msgctl(2)                  DG/UX 4.30                   msgctl(2)



     NAME
          msgctl - Get or set message queue attributes or destroy a
          message queue.

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

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

     PARAMETERS
          msqid          A message queue identifier.


          cmd            The message control operation to be
                         performed.


          buf            The address of a message queue attribute
                         record.  Used only if <cmd> is IPC_STAT or
                         IPC_SET.

     DESCRIPTION
          Msgctl is used to get and set message queue attributes or to
          destroy a message queue.  The subject message queue is
          identified by <msqid>. The action performed by msgctl
          depends on the value of <cmd> as follows:


          IPC_STAT
               The user-visible msqid_ds structure is returned in
               <buf>.

          If an error occurs, the contents of <buf> are undefined.


          IPC_SET
               The following message queue attributes are set to the
               values found in the structure pointed to by <buf>: user
               id (msg_perm.uid), group id (msg_perm.gid), permission
               rights (in msg_perm.mode), and the maximum size
               (msg_qbytes).

          If an error occurs, the message queue remains unchanged.
          Otherwise, the last change time (msg_ctime) is set to the
          current time.





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     msgctl(2)                  DG/UX 4.30                   msgctl(2)



          IPC_RMID
               The message queue is destroyed.  All resources consumed
               by the message queue are freed and the message queue
               identifier is invalidated.  All queued messages are
               lost.

          If an error occurs, the message queue remains unchanged.

     ACCESS CONTROL
          Operation permission depends on the value of <cmd> as
          follows:


          IPC_STAT
               The calling process is required to have read access to
               the message queue.


          IPC_SET
               The effective user id of the calling process must be
               equal to the message queue's user id, the message queue
               creator's user id, or that of the superuser.  If the
               maximum size of the message queue is increased, the
               effective user id of the calling process must be the
               superuser.


          IPC_RMID
               The effective user id of the calling process must be
               equal to the message queue's user id, the message queue
               creator's user id, or that of the superuser.

     RETURN VALUE
          0              Completed successfully.


          -1             An error occurred.  Errno is set to indicate
                         the error.

     EXCEPTIONS
          Errno may be set to one of the following error codes
          regardless of the value of <cmd>:


          EINVAL         <msqid> is not a valid message queue
                         identifier.


          EINVAL         <Cmd> is not a valid command.

          If <cmd> is IPC_STAT, errno may be set to one of these
          values:



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     msgctl(2)                  DG/UX 4.30                   msgctl(2)



          EACCES         Read permission is denied to the calling
                         process.


          EFAULT         <buf> points to an illegal address.

          If <cmd> is IPC_SET, errno may be set to one of these
          values:


          EPERM          Permission to change the message queue
                         attributes is denied to the calling process.


          EPERM          Permission to increase to the maximum size of
                         the message queue is denied to the calling
                         process.


          EFAULT         <buf> points to an illegal address.

          If <cmd> is IPC_RMID, errno may be set to this value:


          EPERM          Permission to remove the message queue is
                         denied to the calling process.

     SEE ALSO
          intro(2), ipcrm(1), ipcs(1), msgget(2), msgrcv(2),
          msgsnd(2).

























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