The Linux kernel currently implements six (out of 10 proposed) namespaces for process separation:
- mnt – mount points, filesystems
- pid – processes
- net – network stack
- ipc – System V IPC
- uts – hostname, domainname
- user – UIDs, GIDs
The last Linux namespace to be fully implemented was the user namespace (CLONE_NEWNS) whose implementation was finally completed in the 3.8 kernel after being started in the 2.6.23 kernel.
The current kernel in RHEL7 is 3.10.0-121. Unfortunately it does not include the user namespace. According to Dan Walsh of Red Hat:
We hope to add the user namespace support to a future Red Hat Enterprise Linux 7.
User namespaces are important for securely implementing Linux Containers. According to the Red Hat Enterprise Linux Blog:
User namespaces isolate the user and group ID number spaces, such that a process’s user and group IDs can be different inside and outside a user namespace. The most interesting case here is that a process can have a normal unprivileged user ID outside a user namespace while at the same time having a user ID of 0 inside the namespace. This means that the process has full root privileges for operations inside the user namespace, but is unprivileged for operations outside the namespace. While very promising, there are still a few kinks to work out before it meets our standards for enabling it in Red Hat Enterprise Linux 7 Beta. Rest assured, we are working on stabilizing the code base and solving the issues so we can consider turning it on in the future when it becomes enterprise ready.
This is a serious omission on the part of Red Hat and should be rectified as soon as possible. My guess is that it was probably omitted because a number of filesystems are not yet namespace-aware.