error setting cgroup config for procHooks process: unable to freeze: unknown

[dabcoder]

Hello,

I am looking for insights for this particular error for a container that tried to start:

failed to create containerd task: failed to create shim task: OCI
            runtime create failed: runc create failed: unable to start container
            process: error during container init: error setting cgroup config
            for procHooks process: unable to freeze: unknown 

I've located that error here unless I'm mistaken. A couple of questions:

• as far as I understand, this is specific to an OS that would use cgroups v1 only, not v2. Is that correct?
  (I also had a look at https://docs.kernel.org/admin-guide/cgroup-v1/freezer-subsystem.html).
• How does that process work for cgroups v2 which doesn't have that subsystem (starting or stopping required tasks)?

Thanks in advance.

[cyphar]

How does that process work for cgroups v2 which doesn't have that subsystem (starting or stopping required tasks)?

cgroupv2 does have freezing, it's just implemented as part of the cgroup core rather than as a separate controller. See /sys/fs/cgroup/.../cgroup.freeze. The design of the cgroupv2 freezer is far more robust than cgroupv1, which is why the bug can only occur on cgroupv1.

[dabcoder]

Thanks @cyphar, all clear. Closing this discussion.

[dabcoder]

Forgot to ask, what does the last unknown error refer to (after unable to freeze:)? Wasn't able to locate it in the codebase.

[cyphar]

It probably comes from containerd. A quick look at the codebase indicates it might refer to the container state after the error, but I don't know.