systemd.slice — Slice unit configuration
slice.slice
A unit configuration file whose name ends in ".slice" encodes information about a slice
unit. A slice unit is a concept for hierarchically managing resources of a group of processes. This management is
performed by creating a node in the Linux Control Group (cgroup) tree. Units that manage processes (primarily scope
and service units) may be assigned to a specific slice. For each slice, certain resource limits may be set that
apply to all processes of all units contained in that slice. Slices are organized hierarchically in a tree. The
name of the slice encodes the location in the tree. The name consists of a dash-separated series of names, which
describes the path to the slice from the root slice. The root slice is named -.slice. Example:
foo-bar.slice is a slice that is located within foo.slice, which in turn
is located in the root slice -.slice.
Note that slice units cannot be templated, nor is possible to add multiple names to a slice unit by creating additional symlinks to its unit file.
By default, service and scope units are placed in
system.slice, virtual machines and containers
registered with
systemd-machined(8)
are found in machine.slice, and user sessions
handled by
systemd-logind(8)
in user.slice. See
systemd.special(7)
for more information.
See systemd.unit(5) for the common options of all unit configuration files. The common configuration items are configured in the generic [Unit] and [Install] sections. The slice specific configuration options are configured in the [Slice] section. Currently, only generic resource control settings as described in systemd.resource-control(5) are allowed.
See the New Control Group Interfaces for an introduction on how to make use of slice units from programs.
The following dependencies are implicitly added:
Slice units automatically gain dependencies of type
After= and Requires= on
their immediate parent slice unit.
The following dependencies are added unless DefaultDependencies=no is set:
Slice units will automatically have dependencies of type Conflicts= and
Before= on
shutdown.target. These ensure that slice units are removed prior to system shutdown.
Only slice units involved with late system shutdown should disable
DefaultDependencies= option.
Slice unit files may include [Unit] and [Install] sections, which are described in systemd.unit(5).
Slice files may include a [Slice] section. Many options that may be used in this section are shared with other unit types. These options are documented in systemd.resource-control(5).
The options specific to the [Slice] section of slice units are the following:
ConcurrencyHardMax=, ConcurrencySoftMax=¶Configures a hard and a soft limit on the maximum number of units assigned to this slice (or any descendent slices) that may be active at the same time. If the hard limit is reached no further units associated with the slice may be activated, and their activation will fail with an error. If the soft limit is reached any further requested activation of units will be queued, but no immediate error is generated. The queued activation job will remain queued until the number of concurrent active units within the slice is below the limit again.
If the special value "infinity" is specified, no concurrency limit is
enforced. This is the default.
Note that if multiple start jobs are queued for units, and all their dependencies are fulfilled
they'll be processed in an order that is dependent on the unit type, the CPU weight (for unit types
that know the concept, such as services), the nice level (similar), and finally in alphabetical order
by the unit name. This may be used to influence dispatching order when using
ConcurrencySoftMax= to pace concurrency within a slice unit.
Note that these options have a hierarchial effect: a limit set for a slice unit will apply to both the units immediately within the slice, but also all units further down the slice tree. Also note that each sub-slice unit counts as one unit each too, and thus when choosing a limit for a slice hierarchy the limit must provide room for both the payload units (i.e. services, mounts, …) and structural units (i.e. slice units), if any are defined.