Re: Need Help Editing Grub

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Author: kitepilot@kitepilot.com
Date:  
To: Main PLUG discussion list
Subject: Re: Need Help Editing Grub
Man, what a stir... :)
After I (sort-of) did read all the posts, I want to try to clear up some
things.
Now, I am not GRUB expert, DON'T SUE ME!

Grub sees the drives in the order they are reported by the BIOS.
When you install Grub, it doesn't register which drive (as reported by the
BIOS) it was installed on.

All Grub cares about, is that menu.lst (not validated by Grub) and the
appropriate "stage files" are present at installation time, because somehow
(not sure of this) the location of the "stage files" will be written into
the boot record.

When you run Grub, all it does is:
root (hd?,?)
learn about which partition of which drive to write the boot record to.

setup(hd?)
AHA!, go see if menu.lst and the "stage files" are present and write me a
boot record.

quit (without period :)
Done...

Now, at boot time the BIOS will follow up its boot sequence until it happens
to find a bootable MBR.

If than MBR happens to be the one we created previously, Grub will find
menu.lst and the "stage files" on the partition specified beforehand (above)
and load them.
I'm not sure how Grub finds menu.lst, but I know that Grub has to have
built-in support for whatever filesystem you are booting from.

menu.lst has to match its directives (hd?,?) to whatever hd? matches the
current BIOS table, and '?' to whatever partition holds the kernel and/or
initrd to boot from, or they won't be found.

Now, as someone said, there some 20 dozens of ways to create the boot
record, all of them are variants of the previous procedure, the result is
the same, and Grub couldn't care less at boot time about how the MBR it is
using was created.
In other words, the boot sequence will be the same regardless of how you got
the MBR to be written.

In Mike's case, as someone said, we had to either create a boot record to
hd1 (the HD we will boot from after butchering the puter) or butch the puter
and boot from a CD to install Grub to a new (and un-bootable hd0)
Clear as mud? :)
Again, YMMV...
ET

PS: On the lighter side, some unwanted wisdom:
The bad part of getting married is the honeymoon.
The worst comes later...




writes:

>>> is there perhaps, a typo?
> No, it's not a typo!
> The drive is still hd1 until you pull the old one.
> Grub doesn't know about which drive, the BIOS tell it to.
> Once you pull the M$ drive and flip the cables, GRUB will see it as hd0.
> ET
>
>
>
> Mark Phillips writes:
>
>> I understand the flow....shouldn't I tell grub somehow that the new boot
>> drive is hd0,0? In your steps below, is there perhaps, a typo?
>>
>> Thanks!
>>
>> Mark
>>
>> On Sun, Jan 24, 2010 at 3:58 PM, <
>> > wrote:
>>
>>> >> 1. How do I change grub on the Linux drive (hdb) to say "the ...
>>> If you are running GRUB 0.XX (GRUB 1.XX is different):
>>> Boot your Debian machine and as root run:
>>> grub
>>> root (hd1,0)
>>> root (hd1)
>>> It should answer that it found the stages, verify that there are no errors.
>>> quit
>>>
>>>
>>> Then take a backup of /boot/grub/menu.lst and and make sure that everything
>>> is either using UUID(s) or labels or every reference to hd1,0 is converted
>>> to hd0,0
>>>
>>> Verify your /etc/fstab likewise.
>>>
>>>
>>> > 2. Do I move the second drive to the first ide port, or leave it as ...
>>> Shutdown, pull the cable from the windoze drive and plug it to Linux drive.
>>> Turn on and pray... :)
>>> Free advice, you can't sue me ;-)
>>> YMMV
>>> ET
>>>
>>>
>>>
>>>
>>> Mark Phillips writes:
>>>
>>> > I have two ide drives in one machine - drive 1 is a Windows drive and
>>> drive
>>> > 2 is a Linux drive. Using grub, I can boot into either windows or debian.
>>> I
>>> > want to remove the windows drive and replace it with a larger, blank
>>> drive
>>> > for backup storage. I have a feeling if I just remove the first drive and
>>> > put the new one there, the machine will not boot, since the MBR is
>>> probably
>>> > on the first drive (it came with the machine, and I just added the second
>>> > drive for Linux). My questions:
>>> >
>>> > 1. How do I change grub on the Linux drive (hdb) to say "the windows
>>> drive
>>> > is dead, boot here instead, long live linux"?
>>> >
>>> > 2. Do I move the second drive to the first ide port, or leave it as the
>>> > second ide drive and put the new drive in the fist ide port?
>>> >
>>> > Thanks!
>>> >
>>> > Mark
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