Bug Report

v2 linux namespaces are not compatible with concourse worker

Steps to Reproduce

Use a linux distribution which switched to namespaces v2.Try to run concourse. All containers (checks, tasks, ... ) fail to spawn.
See also:
https://discuss.concourse-ci.org/t/failing-workers-with-cgroup-already-being-mounted/1966/2

Expected Results

Either be warned about the issue or just work as per usual :)

Actual Results

Failing checks

Additional Context

Reproducible with Fedora 31 which changed the default namespaces from v1 to v2 .

Version Info

• Concourse version: concourse 5.7.2
• Deployment type (BOSH/Docker/binary): binary/worker, docker/web
• Infrastructure/IaaS: Fedora 31
• Browser (if applicable): firefox
• Did this used to work? before there was a v2 namespace impl, yes