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

Mon Sep 22 18:37:05 UTC 2008
Scott Silva <ssilva at sgvwater.com>

on 9-22-2008 11:06 AM MHR spake the following:
> On Mon, Sep 22, 2008 at 10:08 AM, Scott Silva <ssilva-m4n3GYAQT2lWk0Htik3J/w at public.gmane.org> 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
It is more common with the systems that have pata and sata interfaces on them.
The bios first starts its int13 code and maps drives in a certain order, then 
when linux starts, its drivers load and everything re-maps again.
  If you have hard drives on both, it is a crapshoot sometimes.
The newer kernels have supposedly moved the old ide code into the base sata 
drivers, so someday all the drives will show up as sd?.



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