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

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

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?.



MailScanner is like deodorant...
You hope everybody uses it, and
you notice quickly if they don't!!!!

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 250 bytes
Desc: OpenPGP digital signature
Url : http://lists.centos.org/pipermail/centos/attachments/20080922/5508b4e0/signature.bin

More information about the CentOS mailing list