Try to move /sys and /proc to the newroot first instead of just unmounting.

defaults/linuxrc

@@ -733,16 +733,17 @@ echo -ne "${BOLD}.${NORMAL}"
 
 # If devtmpfs is mounted, try move it to the new root
 # If that fails, try to unmount all possible mounts of devtmpfs as stuff breaks otherwise
-if grep -qs "/dev " /proc/mounts
+for fs in /dev /sys /proc
-then
+do
-	if ! mount --move /dev "${CHROOT}"/dev
+	if grep -qs "$fs" /proc/mounts
 	then
-		umount /dev || echo '*: Failed to move and unmount the ramdisk /dev!'
+		if ! mount --move $fs "${CHROOT}"$fs
+		then
+			umount $fs || echo '*: Failed to move and unmount the ramdisk $fs!'
+		fi
 	fi
-fi
+done
 
-umount /sys || echo '*: Failed to unmount the ramdisk /sys!'
-umount /proc || echo '*: Failed to unmount the ramdisk /proc!'
 echo -e "${BOLD}.${NORMAL}"
 
 exec /sbin/switch_root -c "/dev/console" "${CHROOT}" "${REAL_INIT:-/sbin/init}" "${INIT_OPTS}"