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msgget — get message queue
Standard C Library (libc, -lc)
msgget(key_t key, int msgflg);
The msgget() function returns the message queue identifier associated
with key. A message queue identifier is a unique integer greater than
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:
· msg_perm.cuid and msg_perm.uid are set to the effective uid of the
· msg_perm.gid and msg_perm.cgid are set to the effective gid of the
· msg_perm.mode is set to the lower 9 bits of msgflg.
· msg_cbytes, msg_qnum, msg_lspid, msg_lrpid, msg_rtime, and msg_stime
are set to 0.
· msg_qbytes is set to the system wide maximum value for the number of
bytes in a queue (MSGMNB).
· msg_ctime is set to the current time.
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.
[EACCES] A message queue is already associated with key and the
caller has no permission to access it.
[EEXIST] Both IPC_CREAT and IPC_EXCL are set in msgflg, and a
message queue is already associated with key.
[ENOSPC] A new message queue could not be created because the
system limit for the number of message queues has been
[ENOENT] IPC_CREAT was not set in msgflg and no message queue
associated with key was found.
msgctl(2), msgrcv(2), msgsnd(2)
Message queues appeared in the first release of AT&T System V UNIX.