discovering the namespace type
The NS_GET_NSTYPE operation can be used to discover the type of namespace referred to by the file descriptor fd.
fd refers to a /proc/pid/ns/* file.
On success, the return value is one of the CLONE_NEW* values that can be specified to clone(2) or unshare(2) in order to create a namespace.
On error, -1 is returned, and errno is set to indicate the error.
Linux.
Linux 4.11.