Inspecting the content of an initrd file

dybbuk

                               
If you want to look what is inside of an initrd file (don’t ask me why I needed this

), here you can find some information on how you can do that. Depending
on what kernel you are using you might encounter various initrd type of
files.
Uncompressed initrd/cramfs type of file
Older kernels will use a initrd/cramfs type of file. If we want to
look inside this file all we have to do is to mount it (as a loop
device). Example showing how to mount a file called
initrd.img-2.6.8-2-686 (from a default Debian Sarge kernel):
# All work is done in a temporary directory
mkdir /tmp/initrdmount
# Mount the image file directly
mount -o loop /boot/initrd.img-2.6.8-2-686 /tmp/initrdmount
#Investigate its content, etc.
cd /tmp/initrdmount
#Once done un-mount it:
umount /tmp/initrdmount
Seen on: Debian Sarge, kernel 2.6.8
Compressed initrd/cramfs type of file
This is the same as above just that the file is compressed (with
gzip). If we want to look inside this file we need to uncompress it
first and then mount it (as a loop device). Example showing how to
mount a file called initrd-2.4.21-40.EL.img (from a default RHEL3
kernel):
# All work is done in a temporary directory
mkdir /tmp/initrdmount
# Copy the image, uncompress it
cp /boot/initrd-2.4.21-40.EL.img /tmp/initrd.img.gz
gunzip -v /tmp/initrd.img.gz
# Mount the image file
mount -o loop /tmp/initrd.img /tmp/initrdmount
#Investigate its content, etc.
cd /tmp/initrdmount
#Once done un-mount it:
umount /tmp/initrdmount
Seen on: RHEL3, Centos3, kernels 2.4.21
initramfs type of file
Newer kernels will use this type of file. The initramfs is an cpio
archive so all we have to do is to uncompress it to a temporary
directory. The example from bellow uses the file
initrd.img-2.6.15-1-686-smp (from a default Debian Etch kernel):
# All work is done in a temporary directory
mkdir /tmp/initrdmount
# Copy the image, uncompress it
cp /boot/initrd.img-2.6.15-1-686-smp /tmp/initrd.img.gz
gunzip -v /tmp/initrd.img.gz
# Extract the content of the cpio archive
cd /tmp/initrdmount
cpio -i
Seen on: Debian Etch, kernel 2.6.15; RHEL4, Centos4, kernel 2.6.9.
               
               
               
               
               
               
               

本文来自ChinaUnix博客，如果查看原文请点：http://blog.chinaunix.net/u/18103/showart_133495.html