       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.
