Re: Calling Grub in MBR on a USB disk from Grub on a primary disk problem

[Marcin Zajączkowski]

Thanks Muchael for your answer!
I didn't have access to that machine during a week and I couldn't
answer earlier.


On 2009-08-20 15:14:37 -0700 Michael Evans wrote:

> What I've found is that modern PC BIOSes are increasingly trying to
> be too smart and thus acting even more stupid than they should be.
> It seems that they assume an old 1980s based operating system will be
> used and remap the devices such that whichever one is actually
> booting is the 0th and primary bios device.  Your USB device -may-
> look like a floppy to the BIOS.
> 
> My suggestion is to install grub as a whole-disk setup on whatever
> device you want to boot from, and include a file on that device that
> you can search for.  Boot off that device, find the file, and modify
> your device map accordingly.

I checked it, but it seems that my USB disk is always mapped as hd1 when
booted from primary HDD and as hd0 and booted from USB drive, but with
your suggestion I was able to locate boot partition and with following
modifications I'm able to boot!

title Fedora direct
        root (hd1,4)
        kernel /vmlinuz-(...)
        initrd /initrd-(...)

> Unfortunately you should not assume any other devices will remain
> constant, or even predictable.

Mentioned solution works (and I'm very happy with that!), but it
requires to modify grub.conf with every new installed kernel version.

Maybe you have some further ideas how could I debug my system from GRUB
point of view to make GRUB from the secondary disk MBR bootable?


Regards
Marcin