MSGGET(2)                            SysV                            MSGGET(2)



NAME
     msgget - get message queue

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

     int msgget (key, msgflg)
     key_t key;
     int msgflg;

DESCRIPTION
     msgget returns the message queue identifier associated with key.

     A message queue identifier and associated message queue and data
     structure (see intro(2)) are created for key if one of the following are
     true:

     ⊕  key is equal to IPC_PRIVATE.

     ⊕  key does not already have a message queue identifier associated with
        it, and (msgflg & IPC_CREAT) is "true".

     Upon creation, the data structure associated with the new message queue
     identifier is initialized as follows:

     1.   msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and msg_perm.gid are set
          equal to the effective user ID and effective group ID, respectively,
          of the calling process.

     2.   The low-order nine bits of msg_perm.mode are set equal to the low-
          order nine bits of msgflg.

     3.   msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime are set
          equal to 0.

     4.   msg_ctime is set equal to the current time.

     5.   msg_qbytes is set equal to the system limit.

ERRORS
     msgget will fail if one or more of the following are true:

     [EACCES]   A message queue identifier exists for key, but operation
                permission (see intro(2)) as specified by the low-order nine
                bits of msgflg would not be granted.

     [ENOENT]   A message queue identifier does not exist for key and (msgflg
                & IPC_CREAT) is "false".

     [ENOSPC]   A message queue identifier is to be created, but the system-
                imposed limit on the maximum number of allowed message queue
                identifiers system wide would be exceeded.

     [EEXIST]   A message queue identifier exists for key but ((msgflg &
                IPC_CREAT) & (msgflg & IPC_EXCL)) is "true".

SEE ALSO
     intro(2), msgctl(2), msgop(2).

DIAGNOSTICS
     Upon successful completion, a non-negative integer, namely a message
     queue identifier, is returned.  Otherwise, a value of -1 is returned and
     errno is set to indicate the error.