Ubuntu Manpage: systemd.resource-control - Resource control unit settings

Provided by: systemd_255.4-1ubuntu8.4_amd64

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.

Enabling and disabling controllers
Controllers in the cgroup hierarchy are hierarchical, and resource control is realized by
distributing resource assignments between siblings in branches of the cgroup hierarchy.
There is no need to explicitly enable a cgroup controller for a unit. systemd will
instruct the kernel to enable a controller for a given unit when this unit has
configuration for a given controller. For example, when CPUWeight= is set, the cpu
controller will be enabled, and when TasksMax= are set, the pids controller will be
enabled. In addition, various controllers may be also be enabled explicitly via the
MemoryAccounting=/TasksAccounting=/IOAccounting= settings. Because of how the cgroup
hierarchy works, controllers will be automatically enabled for all parent units and for
any sibling units starting with the lowest level at which a controller is enabled. Units
for which a controller is enabled may be subject to resource control even if they don't
have any explicit configuration.

Setting Delegate= enables any delegated controllers for that unit (see below). The
delegatee may then enable controllers for its children as appropriate. In particular, if
the delegatee is systemd (in the user@.service unit), it will repeat the same logic as the
system instance and enable controllers for user units which have resource limits
configured, and their siblings and parents and parents' siblings.

Controllers may be disabled for parts of the cgroup hierarchy with DisableControllers=
(see below).

Example 1. Enabling and disabling controllers

-.slice
/ \
/-----/ \--------------\
/ \
system.slice user.slice
/ \ / \
/ \ / \
/ \ user@42.service user@1000.service
/ \ Delegate= Delegate=yes
a.service b.slice / \
CPUWeight=20 DisableControllers=cpu / \
/ \ app.slice session.slice
/ \ CPUWeight=100 CPUWeight=100
/ \
b1.service b2.service
CPUWeight=1000

In this hierarchy, the cpu controller is enabled for all units shown except b1.service and
b2.service. Because there is no explicit configuration for system.slice and user.slice,
CPU resources will be split equally between them. Similarly, resources are allocated
equally between children of user.slice and between the child slices beneath
user@1000.service. Assuming that there is no further configuration of resources or
delegation below slices app.slice or session.slice, the cpu controller would not be
enabled for units in those slices and CPU resources would be further allocated using other
mechanisms, e.g. based on nice levels. The manager for user 42 has delegation enabled
without any controllers, i.e. it can manipulate its subtree of the cgroup hierarchy, but
without resource control.

In the slice system.slice, CPU resources are split 1:6 for service a.service, and 5:6 for
slice b.slice, because slice b.slice gets the default value of 100 for cpu.weight when
CPUWeight= is not set.

CPUWeight= setting in service b2.service is neutralized by DisableControllers= in slice
b.slice, so the cpu controller would not be enabled for services b1.service and
b2.service, and CPU resources would be further allocated using other mechanisms, e.g.
based on nice levels.

Setting resource controls for a group of related units
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.

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:

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

OPTIONS

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

CPU Accounting and Control
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).

Under the unified cgroup hierarchy, CPU accounting is available for all units and this
setting has no effect.

Added in version 208.

CPUWeight=weight, StartupCPUWeight=weight
These settings control the cpu controller in the unified hierarchy.

These options accept an integer value or a the special string "idle":

• If set to an integer value, assign the specified CPU time weight to the processes
executed, if the unified control group hierarchy is used on the system. These
options control the "cpu.weight" control group attribute. The allowed range is 1
to 10000. Defaults to unset, but the kernel default is 100. For details about this
control group attribute, see Control Groups v2[2] and CFS Scheduler[3]. The
available CPU time is split up among all units within one slice relative to their
CPU time weight. A higher weight means more CPU time, a lower weight means less.

• If set to the special string "idle", mark the cgroup for "idle scheduling", which
means that it will get CPU resources only when there are no processes not marked
in this way to execute in this cgroup or its siblings. This setting corresponds to
the "cpu.idle" cgroup attribute.

Note that this value only has an effect on cgroup-v2, for cgroup-v1 it is
equivalent to the minimum weight.

While StartupCPUWeight= applies to the startup and shutdown phases of the system,
CPUWeight= applies to normal runtime of the system, and if the former is not set also
to the startup and shutdown phases. Using StartupCPUWeight= allows prioritizing
specific services at boot-up and shutdown differently than during normal runtime.

In addition to the resource allocation performed by the cpu controller, the kernel may
automatically divide resources based on session-id grouping, see "The autogroup
feature" in sched(7). The effect of this feature is similar to the cpu controller with
no explicit configuration, so users should be careful to not mistake one for the
other.

Added in version 232.

CPUQuota=
This setting controls the cpu controller in the unified hierarchy.

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 CFS Bandwidth
Control[4]. Setting CPUQuota= to an empty value unsets the quota.

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

Added in version 213.

CPUQuotaPeriodSec=
This setting controls the cpu controller in the unified hierarchy.

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[3].

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

Added in version 242.

AllowedCPUs=, StartupAllowedCPUs=
This setting controls the cpuset controller in the unified hierarchy.

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= or StartupAllowedCPUs= 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=.

While StartupAllowedCPUs= applies to the startup and shutdown phases of the system,
AllowedCPUs= applies to normal runtime of the system, and if the former is not set
also to the startup and shutdown phases. Using StartupAllowedCPUs= allows prioritizing
specific services at boot-up and shutdown differently than during normal runtime.

This setting is supported only with the unified control group hierarchy.

Added in version 244.

Memory Accounting and Control
MemoryAccounting=
This setting controls the memory controller in the unified hierarchy.

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).

Added in version 208.

MemoryMin=bytes, MemoryLow=bytes, StartupMemoryLow=bytes, DefaultStartupMemoryLow=bytes
These settings control the memory controller in the unified hierarchy.

Specify the memory usage protection of the executed processes in this unit. When
reclaiming memory, the unit is treated as if it was using less memory resulting in
memory to be preferentially reclaimed from unprotected units. Using MemoryLow= results
in a weaker protection where memory may still be reclaimed to avoid invoking the OOM
killer in case there is no other reclaimable memory.

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 Memory Interface Files[5].

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=, or DefaultStartupMemoryLow= which has the same semantics as
StartupMemoryLow=. 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.

While StartupMemoryLow= applies to the startup and shutdown phases of the system,
MemoryMin= applies to normal runtime of the system, and if the former is not set also
to the startup and shutdown phases. Using StartupMemoryLow= allows prioritizing
specific services at boot-up and shutdown differently than during normal runtime.

Added in version 240.

MemoryHigh=bytes, StartupMemoryHigh=bytes
These settings control the memory controller in the unified hierarchy.

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[5].

While StartupMemoryHigh= applies to the startup and shutdown phases of the system,
MemoryHigh= applies to normal runtime of the system, and if the former is not set also
to the startup and shutdown phases. Using StartupMemoryHigh= allows prioritizing
specific services at boot-up and shutdown differently than during normal runtime.

Added in version 231.

MemoryMax=bytes, StartupMemoryMax=bytes
These settings control the memory controller in the unified hierarchy.

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[5].

While StartupMemoryMax= applies to the startup and shutdown phases of the system,
MemoryMax= applies to normal runtime of the system, and if the former is not set also
to the startup and shutdown phases. Using StartupMemoryMax= allows prioritizing
specific services at boot-up and shutdown differently than during normal runtime.

Added in version 231.

MemorySwapMax=bytes, StartupMemorySwapMax=bytes
These settings control the memory controller in the unified hierarchy.

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. These settings control the "memory.swap.max" control group attribute. For
details about this control group attribute, see Memory Interface Files[5].

While StartupMemorySwapMax= applies to the startup and shutdown phases of the system,
MemorySwapMax= applies to normal runtime of the system, and if the former is not set
also to the startup and shutdown phases. Using StartupMemorySwapMax= allows
prioritizing specific services at boot-up and shutdown differently than during normal
runtime.

Added in version 232.

MemoryZSwapMax=bytes, StartupMemoryZSwapMax=bytes
These settings control the memory controller in the unified hierarchy.

Specify the absolute limit on zswap usage of the processes in this unit. Zswap is a
lightweight compressed cache for swap pages. It takes pages that are in the process of
being swapped out and attempts to compress them into a dynamically allocated RAM-based
memory pool. If the limit specified is hit, no entries from this unit will be stored
in the pool until existing entries are faulted back or written out to disk. See the
kernel's Zswap[6] documentation for more details.

Takes a size in bytes. If the value is suffixed with K, M, G or T, the specified size
is parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024),
respectively. If assigned the special value "infinity", no limit is applied. These
settings control the "memory.zswap.max" control group attribute. For details about
this control group attribute, see Memory Interface Files[5].

While StartupMemoryZSwapMax= applies to the startup and shutdown phases of the system,
MemoryZSwapMax= applies to normal runtime of the system, and if the former is not set
also to the startup and shutdown phases. Using StartupMemoryZSwapMax= allows
prioritizing specific services at boot-up and shutdown differently than during normal
runtime.

Added in version 253.

AllowedMemoryNodes=, StartupAllowedMemoryNodes=
These settings control the cpuset controller in the unified hierarchy.

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 NUMA nodes indices separated by
a dash.

Setting AllowedMemoryNodes= or StartupAllowedMemoryNodes= 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=.

While StartupAllowedMemoryNodes= applies to the startup and shutdown phases of the
system, AllowedMemoryNodes= applies to normal runtime of the system, and if the former
is not set also to the startup and shutdown phases. Using StartupAllowedMemoryNodes=
allows prioritizing specific services at boot-up and shutdown differently than during
normal runtime.

This setting is supported only with the unified control group hierarchy.

Added in version 244.

Process Accounting and Control
TasksAccounting=
This setting controls the pids controller in the unified hierarchy.

Turn on task accounting for this unit. Takes a boolean argument. If enabled, the
kernel will keep track of the total number of tasks in the unit and its children. This
number includes both kernel threads and userspace processes, with each thread counted
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).

Added in version 227.

TasksMax=N
This setting controls the pids controller in the unified hierarchy.

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, the pids
controller[7].

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

Added in version 227.

IO Accounting and Control
IOAccounting=
This setting controls the io controller in the unified hierarchy.

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).

Added in version 230.

IOWeight=weight, StartupIOWeight=weight
These settings control the io controller in the unified hierarchy.

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. A higher weight means
more I/O bandwidth, a lower weight means less.

While StartupIOWeight= applies to the startup and shutdown phases of the system,
IOWeight= applies to the later runtime of the system, and if the former is not set
also to the startup and shutdown phases. This allows prioritizing specific services at
boot-up and shutdown differently than during runtime.

Added in version 230.

IODeviceWeight=device weight
This setting controls the io controller in the unified hierarchy.

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].

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.

Added in version 230.

IOReadBandwidthMax=device bytes, IOWriteBandwidthMax=device bytes
These settings control the io controller in the unified hierarchy.

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].

Similar restrictions on block device discovery as for IODeviceWeight= apply, see
above.

Added in version 230.

IOReadIOPSMax=device IOPS, IOWriteIOPSMax=device IOPS
These settings control the io controller in the unified hierarchy.

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].

Similar restrictions on block device discovery as for IODeviceWeight= apply, see
above.

Added in version 230.

IODeviceLatencyTargetSec=device target
This setting controls the io controller in the unified hierarchy.

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.

Added in version 240.

Network Accounting and Control
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).

Added in version 235.

IPAddressAllow=ADDRESS[/PREFIXLENGTH]..., IPAddressDeny=ADDRESS[/PREFIXLENGTH]...
Turn on 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 after a "/"
character. If the suffix is omitted, the address is considered a host address, i.e.
the filter covers the whole address (32 bits for IPv4, 128 bits 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 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:

• Access is granted when the checked IP address matches an entry in the
IPAddressAllow= list.

• Otherwise, access is denied when the checked IP address matches an entry in the
IPAddressDeny= list.

• Otherwise, access is granted.

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 use case.

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.

This option cannot be bypassed by prefixing "+" to the executable path in the service
unit, as it applies to the whole control group.

Added in version 235.

SocketBindAllow=bind-rule, SocketBindDeny=bind-rule
Allow or deny binding a socket address to a socket by matching it with the bind-rule
and applying a corresponding action if there is a match.

bind-rule describes socket properties such as address-family, transport-protocol and
ip-ports.

bind-rule := { [address-family:][transport-protocol:][ip-ports] | any }

address-family := { ipv4 | ipv6 }

transport-protocol := { tcp | udp }

ip-ports := { ip-port | ip-port-range }

An optional address-family expects ipv4 or ipv6 values. If not specified, a rule will
be matched for both IPv4 and IPv6 addresses and applied depending on other socket
fields, e.g. transport-protocol, ip-port.

An optional transport-protocol expects tcp or udp transport protocol names. If not
specified, a rule will be matched for any transport protocol.

An optional ip-port value must lie within 1...65535 interval inclusively, i.e. dynamic
port 0 is not allowed. A range of sequential ports is described by ip-port-range :=
ip-port-low-ip-port-high, where ip-port-low is smaller than or equal to ip-port-high
and both are within 1...65535 inclusively.

A special value any can be used to apply a rule to any address family, transport
protocol and any port with a positive value.

To allow multiple rules assign SocketBindAllow= or SocketBindDeny= multiple times. To
clear the existing assignments pass an empty SocketBindAllow= or SocketBindDeny=
assignment.

For each of SocketBindAllow= and SocketBindDeny=, maximum allowed number of
assignments is 128.

• Binding to a socket is allowed when a socket address matches an entry in the
SocketBindAllow= list.

• Otherwise, binding is denied when the socket address matches an entry in the
SocketBindDeny= list.

• Otherwise, binding is allowed.

The feature is implemented with cgroup/bind4 and cgroup/bind6 cgroup-bpf hooks.

Examples:

...
# Allow binding IPv6 socket addresses with a port greater than or equal to 10000.
[Service]
SocketBindAllow=ipv6:10000-65535
SocketBindDeny=any
...
# Allow binding IPv4 and IPv6 socket addresses with 1234 and 4321 ports.
[Service]
SocketBindAllow=1234
SocketBindAllow=4321
SocketBindDeny=any
...
# Deny binding IPv6 socket addresses.
[Service]
SocketBindDeny=ipv6
...
# Deny binding IPv4 and IPv6 socket addresses.
[Service]
SocketBindDeny=any
...
# Allow binding only over TCP
[Service]
SocketBindAllow=tcp
SocketBindDeny=any
...
# Allow binding only over IPv6/TCP
[Service]
SocketBindAllow=ipv6:tcp
SocketBindDeny=any
...
# Allow binding ports within 10000-65535 range over IPv4/UDP.
[Service]
SocketBindAllow=ipv4:udp:10000-65535
SocketBindDeny=any
...

This option cannot be bypassed by prefixing "+" to the executable path in the service
unit, as it applies to the whole control group.

Added in version 249.

RestrictNetworkInterfaces=
Takes a list of space-separated network interface names. This option restricts the
network interfaces that processes of this unit can use. By default processes can only
use the network interfaces listed (allow-list). If the first character of the rule is
"~", the effect is inverted: the processes can only use network interfaces not listed
(deny-list).

This option can appear multiple times, in which case the network interface names are
merged. If the empty string is assigned the set is reset, all prior assignments will
have not effect.

If you specify both types of this option (i.e. allow-listing and deny-listing), the
first encountered will take precedence and will dictate the default action (allow vs
deny). Then the next occurrences of this option will add or delete the listed network
interface names from the set, depending of its type and the default action.

The loopback interface ("lo") is not treated in any special way, you have to configure
it explicitly in the unit file.

Example 1: allow-list

RestrictNetworkInterfaces=eth1
RestrictNetworkInterfaces=eth2

Programs in the unit will be only able to use the eth1 and eth2 network interfaces.

Example 2: deny-list

RestrictNetworkInterfaces=~eth1 eth2

Programs in the unit will be able to use any network interface but eth1 and eth2.

Example 3: mixed

RestrictNetworkInterfaces=eth1 eth2
RestrictNetworkInterfaces=~eth1

Programs in the unit will be only able to use the eth2 network interface.

This option cannot be bypassed by prefixing "+" to the executable path in the service
unit, as it applies to the whole control group.

Added in version 250.

NFTSet=family:table:set
This setting provides a method for integrating dynamic cgroup, user and group IDs into
firewall rules with NFT[9] sets. The benefit of using this setting is to be able to
use the IDs as selectors in firewall rules easily and this in turn allows more fine
grained filtering. NFT rules for cgroup matching use numeric cgroup IDs, which change
every time a service is restarted, making them hard to use in systemd environment
otherwise. Dynamic and random IDs used by DynamicUser= can be also integrated with
this setting.

This option expects a whitespace separated list of NFT set definitions. Each
definition consists of a colon-separated tuple of source type (one of "cgroup", "user"
or "group"), NFT address family (one of "arp", "bridge", "inet", "ip", "ip6", or
"netdev"), table name and set name. The names of tables and sets must conform to
lexical restrictions of NFT table names. The type of the element used in the NFT
filter must match the type implied by the directive ("cgroup", "user" or "group") as
shown in the table below. When a control group or a unit is realized, the
corresponding ID will be appended to the NFT sets and it will be be removed when the
control group or unit is removed. systemd only inserts elements to (or removes from)
the sets, so the related NFT rules, tables and sets must be prepared elsewhere in
advance. Failures to manage the sets will be ignored.

Table 2. Defined source type values
┌────────────┬──────────────────┬────────────────────────┐
│Source type │ Description │ Corresponding NFT type │
│ │ │ name │
├────────────┼──────────────────┼────────────────────────┤
│"cgroup" │ control group ID │ "cgroupsv2" │
├────────────┼──────────────────┼────────────────────────┤
│"user" │ user ID │ "meta skuid" │
├────────────┼──────────────────┼────────────────────────┤
│"group" │ group ID │ "meta skgid" │
└────────────┴──────────────────┴────────────────────────┘
If the firewall rules are reinstalled so that the contents of NFT sets are destroyed,
command systemctl daemon-reload can be used to refill the sets.

Example:

[Unit]
NFTSet=cgroup:inet:filter:my_service user:inet:filter:serviceuser

Corresponding NFT rules:

table inet filter {
set my_service {
type cgroupsv2
}
set serviceuser {
typeof meta skuid
}
chain x {
socket cgroupv2 level 2 @my_service accept
drop
}
chain y {
meta skuid @serviceuser accept
drop
}
}

Added in version 255.

BPF Programs
IPIngressFilterPath=BPF_FS_PROGRAM_PATH, IPEgressFilterPath=BPF_FS_PROGRAM_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.

If the path BPF_FS_PROGRAM_PATH in IPIngressFilterPath= assignment is already being
handled by BPFProgram= ingress hook, e.g. BPFProgram=ingress:BPF_FS_PROGRAM_PATH, the
assignment will be still considered valid and the program will be attached to a
cgroup. Same for IPEgressFilterPath= path and egress hook.

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 use case.

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.

Added in version 243.

BPFProgram=type:program-path
BPFProgram= allows attaching custom BPF programs to the cgroup of a unit. (This
generalizes the functionality exposed via IPEgressFilterPath= and IPIngressFilterPath=
for other hooks.) Cgroup-bpf hooks in the form of BPF programs loaded to the BPF
filesystem are attached with cgroup-bpf attach flags determined by the unit. For
details about attachment types and flags see bpf.h[10]. Also refer to the general BPF
documentation[11].

The specification of BPF program consists of a pair of BPF program type and program
path in the file system, with ":" as the separator: type:program-path.

The BPF program type is equivalent to the BPF attach type used in bpftool(8) It may be
one of egress, ingress, sock_create, sock_ops, device, bind4, bind6, connect4,
connect6, post_bind4, post_bind6, sendmsg4, sendmsg6, sysctl, recvmsg4, recvmsg6,
getsockopt, or setsockopt.

The specified program path must be an absolute path referencing a BPF program inode in
the bpffs file system (which generally means it must begin with /sys/fs/bpf/). If a
specified program does not exist (i.e. has not been uploaded to the BPF subsystem of
the kernel yet), it will not be installed but unit activation will continue (a warning
will be printed to the logs).

Setting BPFProgram= to an empty value makes previous assignments ineffective.

Multiple assignments of the same program type/path pair have the same effect as a
single assignment: the program will be attached just once.

If BPF egress pinned to program-path path is already being handled by
IPEgressFilterPath=, BPFProgram= assignment will be considered valid and BPFProgram=
will be attached to a cgroup. Similarly for ingress hook and IPIngressFilterPath=
assignment.

BPF programs passed with BPFProgram= are attached to the cgroup of a unit with BPF
attach flag multi, that allows further attachments of the same type within cgroup
hierarchy topped by the unit cgroup.

Examples:

BPFProgram=egress:/sys/fs/bpf/egress-hook
BPFProgram=bind6:/sys/fs/bpf/sock-addr-hook

Added in version 249.

Device Access
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 nodes by the unit
(mknod), respectively. This functionality is implemented using eBPF filtering.

When access to all physical devices should be disallowed, PrivateDevices= may be used
instead. See systemd.exec(5).

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
...

This option cannot be bypassed by prefixing "+" to the executable path in the service
unit, as it applies to the whole control group.

Added in version 208.

DevicePolicy=auto|closed|strict
Control the policy for allowing device access:

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

Added in version 208.

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

Added in version 208.

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

Added in version 208.

This option cannot be bypassed by prefixing "+" to the executable path in the service
unit, as it applies to the whole control group.

Added in version 208.

Control Group Management
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.

Added in version 208.

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 at the level of the unit's control group and
above (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 (possibly empty) 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. Assigning the empty string will enable delegation, but reset the
list of controllers, and all assignments prior to this will have no effect. Note that
additional controllers other than the ones specified might be made available as well,
depending on configuration of the containing slice unit or other units contained in
it. 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.

Note that because of the hierarchical nature of cgroup hierarchy, any controllers that
are delegated will be enabled for the parent and sibling units of the unit with
delegation.

For further details on the delegation model consult Control Group APIs and
Delegation[12].

Added in version 218.

DelegateSubgroup=
Place unit processes in the specified subgroup of the unit's control group. Takes a
valid control group name (not a path!) as parameter, or an empty string to turn this
feature off. Defaults to off. The control group name must be usable as filename and
avoid conflicts with the kernel's control group attribute files (i.e. cgroup.procs is
not an acceptable name, since the kernel exposes a native control group attribute file
by that name). This option has no effect unless control group delegation is turned on
via Delegate=, see above. Note that this setting only applies to "main" processes of a
unit, i.e. for services to ExecStart=, but not for ExecReload= and similar. If
delegation is enabled, the latter are always placed inside a subgroup named .control.
The specified subgroup is automatically created (and potentially ownership is passed
to the unit's configured user/group) when a process is started in it.

This option is useful to avoid manually moving the invoked process into a subgroup
after it has been started. Since no processes should live in inner nodes of the
control group tree it's almost always necessary to run the main ("supervising")
process of a unit that has delegation turned on in a subgroup.

Added in version 254.

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 configuration in child units from being able to implicitly
or explicitly enable a controller. Defaults to empty.

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.

It may not be possible to disable a controller after units have been started, 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.

The following controller names may be specified: cpu, cpuacct, cpuset, io, blkio,
memory, devices, pids, bpf-firewall, and bpf-devices.

Added in version 240.

Memory Pressure Control
ManagedOOMSwap=auto|kill, ManagedOOMMemoryPressure=auto|kill
Specifies how systemd-oomd.service(8) will act on this unit's cgroups. Defaults to
auto.

When set to kill, the unit becomes a candidate for monitoring by systemd-oomd. If the
cgroup passes the limits set by oomd.conf(5) or the unit configuration, systemd-oomd
will select a descendant cgroup and send SIGKILL to all of the processes under it. 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 result in 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 a candidate for systemd-oomd to terminate.

Added in version 247.

ManagedOOMMemoryPressureLimit=
Overrides the default memory pressure limit set by oomd.conf(5) for this unit
(cgroup). Takes a percentage value between 0% and 100%, inclusive. This property is
ignored unless ManagedOOMMemoryPressure=kill. Defaults to 0%, which means to use the
default set by oomd.conf(5).

Added in version 247.

ManagedOOMPreference=none|avoid|omit
Allows deprioritizing or omitting this unit's cgroup as a candidate when systemd-oomd
needs to act. Requires support for extended attributes (see xattr(7)) in order to use
avoid or omit.

When calculating candidates to relieve swap usage, systemd-oomd will only respect
these extended attributes if the unit's cgroup is owned by root.

When calculating candidates to relieve memory pressure, systemd-oomd will only respect
these extended attributes if the unit's cgroup is owned by root, or if the unit's
cgroup owner, and the owner of the monitored ancestor cgroup are the same. For
example, if systemd-oomd is calculating candidates for -.slice, then extended
attributes set on descendants of /user.slice/user-1000.slice/user@1000.service/ will
be ignored because the descendants are owned by UID 1000, and -.slice is owned by UID
0. But, if calculating candidates for /user.slice/user-1000.slice/user@1000.service/,
then extended attributes set on the descendants would be respected.

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).

Added in version 248.

MemoryPressureWatch=
Controls memory pressure monitoring for invoked processes. Takes one of "off", "on",
"auto" or "skip". If "off" tells the service not to watch for memory pressure events,
by setting the $MEMORY_PRESSURE_WATCH environment variable to the literal string
/dev/null. If "on" tells the service to watch for memory pressure events. This enables
memory accounting for the service, and ensures the memory.pressure cgroup attribute
file is accessible for reading and writing by the service's user. It then sets the
$MEMORY_PRESSURE_WATCH environment variable for processes invoked by the unit to the
file system path to this file. The threshold information configured with
MemoryPressureThresholdSec= is encoded in the $MEMORY_PRESSURE_WRITE environment
variable. If the "auto" value is set the protocol is enabled if memory accounting is
anyway enabled for the unit, and disabled otherwise. If set to "skip" the logic is
neither enabled, nor disabled and the two environment variables are not set.

Note that services are free to use the two environment variables, but it's
unproblematic if they ignore them. Memory pressure handling must be implemented
individually in each service, and usually means different things for different
software. For further details on memory pressure handling see Memory Pressure Handling
in systemd[13].

Services implemented using sd-event(3) may use sd_event_add_memory_pressure(3) to
watch for and handle memory pressure events.

If not explicit set, defaults to the DefaultMemoryPressureWatch= setting in systemd-
system.conf(5).

Added in version 254.

MemoryPressureThresholdSec=
Sets the memory pressure threshold time for memory pressure monitor as configured via
MemoryPressureWatch=. Specifies the maximum allocation latency before a memory
pressure event is signalled to the service, per 2s window. If not specified defaults
to the DefaultMemoryPressureThresholdSec= setting in systemd-system.conf(5) (which in
turn defaults to 200ms). The specified value expects a time unit such as "ms" or "μs",
see systemd.time(7) for details on the permitted syntax.

Added in version 254.

Coredump Control
CoredumpReceive=
Takes a boolean argument. This setting is used to enable coredump forwarding for
containers that belong to this unit's cgroup. Units with CoredumpReceive=yes must also
be configured with Delegate=yes. Defaults to false.

When systemd-coredump is handling a coredump for a process from a container, if the
container's leader process is a descendant of a cgroup with CoredumpReceive=yes and
Delegate=yes, then systemd-coredump will attempt to forward the coredump to
systemd-coredump within the container.

Added in version 255.

HISTORY

       systemd 252
           Options for controlling the Legacy Control Group Hierarchy (Control Groups version
           1[14]) are now fully deprecated: CPUShares=weight, StartupCPUShares=weight,
           MemoryLimit=bytes, BlockIOAccounting=, BlockIOWeight=weight,
           StartupBlockIOWeight=weight, BlockIODeviceWeight=device weight,
           BlockIOReadBandwidth=device bytes, BlockIOWriteBandwidth=device bytes. Please switch
           to the unified cgroup hierarchy.

           Added in version 252.

NOTES

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

        2. Control Groups v2
           https://docs.kernel.org/admin-guide/cgroup-v2.html

        3. CFS Scheduler
           https://docs.kernel.org/scheduler/sched-design-CFS.html

        4. CFS Bandwidth Control
           https://docs.kernel.org/scheduler/sched-bwc.html

        5. Memory Interface Files
           https://docs.kernel.org/admin-guide/cgroup-v2.html#memory-interface-files

        6. Zswap
           https://www.kernel.org/doc/html/latest/admin-guide/mm/zswap.html

        7. pids controller
           https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#pid

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

        9. NFT
           https://netfilter.org/projects/nftables/index.html

       10. bpf.h
           https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/include/uapi/linux/bpf.h

       11. BPF documentation
           https://docs.kernel.org/bpf/

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

       13. Memory Pressure Handling in systemd
           https://systemd.io/MEMORY_PRESSURE

       14. Control Groups version 1
           https://docs.kernel.org/admin-guide/cgroup-v1/index.html

NAME

SYNOPSIS

DESCRIPTION

IMPLICIT DEPENDENCIES

OPTIONS

HISTORY

SEE ALSO

NOTES