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SYSTEMD.RESOURCE-CONTROL(5)systemd.resource-controlSYSTEMD.RESOURCE-CONTROL(5)

NAME
       systemd.resource-control - Resource control unit settings

SYNOPSIS
       slice.slice, scope.scope, service.service, socket.socket, mount.mount,
       swap.swap

DESCRIPTION
       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 New Control Group Interfaces[1] for an introduction on how to
       make use of resource control APIs from programs.

IMPLICIT DEPENDENCIES
       The following dependencies are implicitly added:

       o   Units with the Slice= setting set automatically acquire Requires=
           and After= dependencies on the specified slice unit.

UNIFIED AND LEGACY CONTROL GROUP HIERARCHIES
       The unified control group hierarchy is the new version of kernel
       control group interface, see Control Groups v2[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
           CPUWeight= and StartupCPUWeight= replace CPUShares= and
           StartupCPUShares=, respectively.

           The "cpuacct" controller does not exist separately on the unified
           hierarchy.

       Memory
           MemoryMax= replaces MemoryLimit=.  MemoryLow= and MemoryHigh= are
           effective only on unified hierarchy.

       IO
           "IO"-prefixed settings are a superset of and replace
           "BlockIO"-prefixed ones. On unified hierarchy, IO resource control
           also applies to buffered writes.

       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 Control Groups version 1[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).

OPTIONS
       Units of the types listed above can have settings for resource control
       configuration:

       CPUAccounting=
           Turn on CPU usage accounting for this unit. Takes a boolean
           argument. Note that turning on CPU accounting for one unit will
           also implicitly turn it on for all units contained in the same
           slice and for all its parent slices and the units contained
           therein. The system default for this setting may be controlled with
           DefaultCPUAccounting= in systemd-system.conf(5).

       CPUWeight=weight, StartupCPUWeight=weight
           Assign the specified CPU time weight to the processes executed, if
           the unified control group hierarchy is used on the system. These
           options take an integer value and control the "cpu.weight" control
           group attribute. The allowed range is 1 to 10000. Defaults to 100.
           For details about this control group attribute, see Control Groups
           v2[2] and CFS Scheduler[4]. The available CPU time is split up
           among all units within one slice relative to their CPU time 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=
           Assign the specified CPU time quota to the processes executed.
           Takes a percentage value, suffixed with "%". The percentage
           specifies how much CPU time the unit shall get at maximum, relative
           to the total CPU time available on one CPU. Use values > 100% for
           allotting CPU time on more than one CPU. This controls the
           "cpu.max" attribute on the unified control group hierarchy and
           "cpu.cfs_quota_us" on legacy. For details about these control group
           attributes, see Control Groups v2[2] and sched-bwc.txt[5].

           Example: CPUQuota=20% ensures that the executed processes will
           never get more than 20% CPU time on one CPU.

       CPUQuotaPeriodSec=
           Assign the duration over which the CPU time quota specified by
           CPUQuota= is measured. Takes a time duration value in seconds, with
           an optional suffix such as "ms" for milliseconds (or "s" for
           seconds.) The default setting is 100ms. The period is clamped to
           the range supported by the kernel, which is [1ms, 1000ms].
           Additionally, the period is adjusted up so that the quota interval
           is also at least 1ms. Setting CPUQuotaPeriodSec= to an empty value
           resets it to the default.

           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 Control
           Groups v2[2] and CFS Scheduler[4].

           Example: CPUQuotaPeriodSec=10ms to request that the CPU quota is
           measured in periods of 10ms.

       AllowedCPUs=
           Restrict processes to be executed on specific CPUs. Takes a list of
           CPU indices or ranges separated by either whitespace or commas. CPU
           ranges are specified by the lower and upper CPU indices separated
           by a dash.

           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=
           Restrict processes to be executed on specific memory NUMA nodes.
           Takes a list of memory NUMA nodes indices or ranges separated by
           either whitespace or commas. Memory NUMA nodes ranges are specified
           by the lower and upper CPU indices separated by a dash.

           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=
           Turn on process and kernel memory accounting for this unit. Takes a
           boolean argument. Note that turning on memory accounting for one
           unit will also implicitly turn it on for all units contained in the
           same slice and for all its parent slices and the units contained
           therein. The system default for this setting may be controlled with
           DefaultMemoryAccounting= in systemd-system.conf(5).

       MemoryMin=bytes
           Specify the memory usage protection of the executed processes in
           this unit. If the memory usages of this unit and all its ancestors
           are below their minimum boundaries, this unit's memory won't be
           reclaimed.

           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" control group attribute. For details about this
           control group attribute, see Memory Interface Files[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" value by
           specifying DefaultMemoryMin=, which has the same semantics as
           MemoryMin=. This setting does not affect "memory.min" in the unit
           itself.

       MemoryLow=bytes
           Specify the best-effort memory usage protection of the executed
           processes in this unit. If the memory usages of this unit and all
           its ancestors are below their low boundaries, this unit's memory
           won't be reclaimed as long as memory can be reclaimed from
           unprotected units.

           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.low" control group attribute. For details about this
           control group attribute, see Memory Interface Files[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.low" value by
           specifying DefaultMemoryLow=, which has the same semantics as
           MemoryLow=. This setting does not affect "memory.low" in the unit
           itself.

       MemoryHigh=bytes
           Specify the throttling limit on memory usage of the executed
           processes in this unit. Memory usage may go above the limit if
           unavoidable, but the processes are heavily slowed down and memory
           is taken away aggressively in such cases. This is the main
           mechanism to control memory usage of a unit.

           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 Memory
           Interface Files[6].

           This setting is supported only if the unified control group
           hierarchy is used and disables MemoryLimit=.

       MemoryMax=bytes
           Specify the absolute limit on memory usage of the executed
           processes in this unit. If memory usage cannot be contained under
           the limit, out-of-memory killer is invoked inside the unit. It is
           recommended to use MemoryHigh= as the main control mechanism and
           use MemoryMax= as the last line of defense.

           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 Memory Interface Files[6].

           This setting replaces MemoryLimit=.

       MemorySwapMax=bytes
           Specify the absolute limit on swap usage of the executed processes
           in this unit.

           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 Memory Interface
           Files[6].

           This setting is supported only if the unified control group
           hierarchy is used and disables MemoryLimit=.

       TasksAccounting=
           Turn on task accounting for this unit. Takes a boolean argument. If
           enabled, the system manager will keep track of the number of tasks
           in the unit. The number of tasks accounted this way includes both
           kernel threads and userspace processes, with each thread counting
           individually. Note that turning on tasks accounting for one unit
           will also implicitly turn it on for all units contained in the same
           slice and for all its parent slices and the units contained
           therein. The system default for this setting may be controlled with
           DefaultTasksAccounting= in systemd-system.conf(5).

       TasksMax=N
           Specify the maximum number of tasks that may be created in the
           unit. This ensures that the number of tasks accounted for the unit
           (see above) stays below a specific limit. This either takes an
           absolute number of tasks or a percentage value that is taken
           relative to the configured maximum number of tasks on the system.
           If assigned the special value "infinity", no tasks limit is
           applied. This controls the "pids.max" control group attribute. For
           details about this control group attribute, see Process Number
           Controller[7].

           The system default for this setting may be controlled with
           DefaultTasksMax= in systemd-system.conf(5).

       IOAccounting=
           Turn on Block I/O accounting for this unit, if the unified control
           group hierarchy is used on the system. Takes a boolean argument.
           Note that turning on block I/O accounting for one unit will also
           implicitly turn it on for all units contained in the same slice and
           all for its parent slices and the units contained therein. The
           system default for this setting may be controlled with
           DefaultIOAccounting= in systemd-system.conf(5).

           This setting replaces BlockIOAccounting= and disables settings
           prefixed with BlockIO or StartupBlockIO.

       IOWeight=weight, StartupIOWeight=weight
           Set the default overall block I/O weight for the executed
           processes, if the unified control group hierarchy is used on the
           system. Takes a single weight value (between 1 and 10000) to set
           the default block I/O weight. This controls the "io.weight" control
           group attribute, which defaults to 100. For details about this
           control group attribute, see IO Interface Files[8]. The available
           I/O bandwidth is split up among all units within one slice relative
           to their block I/O 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
           Set the per-device overall block I/O weight for the executed
           processes, if the unified control group hierarchy is used on the
           system. Takes a space-separated pair of a file path and a weight
           value to specify the device specific weight value, between 1 and
           10000. (Example: "/dev/sda 1000"). The file path may be specified
           as path to a block device node or as any other file, in which case
           the backing block device of the file system of the file is
           determined. This controls the "io.weight" control group attribute,
           which defaults to 100. Use this option multiple times to set
           weights for multiple devices. For details about this control group
           attribute, see IO Interface Files[8].

           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
           Set the per-device overall block I/O bandwidth maximum limit for
           the executed processes, if the unified control group hierarchy is
           used on the system. This limit is not work-conserving and the
           executed processes are not allowed to use more even if the device
           has idle capacity. Takes a space-separated pair of a file path and
           a bandwidth value (in bytes per second) to specify the device
           specific bandwidth. The file path may be a path to a block device
           node, or as any other file in which case the backing block device
           of the file system of the file is used. If the bandwidth is
           suffixed with K, M, G, or T, the specified bandwidth is parsed as
           Kilobytes, Megabytes, Gigabytes, or Terabytes, respectively, to the
           base of 1000. (Example:
           "/dev/disk/by-path/pci-0000:00:1f.2-scsi-0:0:0:0 5M"). This
           controls the "io.max" control group attributes. Use this option
           multiple times to set bandwidth limits for multiple devices. For
           details about this control group attribute, see IO Interface
           Files[8].

           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
           Set the per-device overall block I/O IOs-Per-Second maximum limit
           for the executed processes, if the unified control group hierarchy
           is used on the system. This limit is not work-conserving and the
           executed processes are not allowed to use more even if the device
           has idle capacity. Takes a space-separated pair of a file path and
           an IOPS value to specify the device specific IOPS. The file path
           may be a path to a block device node, or as any other file in which
           case the backing block device of the file system of the file is
           used. If the IOPS is suffixed with K, M, G, or T, the specified
           IOPS is parsed as KiloIOPS, MegaIOPS, GigaIOPS, or TeraIOPS,
           respectively, to the base of 1000. (Example:
           "/dev/disk/by-path/pci-0000:00:1f.2-scsi-0:0:0:0 1K"). This
           controls the "io.max" control group attributes. Use this option
           multiple times to set IOPS limits for multiple devices. For details
           about this control group attribute, see IO Interface Files[8].

           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
           Set the per-device average target I/O latency for the executed
           processes, if the unified control group hierarchy is used on the
           system. Takes a file path and a timespan separated by a space to
           specify the device specific latency target. (Example: "/dev/sda
           25ms"). The file path may be specified as path to a block device
           node or as any other file, in which case the backing block device
           of the file system of the file is determined. This controls the
           "io.latency" control group attribute. Use this option multiple
           times to set latency target for multiple devices. For details about
           this control group attribute, see IO Interface Files[8].

           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=
           Takes a boolean argument. If true, turns on IPv4 and IPv6 network
           traffic accounting for packets sent or received by the unit. When
           this option is turned on, all IPv4 and IPv6 sockets created by any
           process of the unit are accounted for.

           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]...
           Turn on address range network traffic filtering for IP packets sent
           and received over AF_INET and AF_INET6 sockets. Both directives
           take a space separated list of IPv4 or IPv6 addresses, each
           optionally suffixed with an address prefix length in bits
           (separated by a "/" character). If the latter is omitted, the
           address is considered a host address, i.e. the prefix covers the
           whole address (32 for IPv4, 128 for IPv6).

           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 all 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. When configured the lists are enforced as follows:

           o   Access will be granted in case an IP packet's
               destination/source address matches any entry in the
               IPAddressAllow= setting.

           o   Otherwise, access will be denied in case its destination/source
               address matches any entry in the IPAddressDeny= setting.

           o   Otherwise, access will be granted.

           In order to implement a whitelisting 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, however it often makes 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      | All link-local IP   |
           |              | fe80::/64           | addresses           |
           +--------------+---------------------+---------------------+
           |multicast     | 224.0.0.0/4         | All IP multicasting |
           |              | ff00::/8            | 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_PROGRAMM_PATH,
       IPEgressFilterPath=BPF_FS_PROGRAMM_PATH
           Add custom network traffic filters implemented as BPF programs,
           applying to all IP packets sent and received over AF_INET and
           AF_INET6 sockets. Takes an absolute path to a pinned BPF program in
           the BPF virtual filesystem (/sys/fs/bpf/).

           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=
           Control access to specific device nodes by the executed processes.
           Takes two space-separated strings: a device node specifier followed
           by a combination of r, w, m to control reading, writing, or
           creation of the specific device node(s) by the unit (mknod),
           respectively. On cgroup-v1 this controls the "devices.allow"
           control group attribute. For details about this control group
           attribute, see Device Whitelist Controller[9]. In the unified
           cgroup hierarchy this functionality is implemented using eBPF
           filtering.

           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 whitelist 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 whitelists 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
           whitelist. 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
           Control the policy for allowing device access:

           strict
               means to only allow types of access that are explicitly
               specified.

           closed
               in addition, allows access to standard pseudo devices including
               /dev/null, /dev/zero, /dev/full, /dev/random, and /dev/urandom.

           auto
               in addition, allows access to all devices if no explicit
               DeviceAllow= is present. This is the default.

       Slice=
           The name of the slice unit to place the unit in. Defaults to
           system.slice for all non-instantiated units of all unit types
           (except for slice units themselves see below). Instance units are
           by default placed in a subslice of system.slice that is named after
           the template name.

           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=
           Turns on delegation of further resource control partitioning to
           processes of the unit. Units where this is enabled may create and
           manage their own private subhierarchy of control groups below the
           control group of the unit itself. For unprivileged services (i.e.
           those using the User= setting) the unit's control group will be
           made accessible to the relevant user. When enabled the service
           manager will refrain from manipulating control groups or moving
           processes below the unit's control group, so that a clear concept
           of ownership is established: the control group tree above the
           unit's control group (i.e. towards the root control group) is owned
           and managed by the service manager of the host, while the control
           group tree below the unit's control group is owned and managed by
           the unit itself. Takes either a boolean argument or a list of
           control group controller names. If true, delegation is turned on,
           and all supported controllers are enabled for the unit, making them
           available to the unit's processes for management. If false,
           delegation is turned off entirely (and no additional controllers
           are enabled). If set to a list of controllers, delegation is turned
           on, and the specified controllers are enabled for the unit. Note
           that additional controllers than the ones specified might be made
           available as well, depending on configuration of the containing
           slice unit or other units contained in it. Note that assigning the
           empty string will enable delegation, but reset the list of
           controllers, all assignments prior to this will have no effect.
           Defaults to false.

           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 Control Group
           APIs and Delegation[10].

       DisableControllers=
           Disables controllers from being enabled for a unit's children. If a
           controller listed is already in use in its subtree, the controller
           will be removed from the subtree. This can be used to avoid child
           units being able to implicitly or explicitly enable a controller.
           Defaults to not disabling any controllers.

           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.

DEPRECATED OPTIONS
       The following options are deprecated. Use the indicated superseding
       options instead:

       CPUShares=weight, StartupCPUShares=weight
           Assign the specified CPU time share weight to the processes
           executed. These options take an integer value and control the
           "cpu.shares" control group attribute. The allowed range is 2 to
           262144. Defaults to 1024. For details about this control group
           attribute, see CFS Scheduler[4]. The available CPU time is split up
           among all units within one slice relative to their CPU time share
           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
           Specify the limit on maximum memory usage of the executed
           processes. The limit specifies how much process and kernel memory
           can be used by tasks in this unit. 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.limit_in_bytes"
           control group attribute. For details about this control group
           attribute, see Memory Resource Controller[11].

           Implies "MemoryAccounting=yes".

           This setting is deprecated. Use MemoryMax= instead.

       BlockIOAccounting=
           Turn on Block I/O accounting for this unit, if the legacy control
           group hierarchy is used on the system. Takes a boolean argument.
           Note that turning on block I/O accounting for one unit will also
           implicitly turn it on for all units contained in the same slice and
           all for its parent slices and the units contained therein. The
           system default for this setting may be controlled with
           DefaultBlockIOAccounting= in systemd-system.conf(5).

           This setting is deprecated. Use IOAccounting= instead.

       BlockIOWeight=weight, StartupBlockIOWeight=weight
           Set the default overall block I/O weight for the executed
           processes, if the legacy control group hierarchy is used on the
           system. Takes a single weight value (between 10 and 1000) to set
           the default block I/O weight. This controls the "blkio.weight"
           control group attribute, which defaults to 500. For details about
           this control group attribute, see Block IO Controller[12]. The
           available I/O bandwidth is split up among all units within one
           slice relative to their block I/O 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
           Set the per-device overall block I/O weight for the executed
           processes, if the legacy control group hierarchy is used on the
           system. Takes a space-separated pair of a file path and a weight
           value to specify the device specific weight value, between 10 and
           1000. (Example: "/dev/sda 500"). The file path may be specified as
           path to a block device node or as any other file, in which case the
           backing block device of the file system of the file is determined.
           This controls the "blkio.weight_device" control group attribute,
           which defaults to 1000. Use this option multiple times to set
           weights for multiple devices. For details about this control group
           attribute, see Block IO Controller[12].

           Implies "BlockIOAccounting=yes".

           This setting is deprecated. Use IODeviceWeight= instead.

       BlockIOReadBandwidth=device bytes, BlockIOWriteBandwidth=device bytes
           Set the per-device overall block I/O bandwidth limit for the
           executed processes, if the legacy control group hierarchy is used
           on the system. Takes a space-separated pair of a file path and a
           bandwidth value (in bytes per second) to specify the device
           specific bandwidth. The file path may be a path to a block device
           node, or as any other file in which case the backing block device
           of the file system of the file is used. If the bandwidth is
           suffixed with K, M, G, or T, the specified bandwidth is parsed as
           Kilobytes, Megabytes, Gigabytes, or Terabytes, respectively, to the
           base of 1000. (Example:
           "/dev/disk/by-path/pci-0000:00:1f.2-scsi-0:0:0:0 5M"). This
           controls the "blkio.throttle.read_bps_device" and
           "blkio.throttle.write_bps_device" control group attributes. Use
           this option multiple times to set bandwidth limits for multiple
           devices. For details about these control group attributes, see
           Block IO Controller[12].

           Implies "BlockIOAccounting=yes".

           These settings are deprecated. Use IOReadBandwidthMax= and
           IOWriteBandwidthMax= instead.

SEE ALSO
       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), The documentation for
       control groups and specific controllers in the Linux kernel: Control
       Groups v2[2].

NOTES
        1. New Control Group Interfaces
           https://www.freedesktop.org/wiki/Software/systemd/ControlGroupInterface/

        2. Control Groups v2
           https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html

        3. Control Groups version 1
           https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/

        4. CFS Scheduler
           https://www.kernel.org/doc/html/latest/scheduler/sched-design-CFS.html

        5. sched-bwc.txt
           https://www.kernel.org/doc/Documentation/scheduler/sched-bwc.txt

        6. Memory Interface Files
           https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#memory-interface-files

        7. Process Number Controller
           https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/pids.html

        8. IO Interface Files
           https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#io-interface-files

        9. Device Whitelist Controller
           https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/devices.html

       10. Control Group APIs and Delegation
           https://systemd.io/CGROUP_DELEGATION

       11. Memory Resource Controller
           https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/memory.html

       12. Block IO Controller
           https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/blkio-controller.html

systemd 245                                        SYSTEMD.RESOURCE-CONTROL(5)

NAME | SYNOPSIS | DESCRIPTION | IMPLICIT DEPENDENCIES | UNIFIED AND LEGACY CONTROL GROUP HIERARCHIES | OPTIONS | DEPRECATED OPTIONS | SEE ALSO | NOTES