How does grub2 know what to boot?

[Cristian Sava]

On Mon, 2013-06-10 at 10:25 -0400, Tom Horsley wrote:
> I just installed f19 beta, and it overwrote my MBR with
> grub2ness (as expected).
> 
> But now I'm wondering - the actual installation of
> f19 is entirely on /dev/sda2 (including the /boot
> directory which is just a subdirectory of /, not
> a separate partition).
> 
> My old f18 /dev/sda3 partition is the only one marked
> as "boot".
> 
> So how the heck is grub2 locating and booting the
> /dev/sda2 /boot stuff? Is there a pointer stashed in
> the MBR telling it where to look?
> 
> Just curious :-).
Sometime back I had a similar problem and I discovered that my old grub
install (other partition) was used. Do you mind to check?

Cristian Sava