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.
