Packing and unpacking initrd

modify initird.img or other similar images

To extract initird.img:

# Go to an empty directory before extracting the image.
# eg: mkdir -p /mnt/initrd_extract && cd /mnt/initrd_extract
gzip -dc < ../initrd.img | cpio -i

To pack files back into initrd.img

# Go to the directory containing the contents of the image.
# eg: cd /mnt/initrd_extract
find . | cpio -o -c | gzip -9 > ../initrd.img