msgctl(2)							     msgctl(2)

Name
       msgctl - message control operations

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

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

Description
       The  system  call  provides  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

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

IPC_RMID       Remove the message queue identifier specified by msqid from the
	       system and destroy the message queue and data structure associ‐
	       ated with it. This command can only be executed	by  a  process
	       that has an effective user ID equal to either that of the supe‐
	       ruser or to the value of msg_perm.uid  in  the  data  structure
	       associated with msquid.

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

Diagnostics
       The system call fails under the following conditions:

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

       [EINVAL]	      The cmd is not a valid command.

       [EACCES]	      The cmd is equal to IPC_STAT and read operation  permis‐
		      sion  is	denied	to  the	 calling process.  For further
		      information, see

       [EPERM]	      The cmd is equal to IPC_RMID or IPC_SET and  the	effec‐
		      tive user ID of the calling process is not equal to that
		      of the superuser or to the value of msg_perm.uid in  the
		      data structure associated with msqid.

       [EPERM]	      The 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
		      superuser.

       [EFAULT]	      The buf points to an illegal address.

See Also
       msgget(2), msgop(2)

								     msgctl(2)

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