My kernel supports cgroup
and cgroup2
and both of them are mounted. I'm interested in finding out if any of the applications I am running are using the legacy cgroup
version 1? Is there anyway to determine what application has not been upgraded to use cgroup
version 2?
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Evan Carroll
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I would like better information then this, it's an assumption that I will delete if this gets a proper answer.
cgroup
v2 which I know is in use on my system will not permit the unmounting,
$ sudo umount -f /sys/fs/cgroup/unified
umount: /sys/fs/cgroup/unified: target is busy.
However, the cgroup
v1 dirs can be unmounted just fine, regardless of systemd
having set them up at boot. I assume this is because nothing is using them; I assume further that if cgroup
v2 were not in use, they could be unmounted.
So on the basis of not being able to unmount cgroup
version 2, and assuming a similar behavior of cgroup
version 1 you can determine if anything is using cgroup version 1 by simply trying ot unmount it.

Evan Carroll
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lsof
command,sudo lsof 2>&1 | grep '/sys/fs/cgroup'
. – eshizhan Mar 18 '23 at 15:27