Re: Grub and two distros



Anne Wilson wrote:
I've read everything I can, including the thread mentioned above, and I'm
still not happy. I think it's a complete lack of understanding of the boot
process. I have always installed grub to the MBR, and thought that this
simply called up menu.lst, read the stanzas there and proceeded to carry out
the selected stanza. Now it seems that things are not that simple, so I have
to ask you to return to absolute basics.

You are installing a boot loader in the MBR (Stage 1) that then
loads the next stage. This is usually the stage 1.5 that can read
the file system that stage 2 is on. Stage 2 is the part that loads
and displays the menu. It also takes care of processing your menu
choice.

It seems that I should install grub into the root partition for the particular
distro - correct?

If you are using a /boot partition, and a copy of Grub for each
distribution, that is where to install the grub for that
distribution. This is especially true if the root partition is on a
LVM volume. For most BIOS, the partition has to be marked as
bootable for the BIOS to use the boot loader on the boot record on
that partition. Grub, on the other hand, can chainload to that boot
loader without the partition being marked bootable.


If the other distro is not automatically added I then will need to manually
edit menu.lst to add a stanza for the other distro - correct?

If you are using Grub as your first boot manager, then you will need
to. If you are using another boot manager, then you will need an
entry for the Grub boot loader. I will cover this more at the end.

I presume that I will also have to manually edit the menu.lst on the other
distro?

Maybe - it depends on the method used.

Exactly how does either of these get called? IOW, what tells it which one to
call?

The one on the partition marked as bootable usually, unless you have
a boot loader on the MBR.

Then there's the matter of kernel updates. Fedora has a default number for
keeping kernels - how will it know to only handle its own kernels and kernel
entries in menu.lst? And if it doesn't, will I have to manually edit menu.lst
every time there is a kernel update (having made a routine of backing up
menu.lst)?

The example I downloaded, which concerned a RHLinux install and a Mandrake
one, only used chainloader for the floppy stanza. I know it gets used for a
Windows stanza. Does that mean that it doesn't get used for two Linux
distros?

I think that most of my questions covered. Maybe I'll feel more confident
when I understand these issues better :-)

One way to handle multiple distributions in one system is to use
more then one copy of Grub. You have one copy that is installed on
the MBR, and has its own partition for its menu and stage 1.5 and
stage 2. This copy just chainloads to Windows, or the copy of Grub
on the /boot or /root partition of the distribution. From there, the
windows boot loader, or the copy of Grub for that distribution. This
has the advantage of not messing with the kernel update process of
the distribution.

A second method is to use the Windows boot loader and add entries
for each distribution. This involves coping the installed boot
loader for each distribution. (Grub first stage from the boot record
of the partition for that distribution.) If you update Grub, you
will need to update the file on Windows.

A third method is to use Grub for one distribution as your as your
master copy, and have entries for the other distributions and for
Windows. This works fine as long as you don't mess up that copy of
Grub. You will also want to keep a copy of your grub.conf in case
you upgrade that distribution, so you can merge the entries for the
other distributions back in.

In any case, the entry for each distribution looks like the entry
for Windows, with the root statement changed to reflect the
partition that Grub is installed to. (/boot for that distribution.)

If you want more detailed instructions for any of these methods, or
more on the advantages/disadvantages of each method, let me know.

Mikkel (working on his first cup of coffee this morning.)
--

Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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