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.
