How to rebuild RedHat 6.2 isolinux/initrd.img?

[xieiwu]

I copy isolinux/initrd.img from RedHat 6.2 DVD to local floder. I want to add a file to initrd.img. I tried many command(gunzip,cpio...), but failed. I run "file initrd.img" and it shows "initrd.img: data". But I can mount it with command "mount -t sysfs initrd.img /mnt/initrd", but I can not add file to it. Could anybody help?

[xieiwu]

I found the solution:

1) Extract
mv initrd.img initrd.img.xz
xz --format=lzma initrd.img.xz --decompress
mkdir initrd-new
cd initrd-new
cpio -ivdum < ../initrd.img

2) Add/delete/modify files

3) Build
find . -print |cpio -o -H newc | xz --format=lzma > ../initrd.img

[evinrude]

Extract:

mkdir initrd && cd initrd
gzip -cd < ../initrd.img | cpio -id

Compress:

find . -print0 | cpio --null -o --format=newc | gzip -9 > ../initrd.img