the default target in the initrd, 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.
Added in version 245.
.RE
.PP initrd-fs.target
systemd-fstab-generator(8) automatically adds dependencies of type
Before= to sysroot-usr.mount and all mount points found in /etc/fstab
that have the x-initrd.mount mount option set and do not have the
noauto mount option set. It is also indirectly ordered after
sysroot.mount. Thus, once this target is reached the /sysroot/ hierarchy is
fully set up, in preparation for the transition to the host OS.
Added in version 199.
.RE
.PP 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(8) and systemd-gpt-auto-generator(8)
automatically set up the appropriate dependencies to make this happen.
Added in version 230.
.RE
.PP initrd-root-fs.target
systemd-fstab-generator(8) automatically adds dependencies of type
Before= to the sysroot.mount unit, which is generated from the kernel
command line's root= setting (or equivalent).
Added in version 199.
.RE
.PP initrd-usr-fs.target
systemd-fstab-generator(8) automatically adds dependencies of type
Before= to the sysusr-usr.mount unit, which is generated from the
kernel command line's usr= switch. Services may order themselves
after this target unit in order to run once the /sysusr/ hierarchy becomes
available, on systems that come up initially without a root file system, but
with an initialized /usr/ and need to access that before setting up the root
file system to ultimately switch to. On systems where usr= is not
used this target is ordered after sysroot.mount and thus mostly equivalent
to initrd-root-fs.target. In effect on any system once this target is
reached the file system backing /usr/ is mounted, though possibly at two
different locations, either below the /sysusr/ or the /sysroot/
hierarchies.
Added in version 249.
.RE
.PP 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.
.RE
.PP 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-logind(8)'s
org.freedesktop.login1.Manager.RebootWithFlags() D-Bus method
directly.
See systemd-kexec.service(8) for further details of the operation this
target pulls in.
.RE
.PP local-fs.target
systemd-fstab-generator(8) 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.
.RE
.PP machines.target
A standard target unit for starting all the containers and other virtual
machines. See systemd-nspawn@.service for an example.
Added in version 233.
.RE
.PP 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.
.RE
.PP 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[2] 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 (as opposed to
consume functionality of 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.
Added in version 200.
.RE
.PP 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.
Added in version 199.
.RE
.PP 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.
.RE
.PP 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.
See systemd-reboot.service(8) for further details of the operation
this target pulls in.
.RE
.PP remote-cryptsetup.target
Similar to cryptsetup.target, but for encrypted devices which are accessed
over the network. It is used for crypttab(5) entries marked with
_netdev.
Added in version 235.
.RE
.PP remote-integritysetup.target
Similar to integritysetup.target, but for integrity protected devices which
are accessed over the network. It is used for integritytab(5) entries
marked with _netdev.
Added in version 258.
.RE
.PP remote-veritysetup.target
Similar to veritysetup.target, but for verity protected devices which are
accessed over the network. It is used for veritytab(5) entries marked
with _netdev.
Added in version 248.
.RE
.PP remote-fs.target
Similar to local-fs.target, but for remote mount points.
.RE
.PP 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.
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.
.RE
.PP 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).
.RE
.PP 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.
.RE
.PP sleep.target
A special target unit that is pulled in by suspend.target, hibernate.target,
suspend-then-hibernate.target, and hybrid-sleep.target and may be used to
hook units into the sleep state logic.
In order to hook external programs before the actual system sleep
operation, place their command line in a service unit file's
ExecStart= line (use Type=oneshot), and ensure the unit is
pulled in by sleep.target and ordered before it. In order to hook program
code after the actual system sleep operation (i.e. to be run after
the system woke up again), place the command in ExecStop= instead,
and make sure to enable StopWhenUnneeded= and
RemainAfterExit=. Both approaches can be combined into one unit file
in order to run programs both before and after the sleep operation.
.PP Example 1. Combined Example
[Unit] DefaultDependencies=no StopWhenUnneeded=yes Before=sleep.target [Service] Type=oneshot RemainAfterExit=yes ExecStart=/usr/bin/some-before-command ExecStop=/usr/bin/some-after-command [Install] WantedBy=sleep.target
.RE
.PP 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.
Added in version 229.
.RE
.PP 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.
.RE
.PP soft-reboot.target
A special target unit for shutting down and rebooting the userspace of the
system (leaving the kernel running).
Applications wanting to reboot the system should not start this unit
directly, but should instead execute systemctl soft-reboot (possibly
with the --no-block option) or call systemd-logind(8)'s
org.freedesktop.login1.Manager.RebootWithFlags() D-Bus method
directly.
See systemd-soft-reboot.service(8) for further details of the
operation this target pulls in.
Added in version 254.
.RE
.PP storage-target-mode.target
A special target unit that can be booted into that selects the "Storage
Target Mode" for the OS. In this mode all local storage disks are
exposed to external systems as block devices. This invokes
systemd-storagetm.service(8) which exposes all local disks as
NVMe-TCP devices for access over the network. It might as well invoke other
services too that make local disks available via other mechanisms.
Added in version 255.
.RE
.PP suspend.target
A special target unit for suspending the system. This pulls in
sleep.target.
.RE
.PP swap.target
Similar to local-fs.target, but for swap partitions and swap files.
.RE
.PP 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).
.RE
.PP 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[3]
document.
.RE
.PP 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 or /etc/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 or /etc/system-update
still exists after system-update.target is reached,
system-update-cleanup.service will remove the symlinks and reboot the
machine.
Added in version 186.
.RE
.PP 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.
Added in version 199.
.RE
.PP 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).
.RE
.SS "Special System Units for Devices"
.PP 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.
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
Added in version 242.
.RE
.PP tpm2.target
This target is started automatically if a TPM2 device is discovered, either
by the OS or by the firmware. It acts as synchronization point for services
that require TPM2 device access. The target unit is enqueued by
systemd-tpm2-generator(8) if it detects that the firmware has
discovered a TPM2 device but the OS kernel has not activated a driver for it
yet. It is also pulled in whenever systemd-udevd.service(8) discovers
a TPM2 device. The target unit is ordered after the /dev/tpmrm0 device node,
so that it only becomes active once the TPM2 device is actually accessible.
Early boot programs that intend to access the TPM2 device should hence order
themselves after this target unit, but not pull it in.
Added in version 256.
.RE
.SS "Special Passive System Units"
.PP 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).
.PP 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.
.PP 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(8)/
systemd-veritysetup@.service(8)) 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.
Added in version 245.
.RE
.PP 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.
Added in version 215.
.RE
.PP veritysetup-pre.target
This passive target unit may be pulled in by services that want to run before
any verity integrity protected block device is set up. All verity integrity
protected 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 verity integrity protected block devices are fully
stopped.
Added in version 248.
.RE
.PP first-boot-complete.target
This passive target is intended as a synchronization point for units that
need to run once during the first boot. Only after all units ordered before
this target have finished, will the machine-id(5) be committed to
disk, marking the first boot as completed. If the boot is aborted at any
time before that, the next boot will re-run any units with
ConditionFirstBoot=yes.
Added in version 247.
.RE
.PP 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.
Added in version 235.
.RE
.PP imports-pre.target
A passive unit that is ordered before all disk image download jobs to execute
on system boot. This is used by systemd-import-generator(8).
Added in version 258.
.RE
.PP 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.
.RE
.PP 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. However,
the following should apply at minimum:
.sp
It must emphasized that at start-up there's no guarantee that hardware-based
devices have shown up by the time this target is reached, or even acquired
complete IP configuration. For that purpose use network-online.target as
described above.
.RE
.PP 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. Also see Running Services After the Network Is Up[2]
for more information.
Added in version 214.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP remote-fs-pre.target
This target unit is automatically ordered before all mount point units (see
above) and cryptsetup/veritysetup 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).
.RE
.PP rpcbind.target
The portmapper/rpcbind pulls in this target and orders itself before it, to
indicate its availability.
.RE
.PP ssh-access.target
Service and socket units that provide remote SSH secure shell access to the
local system should pull in this unit and order themselves before this unit.
It's supposed to act as a milestone indicating if and when SSH access into
the system is available. It should only become active when an SSH port is
bound for remote clients (i.e. if SSH is used as a local privilege
escalation mechanism, it should not involve this target unit),
regardless of the protocol choices, i.e. regardless of whether IPv4, IPv6 or
AF_VSOCK is used.
Added in version 256.
.RE
.PP time-set.target
Services responsible for setting the system clock (CLOCK_REALTIME)
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, roughly monotonic 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 (see
below), however does not depend on remote clock sources to be reachable,
i.e. the target is typically not delayed by network problems and similar.
Use of this target is recommended for services where approximate clock
accuracy and rough monotonicity is desired but activation shall not be
delayed for possibly unreliable network communication.
The service manager automatically adds dependencies of type After= for
this target unit to all timer units with at least one OnCalendar=
directive.
The systemd-timesyncd.service(8) service is a simple daemon that pulls
in this target and orders itself before it. Besides implementing the SNTP
network protocol it maintains a timestamp file on disk whose modification
time is regularly updated. At service start-up the local system clock is set
from that modification time, ensuring it increases roughly
monotonically.
Note that ordering a unit after time-set.target only has effect if there's
actually a service ordered before it that delays it until the clock is
adjusted for rough monotonicity. Otherwise, this target might get reached
before the clock is adjusted to be roughly monotonic. Enable
systemd-timesyncd.service(8), or an alternative NTP implementation to
delay the target.
Added in version 242.
.RE
.PP time-sync.target
Services indicating completed synchronization of the system clock
(CLOCK_REALTIME) to a remote source should pull in this target and
order themselves before it. Services where accurate time is essential should
be ordered after this unit, but not pull it in.
The service manager automatically adds dependencies of type After= for
this target unit to all timer units with at least one OnCalendar=
directive.
This target provides stricter clock accuracy guarantees than time-set.target
(see above), but likely requires network communication and thus introduces
unpredictable delays. Services that require clock accuracy and where network
communication delays are acceptable should use this target. Services that
require a less accurate clock, and only approximate and roughly monotonic
clock behaviour should use time-set.target instead.
Note that ordering a unit after time-sync.target only has effect if there's
actually a service ordered before it that delays it until clock
synchronization is reached. Otherwise, this target might get reached before
the clock is synchronized to any remote accurate reference clock. When using
systemd-timesyncd.service(8), enable
systemd-time-wait-sync.service(8) to delay the target; or use an
equivalent service for other NTP implementations.
.sp
Table 1. Comparison
| time-set.target | time-sync.target |
| "quick" to reach | "slow" to reach |
| typically uses local clock sources, boot process not affected by availability of external resources | typically uses remote clock sources, inserts dependencies on remote resources into boot process |
| reliable, because local | unreliable, because typically network involved |
| typically guarantees an approximate and roughly monotonic clock only | typically guarantees an accurate clock |
| implemented by systemd-timesyncd.service | implemented by systemd-time-wait-sync.service |
.RE
.SS "Special Slice Units"
.PP 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(5) for details about slice units.
.PP -.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.
Added in version 206.
.RE
.PP 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.
Added in version 206.
.RE
.PP capsule.slice
By default, all capsules encapsulated in capsule@.service are found in this
slice.
Added in version 255.
.RE
.PP system.slice
By default, all system services started by systemd are found in this
slice.
Added in version 206.
.RE
.PP 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.
Added in version 206.
.RE
.SH "UNITS MANAGED BY THE USER SERVICE MANAGER"
.SS "Special User Units"
.PP When systemd runs as a user instance, the following special units are
available:
.PP default.target
This is the main target of the user service manager, started by default when
the service manager is invoked. 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.
Added in version 242.
.RE
.PP capsule@.target
This is the main target of capsule service managers, started by default,
instantiated with the capsule name. This may be used to define different
sets of units that are started for different capsules via generic unit
definitions. For details about capsules see capsule@.service(5).
Added in version 255.
.RE
.PP 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.
.SS "Special Passive User Units"
.PP 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).
.PP Example 2. 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] ...
Added in version 234.
.RE
.PP 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.
Added in version 234.
.RE
.PP xdg-desktop-autostart.target
The XDG specification defines a way to autostart applications using XDG
desktop files. systemd ships systemd-xdg-autostart-generator(8) for
the XDG desktop files in autostart directories. Desktop Environments can
opt-in to use this service by adding a Wants= dependency on
xdg-desktop-autostart.target.
Added in version 246.
.RE
.SS "Special User Slice Units"
.PP There are four .slice units which form the basis of the user hierarchy
for assignment of resources for user applications and services. See
systemd.slice(5) for details about slice units and the documentation
about Desktop Environments[4] for further information.
.PP -.slice
The root slice is the root of the user's slice hierarchy. It usually does not
contain units directly, but may be used to set defaults for the whole
tree.
Added in version 247.
.RE
.PP app.slice
By default, all user services and applications managed by systemd are
found in this slice. All interactively launched applications like web
browsers and text editors as well as non-critical services should be placed
into this slice.
Added in version 247.
.RE
.PP session.slice
All essential services and applications required for the session should use
this slice. These are services that either cannot be restarted easily or
where latency issues may affect the interactivity of the system and
applications. This includes the display server, screen readers and other
services such as DBus or XDG portals. Such services should be configured to
be part of this slice by adding Slice=session.slice to their unit
files.
Added in version 247.
.RE
.PP background.slice
All services running low-priority background tasks should use this slice.
This permits resources to be preferentially assigned to the other slices.
Examples include non-interactive tasks like file indexing or backup
operations where latency is not important.
Added in version 247.
.RE
.SH "SEE ALSO"
.PP 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.
- Factory Reset
- 2.
- Running Services After the Network Is Up
- 3.
- Syslog Interface
- 4.
- Desktop Environments
| systemd 262.2 |