To connect to the kernel for z/OS UNIX System Services, you make an address space known to it. This process is called dubbing. After it has been dubbed, the address space is considered to be a process. Address spaces that are created by fork are automatically dubbed when they are created. Other address spaces become dubbed if they invoke a z/OS UNIX service. Dubbing also applies to MVS™ tasks. A dubbed task is considered a thread. Tasks created by pthread_create are automatically dubbed threads; other tasks are dubbed if they invoke a z/OS UNIX service.
Undub is the inverse of dub. Normally, a task (dubbed a thread) is undubbed when it ends. An address space (dubbed a process) is undubbed when the last thread ends.
If, when a thread or process is being dubbed, the calling task has a task-level ACEE that does not have a USP connected to it, an INITUSP is done against the task-level ACEE. This causes z/OS UNIX security information to be associated with the task-level ACEE.