fix(cli): improve container detection when cgroupns=private #15156
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Fixes #12721
If a container in docker is started with
--cgroupns=private(which is the default behaviour in docker) then/proc/1/cgrouphas the following content:If a container in docker is started with
--cgroupns=hostthen/proc/1/cgrouphas the following content (hash will vary):Currently we are determining if a host is containerized by assuming the second scenario. This means the existing behaviour of sniffing
/proc/1/cgroupis not always sufficient for checking if a host is containerized.According to the cgroups(7) man-page there exists a
cgroup.typefile in a nonroot cgroup. This exists in Linux versions after4.14.This means we can check for the existence of
/sys/fs/cgroup/cgroup.typeto see if we are in a container or not.