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MSGGET(2) System Calls Manual MSGGET(2)

get message queue

#include <sys/msg.h>
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.
was not set in msgflg and no message queue associated with key was found.

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

Message queues appeared in AT&T System V Release 1 UNIX.
November 15, 2014 OpenBSD-5.9