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 sus-
       pended.  Thus, stty and similar programs have no effect when the
       tty  is frozen.  Without options it reports whether the terminal
       is frozen or not.
