linux-kernel - Re: Initramfs from existing vmlinuz

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Message-Id: <4953E53C.3D93.006F.0@nwu.ac.za>
Date:	Thu, 25 Dec 2008 19:55:40 +0200
From:	"Martin Schlemmer" <Martin.Schlemmer@....ac.za>
To:	"Willy Tarreau" <w@....eu>
Cc:	<linux-kernel@...r.kernel.org>
Subject: Re: Initramfs from existing vmlinuz

>>> On 2008/12/24 at 01:37 PM, "Martin Schlemmer" <Martin.Schlemmer@....ac.za>
wrote:
>>>> On 2008/12/24 at 01:34 AM, Willy Tarreau <w@....eu> wrote:
>> On Wed, Dec 24, 2008 at 12:28:53AM +0200, Martin Schlemmer wrote:
 
Hi
 
>>> I had a bit of an accident, and wondered if somebody already had to try to 
>> extract the initramfs image from an existing vmlinuz?
>>> 
>>>  I did try google, but either my search terms was not right, or nobody 
>> really touched on the subject before, because all the results mostly dealt 
>> with an external image.
>>> 
>>> Any advice will be appreciated.
>> 
>> yes, it happens to me from time to time.
>> You first have to extract and uncompress the ELF image from vmlinuz. For
>> this, look for the gzip signature 1F 8B 08 in your vmlinuz, and feed all
>> data starting from this point to zcat. Either you do the same on the
>> resulting file -and you may find several compressed images- or you simply
>> pass it through "objdump -h". It will show you a .init.ramfs section. Use
>> the fourth field as the file offset, and dump from that position. You'll
>> find your initramfs, likely starting with 1F 8B 08 since it's supposed
>> to be compressed with gzip.
>> 
>> You need an hex editor, dd, zcat and objdump for this. It's not much
>> complicated once you have the tools, but it might require a few attempts
>> before finding the right image (I tend to find config.gz before initramfs).
>> 
> 
> Appreciated, I should be able to go from here now - just getting the starting 
> point is sometimes the main issue.
> 

Simple Perl script to do above in case anybody might find it useful in the future.


M



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