systemd.target
systemd
Developer
Lennart
Poettering
lennart@poettering.net
systemd.target
5
systemd.target
Target unit configuration
target.target
Description
A unit configuration file whose name ends in
.target encodes information about a target unit
of systemd, which is used for grouping units and as well-known
synchronization points during start-up.
This unit type has no specific options. See
systemd.unit5
for the common options of all unit configuration files. The common
configuration items are configured in the generic [Unit] and
[Install] sections. A separate [Target] section does not exist,
since no target-specific options may be configured.
Target units do not offer any additional functionality on
top of the generic functionality provided by units. They exist
merely to group units via dependencies (useful as boot targets),
and to establish standardized names for synchronization points
used in dependencies between units. Among other things, target
units are a more flexible replacement for SysV runlevels in the
classic SysV init system. (And for compatibility reasons special
target units such as runlevel3.target exist
which are used by the SysV runlevel compatibility code in systemd.
See
systemd.special7
for details).
Automatic Dependencies
Implicit Dependencies
There are no implicit dependencies for target units.
Default Dependencies
The following dependencies are added unless
DefaultDependencies=no is set:
Target units will automatically complement all
configured dependencies of type Wants= or
Requires= with dependencies of type
After= unless DefaultDependencies=no
is set in the specified units. Note that Wants= or
Requires= must be defined in the target unit itself — if
you for example define Wants=some.target in
some.service, the automatic ordering will not be added.
Target units automatically gain Conflicts=
dependency against shutdown.target.
Example
Simple standalone target
# emergency-net.target
[Unit]
Description=Emergency Mode with Networking
Requires=emergency.target systemd-networkd.service
After=emergency.target systemd-networkd.service
AllowIsolate=yes
When adding dependencies to other units, it's important to check if they set
DefaultDependencies=. Service units, unless they set
DefaultDependencies=no, automatically get a dependency on
sysinit.target. In this case, both
emergency.target and systemd-networkd.service
have DefaultDependencies=no, so they are suitable for use
in this target, and do not pull in sysinit.target.
You can now switch into this emergency mode by running systemctl
isolate emergency-net.target or by passing the option
systemd.unit=emergency-net.target on the kernel command
line.
Other units can have WantedBy=emergency-net.target in the
[Install] section. After they are enabled using
systemctl enable, they will be started before
emergency-net.target is started. It is also possible to add
arbitrary units as dependencies of emergency.target without
modifying them by using systemctl add-wants.
See Also
systemd1,
systemctl1,
systemd.unit5,
systemd.special7,
systemd.directives7