Message queues¶

System V message queues allow data to be exchanged in units called messages. Each message can have an associated priority. POSIX message queues provide an alternative API for achieving the same result; see mq_overview(7).

The System V message queue API consists of the following system calls:

msgget(2)

Create a new message queue or obtain the ID of an existing message queue. This call returns an identifier that is used in the remaining APIs.

msgsnd(2)

Add a message to a queue.

msgrcv(2)

Remove a message from a queue.

msgctl(2)

Perform various control operations on a queue, including deletion.

Semaphore sets¶

System V semaphores allow processes to synchronize their actions. System V semaphores are allocated in groups called sets; each semaphore in a set is a counting semaphore. POSIX semaphores provide an alternative API for achieving the same result; see sem_overview(7).

The System V semaphore API consists of the following system calls:

semget(2)

Create a new set or obtain the ID of an existing set. This call returns an identifier that is used in the remaining APIs.

semop(2)

Perform operations on the semaphores in a set.

semctl(2)

Perform various control operations on a set, including deletion.

Shared memory segments¶

System V shared memory allows processes to share a region a memory (a "segment"). POSIX shared memory is an alternative API for achieving the same result; see shm_overview(7).

The System V shared memory API consists of the following system calls:

shmget(2)

Create a new segment or obtain the ID of an existing segment. This call returns an identifier that is used in the remaining APIs.

shmat(2)

Attach an existing shared memory object into the calling process's address space.

shmdt(2)

Detach a segment from the calling process's address space.

shmctl(2)

Perform various control operations on a segment, including deletion.

IPC namespaces¶

For a discussion of the interaction of System V IPC objects and IPC namespaces, see ipc_namespaces(7).