When chromium is running I see processes in
/proc/[PID]/ where some of the namespace links inside
/proc/[PID]/ns/do link to nothing, that is, they cannot be
readlinked and return errors instead. Also an
ls -l throws error for them. This applies only to some namespaces, such as the network namespace. This happens with superuser rights inside the root namespaces looking at
/proc/[PID]/ns/net for some chromium-related processes.
The system is a recently updated Debian 9 Stretch.
Can someone please explain how it is possible that a process can be dejoined from certain namespaces completely? I've never seen anything being mentioned in the Linux namespace man pages, so how is this possible and what's the meaning?