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