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MSGSND(2)		       System Calls Manual		       MSGSND(2)

NAME
     msgsnd -- send a message to a message queue

LIBRARY
     Standard C Library (libc, -lc)

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

     int
     msgsnd(int msqid, const void *msgp, size_t msgsz, int msgflg);

DESCRIPTION
     The  msgsnd()  function  sends  a message to the message queue specified in
     msqid.  The msgp argument points to a  structure  containing  the	message.
     This structure should consist of the following members:

	 long mtype;	/* message type */
	 char mtext[1]; /* body of message */

     mtype  is an integer greater than 0 that can be used for selecting messages
     (see msgrcv(2)), mtext is an array of msgsz bytes.  The argument msgsz  can
     range from 0 to a system-imposed maximum, MSGMAX.

     If  the  number  of bytes already on the message queue plus msgsz is bigger
     than the maximum number of bytes on the message queue (msg_qbytes, see  ms-
     gctl(2)),	or  the  number of messages on all queues system-wide is already
     equal to the system limit, msgflg determines the action  of  msgsnd().   If
     msgflg has IPC_NOWAIT mask set in it, the call will return immediately.  If
     msgflg does not have IPC_NOWAIT set in it, the call will block until:

     *	 The condition which caused the call to block does no longer exist.  The
	 message will be sent.

     *	 The  message  queue  is removed, in which case -1 will be returned, and
	 errno is set to EINVAL.

     *	 The caller catches a signal.  The call returns with errno set to EINTR.

     After a successful call, the data structure  associated  with  the  message
     queue is updated in the following way:

     *	 msg_cbytes is incremented by the size of the message.

     *	 msg_qnum is incremented by 1.

     *	 msg_lspid is set to the pid of the calling process.

     *	 msg_stime is set to the current time.

RETURN VALUES
     The  msgsnd()  function  returns  the  value 0 if successful; otherwise the
     value -1 is returned and the global variable errno is set to  indicate  the
     error.

ERRORS
     The msgsnd() function will fail if:

     [EINVAL]		The  msqid argument is not a valid message queue identi-
			fier.

			The message queue was removed while msgsnd() was waiting
			for a resource to become available in order  to  deliver
			the message.

			The msgsz argument is greater than msg_qbytes.

			The mtype argument is not greater than 0.

     [EACCES]		The  calling  process  does not have write access to the
			message queue.

     [EAGAIN]		There was no space for this message either on the queue,
			or in the  whole  system,  and	IPC_NOWAIT  was  set  in
			msgflg.

     [EFAULT]		The msgp argument points to an invalid address.

     [EINTR]		The  system  call  was	interrupted by the delivery of a
			signal.

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

BUGS
     NetBSD and FreeBSD do not define the EIDRM error  value,  which  should  be
     used in the case of a removed message queue.

FreeBSD ports 15.quarterly	  July 9, 2009			       MSGSND(2)

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