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  ter-
       minal is frozen or not.
