MSGGET(2)                 FreeBSD System Calls Manual                MSGGET(2)

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.

FreeBSD 13.1-RELEASE-p6          March 4, 2018         FreeBSD 13.1-RELEASE-p6