To make a ramdisk image
1) Copy a root file system in a common directory.
2) Make a dummy image file
$ dd if=/dev/zero of=ramdisk.img bs=1M count=16
3) Format the image with ext2 file system
$ mke2fs -F ramdisk.img
4) Mount the image as loop device
$ mount -o loop ramdisk.img tmp
5) Copy the content of the root file system
$ cp rootimg tmp -rf
$ sync
6) Unmount the loop image
$ umout tmp
7) This ramdisk can be used to write on the ramdisk partition.
