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MSGGET(2)                DragonFly System Calls Manual               MSGGET(2)


NAME

     msgget -- get message queue


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

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

     int
     msgget(key_t key, int msgflg);


DESCRIPTION

     The msgget() system call 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:

     o   msg_perm.cuid and msg_perm.uid are set to the effective uid of the
         calling process.

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

     o   msg_perm.mode is set to the lower 9 bits of msgflg.

     o   msg_cbytes, msg_qnum, msg_lspid, msg_lrpid, msg_rtime, and msg_stime
         are set to 0.

     o   msg_qbytes is set to the system wide maximum value for the number of
         bytes in a queue (MSGMNB).

     o   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.


ENVIRONMENT

     The XSI Interprocess Communication family of functions is also available
     as an implementation in userspace.  To use it, the sysvipcd(8) daemon has
     to be running.

     If the USR_SYSVIPC variable is set in a process' environment, the process
     and its children will use the userspace implementation.


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.


AUTHORS

     The DragonFly specific userspace implementation (see ENVIRONMENT) was
     written by Larisa Grigore.

DragonFly 3.7                   January 4, 2014                  DragonFly 3.7

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