用命令行：
dd if=/dev/zero of=initrd bs=1M count=6
mke2fs -F -m 0 -b 1024 initrd
mkdir /mnt/initrd
mount -t ext2 -o loop initrd /mnt/initrd
##copy your files to /mnt/initrd
umount /mnt/initrd
gzip initrd
## then
generate a file named initrd.gz and that's the ramdisk you need
