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Namespaces compatibility list
This document contains the information about the problems user
may have when creating tasks living in different namespaces.
Here's the summary. This matrix shows the known problems, that
occur when tasks share some namespace (the columns) while living
in different other namespaces (the rows):
UTS IPC VFS PID User Net
IPC X 1
PID 1 1 X
User 2 2 X
1. Both the IPC and the PID namespaces provide IDs to address
object inside the kernel. E.g. semaphore with IPCID or
process group with pid.
In both cases, tasks shouldn't try exposing this ID to some
other task living in a different namespace via a shared filesystem
or IPC shmem/message. The fact is that this ID is only valid
within the namespace it was obtained in and may refer to some
other object in another namespace.
2. Intentionally, two equal user IDs in different user namespaces
should not be equal from the VFS point of view. In other
words, user 10 in one user namespace shouldn't have the same
access permissions to files, belonging to user 10 in another
The same is true for the IPC namespaces being shared - two users
from different user namespaces should not access the same IPC objects
even having equal UIDs.
But currently this is not so.