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 sim-
       ilar 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.
