User:Johannbg/QA/Systemd/Systemd.special

Name
systemd.special — special systemd units

Synopsis
basic.target, ctrl-alt-del.target, dbus.service, dbus.target, default.target, display-manager.service, emergency.target, exit.service, graphical.target, halt.target, kbrequest.target, local-fs.target, mail-transfer-agent.target, multi-user.target, network.target, nss-lookup.target, poweroff.target, reboot.target, remote-fs.target, rescue.target, rpcbind.target, rtc-set.target, runlevel2.target, runlevel3.target, runlevel4.target, runlevel5.target, shutdown.target, sigpwr.target, sockets.target, swap.target, sysinit.target, rsyslog.service, syslog.target, systemd-initctl.service, systemd-initctl.socket, systemd-logger.service, systemd-logger.socket, umount.target

Description
A few units are treated specially by systemd. They have special internal semantics and cannot be renamed.

Special System Units
basic.target A special target unit covering early boot-up.

systemd automatically adds dependencies of the types Requires and After for this target unit to all SysV service units configured for runlevel 1 to 5.

Usually this should pull-in all sockets, mount points, swap devices and other basic initialization necessary for the general purpose daemons. Most normal daemons should have dependencies of type After and Requires on this unit.

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.

dbus.service A special unit for the D-Bus system bus. As soon as this service is fully started up systemd will connect to it and register its service.

Units should generally avoid depending on this unit directly and instead refer to the dbus.target unit instead, which pulls this one in directly or indirectly via socket-based activation.

dbus.target Administrators should ensure that this target pulls in a service unit with the name or alias of dbus.service (or a socket unit that activates this service).

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 overriden with the systemd.default= kernel command line option.

display-manager.service The display manager service. Usually this should be aliased (symlinked) to xdm.service or a similar display manager service.

systemd automatically adds dependencies of type After for this target unit to all SysV init script service units with a LSB header referring to the $x-display-manager facility, for compatibility with Debian.

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.default= and has otherwise little use.

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 login shall add Wants dependencies for their unit to this unit (or multi-user.target) during installation.

halt.target A special target unit for shutting down and halting the system.

Applications wanting to halt the system should start this unit.

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.

local-fs.target systemd automatically adds dependencies of type After to all mount units that refer to local mount points for this target unit. In addition, systemd adds dependencies of type Wants to this target unit for those mounts listed in /etc/fstab that have the auto and comment=systemd.mount mount options 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.

mail-transfer-agent.target The mail transfer agent (MTA) service. Usually this should pull-in all units necessary for sending/receiving mails on the local host.

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 $mail-transfer-argent or $mail-transport-agent facilities, for compatibility with Debian.

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 to this unit for their unit during installation.

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.

nss-lookup.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 $named facility.

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.

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 $rpcbind facility.

rtc-set.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.

runlevel2.target This is a target that is called whever the SysV compatibility code asks for runlevel 2. It is a good idea to make this an alias for (i.e. symlink to) multi-user.target.

runlevel3.target This is a target that is called whever the SysV compatibility code asks for runlevel 3. It is a good idea to make this an alias for (i.e. symlink to) multi-user.target or graphical.target.

runlevel4.target This is a target that is called whever the SysV compatibility code asks for runlevel 4. It is a good idea to make this an alias for (i.e. symlink to) multi-user.target or graphical.target.

runlevel5.target This is a target that is called whever the SysV compatibility code asks for runlevel 5. It is a good idea to make this an alias for (i.e. symlink to) multi-user.target or graphical.target.

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).

systemd automatically adds dependencies of type Conflicts to this target unit for all SysV init script service units that shall be terminated in SysV runlevels 0 or 6.

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.

sockets.target A special target unit that sets up all service sockets.

Services that can be socket-activated shall add Wants dependencies to this unit for their socket unit during installation.

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.

systemd automatically adds dependencies of the types Wants and After for all SysV service units configured for runlevels that are not 0 to 6 to this target unit. This covers the special boot-up runlevels some distributions have, such as S or b.

rsyslog.service A special unit for the syslog daemon. As soon as this service is fully started up systemd will connect to it and use it for logging if it has been configured for that.

Units should generally avoid depending on this unit directly and instead refer to the syslog.target unit instead, which pulls this one in directly or indirectly via socket-based activation.

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.

Administrators should ensure that this target pulls in a service unit with the name or alias of rsyslog.service (or a socket unit that activates this service).

systemd-initctl.service This provides compatibility with the SysV /dev/initctl file system FIFO for communication with the init system.

This is a socket-activated service, see system-initctl.socket.

systemd-initctl.socket Socket activation unit for system-initctl.service.

systemd-logger.service This is internally used by systemd to provide syslog logging to the processes it maintains.

This is a socket-activated service, see system-logger.socket.

systemd-logger.socket Socket activation unit for system-logger.service. systemd will automatically add dependencies of types Requires and After to all units that have been configured for stdout or stderr to be connected to syslog or the kernel log buffer.

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 Session Units
When systemd runs as a service instance, the following special units are available, which have similar definitions as their system counterparts: default.target, local-fs.target, remote-fs.target, shutdown.target, sockets.target, swap.target.

In addition the following special unit is understood only when systemd runs as service instance: exit.service A special service unit for shutting down the session.

Applications wanting to terminate the session should start this unit. If systemd receives SIGTERM or SIGINT when running as session 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 session exit.