ttyctl [ -fu ]
       The  -f  option freezes the tty (i.e. terminal or terminal emula-
       tor), 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 simi-
       lar programs have no effect when the tty is frozen.  Freezing the
       tty does not cause the current state to be  remembered:  instead,
       it causes future changes to the state to be blocked.

       Without options it reports whether the terminal is frozen or not.

       Note  that,  regardless  of whether the tty is frozen or not, the
       shell needs to change the settings when the line  editor  starts,
       so  unfreezing  the  tty  does not guarantee settings made on the
       command line are preserved.   Strings  of  commands  run  between
       editing  the  command  line will see a consistent tty state.  See
       also the shell variable STTY for a means of initialising the  tty
       before running external commands and/or freezing the tty around a
       single command.
