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     msgget — get message queue


     Standard C Library (libc, -lc)


     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/msg.h>

     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
         calling process.

     ·   msg_perm.gid and msg_perm.cgid are set to the effective gid of the
         calling process.

     ·   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.