ttyctl [ -fu ]
       The -f option freezes the tty (i.e. terminal or terminal emulator),
       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 ef-
       fect 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.
