open-nandra

How to simple create initrd? Question which arise also for me when doing some modifications on rootfs and then need to compress it.

In this article I try to describe how to do it.
You need rootfs or initrd image which you would like to extract.

Extraction:

1. check initrd file:

file initrd-2.6.25.20-0.1-pae

initrd-2.6.25.20-0.1-pae: gzip compressed data, from Unix, last modified: Wed Jan 28 18:51:41 2009, max compression

Image is rootfs compressed with help of gzip and cpio.

2. use command for extraction:

zcat initfs.img |cpio -id --no-absolute-filenames

You need to be root when you perform create/extract actions.
If not then you can get errors because initrd could contain /dev nodes which have root privileges.

Creation:

1. run command in root directory tree which sould be add to initrd image

find |cpio -H newc -o |gzip -c > initfs.img

Note: inird file could be compressed into different filesystems (e.g squashfs …) use then appropriate command to create and extract initrd.

Marek