Fwd: Re: MBR was destroyed

Saulius Krasuckas saulius2 at ar.fi.lt
Tue Nov 22 05:30:02 CST 2005

* On Mon, 21 Nov 2005 wino at piments.com wrote:
> * On Mon, 21 Nov 2005 15:05:28 +0100, seorge <seorge at gmail.com> wrote:
> > 
> > Please tell me, what exact information should I provide the developers 
> > with the experiment described below.
> You may run dd command to retrieve MBR at every moment, calculate it's
> checksum and see whether it differs or not.

BTW, after the Alexandre reply about volume changing I guess this possibly 
should be partition boot sector that is destroyed, not a MBR.  

Seorge, can you explain, how did you exactly restored MBR using GRUB, 

> fiddle with wine, one step at a time , running the following check at 
> each step, keeping notes on what is done each time.
> dd if=/dev/hda of=/boot/hda.wine1.mbr bs=512 count=1
> diff /tmp/*0.mbr /tmp/*1.mbr

BTW, I think only the text files should be diffed (and -u flag makes 
output very understandable for me):

 cat /tmp/hda.wine0.mbr | od -t x1 > /tmp/0.mbr.txt
 cat /boot/hda.wine1.mbr | od -t x1 > /tmp/1.mbr.txt
 diff -u /tmp/0.mbr.txt /tmp/1.mbr.txt

That would show how much different MBRs are.  And if they don't start to 
differ ever, maybe we should refer to appropriate partition (system from 
which cannot boot later)?  Then "hda" string should be replaced with a 
partition name - "hda1" or so.

But comparing hexadecimal dumps should be the only and the final step, as 
it says not only whether sectors are different, but also how much they 
differ.  Which isn't interesting at start of hunting.

> The main thing is to establish exactly what you did, it may not be quite 
> where you thought and it will make finding the offending code a lot 
> quicker if it is precisely linked to one event.

It would be interesting to know, whether latest CVS helps, as Alexandre 
has put some fixes in regarding this issue, I guess:


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