How do I restore an accidentally deleted initrd image?

Question

I accidentally deleted the initrd image on my system. How do I restore it?

Answer 1

The initrd image for each kernel is built at kernel installation time from the modules and applications on the machine. You can simply build a missing initrd using the command below:

update-initramfs -c -k <version>

(Do remember to subsitute in the appropriate version for your kernel.)

Answer 2

This is a better way to solve the OP problem posted in the comments

I'm trying to use initrd from a livecd on my ubuntu install. Deleted it accidently. – Binoy Babu

To make an initramfs , first boot an alternate kernel (older is fine)

Then run

sudo mkinitramfs 3.2.0-15-generic-pae -o /boot/initrd.img-3.2.0-15-generic-pae

I do not have the pae kernel installed, if "3.2.0-15-generic-pae" does not work, list the contents of /lib/modules to get the name

ls /lib/modules

If you do not have an older kernel, you can boot a live CD and use chroot, let me know and I can add instructions to do that (chroot).

Answer 3

This is the answer to the original question, how to extract the initrd.lz from the live CD, typically used if you are making a custom live CD.

copy the initrd.lz to a working directory ( ~)

cp /media/cdrom/initrd.lz ~

Make a directory to extract the contents to, I will use initrd, cd into the directory

mkdir ~/initrd
cd ~/initrd

Extract

lzma -dc -S .lz ../initrd.lz | cpio -imvd --no-absolute-filenames

Make any changes you might need, re-package

cd ~/initrd
find . | cpio --quiet --dereference -o -H newc | lzma -7 > ../cusotm.initrd.lz

Your new initrd will be in your home directory and called cusotm.initrd.lz