Couldn't modiry the configuration files, when the bsd machine is booted in single mode

[fred]

   Hi, =20 =20 My machine with the freebsd 4.6 is crashed, when I use
   the=20 =20 boot -s=20 =20 command to enter the single mode, I found I
   couldn't modiry the configr= ation files of the system. =20 It seems
   the whole filesytem is readonly. =20 =20 Could any one show me a way?
   =20 =20 =20 Regards, Fred Zhang