update-grub help

Dave Howorth dhoworth at mrc-lmb.cam.ac.uk
Wed Jun 2 09:54:56 UTC 2010

Tom H wrote (rearranged):
> Before you do this you could check whether the new device map file
> allows you to find the OpenSuse partition with grub-probe with
> grub-probe --device-map=/root/device.map --target=drive --device /dev/hdg
> which should output (hd6), assuming that /dev/sdg is the OpenSuse
> disk.

I did this and it does indeed output (hd6)

> Run either
> grub-setup --root-device='(hd0,X)' --device-map=/root/device.map '(hd0)'
> where X is X of the sdaX on which /boot resides
> or
> grub-setup --device-map=/root/device.map '(hd0)'

I ran the latter one but when I rebooted it behaved the same as before.
It seems that grub just doesn't see hd6. A grub ls command prints info
for hd0 through hd5, correctly listing the partitions. But no mention of

It's another one of these situations where running grub commands from
within a running Linux system gives different results than when running
grub 'raw' at boot time.

FWIW, I've put the output from boot_info_script at
<http://pastebin.ubuntu.com/443239/> AFAICT, it's exactly what I'd
expect. sda is the Ubuntu disk, sdf is the openSUSE one.

I'll keep googling for ways to let the BIOS know about the drive (the
mobo BIOS does load the plugin card's BIOS while initialising) and/or
ways to let grub2 use drives that the BIOS can't see but Linux can.

Cheers, Dave

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