What mechanism was used in Linux before the introduction of the namespace concept?

Before the introduction of the namespace concept in Linux for process and resource isolation, the chroot mechanism was used. It allows changing the root directory of a process, limiting its visible filesystem.

However, chroot does not provide complete isolation, as processes can see other system resources and do not isolate aspects such as PIDs, network interfaces, etc. The namespace, on the other hand, offers a deeper and more comprehensive isolation at the kernel level.