Linux initrd - Customization

Extraction -> Customization -> Rebuilding

- commands issued under the temporary working directory.
- switch to root if required like mknod needs privilege.

GZ Based (Debian)

Extraction

gzip -dc ../initrd.gz | cpio -idmv --no-absolute-filenames

Rebuilding

find . | cpio -o -H newc | gzip -9 > ../initrd.gz

XZ Based (Redhat)

Extraction

xz -dc ../initrd.img | cpio -idmv --no-absolute-filenames

Rebuilding

find . | cpio -o -H newc | xz -9 > ../initrd.img

Other Distros

Analyze file format then do extraction and rebuilding accordingly.

---