On Linux, Nomad uses cgroups to control access to resources like CPU and memory.
Nomad supports both [cgroups
v2](https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html) and the
legacy [cgroups
v1](https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/cgroups.html).
When Nomad clients start, they determine the available cgroup controllers and
include the attribute `os.cgroups.version` in their fingerprint.

On cgroups v2, you can run the following command to verify that you have all
required controllers.

```shell-session
$ cat /sys/fs/cgroup/cgroup.controllers
cpuset cpu io memory pids
```

On legacy cgroups v1, this same list of required controllers appears as a series
of sub-directories under the directory `/sys/fs/cgroup`.

Refer to the [cgroup controller
requirements](/nomad/docs/install/production/requirements#cgroup-controllers)
for more details and to enable missing cgroups.
