plucky (2) msgget.2freebsd.gz

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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.