Question: How do I view, modify and recreate the new initrd.img on Ubuntu, Debian, CentOS, Fedora, Red-Hat, Arch Linux, or SUSE distributions?
1. How To View Content Of initrd.img file?
initrd.img is in gzip format. So move initrd.img to initrd.gz as shown below.
# cp /tftpboot/el5/initrd.img . # ls cdrom initrd.img # mv initrd.img initrd.gz
Unzip the initrd.gz file as shown below.
# gunzip initrd.gz # ls cdrom initrd
After unziping the initrd.gz file, the initrd is further in cpio ‘newc’ format. So extract the files from initrd using cpio ‘newc’ format as shown below.
Note: info cpio will give more information about ‘newc’ format.
# mkdir tmp2 # cd tmp2/ # cpio -id < ../initrd 16524 blocks
Now you can view the content of initrd.img file
# ls bin dev etc init modules proc sbin selinux sys tmp var
2. How To Modify Content of Image and Recreate New Image?
After extracting the file as shown below, make appropriate modification to any of those files. Then pack the files back into the archive using the following commands. Pack the modified files back to cpio ‘newc’ format.
# find . | cpio --create --format='newc' > /tmp/newinitrd 16524 blocks # ls /tmp/ cdrom initrd newinitrd tmp2 # ls -l /tmp/newinitrd -rw-r--r-- 1 root root 8460288 Jul 2 14:50 /tmp/newinitrd
Gzip the archive file.
# gzip newinitrd # ls cdrom initrd newinitrd.gz tmp2 # ls -l newinitrd.gz -rw-r--r-- 1 root root 6649867 Jul 2 14:50 newinitrd.gz
Move file as an image file. You can use the newinitrd.img as your new boot image.
# mv newinitrd.gz newinitrd.img # ls -l newinitrd.img -rw-r--r-- 1 root root 6649867 Jul 2 14:50 newinitrd.img
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Nice one…
Neat!
I have always done my initrd’s using Debian’s make-kpgk utils… but this hack is real neat!
Kudos for your site!
This is very useful.
@Lakshmanan, @beparas, Thanks for your comments. I’m very glad that you found this helpful.
@runlevel0, Building kernel using make-kpkg by installing ‘kernel-package’ and ‘fakeroot’ packages definitely has it’s own advantages. Thanks for bringing make-kpkg utility to our attention.
hello!
I want to know if I recreate new image file after modify something.using:
dd if=tmp2 of=newinitrd.img
I want to know It’s right or wrong?why?