How do I check cgroup v2 is installed on my machine?

Question

I want to try cgroup v2 but am not sure if it is installed on my linux machine

>> uname -r
4.14.66-041466-generic

Since cgroup v2 is available in 4.12.0-rc5, I assume it should be available in the kernel version I am using.

https://www.infradead.org/~mchehab/kernel_docs/unsorted/cgroup-v2.html

However, it does not seem like my system has cgroup v2 as the memory interface files mentioned in its documentation are not available on my system.

https://www.kernel.org/doc/Documentation/cgroup-v2.txt

It seems like I still have cgroup v1.

/sys/fs/cgroup/memory# ls
cgroup.clone_children  memory.kmem.failcnt                 memory.kmem.tcp.usage_in_bytes   memory.memsw.usage_in_bytes      memory.swappiness
cgroup.event_control   memory.kmem.limit_in_bytes          memory.kmem.usage_in_bytes       memory.move_charge_at_immigrate  memory.usage_in_bytes
cgroup.procs           memory.kmem.max_usage_in_bytes      memory.limit_in_bytes            memory.numa_stat                 memory.use_hierarchy
cgroup.sane_behavior   memory.kmem.slabinfo                memory.max_usage_in_bytes        memory.oom_control               notify_on_release
docker                 memory.kmem.tcp.failcnt             memory.memsw.failcnt             memory.pressure_level            release_agent
memory.failcnt         memory.kmem.tcp.limit_in_bytes      memory.memsw.limit_in_bytes      memory.soft_limit_in_bytes       tasks
memory.force_empty     memory.kmem.tcp.max_usage_in_bytes  memory.memsw.max_usage_in_bytes  memory.stat 

Follow-up questions Thanks Brian for the help. Please let me know if I should be creating a new question but I think it might be helpful to other if I just ask my questions here.

1) I am unable to add cgroup controllers, following the command in the doc

>> echo "+cpu +memory -io" > cgroup.subtree_control

However, I got "echo: write error: Invalid argument". Am I missing a prerequisite to this step?

2) I ran a docker container but the docker daemon log complained about not able to find "/sys/fs/cgroup/cpuset/docker/cpuset.cpus". It seems like docker is still expecting cgroupv1. What is the best way to enable cgroupv2 support on my docker daemon?

docker -v
Docker version 17.09.1-ce, build aedabb7

Answer 1

You could run the following command:

grep cgroup /proc/filesystems

If your system supports cgroupv2, you would see:

nodev   cgroup
nodev   cgroup2

On a system with only cgroupv1, you would only see:

nodev   cgroup

Answer 2

The easiest way is to attempt to mount the pseudo-filesystem. If you can mount it to a location, then you can attempt to manage processes with the interface:

mount -t cgroup2 none $MOUNT_POINT

I see that you cited the documentation above. One of the points you may be missing is that the paths still need to be created. There's no reason you must manage cgroup resources at any particular location. It's just convention.

For example, you could totally present procfs at /usr/monkeys... as long as the directory /usr/monkeys exists:

$ sudo mkdir /usr/monkeys
$ sudo mount -t proc none /usr/monkeys
$ ls -l /usr/monkeys
...
...
-r--r--r--.  1 root        root                      0 Sep 25 19:00 uptime
-r--r--r--.  1 root        root                      0 Sep 25 23:17 version
-r--------.  1 root        root                      0 Sep 25 23:17 vmallocinfo
-r--r--r--.  1 root        root                      0 Sep 25 18:57 vmstat
-r--r--r--.  1 root        root                      0 Sep 25 23:17 zoneinfo
$ sudo umount /usr/monkeys

In the same way I can do this with the cgroup v2 pseudo-filesystem:

$ sudo mount -t cgroup2 none /usr/monkeys
$ ls -l /usr/monkeys
total 0
-r--r--r--.  1 root root 0 Sep 23 16:58 cgroup.controllers
-rw-r--r--.  1 root root 0 Sep 23 16:58 cgroup.max.depth
-rw-r--r--.  1 root root 0 Sep 23 16:58 cgroup.max.descendants
-rw-r--r--.  1 root root 0 Sep 23 16:58 cgroup.procs
-r--r--r--.  1 root root 0 Sep 23 16:58 cgroup.stat
-rw-r--r--.  1 root root 0 Sep 23 16:58 cgroup.subtree_control
-rw-r--r--.  1 root root 0 Sep 23 16:58 cgroup.threads
drwxr-xr-x.  2 root root 0 Sep 23 16:58 init.scope
drwxr-xr-x.  2 root root 0 Sep 23 16:58 machine.slice
drwxr-xr-x. 59 root root 0 Sep 23 16:58 system.slice
drwxr-xr-x.  4 root root 0 Sep 23 16:58 user.slice
$ sudo umount /usr/monkeys

Answer 3

It might be not relevant not only to see if cgroups v2 are supported, but also whether they are enabled and for that following command can be used:

stat -fc %T /sys/fs/cgroup/

In case the output states cgroup2fs then cgroups v2 are used, tmpfs in case cgroups v1. In case system supports cgroups v2, but not activated by default then it could be enabled by setting systemd.unified_cgroup_hierarchy=1 as kernel parameter (eg. GRUB_CMDLINE_LINUX="systemd.unified_cgroup_hierarchy=1" in systems with GRUB)

Answer 4

To check if your Linux system supports cgroup v2 check for the existence of cgroup.controllers:

$ cat /sys/fs/cgroup/cgroup.controllers

cpuset cpu io memory hugetlb pids rdma

To boot the host with cgroup v2, add the following string to the GRUB_CMDLINE_LINUX line in /etc/default/grub and then run sudo update-grub:

---

• systemd.unified_cgroup_hierarchy=1

---

• Current Linux distros that support cgroups v2

• Docker 20.10 recommended for cgroups v2

---

Also helpful - checking if you are in an unprivileged namespace

Answer 5

Some systems will mount cgroup v1 and cgroup v2 by default, just in different locations. It can help to see where those are with:

grep ^cgroup /etc/mtab

Example output (on Ubuntu 20.04 LTS):

cgroup2 /sys/fs/cgroup/unified cgroup2 rw,nosuid,nodev,noexec,relatime 0 0
cgroup /sys/fs/cgroup/systemd cgroup rw,nosuid,nodev,noexec,relatime,xattr,name=systemd 0 0
cgroup /sys/fs/cgroup/cpu,cpuacct cgroup rw,nosuid,nodev,noexec,relatime,cpu,cpuacct 0 0
cgroup /sys/fs/cgroup/devices cgroup rw,nosuid,nodev,noexec,relatime,devices 0 0
cgroup /sys/fs/cgroup/memory cgroup rw,nosuid,nodev,noexec,relatime,memory 0 0
cgroup /sys/fs/cgroup/freezer cgroup rw,nosuid,nodev,noexec,relatime,freezer 0 0
cgroup /sys/fs/cgroup/rdma cgroup rw,nosuid,nodev,noexec,relatime,rdma 0 0
cgroup /sys/fs/cgroup/cpuset cgroup rw,nosuid,nodev,noexec,relatime,cpuset 0 0
cgroup /sys/fs/cgroup/blkio cgroup rw,nosuid,nodev,noexec,relatime,blkio 0 0
cgroup /sys/fs/cgroup/net_cls,net_prio cgroup rw,nosuid,nodev,noexec,relatime,net_cls,net_prio 0 0
cgroup /sys/fs/cgroup/pids cgroup rw,nosuid,nodev,noexec,relatime,pids 0 0
cgroup /sys/fs/cgroup/hugetlb cgroup rw,nosuid,nodev,noexec,relatime,hugetlb 0 0
cgroup /sys/fs/cgroup/perf_event cgroup rw,nosuid,nodev,noexec,relatime,perf_event 0 0

However, this does not strictly tell you if your system supports cgroup v2. As the other answer mentioned, grep cgroup /proc/filesystems is great for that.

Answer 6

The most straightforward answer today may be provided by podman:

podman info --format {{.Host.CgroupsVersion}}

This will display either v1 or v2.

Name and position of the key has changed over the years, so if you get a template error, you can try this instead:

podman info |grep -i cgroup

Podman has added cgroups v2 support in 2019, with version 1.6.0. So this won't work on very old systems that has older podman available.

Of course one caveat is that you need podman installed. Most distributions should have it in the repos.