[gentoo-dev] grub device mapping

[Jonas Berlin]

Hi. 

Regarding the installation instructions at
http://www.gentoo.org/index-download.html

Occasionally, when
  a) recovering from master-disasters
  b) installing a new linux distro
  c) adding new hardware

... I happen to use the feature of BIOS to make another hard disk than the
first bootable. This works ok until you want to re-install grub, if you
temporarily want to keep this mixed configuration. Another situation might
be that BIOS didn't detect some of your harddisks but Linux did.

Anyway, the situation is that if you have harddisks hda hdc hdd in linux,
but they don't show up as hd0 hd1 hd2, but as hd1 hd0 hd2 for example.

If you start grub like this:

$ grub --device-map=/boot/grub/device.map

.. and have a file /boot/grub/device.map like this:

(fd0) /dev/fd0
(hd0) /dev/hdc
(hd1) /dev/hda
(hd2) /dev/hdd

And grub will know how the disk setup looks like at boot time.