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MSGCTL(2)			    Linux Programmer's Manual				MSGCTL(2)

       msgctl - message control operations

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

       int msgctl(int msqid, int cmd, struct msqid_ds *buf);

       This  function  performs  the control operation specified by cmd on the message queue with
       identifier msqid.  Legal values for cmd are:

	      Copy info from the message queue data structure  associated  with  msqid	into  the
	      structure  pointed  to by buf.  The caller must have read permission on the message

	      Write the values of some members of the msqid_ds structure pointed to by buf to the
	      message  queue  data  structure, updating also its msg_ctime member.  The following
	      members of the structure can be updated:

		   msg_perm.mode  /* only lowest 9-bits */

	      The calling process must have appropriate (probably, root) privileges or its effec-
	      tive user-ID must be that of the creator (msg_perm.cuid) or owner (msg_perm.uid) of
	      the message queue.  Appropriate (probably, root) privileges are required	to  raise
	      the msg_qbytes value beyond the system parameter MSGMNB.

	      Immediately  remove  the message queue and its associated data structure, awakening
	      all waiting reader and writer processes (with an error  return  and  errno  set  to
	      EIDRM).	The  calling process must have appropriate (probably, root) privileges or
	      its effective user-ID must be either that of the creator or owner  of  the  message

       On success, the return value will be 0, otherwise -1 with errno indicating the error.

       On failure, errno is set to one of the following:

       EACCES	  The  argument  cmd  is  equal to IPC_STAT but the calling process does not have
		  read permission on the message queue msqid.

       EFAULT	  The argument cmd has the value IPC_SET or IPC_STAT, but the address pointed  to
		  by buf isn't accessible.

       EIDRM	  The message queue was removed.

       EINVAL	  Invalid value for cmd or msqid.

       EPERM	  The argument cmd has the value IPC_SET or IPC_RMID, but the calling process has
		  insufficient privileges to execute the command.

       The IPC_INFO, MSG_STAT and MSG_INFO control calls are used by the ipcs(8) program to  pro-
       vide information on allocated resources.  In the future these may be modified as needed or
       moved to a proc file system interface.

       Various fields in a struct msqid_ds were shorts under Linux  2.2  and  have  become  longs
       under  Linux  2.4.  To take advantage of this, a recompilation under glibc-2.1.91 or later
       should suffice.	(The kernel distinguishes old and new calls by a IPC_64 flag in cmd.)

       SVr4, SVID.  SVID does not document the EIDRM error condition.

       ipc(5), msgget(2), msgsnd(2), msgrcv(2)

Linux 2.4.1				    2001-02-18					MSGCTL(2)
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