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