[arch-general] How big really is the MBR?

[Aljosha Papsch]

On Sat, 3 Sep 2011 18:09:10 -0400 Eric Griffith <egriffith92 at gmail.com>
wrote:

> Whats up guys, Was planning on re-install Arch on my laptop, started
> writing a couple scripts to handle the usual things I do. One of the
> NEW things im going to be trying is grub2. Now, the Grub2 wiki says to
> run
> 
> dd if=/dev/zero of=/dev/sda bs=440 count=1
> 
> to wipe out grub-legacy from the MBR.
> 
> And since the Arch-devs removed "No Bootloader" as an option in the
> AIF, you can't follow the "during installation" instructions for
> Grub2.
> 
> Here's my problem, just by sheer luck was I roaming the web today, and
> noticed a few other threads (in various forums for various distros /
> blogs) and they all had a similar command to run if youre grub-legacy
> was screwed and you needed to write over it. The only issue, and the
> reason for this email? They had different commands.
> 
> Not completly different, but different enough that raised an eyebrow.
> In
> 
> dd if=/dev/zero of=/dev/sda bs=440 count=1
> 
> They had various numbers for bs=,  some 440, some 446, some 506, and
> some 512. Normally I would've just shrugged and followed the wiki, but
> notice on one said that if you zero out too far, you wipe out hte
> partition table...which I wouldn't enjoy haha.
> 
> So can anyone confirm that the command above, from the wiki, is
> correct? And that it IS 440, and not something different. I'd hate to
> pick the wrong one and zero out my partition table, or not completly
> zero out grub-legacy and run into a whole different set of problems.
> 
> Thanks!


grub gets installed in the first 440 (446) bytes, then some
disk-specific data (optional), the rest takes up the partition table up
to the 512th byte. look also at
https://secure.wikimedia.org/wikipedia/en/wiki/Master_boot_record
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