Re: GRUB advice needed.

On Sun, 29 Jan 2006 12:04:07 -0700, Douglas Mayne wrote:

> On Sun, 29 Jan 2006 17:45:07 +0000, Charles Sullivan wrote:
>
>> In the past I've partitioned my Linux i86 HDD like this:
>> hda1 boot
>> hda2 extended
>> hda5 home (1)
>> hda6 swap
>> hda7 root (1)
>> hda8 home (2)
>> hda9 root (2)
>>
>> and moved back and forth between (1) and (2) when installing
>> new releases in the same general family of Linuxes - e.g.,
>> FC 1 -> FC 2 -> FC 3, etc.
>>
>> However I'm a little concerned about mucking up the boot
>> partition if I install something different, like Debian, or want
>> to add something very different like FreeBSD.
>>
>> I understand I can install the kernel and boot info in a /boot
>> directory under each root partition, but I'm confused as to where
>> GRUB is actually located on the HDD under that situation. I didn't
>> think there was enough room in the MBR for it. If in one of the
>> root partitions, then it would be destroyed when I installed a
>> new release in that partition. Can anyone clarify?
>>
> This is best understood by considering the process which grub itself is
> installed, not when grub is working properly as the loader.
>
> The setup sequence for grub is generally as follows:
>
> 1. Grub files are copied to /boot/grub (i.e. the stage files)
>
> 2. The configuration file /boot/grub/menu.lst file is created/modified to
> include parameters appropriate for your system. *Actually, this step is
> optional; grub will still work as a loader if you can manually provide
> the correct information at boot.
>
> 3. The grub shell is used to interactively setup the loader:
>
> # grub
>
> grub> root (hd0,0)
> grub> setup (hd0)
> grub> quit
>
> Going through these steps one at a time:
> 1. The root command tells grub where to look for _its_ files. Don't
> confuse this with other meanings for the word _root_.
>
> 2. The setup command tells grub to proceed with the install, based on what
> partition type is in use at _its_ root partition. Specifically, it
> builds links between the first stage loader (MBR), and the other stage
> files. The later stage files give the loader the ability to read
> filesystems (ext2, xfs, reiserfs, etc.) The link is set based on the
> type of partition in use at the time of the install. With this link in
> place, the loader will be able to read the partition dynamically in the
> future. This ability is grub's big advantage over other loaders. It will
> be able to find any file on _its_ root partition.
>
> And note, similar links are required if the stage1 loader is installed
> on the partition (BPB), instead of the MBR.
>
> 3. quit: exit the grub shell
>
> Once it is setup, it will just work, unless it becomes broken. It can
> read any file that is on _its_ root partition (the boot partition).
> Note: it can be broken by reformatting the partition or by
> deleting/changing the "stage" files at /boot/grub. The links from the
> MBR/BPB to the partition must remain consistent with the stage files.
>
> Final note: If you have a boot partition, then entries in menu.lst will be
> relative to that partition (i.e. /grub, not /boot/grub.)
>
> Grub is a very flexible loader. After thinking about it just now, I
> see that there are even more ways it can be used. My explanation covers
> the basic case, though.

Thanks for the detailed explanation Douglas, but I'm still a little
unclear. Suppose I want to install two Linux distros on a new HDD
and not use a boot partition. Do I end up with something like
this:
MBR -> grub stage1
hda1 extended
hda5 swap
hda6 home (1)
hda7 root (1)
/boot
kernel (1) and other boot files
/grub
grub stage 2 (1) files
hda8 home (2)
hda9 root (2)
/boot
kernel (2) and other boot files
/grub
grub stage 2 (2) files

Do I still get the GRUB version selection menu (Fedora) when I
reboot the system, or would I have to (Ugh!) boot from a floppy
or CD each time? Or do the grub stage 2 files exist in only
one of the root partitions?

And if hda6 and 7 are later reformatted (same partitions, just
cleared) and a new version of Linux installed, will GRUB still
work or will I wipe out something critical?

Or should I forget the whole thing and continue to use a boot
partition? :-)

Regards,
Charles Sullivan


.

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