UNIX Shared Memory IPC: Using shmget()

Inter-Process Communication (IPC) allows different processes to exchange data. Shared memory is an efficient IPC method where processes can access a common region of memory.

System Call Analysis for Shared Memory

The question asks for the UNIX system call specifically used for creating or accessing shared memory segments.

• pipe(): This system call creates a unidirectional data stream (a pipe) between processes. It's used for stream-based communication, not direct memory access.
• msgget(): This system call is used with message queues. It retrieves a message queue identifier, facilitating message-based IPC, not shared memory.
• shmget(): This system call is used to obtain a shared memory identifier. It either creates a new shared memory segment or returns the identifier of an existing one based on the provided key. This is the primary system call for managing shared memory segments.
• semctl(): This system call performs control operations on semaphores. Semaphores are often used to synchronize access to shared resources (like shared memory), but $semctl()$ itself doesn't manage the shared memory segment.

Therefore, $shmget()$ is the correct system call for initiating shared memory inter-process communication in UNIX.