SYSTEMD.SPECIAL(7) | systemd.special | SYSTEMD.SPECIAL(7) |
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, getty-pre.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-cryptsetup.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, 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 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
cryptsetup.target
dbus.service
dbus.socket
default.target
The default unit systemd starts at bootup can be overridden with the systemd.unit= kernel command line option.
display-manager.service
emergency.target
final.target
getty.target
getty-pre.target
graphical.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
hybrid-sleep.target
halt.target
Applications wanting to halt the system should start this unit.
initrd-fs.target
kbrequest.target
kexec.target
Applications wanting to reboot the system with kexec should start this unit.
local-fs.target
multi-user.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
Note the distinction between this unit and network.target. This unit is an active unit (i.e. pulled in by the consumer rather than the provider of this functionality) and pulls in a service which possibly adds substantial delays to further execution. In contrast, network.target is a passive unit (i.e. pulled in by the provider of the functionality, rather than the consumer) that usually does not delay execution much. Usually, network.target is part of the boot of most systems, while network-online.target is not, except when at least one unit requires it. Also see Running Services After the Network is up[1] for more information.
All mount units for remote network file systems automatically pull in this unit, and order themselves after it. Note that networking daemons that simply provide functionality to other hosts generally do not need to pull this in.
paths.target
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
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
Applications wanting to reboot the system should start this unit.
runlevel6.target is an alias for this target unit, for compatibility with SysV.
remote-cryptsetup.target
remote-fs.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 "$remote_fs" facility.
rescue.target
runlevel1.target is an alias for this target unit, for compatibility with SysV.
initrd-root-fs.target
runlevel2.target, runlevel3.target, runlevel4.target, runlevel5.target
shutdown.target
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
sleep.target
sockets.target
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
swap.target
sysinit.target
syslog.socket
system-update.target
timers.target
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
Mounts that shall be unmounted on system shutdown shall add Conflicts dependencies to this unit for their mount unit, which is implicitly done when DefaultDependencies=yes is set (the default).
SPECIAL SYSTEM UNITS FOR DEVICES¶
Some target units are automatically pulled in as devices of certain kinds show up in the system. These may be used to automatically activate various services based on the specific type of the available hardware.
bluetooth.target
This may be used to pull in Bluetooth management daemons dynamically when Bluetooth hardware is found.
printer.target
This may be used to pull in printer management daemons dynamically when printer hardware is found.
smartcard.target
This may be used to pull in smartcard management daemons dynamically when smartcard hardware is found.
sound.target
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.
cryptsetup-pre.target
local-fs-pre.target
network.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 "$network" facility.
network-pre.target
nss-lookup.target
nss-user-lookup.target
remote-fs-pre.target
rpcbind.target
time-sync.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.
-.slice
system.slice
user.slice
machine.slice
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)
NOTES¶
- 1.
- Running Services After the Network is up
- 2.
- Syslog Interface
- 3.
- System Updates Specification
systemd 219 |