The FSTAB coincides with this script..

# /etc/fstab: static file system information.
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>

## COMMON

proc            /proc           proc    defaults        0       0
none            /tmp            tmpfs   defaults        0       0

/dev/hda1       /boot           ext2     defaults,noauto 0       0
/dev/hda2       /               squashfs defaults,ro     0       0
/dev/hda4       /union          ext2     defaults        0       0

#UnionFS
none            /usr            unionfs dirs=/union/usr=rw:/usr=ro        0 0
none            /var            unionfs dirs=/union/var=rw:/var=ro        0 0
none            /etc            unionfs dirs=/union/etc=rw:/etc=ro        0 0
none            /home            unionfs dirs=/union/home=rw:/home=ro     0 0
none            /root            unionfs dirs=/union/root=rw:/root=ro     0 0
none            /bin             unionfs dirs=/union/bin=rw:/bin=ro       0 0
none            /sbin            unionfs dirs=/union/sbin=rw:/sbin=ro     0 0
none            /lib             unionfs dirs=/union/lib=rw:/lib=ro       0 0

-----------------------------------------------------------------------------------
/etc/rcS.d/S11formatunion.sh
#
# formatunion.sh        Reformat and populate proprietary unionfs root
#
# Version:      @(#)formatunion.sh  0.001 Mar-21-2005 shane@bogomip.com
#

VERBOSE=yes

TMPTIME=0
[ -f /etc/default/rcS ] && . /etc/default/rcS

exec 9>&0 </etc/fstab
while read dev mnt type opts dump pass junk
do
        case "$dev" in
                ""|\#*)
                        continue;
                        ;;


                *)

                        if [ "$mnt" = "/union" ]; then
                                mke2fs -q $dev
                                tune2fs -c 0 -i 0 $dev > /dev/null
                                mount /union
                                tar xf /union.tar -C /union/

                                mount /dev/hda3 /mnt/ -o ro
                                rsync -a /mnt/ /union/
                                umount /mnt/
                                #tar xfz /dev/hda3 -C /union/

                                echo "Reformatted/populated /union/"
                                mount /etc
                                mount /bin
                                mount /sbin
                                mount /lib
                                echo "Mounted /etc,/bin,/sbin,/lib for sanity"
                        fi

                        ;;

        esac
done
exec 0>&9 9>&-