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?
very good article..
thanks.
Thank you so much for this article !
Thank you soo much!!!
This was the ticket I could modify the grub and logon screens but the boot splash that was the hard one. Not any more! I have my own theme from end to end now!
YOU ROCK!!!!!
Coog
Thanks for the article. I tend to have a use for this about once or twice a year.
The extraction can be merged into a single command, simplifying this a bit:
mkdir /tmp/initrd; cd /tmp/initrd
gunzip -c ../newinitrd.img
Hi fellas, just wanted to say I appreciate this post. I was able to prevent the loading of modules I didn’t want by changing the file under /conf in the archive. I found it easier to copy the thing to my home directory and then do all the stuff. About to see if I can use XZ to compress the image and make it take up less space ( I know it’s pointless but I don’t care 🙂 ). Thank you for the post. I now have more useful tools 🙂
-Dave
Thanks! This saved my day.
Just fixed one virtual machine with this information. Copied initrd from other virtual machine and then edited initrd to fit in vm configuration. Needed to edit run_all.sh and config/* scripts and replace rootdevice information and filesystem type and added correct fsck.
Thanks. I wanted to inspect the contents of an initrd image and I found most of the articles on the web misleading / partially correct. Most of them either assume the image to be a gzipped image, or a cpio file or a plain image. The fact is that (at least on my Linux distro), it is a gzipped cpio archive. Your article was helpful.
Another way I could mount the image is using sysfs
ex.: mount -t sysfs initrd-2.6.18-1.2798.fc6.img drtini
A lot of information about initrd/initramfs is available at http://en.wikipedia.org/wiki/Initrd. This article explains the old initrd format (compressed image) and the newer initramfs format (cpio archive – optionally compressed).
Nice one 🙂
Hello everybody,
can anyone tell me how to modify the boot image and resave the cpio file
for changing the plymouth theme (custom) in rhel6
Modern linuxes (eg: CentOS 6.4) use a new compression format – here’s how I just added a new driver module:
[root@z600 ~]# mkdir tmo
[root@z600 ~]# cd tmo
[root@z600 tmo]# cat /media/LIVE/syslinux/initrd.img | xz –format=lzma –decompress –stdout | cpio -id
147921 blocks
[root@z600 tmo]# cp /media/LIVE/ocz10xx.ko modules/2.6.32-358.el6.x86_64/extra/
[root@z600 tmo]# find . | cpio –create –format=’newc’ | xz –format=lzma –compress –stdout >/tmp/newinitrd.img
153313 blocks
[root@z600 tmo]# ls -lsa /media/LIVE/syslinux/initrd.img /media/LIVE/ocz10xx.ko /tmp/newinitrd.img
2696 -rwxr-xr-x. 1 cnd cnd 2760604 Dec 11 2012 /media/LIVE/ocz10xx.ko
31732 -rwxr-xr-x. 1 cnd cnd 32491856 Sep 11 19:13 /media/LIVE/syslinux/initrd.img
32764 -rw-r–r–. 1 root root 33546904 Sep 11 20:05 /tmp/newinitrd.img
[root@z600 tmo]# cp /media/LIVE/syslinux/initrd.img /tmp/
[root@z600 tmo]# cp /tmp/newinitrd.img /media/LIVE/syslinux/initrd.img
cp: overwrite `/media/LIVE/syslinux/initrd.img’? y
[root@z600 tmo]# reboot
I am not getting the dev directory after cpio option
# cpio -id < ../initrd
92370 blocks
when Iview the content of initrd.img file
# ls
bin dev(missing) etc init modules proc sbin selinux sys tmp var(missing)
also I am getting cpio : cannot symlink to Readonly File System
can anyone tell me how to modify the boot image and resave the cpio file
for changing the plymouth theme (custom) in rhel6..
thanks in advance
Hello, I can’t see the root filesystem but I only see this:
[code]
$mkdir tmp2
$cd tmp2
$cpio -id < ../initrd.img
896 lohkoa
$ls
kernel
$ls kernel/
x86
$ls kernel/x86/
microcode
$ls kernel/x86/microcode/
GenuineIntel.bin
[/code]
Tonza wrote “I can’t see the root filesystem but I only see this”
This is because you have a multi-part initramfs file which are becoming standard on most distributions. As you observed, this first part on the initramfs file contains the code to load the corrective Intel microcode for your x86 processor.
The actual normal initramfs files are in a subsequent part of the file. Assuming you have a two part initramfs, the simplest way to extract the “init” section is to grab the skipcpio program (available in the dracut -core package) and to do
skipcpio initrd.img-{kernel_version} > intrd.img.part2.gz
(assuming it has been gzip compressed — you can check wifh file on the output file and then rename it appropriately according to the compression type)
then gunzip intrd.img.part2.gz and then do the
mkdir initrd
cd initrd
cpio -id < intrd.img.part2
Nice article thanks.