cgroups(7) - Linux manual page (original) (raw)
cgroups(7) Miscellaneous Information Manual cgroups(7)
NAME top
cgroups - Linux control groupsDESCRIPTION top
Control groups, usually referred to as cgroups, are a Linux kernel
feature which allow processes to be organized into hierarchical
groups whose usage of various types of resources can then be
limited and monitored. The kernel's cgroup interface is provided
through a pseudo-filesystem called cgroupfs. Grouping is
implemented in the core cgroup kernel code, while resource
tracking and limits are implemented in a set of per-resource-type
subsystems (memory, CPU, and so on).Terminology A cgroup is a collection of processes that are bound to a set of limits or parameters defined via the cgroup filesystem.
A _subsystem_ is a kernel component that modifies the behavior of
the processes in a cgroup. Various subsystems have been
implemented, making it possible to do things such as limiting the
amount of CPU time and memory available to a cgroup, accounting
for the CPU time used by a cgroup, and freezing and resuming
execution of the processes in a cgroup. Subsystems are sometimes
also known as _resource controllers_ (or simply, controllers).
The cgroups for a controller are arranged in a _hierarchy_. This
hierarchy is defined by creating, removing, and renaming
subdirectories within the cgroup filesystem. At each level of the
hierarchy, attributes (e.g., limits) can be defined. The limits,
control, and accounting provided by cgroups generally have effect
throughout the subhierarchy underneath the cgroup where the
attributes are defined. Thus, for example, the limits placed on a
cgroup at a higher level in the hierarchy cannot be exceeded by
descendant cgroups.Cgroups version 1 and version 2 The initial release of the cgroups implementation was in Linux 2.6.24. Over time, various cgroup controllers have been added to allow the management of various types of resources. However, the development of these controllers was largely uncoordinated, with the result that many inconsistencies arose between controllers and management of the cgroup hierarchies became rather complex. A longer description of these problems can be found in the kernel source file Documentation/admin-guide/cgroup-v2.rst (or Documentation/cgroup-v2.txt in Linux 4.17 and earlier).
Because of the problems with the initial cgroups implementation
(cgroups version 1), starting in Linux 3.10, work began on a new,
orthogonal implementation to remedy these problems. Initially
marked experimental, and hidden behind the
_-o _DEVEL_sanebehavior_ mount option, the new version (cgroups
version 2) was eventually made official with the release of Linux
4.5. Differences between the two versions are described in the
text below. The file _cgroup.sanebehavior_, present in cgroups v1,
is a relic of this mount option. The file always reports "0" and
is only retained for backward compatibility.
Although cgroups v2 is intended as a replacement for cgroups v1,
the older system continues to exist (and for compatibility reasons
is unlikely to be removed). Currently, cgroups v2 implements only
a subset of the controllers available in cgroups v1. The two
systems are implemented so that both v1 controllers and v2
controllers can be mounted on the same system. Thus, for example,
it is possible to use those controllers that are supported under
version 2, while also using version 1 controllers where version 2
does not yet support those controllers. The only restriction here
is that a controller can't be simultaneously employed in both a
cgroups v1 hierarchy and in the cgroups v2 hierarchy.CGROUPS VERSION 1 top
Under cgroups v1, each controller may be mounted against a
separate cgroup filesystem that provides its own hierarchical
organization of the processes on the system. It is also possible
to comount multiple (or even all) cgroups v1 controllers against
the same cgroup filesystem, meaning that the comounted controllers
manage the same hierarchical organization of processes.
For each mounted hierarchy, the directory tree mirrors the control
group hierarchy. Each control group is represented by a
directory, with each of its child control cgroups represented as a
child directory. For instance, _/user/joe/1.session_ represents
control group _1.session_, which is a child of cgroup _joe_, which is
a child of _/user_. Under each cgroup directory is a set of files
which can be read or written to, reflecting resource limits and a
few general cgroup properties.Tasks (threads) versus processes In cgroups v1, a distinction is drawn between processes and tasks. In this view, a process can consist of multiple tasks (more commonly called threads, from a user-space perspective, and called such in the remainder of this man page). In cgroups v1, it is possible to independently manipulate the cgroup memberships of the threads in a process.
The cgroups v1 ability to split threads across different cgroups
caused problems in some cases. For example, it made no sense for
the _memory_ controller, since all of the threads of a process share
a single address space. Because of these problems, the ability to
independently manipulate the cgroup memberships of the threads in
a process was removed in the initial cgroups v2 implementation,
and subsequently restored in a more limited form (see the
discussion of "thread mode" below).Mounting v1 controllers The use of cgroups requires a kernel built with the CONFIG_CGROUP option. In addition, each of the v1 controllers has an associated configuration option that must be set in order to employ that controller.
In order to use a v1 controller, it must be mounted against a
cgroup filesystem. The usual place for such mounts is under a
[tmpfs(5)](../man5/tmpfs.5.html) filesystem mounted at _/sys/fs/cgroup_. Thus, one might
mount the _cpu_ controller as follows:
mount -t cgroup -o cpu none /sys/fs/cgroup/cpu
It is possible to comount multiple controllers against the same
hierarchy. For example, here the _cpu_ and _cpuacct_ controllers are
comounted against a single hierarchy:
mount -t cgroup -o cpu,cpuacct none /sys/fs/cgroup/cpu,cpuacct
Comounting controllers has the effect that a process is in the
same cgroup for all of the comounted controllers. Separately
mounting controllers allows a process to be in cgroup _/foo1_ for
one controller while being in _/foo2/foo3_ for another.
It is possible to comount all v1 controllers against the same
hierarchy:
mount -t cgroup -o all cgroup /sys/fs/cgroup
(One can achieve the same result by omitting _-o all_, since it is
the default if no controllers are explicitly specified.)
It is not possible to mount the same controller against multiple
cgroup hierarchies. For example, it is not possible to mount both
the _cpu_ and _cpuacct_ controllers against one hierarchy, and to
mount the _cpu_ controller alone against another hierarchy. It is
possible to create multiple mounts with exactly the same set of
comounted controllers. However, in this case all that results is
multiple mount points providing a view of the same hierarchy.
Note that on many systems, the v1 controllers are automatically
mounted under _/sys/fs/cgroup_; in particular, [systemd(1)](../man1/systemd.1.html)
automatically creates such mounts.Unmounting v1 controllers A mounted cgroup filesystem can be unmounted using the umount(8) command, as in the following example:
umount /sys/fs/cgroup/pids
_But note well_: a cgroup filesystem is unmounted only if it is not
busy, that is, it has no child cgroups. If this is not the case,
then the only effect of the [umount(8)](../man8/umount.8.html) is to make the mount
invisible. Thus, to ensure that the mount is really removed, one
must first remove all child cgroups, which in turn can be done
only after all member processes have been moved from those cgroups
to the root cgroup.Cgroups version 1 controllers Each of the cgroups version 1 controllers is governed by a kernel configuration option (listed below). Additionally, the availability of the cgroups feature is governed by the CONFIG_CGROUPS kernel configuration option.
_cpu_ (since Linux 2.6.24; **CONFIG_CGROUP_SCHED**)
Cgroups can be guaranteed a minimum number of "CPU shares"
when a system is busy. This does not limit a cgroup's CPU
usage if the CPUs are not busy. For further information,
see _Documentation/scheduler/sched-design-CFS.rst_ (or
_Documentation/scheduler/sched-design-CFS.txt_ in Linux 5.2
and earlier).
In Linux 3.2, this controller was extended to provide CPU
"bandwidth" control. If the kernel is configured with
**CONFIG_CFS_BANDWIDTH**, then within each scheduling period
(defined via a file in the cgroup directory), it is
possible to define an upper limit on the CPU time allocated
to the processes in a cgroup. This upper limit applies
even if there is no other competition for the CPU. Further
information can be found in the kernel source file
_Documentation/scheduler/sched-bwc.rst_ (or
_Documentation/scheduler/sched-bwc.txt_ in Linux 5.2 and
earlier).
_cpuacct_ (since Linux 2.6.24; **CONFIG_CGROUP_CPUACCT**)
This provides accounting for CPU usage by groups of
processes.
Further information can be found in the kernel source file
_Documentation/admin-guide/cgroup-v1/cpuacct.rst_ (or
_Documentation/cgroup-v1/cpuacct.txt_ in Linux 5.2 and
earlier).
_cpuset_ (since Linux 2.6.24; **CONFIG_CPUSETS**)
This cgroup can be used to bind the processes in a cgroup
to a specified set of CPUs and NUMA nodes.
Further information can be found in the kernel source file
_Documentation/admin-guide/cgroup-v1/cpusets.rst_ (or
_Documentation/cgroup-v1/cpusets.txt_ in Linux 5.2 and
earlier).
_memory_ (since Linux 2.6.25; **CONFIG_MEMCG**)
The memory controller supports reporting and limiting of
process memory, kernel memory, and swap used by cgroups.
Further information can be found in the kernel source file
_Documentation/admin-guide/cgroup-v1/memory.rst_ (or
_Documentation/cgroup-v1/memory.txt_ in Linux 5.2 and
earlier).
_devices_ (since Linux 2.6.26; **CONFIG_CGROUP_DEVICE**)
This supports controlling which processes may create
(mknod) devices as well as open them for reading or
writing. The policies may be specified as allow-lists and
deny-lists. Hierarchy is enforced, so new rules must not
violate existing rules for the target or ancestor cgroups.
Further information can be found in the kernel source file
_Documentation/admin-guide/cgroup-v1/devices.rst_ (or
_Documentation/cgroup-v1/devices.txt_ in Linux 5.2 and
earlier).
_freezer_ (since Linux 2.6.28; **CONFIG_CGROUP_FREEZER**)
The _freezer_ cgroup can suspend and restore (resume) all
processes in a cgroup. Freezing a cgroup _/A_ also causes
its children, for example, processes in _/A/B_, to be frozen.
Further information can be found in the kernel source file
_Documentation/admin-guide/cgroup-v1/freezer-subsystem.rst_
(or _Documentation/cgroup-v1/freezer-subsystem.txt_ in Linux
5.2 and earlier).
_netcls_ (since Linux 2.6.29; **CONFIG_CGROUP_NET_CLASSID**)
This places a classid, specified for the cgroup, on network
packets created by a cgroup. These classids can then be
used in firewall rules, as well as used to shape traffic
using [tc(8)](../man8/tc.8.html). This applies only to packets leaving the
cgroup, not to traffic arriving at the cgroup.
Further information can be found in the kernel source file
_Documentation/admin-guide/cgroup-v1/netcls.rst_ (or
_Documentation/cgroup-v1/netcls.txt_ in Linux 5.2 and
earlier).
_blkio_ (since Linux 2.6.33; **CONFIG_BLK_CGROUP**)
The _blkio_ cgroup controls and limits access to specified
block devices by applying IO control in the form of
throttling and upper limits against leaf nodes and
intermediate nodes in the storage hierarchy.
Two policies are available. The first is a proportional-
weight time-based division of disk implemented with CFQ.
This is in effect for leaf nodes using CFQ. The second is
a throttling policy which specifies upper I/O rate limits
on a device.
Further information can be found in the kernel source file
_Documentation/admin-guide/cgroup-v1/blkio-controller.rst_
(or _Documentation/cgroup-v1/blkio-controller.txt_ in Linux
5.2 and earlier).
_perfevent_ (since Linux 2.6.39; **CONFIG_CGROUP_PERF**)
This controller allows _perf_ monitoring of the set of
processes grouped in a cgroup.
Further information can be found in the kernel source files
_netprio_ (since Linux 3.3; **CONFIG_CGROUP_NET_PRIO**)
This allows priorities to be specified, per network
interface, for cgroups.
Further information can be found in the kernel source file
_Documentation/admin-guide/cgroup-v1/netprio.rst_ (or
_Documentation/cgroup-v1/netprio.txt_ in Linux 5.2 and
earlier).
_hugetlb_ (since Linux 3.5; **CONFIG_CGROUP_HUGETLB**)
This supports limiting the use of huge pages by cgroups.
Further information can be found in the kernel source file
_Documentation/admin-guide/cgroup-v1/hugetlb.rst_ (or
_Documentation/cgroup-v1/hugetlb.txt_ in Linux 5.2 and
earlier).
_pids_ (since Linux 4.3; **CONFIG_CGROUP_PIDS**)
This controller permits limiting the number of process that
may be created in a cgroup (and its descendants).
Further information can be found in the kernel source file
_Documentation/admin-guide/cgroup-v1/pids.rst_ (or
_Documentation/cgroup-v1/pids.txt_ in Linux 5.2 and earlier).
_rdma_ (since Linux 4.11; **CONFIG_CGROUP_RDMA**)
The RDMA controller permits limiting the use of RDMA/IB-
specific resources per cgroup.
Further information can be found in the kernel source file
_Documentation/admin-guide/cgroup-v1/rdma.rst_ (or
_Documentation/cgroup-v1/rdma.txt_ in Linux 5.2 and earlier).Creating cgroups and moving processes A cgroup filesystem initially contains a single root cgroup, '/', which all processes belong to. A new cgroup is created by creating a directory in the cgroup filesystem:
mkdir /sys/fs/cgroup/cpu/cg1
This creates a new empty cgroup.
A process may be moved to this cgroup by writing its PID into the
cgroup's _cgroup.procs_ file:
echo <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow></mrow><annotation encoding="application/x-tex"></annotation></semantics></math></span><span class="katex-html" aria-hidden="true"></span></span> > /sys/fs/cgroup/cpu/cg1/cgroup.procs
Only one PID at a time should be written to this file.
Writing the value 0 to a _cgroup.procs_ file causes the writing
process to be moved to the corresponding cgroup.
When writing a PID into the _cgroup.procs_, all threads in the
process are moved into the new cgroup at once.
Within a hierarchy, a process can be a member of exactly one
cgroup. Writing a process's PID to a _cgroup.procs_ file
automatically removes it from the cgroup of which it was
previously a member.
The _cgroup.procs_ file can be read to obtain a list of the
processes that are members of a cgroup. The returned list of PIDs
is not guaranteed to be in order. Nor is it guaranteed to be free
of duplicates. (For example, a PID may be recycled while reading
from the list.)
In cgroups v1, an individual thread can be moved to another cgroup
by writing its thread ID (i.e., the kernel thread ID returned by
[clone(2)](../man2/clone.2.html) and [gettid(2)](../man2/gettid.2.html)) to the _tasks_ file in a cgroup directory.
This file can be read to discover the set of threads that are
members of the cgroup.Removing cgroups To remove a cgroup, it must first have no child cgroups and contain no (nonzombie) processes. So long as that is the case, one can simply remove the corresponding directory pathname. Note that files in a cgroup directory cannot and need not be removed.
Cgroups v1 release notification Two files can be used to determine whether the kernel provides notifications when a cgroup becomes empty. A cgroup is considered to be empty when it contains no child cgroups and no member processes.
A special file in the root directory of each cgroup hierarchy,
_releaseagent_, can be used to register the pathname of a program
that may be invoked when a cgroup in the hierarchy becomes empty.
The pathname of the newly empty cgroup (relative to the cgroup
mount point) is provided as the sole command-line argument when
the _releaseagent_ program is invoked. The _releaseagent_ program
might remove the cgroup directory, or perhaps repopulate it with a
process.
The default value of the _releaseagent_ file is empty, meaning that
no release agent is invoked.
The content of the _releaseagent_ file can also be specified via a
mount option when the cgroup filesystem is mounted:
mount -o release_agent=pathname ...
Whether or not the _releaseagent_ program is invoked when a
particular cgroup becomes empty is determined by the value in the
_notifyonrelease_ file in the corresponding cgroup directory. If
this file contains the value 0, then the _releaseagent_ program is
not invoked. If it contains the value 1, the _releaseagent_
program is invoked. The default value for this file in the root
cgroup is 0. At the time when a new cgroup is created, the value
in this file is inherited from the corresponding file in the
parent cgroup.Cgroup v1 named hierarchies In cgroups v1, it is possible to mount a cgroup hierarchy that has no attached controllers:
mount -t cgroup -o none,name=somename none /some/mount/point
Multiple instances of such hierarchies can be mounted; each
hierarchy must have a unique name. The only purpose of such
hierarchies is to track processes. (See the discussion of release
notification below.) An example of this is the _name=systemd_
cgroup hierarchy that is used by [systemd(1)](../man1/systemd.1.html) to track services and
user sessions.
Since Linux 5.0, the _cgroupnov1_ kernel boot option (described
below) can be used to disable cgroup v1 named hierarchies, by
specifying _cgroupnov1=named_.CGROUPS VERSION 2 top
In cgroups v2, all mounted controllers reside in a single unified
hierarchy. While (different) controllers may be simultaneously
mounted under the v1 and v2 hierarchies, it is not possible to
mount the same controller simultaneously under both the v1 and the
v2 hierarchies.
The new behaviors in cgroups v2 are summarized here, and in some
cases elaborated in the following subsections.
• Cgroups v2 provides a unified hierarchy against which all
controllers are mounted.
• "Internal" processes are not permitted. With the exception of
the root cgroup, processes may reside only in leaf nodes
(cgroups that do not themselves contain child cgroups). The
details are somewhat more subtle than this, and are described
below.
• Active cgroups must be specified via the files
_cgroup.controllers_ and _cgroup.subtreecontrol_.
• The _tasks_ file has been removed. In addition, the
_cgroup.clonechildren_ file that is employed by the _cpuset_
controller has been removed.
• An improved mechanism for notification of empty cgroups is
provided by the _cgroup.events_ file.
For more changes, see the _Documentation/admin-guide/cgroup-v2.rst_
file in the kernel source (or _Documentation/cgroup-v2.txt_ in Linux
4.17 and earlier).
Some of the new behaviors listed above saw subsequent modification
with the addition in Linux 4.14 of "thread mode" (described
below).Cgroups v2 unified hierarchy In cgroups v1, the ability to mount different controllers against different hierarchies was intended to allow great flexibility for application design. In practice, though, the flexibility turned out to be less useful than expected, and in many cases added complexity. Therefore, in cgroups v2, all available controllers are mounted against a single hierarchy. The available controllers are automatically mounted, meaning that it is not necessary (or possible) to specify the controllers when mounting the cgroup v2 filesystem using a command such as the following:
mount -t cgroup2 none /mnt/cgroup2
A cgroup v2 controller is available only if it is not currently in
use via a mount against a cgroup v1 hierarchy. Or, to put things
another way, it is not possible to employ the same controller
against both a v1 hierarchy and the unified v2 hierarchy. This
means that it may be necessary first to unmount a v1 controller
(as described above) before that controller is available in v2.
Since [systemd(1)](../man1/systemd.1.html) makes heavy use of some v1 controllers by
default, it can in some cases be simpler to boot the system with
selected v1 controllers disabled. To do this, specify the
_cgroupnov1=list_ option on the kernel boot command line; _list_ is
a comma-separated list of the names of the controllers to disable,
or the word _all_ to disable all v1 controllers. (This situation is
correctly handled by [systemd(1)](../man1/systemd.1.html), which falls back to operating
without the specified controllers.)
Note that on many modern systems, [systemd(1)](../man1/systemd.1.html) automatically mounts
the _cgroup2_ filesystem at _/sys/fs/cgroup/unified_ during the boot
process.Cgroups v2 mount options The following options (mount -o) can be specified when mounting the group v2 filesystem:
_nsdelegate_ (since Linux 4.15)
Treat cgroup namespaces as delegation boundaries. For
details, see below.
_memorylocalevents_ (since Linux 5.2)
The _memory.events_ should show statistics only for the
cgroup itself, and not for any descendant cgroups. This
was the behavior before Linux 5.2. Since Linux 5.2, the
default behavior is to include statistics for descendant
cgroups in _memory.events_, and this mount option can be used
to revert to the legacy behavior. This option is system
wide and can be set on mount or modified through remount
only from the initial mount namespace; it is silently
ignored in noninitial namespaces.Cgroups v2 controllers The following controllers, documented in the kernel source file Documentation/admin-guide/cgroup-v2.rst (or Documentation/cgroup-v2.txt in Linux 4.17 and earlier), are supported in cgroups version 2:
_cpu_ (since Linux 4.15)
This is the successor to the version 1 _cpu_ and _cpuacct_
controllers.
_cpuset_ (since Linux 5.0)
This is the successor of the version 1 _cpuset_ controller.
_freezer_ (since Linux 5.2)
This is the successor of the version 1 _freezer_ controller.
_hugetlb_ (since Linux 5.6)
This is the successor of the version 1 _hugetlb_ controller.
_io_ (since Linux 4.5)
This is the successor of the version 1 _blkio_ controller.
_memory_ (since Linux 4.5)
This is the successor of the version 1 _memory_ controller.
_perfevent_ (since Linux 4.11)
This is the same as the version 1 _perfevent_ controller.
_pids_ (since Linux 4.5)
This is the same as the version 1 _pids_ controller.
_rdma_ (since Linux 4.11)
This is the same as the version 1 _rdma_ controller.
There is no direct equivalent of the _netcls_ and _netprio_
controllers from cgroups version 1. Instead, support has been
added to [iptables(8)](../man8/iptables.8.html) to allow eBPF filters that hook on cgroup v2
pathnames to make decisions about network traffic on a per-cgroup
basis.
The v2 _devices_ controller provides no interface files; instead,
device control is gated by attaching an eBPF (**BPF_CGROUP_DEVICE**)
program to a v2 cgroup.Cgroups v2 subtree control Each cgroup in the v2 hierarchy contains the following two files:
_cgroup.controllers_
This read-only file exposes a list of the controllers that
are _available_ in this cgroup. The contents of this file
match the contents of the _cgroup.subtreecontrol_ file in
the parent cgroup.
_cgroup.subtreecontrol_
This is a list of controllers that are _active_ (_enabled_) in
the cgroup. The set of controllers in this file is a
subset of the set in the _cgroup.controllers_ of this cgroup.
The set of active controllers is modified by writing
strings to this file containing space-delimited controller
names, each preceded by '+' (to enable a controller) or '-'
(to disable a controller), as in the following example:
echo '+pids -memory' > x/y/cgroup.subtree_control
An attempt to enable a controller that is not present in
_cgroup.controllers_ leads to an **ENOENT** error when writing to
the _cgroup.subtreecontrol_ file.
Because the list of controllers in _cgroup.subtreecontrol_ is a
subset of those _cgroup.controllers_, a controller that has been
disabled in one cgroup in the hierarchy can never be re-enabled in
the subtree below that cgroup.
A cgroup's _cgroup.subtreecontrol_ file determines the set of
controllers that are exercised in the _child_ cgroups. When a
controller (e.g., _pids_) is present in the _cgroup.subtreecontrol_
file of a parent cgroup, then the corresponding controller-
interface files (e.g., _pids.max_) are automatically created in the
children of that cgroup and can be used to exert resource control
in the child cgroups.Cgroups v2 "no internal processes" rule Cgroups v2 enforces a so-called "no internal processes" rule. Roughly speaking, this rule means that, with the exception of the root cgroup, processes may reside only in leaf nodes (cgroups that do not themselves contain child cgroups). This avoids the need to decide how to partition resources between processes which are members of cgroup A and processes in child cgroups of A.
For instance, if cgroup _/cg1/cg2_ exists, then a process may reside
in _/cg1/cg2_, but not in _/cg1_. This is to avoid an ambiguity in
cgroups v1 with respect to the delegation of resources between
processes in _/cg1_ and its child cgroups. The recommended approach
in cgroups v2 is to create a subdirectory called _leaf_ for any
nonleaf cgroup which should contain processes, but no child
cgroups. Thus, processes which previously would have gone into
_/cg1_ would now go into _/cg1/leaf_. This has the advantage of
making explicit the relationship between processes in _/cg1/leaf_
and _/cg1_'s other children.
The "no internal processes" rule is in fact more subtle than
stated above. More precisely, the rule is that a (nonroot) cgroup
can't both (1) have member processes, and (2) distribute resources
into child cgroups—that is, have a nonempty _cgroup.subtreecontrol_
file. Thus, it _is_ possible for a cgroup to have both member
processes and child cgroups, but before controllers can be enabled
for that cgroup, the member processes must be moved out of the
cgroup (e.g., perhaps into the child cgroups).
With the Linux 4.14 addition of "thread mode" (described below),
the "no internal processes" rule has been relaxed in some cases.Cgroups v2 cgroup.events file Each nonroot cgroup in the v2 hierarchy contains a read-only file, cgroup.events, whose contents are key-value pairs (delimited by newline characters, with the key and value separated by spaces) providing state information about the cgroup:
$ **cat mygrp/cgroup.events**
populated 1
frozen 0
The following keys may appear in this file:
_populated_
The value of this key is either 1, if this cgroup or any of
its descendants has member processes, or otherwise 0.
_frozen_ (since Linux 5.2)
The value of this key is 1 if this cgroup is currently
frozen, or 0 if it is not.
The _cgroup.events_ file can be monitored, in order to receive
notification when the value of one of its keys changes. Such
monitoring can be done using [inotify(7)](../man7/inotify.7.html), which notifies changes as
**IN_MODIFY** events, or [poll(2)](../man2/poll.2.html), which notifies changes by returning
the **POLLPRI** and **POLLERR** bits in the _revents_ field.Cgroup v2 release notification Cgroups v2 provides a new mechanism for obtaining notification when a cgroup becomes empty. The cgroups v1 releaseagent and notifyonrelease files are removed, and replaced by the populated key in the cgroup.events file. This key either has the value 0, meaning that the cgroup (and its descendants) contain no (nonzombie) member processes, or 1, meaning that the cgroup (or one of its descendants) contains member processes.
The cgroups v2 release-notification mechanism offers the following
advantages over the cgroups v1 _releaseagent_ mechanism:
• It allows for cheaper notification, since a single process can
monitor multiple _cgroup.events_ files (using the techniques
described earlier). By contrast, the cgroups v1 mechanism
requires the expense of creating a process for each
notification.
• Notification for different cgroup subhierarchies can be
delegated to different processes. By contrast, the cgroups v1
mechanism allows only one release agent for an entire
hierarchy.Cgroups v2 cgroup.stat file Each cgroup in the v2 hierarchy contains a read-only cgroup.stat file (first introduced in Linux 4.14) that consists of lines containing key-value pairs. The following keys currently appear in this file:
_nrdescendants_
This is the total number of visible (i.e., living)
descendant cgroups underneath this cgroup.
_nrdyingdescendants_
This is the total number of dying descendant cgroups
underneath this cgroup. A cgroup enters the dying state
after being deleted. It remains in that state for an
undefined period (which will depend on system load) while
resources are freed before the cgroup is destroyed. Note
that the presence of some cgroups in the dying state is
normal, and is not indicative of any problem.
A process can't be made a member of a dying cgroup, and a
dying cgroup can't be brought back to life.Limiting the number of descendant cgroups Each cgroup in the v2 hierarchy contains the following files, which can be used to view and set limits on the number of descendant cgroups under that cgroup:
_cgroup.max.depth_ (since Linux 4.14)
This file defines a limit on the depth of nesting of
descendant cgroups. A value of 0 in this file means that
no descendant cgroups can be created. An attempt to create
a descendant whose nesting level exceeds the limit fails
(_mkdir_(2) fails with the error **EAGAIN**).
Writing the string _"max"_ to this file means that no limit
is imposed. The default value in this file is _"max"_.
_cgroup.max.descendants_ (since Linux 4.14)
This file defines a limit on the number of live descendant
cgroups that this cgroup may have. An attempt to create
more descendants than allowed by the limit fails (_mkdir_(2)
fails with the error **EAGAIN**).
Writing the string _"max"_ to this file means that no limit
is imposed. The default value in this file is _"max"_.CGROUPS DELEGATION: DELEGATING A HIERARCHY TO A LESS PRIVILEGED USER %%%SH%%% In the context of cgroups, delegation means passing management of some subtree of the cgroup hierarchy to a nonprivileged user. Cgroups v1 provides support for delegation based on file permissions in the cgroup hierarchy but with less strict containment rules than v2 (as noted below). Cgroups v2 supports delegation with containment by explicit design. The focus of the discussion in this section is on delegation in cgroups v2, with some differences for cgroups v1 noted along the way.
Some terminology is required in order to describe delegation. A
_delegater_ is a privileged user (i.e., root) who owns a parent
cgroup. A _delegatee_ is a nonprivileged user who will be granted
the permissions needed to manage some subhierarchy under that
parent cgroup, known as the _delegated subtree_.
To perform delegation, the delegater makes certain directories and
files writable by the delegatee, typically by changing the
ownership of the objects to be the user ID of the delegatee.
Assuming that we want to delegate the hierarchy rooted at (say)
_/dlgtgrp_ and that there are not yet any child cgroups under that
cgroup, the ownership of the following is changed to the user ID
of the delegatee:
_/dlgtgrp_
Changing the ownership of the root of the subtree means
that any new cgroups created under the subtree (and the
files they contain) will also be owned by the delegatee.
_/dlgtgrp/cgroup.procs_
Changing the ownership of this file means that the
delegatee can move processes into the root of the delegated
subtree.
_/dlgtgrp/cgroup.subtreecontrol_ (cgroups v2 only)
Changing the ownership of this file means that the
delegatee can enable controllers (that are present in
_/dlgtgrp/cgroup.controllers_) in order to further
redistribute resources at lower levels in the subtree. (As
an alternative to changing the ownership of this file, the
delegater might instead add selected controllers to this
file.)
_/dlgtgrp/cgroup.threads_ (cgroups v2 only)
Changing the ownership of this file is necessary if a
threaded subtree is being delegated (see the description of
"thread mode", below). This permits the delegatee to write
thread IDs to the file. (The ownership of this file can
also be changed when delegating a domain subtree, but
currently this serves no purpose, since, as described
below, it is not possible to move a thread between domain
cgroups by writing its thread ID to the _cgroup.threads_
file.)
In cgroups v1, the corresponding file that should instead
be delegated is the _tasks_ file.
The delegater should _not_ change the ownership of any of the
controller interfaces files (e.g., _pids.max_, _memory.high_) in
_dlgtgrp_. Those files are used from the next level above the
delegated subtree in order to distribute resources into the
subtree, and the delegatee should not have permission to change
the resources that are distributed into the delegated subtree.
See also the discussion of the _/sys/kernel/cgroup/delegate_ file in
NOTES for information about further delegatable files in cgroups
v2.
After the aforementioned steps have been performed, the delegatee
can create child cgroups within the delegated subtree (the cgroup
subdirectories and the files they contain will be owned by the
delegatee) and move processes between cgroups in the subtree. If
some controllers are present in _dlgtgrp/cgroup.subtreecontrol_,
or the ownership of that file was passed to the delegatee, the
delegatee can also control the further redistribution of the
corresponding resources into the delegated subtree.Cgroups v2 delegation: nsdelegate and cgroup namespaces Starting with Linux 4.13, there is a second way to perform cgroup delegation in the cgroups v2 hierarchy. This is done by mounting or remounting the cgroup v2 filesystem with the nsdelegate mount option. For example, if the cgroup v2 filesystem has already been mounted, we can remount it with the nsdelegate option as follows:
mount -t cgroup2 -o remount,nsdelegate \
none /sys/fs/cgroup/unified
The effect of this mount option is to cause cgroup namespaces to
automatically become delegation boundaries. More specifically,
the following restrictions apply for processes inside the cgroup
namespace:
• Writes to controller interface files in the root directory of
the namespace will fail with the error **EPERM**. Processes inside
the cgroup namespace can still write to delegatable files in
the root directory of the cgroup namespace such as _cgroup.procs_
and _cgroup.subtreecontrol_, and can create subhierarchy
underneath the root directory.
• Attempts to migrate processes across the namespace boundary are
denied (with the error **ENOENT**). Processes inside the cgroup
namespace can still (subject to the containment rules described
below) move processes between cgroups _within_ the subhierarchy
under the namespace root.
The ability to define cgroup namespaces as delegation boundaries
makes cgroup namespaces more useful. To understand why, suppose
that we already have one cgroup hierarchy that has been delegated
to a nonprivileged user, _cecilia_, using the older delegation
technique described above. Suppose further that _cecilia_ wanted to
further delegate a subhierarchy under the existing delegated
hierarchy. (For example, the delegated hierarchy might be
associated with an unprivileged container run by _cecilia_.) Even
if a cgroup namespace was employed, because both hierarchies are
owned by the unprivileged user _cecilia_, the following illegitimate
actions could be performed:
• A process in the inferior hierarchy could change the resource
controller settings in the root directory of that hierarchy.
(These resource controller settings are intended to allow
control to be exercised from the _parent_ cgroup; a process
inside the child cgroup should not be allowed to modify them.)
• A process inside the inferior hierarchy could move processes
into and out of the inferior hierarchy if the cgroups in the
superior hierarchy were somehow visible.
Employing the _nsdelegate_ mount option prevents both of these
possibilities.
The _nsdelegate_ mount option only has an effect when performed in
the initial mount namespace; in other mount namespaces, the option
is silently ignored.
_Note_: On some systems, [systemd(1)](../man1/systemd.1.html) automatically mounts the cgroup
v2 filesystem. In order to experiment with the _nsdelegate_
operation, it may be useful to boot the kernel with the following
command-line options:
cgroup_no_v1=all systemd.legacy_systemd_cgroup_controller
These options cause the kernel to boot with the cgroups v1
controllers disabled (meaning that the controllers are available
in the v2 hierarchy), and tells [systemd(1)](../man1/systemd.1.html) not to mount and use
the cgroup v2 hierarchy, so that the v2 hierarchy can be manually
mounted with the desired options after boot-up.Cgroup delegation containment rules Some delegation containment rules ensure that the delegatee can move processes between cgroups within the delegated subtree, but can't move processes from outside the delegated subtree into the subtree or vice versa. A nonprivileged process (i.e., the delegatee) can write the PID of a "target" process into a cgroup.procs file only if all of the following are true:
• The writer has write permission on the _cgroup.procs_ file in the
destination cgroup.
• The writer has write permission on the _cgroup.procs_ file in the
nearest common ancestor of the source and destination cgroups.
Note that in some cases, the nearest common ancestor may be the
source or destination cgroup itself. This requirement is not
enforced for cgroups v1 hierarchies, with the consequence that
containment in v1 is less strict than in v2. (For example, in
cgroups v1 the user that owns two distinct delegated
subhierarchies can move a process between the hierarchies.)
• If the cgroup v2 filesystem was mounted with the _nsdelegate_
option, the writer must be able to see the source and
destination cgroups from its cgroup namespace.
• In cgroups v1: the effective UID of the writer (i.e., the
delegatee) matches the real user ID or the saved set-user-ID of
the target process. Before Linux 4.11, this requirement also
applied in cgroups v2 (This was a historical requirement
inherited from cgroups v1 that was later deemed unnecessary,
since the other rules suffice for containment in cgroups v2.)
_Note_: one consequence of these delegation containment rules is
that the unprivileged delegatee can't place the first process into
the delegated subtree; instead, the delegater must place the first
process (a process owned by the delegatee) into the delegated
subtree.CGROUPS VERSION 2 THREAD MODE top
Among the restrictions imposed by cgroups v2 that were not present
in cgroups v1 are the following:
• _No thread-granularity control_: all of the threads of a process
must be in the same cgroup.
• _No internal processes_: a cgroup can't both have member
processes and exercise controllers on child cgroups.
Both of these restrictions were added because the lack of these
restrictions had caused problems in cgroups v1. In particular,
the cgroups v1 ability to allow thread-level granularity for
cgroup membership made no sense for some controllers. (A notable
example was the _memory_ controller: since threads share an address
space, it made no sense to split threads across different _memory_
cgroups.)
Notwithstanding the initial design decision in cgroups v2, there
were use cases for certain controllers, notably the _cpu_
controller, for which thread-level granularity of control was
meaningful and useful. To accommodate such use cases, Linux 4.14
added _thread mode_ for cgroups v2.
Thread mode allows the following:
• The creation of _threaded subtrees_ in which the threads of a
process may be spread across cgroups inside the tree. (A
threaded subtree may contain multiple multithreaded processes.)
• The concept of _threaded controllers_, which can distribute
resources across the cgroups in a threaded subtree.
• A relaxation of the "no internal processes rule", so that,
within a threaded subtree, a cgroup can both contain member
threads and exercise resource control over child cgroups.
With the addition of thread mode, each nonroot cgroup now contains
a new file, _cgroup.type_, that exposes, and in some circumstances
can be used to change, the "type" of a cgroup. This file contains
one of the following type values:
_domain_ This is a normal v2 cgroup that provides process-
granularity control. If a process is a member of this
cgroup, then all threads of the process are (by definition)
in the same cgroup. This is the default cgroup type, and
provides the same behavior that was provided for cgroups in
the initial cgroups v2 implementation.
_threaded_
This cgroup is a member of a threaded subtree. Threads can
be added to this cgroup, and controllers can be enabled for
the cgroup.
_domain threaded_
This is a domain cgroup that serves as the root of a
threaded subtree. This cgroup type is also known as
"threaded root".
_domain invalid_
This is a cgroup inside a threaded subtree that is in an
"invalid" state. Processes can't be added to the cgroup,
and controllers can't be enabled for the cgroup. The only
thing that can be done with this cgroup (other than
deleting it) is to convert it to a _threaded_ cgroup by
writing the string _"threaded"_ to the _cgroup.type_ file.
The rationale for the existence of this "interim" type
during the creation of a threaded subtree (rather than the
kernel simply immediately converting all cgroups under the
threaded root to the type _threaded_) is to allow for
possible future extensions to the thread mode modelThreaded versus domain controllers With the addition of threads mode, cgroups v2 now distinguishes two types of resource controllers:
• _Threaded_ controllers: these controllers support thread-
granularity for resource control and can be enabled inside
threaded subtrees, with the result that the corresponding
controller-interface files appear inside the cgroups in the
threaded subtree. As at Linux 4.19, the following controllers
are threaded: _cpu_, _perfevent_, and _pids_.
• _Domain_ controllers: these controllers support only process
granularity for resource control. From the perspective of a
domain controller, all threads of a process are always in the
same cgroup. Domain controllers can't be enabled inside a
threaded subtree.Creating a threaded subtree There are two pathways that lead to the creation of a threaded subtree. The first pathway proceeds as follows:
(1) We write the string _"threaded"_ to the _cgroup.type_ file of a
cgroup _y/z_ that currently has the type _domain_. This has the
following effects:
• The type of the cgroup _y/z_ becomes _threaded_.
• The type of the parent cgroup, _y_, becomes _domain threaded_.
The parent cgroup is the root of a threaded subtree (also
known as the "threaded root").
• All other cgroups under _y_ that were not already of type
_threaded_ (because they were inside already existing
threaded subtrees under the new threaded root) are
converted to type _domain invalid_. Any subsequently
created cgroups under _y_ will also have the type _domain_
_invalid_.
(2) We write the string _"threaded"_ to each of the _domain invalid_
cgroups under _y_, in order to convert them to the type
_threaded_. As a consequence of this step, all threads under
the threaded root now have the type _threaded_ and the threaded
subtree is now fully usable. The requirement to write
_"threaded"_ to each of these cgroups is somewhat cumbersome,
but allows for possible future extensions to the thread-mode
model.
The second way of creating a threaded subtree is as follows:
(1) In an existing cgroup, _z_, that currently has the type _domain_,
we (1.1) enable one or more threaded controllers and (1.2)
make a process a member of _z_. (These two steps can be done
in either order.) This has the following consequences:
• The type of _z_ becomes _domain threaded_.
• All of the descendant cgroups of _z_ that were not already
of type _threaded_ are converted to type _domain invalid_.
(2) As before, we make the threaded subtree usable by writing the
string _"threaded"_ to each of the _domain invalid_ cgroups under
_z_, in order to convert them to the type _threaded_.
One of the consequences of the above pathways to creating a
threaded subtree is that the threaded root cgroup can be a parent
only to _threaded_ (and _domain invalid_) cgroups. The threaded root
cgroup can't be a parent of a _domain_ cgroups, and a _threaded_
cgroup can't have a sibling that is a _domain_ cgroup.Using a threaded subtree Within a threaded subtree, threaded controllers can be enabled in each subgroup whose type has been changed to threaded; upon doing so, the corresponding controller interface files appear in the children of that cgroup.
A process can be moved into a threaded subtree by writing its PID
to the _cgroup.procs_ file in one of the cgroups inside the tree.
This has the effect of making all of the threads in the process
members of the corresponding cgroup and makes the process a member
of the threaded subtree. The threads of the process can then be
spread across the threaded subtree by writing their thread IDs
(see [gettid(2)](../man2/gettid.2.html)) to the _cgroup.threads_ files in different cgroups
inside the subtree. The threads of a process must all reside in
the same threaded subtree.
As with writing to _cgroup.procs_, some containment rules apply when
writing to the _cgroup.threads_ file:
• The writer must have write permission on the cgroup.threads
file in the destination cgroup.
• The writer must have write permission on the _cgroup.procs_ file
in the common ancestor of the source and destination cgroups.
(In some cases, the common ancestor may be the source or
destination cgroup itself.)
• The source and destination cgroups must be in the same threaded
subtree. (Outside a threaded subtree, an attempt to move a
thread by writing its thread ID to the _cgroup.threads_ file in a
different _domain_ cgroup fails with the error **EOPNOTSUPP**.)
The _cgroup.threads_ file is present in each cgroup (including
_domain_ cgroups) and can be read in order to discover the set of
threads that is present in the cgroup. The set of thread IDs
obtained when reading this file is not guaranteed to be ordered or
free of duplicates.
The _cgroup.procs_ file in the threaded root shows the PIDs of all
processes that are members of the threaded subtree. The
_cgroup.procs_ files in the other cgroups in the subtree are not
readable.
Domain controllers can't be enabled in a threaded subtree; no
controller-interface files appear inside the cgroups underneath
the threaded root. From the point of view of a domain controller,
threaded subtrees are invisible: a multithreaded process inside a
threaded subtree appears to a domain controller as a process that
resides in the threaded root cgroup.
Within a threaded subtree, the "no internal processes" rule does
not apply: a cgroup can both contain member processes (or thread)
and exercise controllers on child cgroups.Rules for writing to cgroup.type and creating threaded subtrees A number of rules apply when writing to the cgroup.type file:
• Only the string _"threaded"_ may be written. In other words, the
only explicit transition that is possible is to convert a
_domain_ cgroup to type _threaded_.
• The effect of writing _"threaded"_ depends on the current value
in _cgroup.type_, as follows:
• _domain_ or _domain threaded_: start the creation of a threaded
subtree (whose root is the parent of this cgroup) via the
first of the pathways described above;
• _domain invalid_: convert this cgroup (which is inside a
threaded subtree) to a usable (i.e., _threaded_) state;
• _threaded_: no effect (a "no-op").
• We can't write to a _cgroup.type_ file if the parent's type is
_domain invalid_. In other words, the cgroups of a threaded
subtree must be converted to the _threaded_ state in a top-down
manner.
There are also some constraints that must be satisfied in order to
create a threaded subtree rooted at the cgroup _x_:
• There can be no member processes in the descendant cgroups of
_x_. (The cgroup _x_ can itself have member processes.)
• No domain controllers may be enabled in _x_'s
_cgroup.subtreecontrol_ file.
If any of the above constraints is violated, then an attempt to
write _"threaded"_ to a _cgroup.type_ file fails with the error
**ENOTSUP**.The "domain threaded" cgroup type According to the pathways described above, the type of a cgroup can change to domain threaded in either of the following cases:
• The string _"threaded"_ is written to a child cgroup.
• A threaded controller is enabled inside the cgroup and a
process is made a member of the cgroup.
A _domain threaded_ cgroup, _x_, can revert to the type _domain_ if the
above conditions no longer hold true—that is, if all _threaded_
child cgroups of _x_ are removed and either _x_ no longer has threaded
controllers enabled or no longer has member processes.
When a _domain threaded_ cgroup _x_ reverts to the type _domain_:
• All _domain invalid_ descendants of _x_ that are not in lower-level
threaded subtrees revert to the type _domain_.
• The root cgroups in any lower-level threaded subtrees revert to
the type _domain threaded_.Exceptions for the root cgroup The root cgroup of the v2 hierarchy is treated exceptionally: it can be the parent of both domain and threaded cgroups. If the string "threaded" is written to the cgroup.type file of one of the children of the root cgroup, then
• The type of that cgroup becomes _threaded_.
• The type of any descendants of that cgroup that are not part of
lower-level threaded subtrees changes to _domain invalid_.
Note that in this case, there is no cgroup whose type becomes
_domain threaded_. (Notionally, the root cgroup can be considered
as the threaded root for the cgroup whose type was changed to
_threaded_.)
The aim of this exceptional treatment for the root cgroup is to
allow a threaded cgroup that employs the _cpu_ controller to be
placed as high as possible in the hierarchy, so as to minimize the
(small) cost of traversing the cgroup hierarchy.The cgroups v2 "cpu" controller and realtime threads As at Linux 4.19, the cgroups v2 cpu controller does not support control of realtime threads (specifically threads scheduled under any of the policies SCHED_FIFO, SCHED_RR, described SCHED_DEADLINE; see sched(7)). Therefore, the cpu controller can be enabled in the root cgroup only if all realtime threads are in the root cgroup. (If there are realtime threads in nonroot cgroups, then a write(2) of the string "+cpu" to the cgroup.subtreecontrol file fails with the error EINVAL.)
On some systems, [systemd(1)](../man1/systemd.1.html) places certain realtime threads in
nonroot cgroups in the v2 hierarchy. On such systems, these
threads must first be moved to the root cgroup before the _cpu_
controller can be enabled.ERRORS top
The following errors can occur for [mount(2)](../man2/mount.2.html):
**EBUSY** An attempt to mount a cgroup version 1 filesystem specified
neither the _name=_ option (to mount a named hierarchy) nor a
controller name (or _all_).NOTES top
A child process created via [fork(2)](../man2/fork.2.html) inherits its parent's cgroup
memberships. A process's cgroup memberships are preserved across
[execve(2)](../man2/execve.2.html).
The [clone3(2)](../man2/clone3.2.html) **CLONE_INTO_CGROUP** flag can be used to create a child
process that begins its life in a different version 2 cgroup from
the parent process./proc files /proc/cgroups (since Linux 2.6.24) This file contains information about the controllers that are compiled into the kernel. An example of the contents of this file (reformatted for readability) is the following:
#subsys_name hierarchy num_cgroups enabled
cpuset 4 1 1
cpu 8 1 1
cpuacct 8 1 1
blkio 6 1 1
memory 3 1 1
devices 10 84 1
freezer 7 1 1
net_cls 9 1 1
perf_event 5 1 1
net_prio 9 1 1
hugetlb 0 1 0
pids 2 1 1
The fields in this file are, from left to right:
[1] The name of the controller.
[2] The unique ID of the cgroup hierarchy on which this
controller is mounted. If multiple cgroups v1
controllers are bound to the same hierarchy, then each
will show the same hierarchy ID in this field. The
value in this field will be 0 if:
• the controller is not mounted on a cgroups v1
hierarchy;
• the controller is bound to the cgroups v2 single
unified hierarchy; or
• the controller is disabled (see below).
[3] The number of control groups in this hierarchy using
this controller.
[4] This field contains the value 1 if this controller is
enabled, or 0 if it has been disabled (via the
_cgroupdisable_ kernel command-line boot parameter).
_/proc/_pid_/cgroup_ (since Linux 2.6.24)
This file describes control groups to which the process
with the corresponding PID belongs. The displayed
information differs for cgroups version 1 and version 2
hierarchies.
For each cgroup hierarchy of which the process is a member,
there is one entry containing three colon-separated fields:
hierarchy-ID:controller-list:cgroup-path
For example:
5:cpuacct,cpu,cpuset:/daemons
The colon-separated fields are, from left to right:
[1] For cgroups version 1 hierarchies, this field contains
a unique hierarchy ID number that can be matched to a
hierarchy ID in _/proc/cgroups_. For the cgroups
version 2 hierarchy, this field contains the value 0.
[2] For cgroups version 1 hierarchies, this field contains
a comma-separated list of the controllers bound to the
hierarchy. For the cgroups version 2 hierarchy, this
field is empty.
[3] This field contains the pathname of the control group
in the hierarchy to which the process belongs. This
pathname is relative to the mount point of the
hierarchy./sys/kernel/cgroup files /sys/kernel/cgroup/delegate (since Linux 4.15) This file exports a list of the cgroups v2 files (one per line) that are delegatable (i.e., whose ownership should be changed to the user ID of the delegatee). In the future, the set of delegatable files may change or grow, and this file provides a way for the kernel to inform user-space applications of which files must be delegated. As at Linux 4.15, one sees the following when inspecting this file:
$ **cat /sys/kernel/cgroup/delegate**
cgroup.procs
cgroup.subtree_control
cgroup.threads
_/sys/kernel/cgroup/features_ (since Linux 4.15)
Over time, the set of cgroups v2 features that are provided
by the kernel may change or grow, or some features may not
be enabled by default. This file provides a way for user-
space applications to discover what features the running
kernel supports and has enabled. Features are listed one
per line:
$ **cat /sys/kernel/cgroup/features**
nsdelegate
memory_localevents
The entries that can appear in this file are:
_memorylocalevents_ (since Linux 5.2)
The kernel supports the _memorylocalevents_ mount
option.
_nsdelegate_ (since Linux 4.15)
The kernel supports the _nsdelegate_ mount option.
_memoryrecursiveprot_ (since Linux 5.7)
The kernel supports the _memoryrecursiveprot_ mount
option.SEE ALSO top
[prlimit(1)](../man1/prlimit.1.html), [systemd(1)](../man1/systemd.1.html), [systemd-cgls(1)](../man1/systemd-cgls.1.html), [systemd-cgtop(1)](../man1/systemd-cgtop.1.html),
[clone(2)](../man2/clone.2.html), [ioprio_set(2)](../man2/ioprio%5Fset.2.html), [perf_event_open(2)](../man2/perf%5Fevent%5Fopen.2.html), [setrlimit(2)](../man2/setrlimit.2.html),
[cgroup_namespaces(7)](../man7/cgroup%5Fnamespaces.7.html), [cpuset(7)](../man7/cpuset.7.html), [namespaces(7)](../man7/namespaces.7.html), [sched(7)](../man7/sched.7.html),
[user_namespaces(7)](../man7/user%5Fnamespaces.7.html)
The kernel source file _Documentation/admin-guide/cgroup-v2.rst_.COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-12-04 cgroups(7)
Pages that refer to this page:clone(2), getrlimit(2), ioprio_set(2), poll(2), proc_cgroups(5), proc_pid_cgroup(5), sysfs(5), systemd.exec(5), bpf-helpers(7), cgroup_namespaces(7), cpuset(7), namespaces(7), sched(7)