slice.slice, scope.scope, service.service, socket.socket, mount.mount, swap.swap
Unit configuration files for services, slices, scopes, sockets, mount points, and swap devices share a subset of configuration options for resource control of spawned processes. Internally, this relies on the Linux Control Groups (cgroups) kernel concept for organizing processes in a hierarchical tree of named groups for the purpose of resource management.
This man page lists the configuration options shared by those six unit types. See systemd.unit(5) for the common options of all unit configuration files, and systemd.slice(5), systemd.scope(5), systemd.service(5), systemd.socket(5), systemd.mount(5), and systemd.swap(5) for more information on the specific unit configuration files. The resource control configuration options are configured in the [Slice], [Scope], [Service], [Socket], [Mount], or [Swap] sections, depending on the unit type.
In addition, options which control resources available to programs executed by systemd are listed in systemd.exec(5). Those options complement options listed here.
See the m[blue]New Control Group Interfacesm[][1] for an introduction on how to make use of resource control APIs from programs.
As described in systemd.unit(5), the settings listed here may be set through the main file of a unit and drop-in snippets in *.d/ directories. The list of directories searched for drop-ins includes names formed by repeatedly truncating the unit name after all dashes. This is particularly convenient to set resource limits for a group of units with similar names.
For example, every user gets their own slice user-nnn.slice. Drop-ins with local configuration that affect user 1000 may be placed in /etc/systemd/system/user-1000.slice, /etc/systemd/system/user-1000.slice.d/*.conf, but also /etc/systemd/system/user-.slice.d/*.conf. This last directory applies to all user slices.
The following dependencies are implicitly added:
The unified control group hierarchy is the new version of kernel control group interface, see m[blue]Control Groups v2m[][2]. Depending on the resource type, there are differences in resource control capabilities. Also, because of interface changes, some resource types have separate set of options on the unified hierarchy.
CPU
The "cpuacct" controller does not exist separately on the unified hierarchy.
Memory
IO
To ease the transition, there is best-effort translation between the two versions of settings. For each controller, if any of the settings for the unified hierarchy are present, all settings for the legacy hierarchy are ignored. If the resulting settings are for the other type of hierarchy, the configurations are translated before application.
Legacy control group hierarchy (see m[blue]Control Groups version 1m[][3]), also called cgroup-v1, doesn't allow safe delegation of controllers to unprivileged processes. If the system uses the legacy control group hierarchy, resource control is disabled for the systemd user instance, see systemd(1).
Units of the types listed above can have settings for resource control configuration:
CPUAccounting=
CPUWeight=weight, StartupCPUWeight=weight
While StartupCPUWeight= only applies to the startup phase of the system, CPUWeight= applies to normal runtime of the system, and if the former is not set also to the startup phase. Using StartupCPUWeight= allows prioritizing specific services at boot-up differently than during normal runtime.
These settings replace CPUShares= and StartupCPUShares=.
CPUQuota=
Example: CPUQuota=20% ensures that the executed processes will never get more than 20% CPU time on one CPU.
CPUQuotaPeriodSec=
This controls the second field of "cpu.max" attribute on the unified control group hierarchy and "cpu.cfs_period_us" on legacy. For details about these control group attributes, see m[blue]Control Groups v2m[][2] and m[blue]CFS Schedulerm[][4].
Example: CPUQuotaPeriodSec=10ms to request that the CPU quota is measured in periods of 10ms.
AllowedCPUs=
Setting AllowedCPUs= doesn't guarantee that all of the CPUs will be used by the processes as it may be limited by parent units. The effective configuration is reported as EffectiveCPUs=.
This setting is supported only with the unified control group hierarchy.
AllowedMemoryNodes=
Setting AllowedMemoryNodes= doesn't guarantee that all of the memory NUMA nodes will be used by the processes as it may be limited by parent units. The effective configuration is reported as EffectiveMemoryNodes=.
This setting is supported only with the unified control group hierarchy.
MemoryAccounting=
MemoryMin=bytes, MemoryLow=bytes
For a protection to be effective, it is generally required to set a corresponding allocation on all ancestors, which is then distributed between children (with the exception of the root slice). Any MemoryMin= or MemoryLow= allocation that is not explicitly distributed to specific children is used to create a shared protection for all children. As this is a shared protection, the children will freely compete for the memory.
Takes a memory size in bytes. If the value is suffixed with K, M, G or T, the specified memory size is parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. Alternatively, a percentage value may be specified, which is taken relative to the installed physical memory on the system. If assigned the special value "infinity", all available memory is protected, which may be useful in order to always inherit all of the protection afforded by ancestors. This controls the "memory.min" or "memory.low" control group attribute. For details about this control group attribute, see m[blue]Memory Interface Filesm[][6].
This setting is supported only if the unified control group hierarchy is used and disables MemoryLimit=.
Units may have their children use a default "memory.min" or "memory.low" value by specifying DefaultMemoryMin= or DefaultMemoryLow=, which has the same semantics as MemoryMin= and MemoryLow=. This setting does not affect "memory.min" or "memory.low" in the unit itself. Using it to set a default child allocation is only useful on kernels older than 5.7, which do not support the "memory_recursiveprot" cgroup2 mount option.
MemoryHigh=bytes
Takes a memory size in bytes. If the value is suffixed with K, M, G or T, the specified memory size is parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. Alternatively, a percentage value may be specified, which is taken relative to the installed physical memory on the system. If assigned the special value "infinity", no memory throttling is applied. This controls the "memory.high" control group attribute. For details about this control group attribute, see m[blue]Memory Interface Filesm[][6].
This setting is supported only if the unified control group hierarchy is used and disables MemoryLimit=.
MemoryMax=bytes
Takes a memory size in bytes. If the value is suffixed with K, M, G or T, the specified memory size is parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. Alternatively, a percentage value may be specified, which is taken relative to the installed physical memory on the system. If assigned the special value "infinity", no memory limit is applied. This controls the "memory.max" control group attribute. For details about this control group attribute, see m[blue]Memory Interface Filesm[][6].
This setting replaces MemoryLimit=.
MemorySwapMax=bytes
Takes a swap size in bytes. If the value is suffixed with K, M, G or T, the specified swap size is parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. If assigned the special value "infinity", no swap limit is applied. This controls the "memory.swap.max" control group attribute. For details about this control group attribute, see m[blue]Memory Interface Filesm[][6].
This setting is supported only if the unified control group hierarchy is used and disables MemoryLimit=.
TasksAccounting=
TasksMax=N
The system default for this setting may be controlled with DefaultTasksMax= in systemd-system.conf(5).
IOAccounting=
This setting replaces BlockIOAccounting= and disables settings prefixed with BlockIO or StartupBlockIO.
IOWeight=weight, StartupIOWeight=weight
While StartupIOWeight= only applies to the startup phase of the system, IOWeight= applies to the later runtime of the system, and if the former is not set also to the startup phase. This allows prioritizing specific services at boot-up differently than during runtime.
These settings replace BlockIOWeight= and StartupBlockIOWeight= and disable settings prefixed with BlockIO or StartupBlockIO.
IODeviceWeight=device weight
This setting replaces BlockIODeviceWeight= and disables settings prefixed with BlockIO or StartupBlockIO.
The specified device node should reference a block device that has an I/O scheduler associated, i.e. should not refer to partition or loopback block devices, but to the originating, physical device. When a path to a regular file or directory is specified it is attempted to discover the correct originating device backing the file system of the specified path. This works correctly only for simpler cases, where the file system is directly placed on a partition or physical block device, or where simple 1:1 encryption using dm-crypt/LUKS is used. This discovery does not cover complex storage and in particular RAID and volume management storage devices.
IOReadBandwidthMax=device bytes, IOWriteBandwidthMax=device bytes
These settings replace BlockIOReadBandwidth= and BlockIOWriteBandwidth= and disable settings prefixed with BlockIO or StartupBlockIO.
Similar restrictions on block device discovery as for IODeviceWeight= apply, see above.
IOReadIOPSMax=device IOPS, IOWriteIOPSMax=device IOPS
These settings are supported only if the unified control group hierarchy is used and disable settings prefixed with BlockIO or StartupBlockIO.
Similar restrictions on block device discovery as for IODeviceWeight= apply, see above.
IODeviceLatencyTargetSec=device target
Implies "IOAccounting=yes".
These settings are supported only if the unified control group hierarchy is used.
Similar restrictions on block device discovery as for IODeviceWeight= apply, see above.
IPAccounting=
When this option is used in socket units, it applies to all IPv4 and IPv6 sockets associated with it (including both listening and connection sockets where this applies). Note that for socket-activated services, this configuration setting and the accounting data of the service unit and the socket unit are kept separate, and displayed separately. No propagation of the setting and the collected statistics is done, in either direction. Moreover, any traffic sent or received on any of the socket unit's sockets is accounted to the socket unit --- and never to the service unit it might have activated, even if the socket is used by it.
The system default for this setting may be controlled with DefaultIPAccounting= in systemd-system.conf(5).
IPAddressAllow=ADDRESS[/PREFIXLENGTH]..., IPAddressDeny=ADDRESS[/PREFIXLENGTH]...
The access lists configured with this option are applied to all sockets created by processes of this unit (or in the case of socket units, associated with it). The lists are implicitly combined with any lists configured for any of the parent slice units this unit might be a member of. By default both access lists are empty. Both ingress and egress traffic is filtered by these settings. In case of ingress traffic the source IP address is checked against these access lists, in case of egress traffic the destination IP address is checked. The following rules are applied in turn:
In order to implement an allow-listing IP firewall, it is recommended to use a IPAddressDeny=any setting on an upper-level slice unit (such as the root slice -.slice or the slice containing all system services system.slice - see systemd.special(7) for details on these slice units), plus individual per-service IPAddressAllow= lines permitting network access to relevant services, and only them.
Note that for socket-activated services, the IP access list configured on the socket unit applies to all sockets associated with it directly, but not to any sockets created by the ultimately activated services for it. Conversely, the IP access list configured for the service is not applied to any sockets passed into the service via socket activation. Thus, it is usually a good idea to replicate the IP access lists on both the socket and the service unit. Nevertheless, it may make sense to maintain one list more open and the other one more restricted, depending on the usecase.
If these settings are used multiple times in the same unit the specified lists are combined. If an empty string is assigned to these settings the specific access list is reset and all previous settings undone.
In place of explicit IPv4 or IPv6 address and prefix length specifications a small set of symbolic names may be used. The following names are defined:
Table 1. Special address/network names
| Symbolic Name | Definition |
Meaning
|
| any | 0.0.0.0/0 ::/0 |
Any host
|
| localhost | 127.0.0.0/8 ::1/128 |
All addresses on the local loopback
|
| link-local | 169.254.0.0/16 fe80::/64 |
All link-local IP addresses
|
| multicast | 224.0.0.0/4 ff00::/8 |
All IP multicasting addresses
|
Note that these settings might not be supported on some systems (for example if eBPF control group support is not enabled in the underlying kernel or container manager). These settings will have no effect in that case. If compatibility with such systems is desired it is hence recommended to not exclusively rely on them for IP security.
IPIngressFilterPath=BPF_FS_PROGRAM_PATH, IPEgressFilterPath=BPF_FS_PROGRAM_PATH
The filters configured with this option are applied to all sockets created by processes of this unit (or in the case of socket units, associated with it). The filters are loaded in addition to filters any of the parent slice units this unit might be a member of as well as any IPAddressAllow= and IPAddressDeny= filters in any of these units. By default there are no filters specified.
If these settings are used multiple times in the same unit all the specified programs are attached. If an empty string is assigned to these settings the program list is reset and all previous specified programs ignored.
Note that for socket-activated services, the IP filter programs configured on the socket unit apply to all sockets associated with it directly, but not to any sockets created by the ultimately activated services for it. Conversely, the IP filter programs configured for the service are not applied to any sockets passed into the service via socket activation. Thus, it is usually a good idea, to replicate the IP filter programs on both the socket and the service unit, however it often makes sense to maintain one configuration more open and the other one more restricted, depending on the usecase.
Note that these settings might not be supported on some systems (for example if eBPF control group support is not enabled in the underlying kernel or container manager). These settings will fail the service in that case. If compatibility with such systems is desired it is hence recommended to attach your filter manually (requires Delegate=yes) instead of using this setting.
DeviceAllow=
The device node specifier is either a path to a device node in the file system, starting with /dev/, or a string starting with either "char-" or "block-" followed by a device group name, as listed in /proc/devices. The latter is useful to allow-list all current and future devices belonging to a specific device group at once. The device group is matched according to filename globbing rules, you may hence use the "*" and "?" wildcards. (Note that such globbing wildcards are not available for device node path specifications!) In order to match device nodes by numeric major/minor, use device node paths in the /dev/char/ and /dev/block/ directories. However, matching devices by major/minor is generally not recommended as assignments are neither stable nor portable between systems or different kernel versions.
Examples: /dev/sda5 is a path to a device node, referring to an ATA or SCSI block device. "char-pts" and "char-alsa" are specifiers for all pseudo TTYs and all ALSA sound devices, respectively. "char-cpu/*" is a specifier matching all CPU related device groups.
Note that allow lists defined this way should only reference device groups which are resolvable at the time the unit is started. Any device groups not resolvable then are not added to the device allow list. In order to work around this limitation, consider extending service units with a pair of After=modprobe@xyz.service and Wants=modprobe@xyz.service lines that load the necessary kernel module implementing the device group if missing. Example:
... [Unit] Wants=modprobe@loop.service After=modprobe@loop.service [Service] DeviceAllow=block-loop DeviceAllow=/dev/loop-control ...
DevicePolicy=auto|closed|strict
strict
closed
auto
Slice=
This option may be used to arrange systemd units in a hierarchy of slices each of which might have resource settings applied.
For units of type slice, the only accepted value for this setting is the parent slice. Since the name of a slice unit implies the parent slice, it is hence redundant to ever set this parameter directly for slice units.
Special care should be taken when relying on the default slice assignment in templated service units that have DefaultDependencies=no set, see systemd.service(5), section "Default Dependencies" for details.
Delegate=
Note that controller delegation to less privileged code is only safe on the unified control group hierarchy. Accordingly, access to the specified controllers will not be granted to unprivileged services on the legacy hierarchy, even when requested.
The following controller names may be specified: cpu, cpuacct, cpuset, io, blkio, memory, devices, pids, bpf-firewall, and bpf-devices.
Not all of these controllers are available on all kernels however, and some are specific to the unified hierarchy while others are specific to the legacy hierarchy. Also note that the kernel might support further controllers, which aren't covered here yet as delegation is either not supported at all for them or not defined cleanly.
For further details on the delegation model consult m[blue]Control Group APIs and Delegationm[][10].
DisableControllers=
It may not be possible to successfully disable a controller if the unit or any child of the unit in question delegates controllers to its children, as any delegated subtree of the cgroup hierarchy is unmanaged by systemd.
Multiple controllers may be specified, separated by spaces. You may also pass DisableControllers= multiple times, in which case each new instance adds another controller to disable. Passing DisableControllers= by itself with no controller name present resets the disabled controller list.
The following controller names may be specified: cpu, cpuacct, cpuset, io, blkio, memory, devices, pids, bpf-firewall, and bpf-devices.
ManagedOOMSwap=auto|kill, ManagedOOMMemoryPressure=auto|kill
When set to kill, systemd-oomd will actively monitor this unit's cgroup metrics to decide whether it needs to act. If the cgroup passes the limits set by oomd.conf(5) or its overrides, systemd-oomd will send a SIGKILL to all of the processes under the chosen candidate cgroup. Note that only descendant cgroups can be eligible candidates for killing; the unit that set its property to kill is not a candidate (unless one of its ancestors set their property to kill). You can find more details on candidates and kill behavior at systemd-oomd.service(8) and oomd.conf(5). Setting either of these properties to kill will also automatically acquire After= and Wants= dependencies on systemd-oomd.service unless DefaultDependencies=no.
When set to auto, systemd-oomd will not actively use this cgroup's data for monitoring and detection. However, if an ancestor cgroup has one of these properties set to kill, a unit with auto can still be an eligible candidate for systemd-oomd to act on.
ManagedOOMMemoryPressureLimit=
ManagedOOMPreference=none|avoid|omit
If this property is set to avoid, the service manager will convey this to systemd-oomd, which will only select this cgroup if there are no other viable candidates.
If this property is set to omit, the service manager will convey this to systemd-oomd, which will ignore this cgroup as a candidate and will not perform any actions on it.
It is recommended to use avoid and omit sparingly, as it can adversely affect systemd-oomd's kill behavior. Also note that these extended attributes are not applied recursively to cgroups under this unit's cgroup.
Defaults to none which means systemd-oomd will rank this unit's cgroup as defined in systemd-oomd.service(8) and oomd.conf(5).
The following options are deprecated. Use the indicated superseding options instead:
CPUShares=weight, StartupCPUShares=weight
While StartupCPUShares= only applies to the startup phase of the system, CPUShares= applies to normal runtime of the system, and if the former is not set also to the startup phase. Using StartupCPUShares= allows prioritizing specific services at boot-up differently than during normal runtime.
Implies "CPUAccounting=yes".
These settings are deprecated. Use CPUWeight= and StartupCPUWeight= instead.
MemoryLimit=bytes
Implies "MemoryAccounting=yes".
This setting is deprecated. Use MemoryMax= instead.
BlockIOAccounting=
This setting is deprecated. Use IOAccounting= instead.
BlockIOWeight=weight, StartupBlockIOWeight=weight
While StartupBlockIOWeight= only applies to the startup phase of the system, BlockIOWeight= applies to the later runtime of the system, and if the former is not set also to the startup phase. This allows prioritizing specific services at boot-up differently than during runtime.
Implies "BlockIOAccounting=yes".
These settings are deprecated. Use IOWeight= and StartupIOWeight= instead.
BlockIODeviceWeight=device weight
Implies "BlockIOAccounting=yes".
This setting is deprecated. Use IODeviceWeight= instead.
BlockIOReadBandwidth=device bytes, BlockIOWriteBandwidth=device bytes
Implies "BlockIOAccounting=yes".
These settings are deprecated. Use IOReadBandwidthMax= and IOWriteBandwidthMax= instead.
systemd(1), systemd-system.conf(5), systemd.unit(5), systemd.service(5), systemd.slice(5), systemd.scope(5), systemd.socket(5), systemd.mount(5), systemd.swap(5), systemd.exec(5), systemd.directives(7), systemd.special(7), systemd-oomd.service(8), The documentation for control groups and specific controllers in the Linux kernel: m[blue]Control Groups v2m[][2].