What does the 'pid' namespace control in Linux?

The 'pid' namespace in Linux is responsible for creating unique process identifiers (PIDs) within a specific namespace. This means that processes in different PID namespaces can have the same PID without conflict since each namespace maintains its own set of PIDs. This feature is particularly useful in containerization technologies, such as Docker, where multiple containers may run applications that require separate process trees, ensuring that they do not interfere with each other. By isolating PIDs, the 'pid' namespace enhances process management and improves security and stability in multi-tenant environments. This unique identification is essential for the operating system to track processes efficiently and manage resources related to them.