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msgctl(2)							System Calls Manual							 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
		      associated with it. This command can only be executed by a process that has an effective user ID equal to either that of the
		      superuser 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 permission is denied to the calling process.  For further information, see

       [EPERM]	      The cmd is equal to IPC_RMID or IPC_SET and the effective user ID of the calling process is not equal to that of	the  supe-
		      ruser 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)