[CentOS] Re: Problem with booting/grub (?)

MHR mhullrich at gmail.com
Mon Sep 22 18:06:27 UTC 2008


On Mon, Sep 22, 2008 at 10:08 AM, Scott Silva <ssilva at sgvwater.com> wrote:
>
> Grub boot code is in the mbr so it loads. If it can't find the stage 2 it
> usually quietly dies. I believe it has to load stage 1 to have enough code
> to actually give error messages. The mbr is just too small to get all the
> code into. So changing drives also changed the bios disk order on your
> system, and grub got confused.
>

I sympathize (I'm confused, too).

I can't swear to it, but I'm pretty sure I had rebooted several times
after changing the boot drive and the boot drive order, all without a
hitch.  Then this happened.

I can swear (now) that I have rebooted several times since recovering,
so if I muddled through this correctly, you're saying that it
shouldn't happen again as long as I don't change the drive order
again, right?

One of the things that I found rather irritating in all this was the
utter lack of clarity provided in both the man pages for grub and
grub-install, and the info pages (which are supposed to be more in
detail but are not, really).  How do I know which disk is which from
grub's p.o.v.?  There is no command to list the drives, and I wound up
using the geometry command and my personal knowledge of what those
were supposed to be to figure out which one grub thought was which,
and even that made no sense because what grub saw as hd0 was my
/dev/hda drive (which is not the boot drive) and hd2 was my /dev/sda,
which _is_ the boot drive.  Or do the drive designations change once
the system is up?  (I.e., in my grub.conf, the boot drive is hd0, but
when the system comes up, it's hd2.)

I've looked through the documentation for grub at
http://www.gnu.org/software/grub/manual/html_node/index.html and this
particular ideosyncrasy is not clear.

Thanks, all.

PS: My apologies for the earlier html post - I sent that via Evolution
from home, and apparently it is not configured for text-only by
default (which I completely forgot).

mhr


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