ttyctl -fu
       The  -f  option  freezes the tty, and -u  unfreezes
       tty  is frozen, no changes made to the tty settings
       programs will be honored by the shell,  except  for
       size of the screen; the shell will simply reset the
       their  previous  values as soon as each command ex-
       pended.   Thus,  stty  and similar programs have no
       tty  is frozen.  Without options it reports whether
       is frozen or not.
