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Re: Grub and two distros



On Sat, 2009-01-10 at 09:54 +0000, 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.

No, the MBR has the most basic information to be able to read something
from a drive.  This will be aimed at some partition, where something
larger and more useful (e.g. ordinary disc files rather than half a meg
of space in the boot record) can be used to read something else from the
drive, eventually the GRUB configuration file will be read to start
loading an OS.

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

"Installing GRUB" is perhaps an understated description.  What does
installing it mean?  Installing all of it, or just writing a partition
bootblock.  Changing some of it's set up is usually all that's needed to
make it do something for you, without going through "installing" all of
GRUB.

> 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 whatever automatically configures GRUB for you doesn't notice that
other bootable things are available on your system, for you, then yes.

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

Yes, and no.  You can have one /master/ GRUB installation that's used to
pick which OS to boot.  When you do so, it then loads up another GRUB
instance, one that's particular to that OS.  Each OS does housekeeping
for its own GRUB files.

e.g. sda1 might be a small boot partition.  The BIOS loads the boot
record for it.  It has the bare minimum so you get a menu from it of
other distros to boot.

sda2 might be /boot for Fedora 9, with sda3 / for Fedora 9.
sda5 might be /boot for Ubuntu, with sda6 / for Ubuntu.
sda7 might be C: for Windows

Your sda1 boot would have a menu to chainload sda2, sda5, or sda7, and
that's about all.  It doesn't know what they'll subsequently load up,
it's just passing on the baton in a relay.

sda2 would have a grub.conf (menu.lst) file that's used to boot up
Fedora 9.  As Fedora 9 gets updated, from time to time, with a new
kernel.  It's this sda2/boot/grub/menu.lst file that will be twiddled
with.  When you install Fedora, you'll have it install GRUB to the sda2
bootrecord, and leave the drive MBR alone.

Likewise, sda5 is will have a grub/menu.lst file for Ubuntu, that'll
work in the same way as Fedora's does.

And sda7 would be the partition that all of Windows gets shovelled into.

When you boot, you'll go through two menus.  The first one to pick which
partition/OS to boot up.  The second will be which kernel to use for
that OS.  Normally, you'd set up your defaults for your usual
preferences, but you could override at any time.

-- 
[tim localhost ~]$ uname -r
2.6.27.5-41.fc9.i686

Don't send private replies to my address, the mailbox is ignored.  I
read messages from the public lists.




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