NAME

     msgget — get message queue

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/msg.h>

     int
     msgget(key_t key, int msgflg);

DESCRIPTION

     The msgget() function 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:

     •   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 which are set by ORing these
         constants:

         0400
           Read access for user.

         0200
           Write access for user.

         0040
           Read access for group.

         0020
           Write access for group.

         0004
           Read access for other.

         0002
           Write access for other.

     •   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.

RETURN VALUES

     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.

ERRORS

     [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 reached.

     [ENOENT]           IPC_CREAT was not set in msgflg and no message queue associated with key
                        was found.

SEE ALSO

     msgctl(2), msgrcv(2), msgsnd(2)

HISTORY

     Message queues appeared in the first release of AT&T System V UNIX.