Rapid-guide – Updating RedHat initrd

Warning: This is not the recommended method if you’re not sure you know what you’re doing.

Linux Initial Ram Disk (initrd) is a mechanism to perform disk-independent actions before attempting to mount the ‘/’ disk. These actions usually include loading disk drivers, setting up LVM or software RAID, etc.

The reason these actions are performed within initrd is that it is all based on Ram Disk loaded by the boot loader, and thus it breaks the loop of “how would I load storage drivers without storage access?”

It happens that due to some special even we need to modify it manually. To do so we need first to open it, and then to close it back in, replacing (backup the old one, will you?) the previous one.

This is rather simple. The tools used by us will be ‘gzip’ and ‘cpio’.

Lets begin.

First – create a temporary directory:

mkdir /tmp/initrd

Extracting

We have our temporary directory, so now, we need to extract the initrd into it. I assume the name of the file is /boot/initrd.img. You should replace my line with whatever the name of your initrd file:

cd /tmp/initrd

cat /boot/initrd.img | gzip -dc |  cpio -id

This will extract the contents of the initrd into /tmp/initrd.

Now you can edit its contents directly.

Package

To package initrd back in, we will need to perform the following actions.

Warning – before you do it, make sure you have an available copy of your original initrd file, in case you have created some damage.

cd /tmp/initrd

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

This line packages the initrd, and replaces the old one.

That’s all for today 🙂