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MSGGET(2) System Calls Manual MSGGET(2)

msgget
get message queue

#include <sys/msg.h>

int
msgget(key_t key, int msgflg);

msgget() returns the message queue identifier associated with key. A message queue identifier is a unique integer greater than zero.

A message queue is created if either key is equal to IPC_PRIVATE, or key does not have a message queue identifier associated with it, and the IPC_CREAT bit is set in msgflg.

If a new message queue is created, the data structure associated with it (the msqid_ds structure, see msgctl(2)) is initialized as follows:

Upon successful completion a positive message queue identifier is returned. Otherwise, -1 is returned and the global variable errno is set to indicate the error.

[]
A message queue is already associated with key and the caller has no permission to access it.
[]
Both IPC_CREAT and IPC_EXCL are set in msgflg, and a message queue is already associated with key.
[]
A new message queue could not be created because the system limit for the number of message queues has been reached.
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was not set in msgflg and no message queue associated with key was found.

msgctl(2), msgrcv(2), msgsnd(2), ftok(3)

The msgget() function conforms to the X/Open System Interfaces option of IEEE Std 1003.1-2008 (“POSIX.1”).

Message queues first appeared in AT&T System V Release 1 UNIX and have been available since NetBSD 1.0.
July 18, 2019 OpenBSD-current