ttyctl -fu
          The -f option freezes the tty,  and  -u  unfreezes  it.
          When the tty is frozen, no changes made to the tty set-
          tings by external  programs  will  be  honored  by  the
          shell;  the  shell  will  simply  reset the settings to
          their previous values as soon as  each  command  exits.
          Thus, stty and similar programs have no effect when the
          tty is frozen.