NAME¶systemd.special - Special systemd units
SYNOPSIS¶basic.target, bluetooth.target, ctrl-alt-del.target, cryptsetup.target, cryptsetup-pre.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, network-pre.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-device.target, initrd-root-fs.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
DESCRIPTION¶A few units are treated specially by systemd. They have special internal semantics and cannot be renamed.
SPECIAL SYSTEM UNITS¶basic.target
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.
The default unit systemd starts at bootup can be overridden with the systemd.unit= kernel command line option.
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.
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.
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.
Applications wanting to halt the system should start this unit.
Applications wanting to reboot the system with kexec should start this unit.
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.
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.
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.
Applications wanting to power off the system should start this unit.
runlevel0.target is an alias for this target unit, for compatibility with SysV.
Applications wanting to reboot the system should start this unit.
runlevel6.target is an alias for this target unit, for compatibility with SysV.
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.
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
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).
It's a good idea to add WantedBy=slices.target lines to the "[Install]" section of all slices units that may be installed dynamically.
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.
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).
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.
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.
This may be used to pull in Bluetooth management daemons dynamically when Bluetooth hardware is found.
This may be used to pull in printer management daemons dynamically when printer hardware is found.
This may be used to pull in smartcard management daemons dynamically when smartcard hardware is found.
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.
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.
SPECIAL USER UNITS¶When systemd runs as a user instance, the following special units are available, which have similar definitions as their system counterparts: exit.target, default.target, shutdown.target, sockets.target, timers.target, paths.target, bluetooth.target, printer.target, smartcard.target, sound.target.
SPECIAL PASSIVE USER UNITS¶
graphical-session.target¶This target is active whenever any graphical session is running. It is used to stop user services which only apply to a graphical (X, Wayland, etc.) session when the session is terminated. Such services should have "PartOf=graphical-session.target" in their "[Unit]" section. A target for a particular session (e. g. gnome-session.target) starts and stops "graphical-session.target" with "BindsTo=graphical-session.target".
Which services are started by a session target is determined by the "Wants=" and "Requires=" dependencies. For services that can be enabled independently, symlinks in ".wants/" and ".requires/" should be used, see systemd.unit(5). Those symlinks should either be shipped in packages, or should be added dynamically after installation, for example using "systemctl add-wants", see systemctl(1).
Example 1. Nautilus as part of a GNOME session
"gnome-session.target" pulls in Nautilus as top-level service:
[Unit] Description=User systemd services for GNOME graphical session Wants=nautilus.service BindsTo=graphical-session.target
"nautilus.service" gets stopped when the session stops:
[Unit] Description=Render the desktop icons with Nautilus PartOf=graphical-session.target [Service] ...
graphical-session-pre.target¶This target contains services which set up the environment or global configuration of a graphical session, such as SSH/GPG agents (which need to export an environment variable into all desktop processes) or migration of obsolete d-conf keys after an OS upgrade (which needs to happen before starting any process that might use them). This target must be started before starting a graphical session like gnome-session.target.
SPECIAL SLICE UNITS¶There are four ".slice" units which form the basis of the hierarchy for assignment of resources for services, users, and virtual machines or containers.
SEE ALSO¶systemd(1), systemd.unit(5), systemd.service(5), systemd.socket(5), systemd.target(5), systemd.slice(5), bootup(7), systemd-fstab-generator(8)
- Running Services After the Network is up
- Syslog Interface
- System Updates Specification