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 msgctl(2)							   msgctl(2)




 NAME
      msgctl - message control operations

 SYNOPSIS
      #include <&lt&lt&lt;sys/msg.h>&gt&gt&gt;

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

 DESCRIPTION
      msgctl() provides a variety of message control operations as specified
      by cmd.  The following cmds are available:

	   IPC_STAT	  Place the current value of each member of the data
			  structure associated with msqid into the structure
			  pointed to by buf.  The contents of this structure
			  are defined in glossary(9).

	   IPC_SET	  Set the value of the following members of the data
			  structure associated with msqid to the
			  corresponding value found in the structure pointed
			  to by buf:

			       msg_perm.uid
			       msg_perm.gid
			       msg_perm.mode   /* only low 9 bits */
			       msg_qbytes

			  This cmd can only be executed by a process that
			  has an effective user ID equal to either that of
			  super-user or to the value of either msg_perm.uid
			  or msg_perm.cuid in the data structure associated
			  with msqid.  Only super-user can raise the value
			  of msg_qbytes.

			  WARNING: Programs compiled on HP-UX revisions
			  prior to 11.11 use old 16-bit msqid_ds structure
			  fields (obtained via IPC_STAT) which can describe
			  queue sizes only up to 64KBytes. Care must be
			  taken such that queues shared with such programs
			  are not made larger than 64KBytes (65535).  Or,
			  those existing programs should be recompiled.	 Or,
			  the system administrator should restrict the
			  MSGMNB kernel tunable parameter to 64KBytes or
			  less.

	   IPC_RMID	  Remove the message queue identifier specified by
			  msqid from the system and destroy the message
			  queue and data structure associated with it.	This
			  cmd can only be executed by a process that has an
			  effective user ID equal to either that of super-
			  user or to the value of either msg_perm.uid or



 Hewlett-Packard Company	    - 1 -   HP-UX Release 11i: November 2000






 msgctl(2)							   msgctl(2)




			  msg_perm.cuid in the data structure associated
			  with msqid.

 RETURN VALUE
      Upon successful completion, a value of 0 is returned.  Otherwise, a
      value of -1 is returned and errno is set to indicate the error.

 ERRORS
      msgctl() fails if one or more of the following is true:

      [EINVAL]	     msqid is not a valid message queue identifier.

      [EINVAL]	     cmd is not a valid command, or the command contains
		     invalid parameters.

      [EACCES]	     cmd is equal to IPC_STAT and Read operation permission
		     is denied to the calling process (see message operation
		     permissions in glossary(9)).

      [EPERM]	     cmd is equal to IPC_RMID or IPC_SET and the effective
		     user ID of the calling process is not equal to that of
		     a user who has appropriate privileges and it is not
		     equal to the value of either msg_perm.uid or
		     msg_perm.cuid in the data structure associated with
		     msqid.

      [EPERM]	     cmd is equal to IPC_SET, an attempt is being made to
		     increase to the value of msg_qbytes, and the effective
		     user ID of the calling process is not equal to that of
		     super-user.

      [EFAULT]	     buf points to an illegal address.	Reliable detection
		     of this error is implementation dependent.

 SEE ALSO
      ftok(3C), ipcrm(1), ipcs(1), msgget(2), msgop(2).

 STANDARDS CONFORMANCE
      msgctl(): SVID2, SVID3, XPG2, XPG3, XPG4















 Hewlett-Packard Company	    - 2 -   HP-UX Release 11i: November 2000