I can confirm this bug. The problem appears to be that Grub2 will include the
line
set root=(hdX,Y)
when installing grub on the external hard drive. In my case I had 3 internal
drives on the machine that I used to configure the external drive. So the line
root=(hd3,1) was included which works fine if the machine plugged into
identifies the external drive as (hd3,1) but not if the machine has, say, two
internal drives so identifies the external drive as (hd2,1).
This is a major regression from Grub 0.97 where it was possible to
specify by UUID to avoid such problems. Using the command set
root=UUID=uuid_string_of_numbers dosn't appear to work in Grub2. This
is my original menuentry in /boot/grub/grub.cfg:-
menuentry "Ubuntu, Linux 2.6.31-17-generic" {
recordfail=1
if [ -n ${have_grubenv} ]; then save_env recordfail; fi
set quiet=1
insmod ext2
set root=(hd3,1)
search --no-floppy --fs-uuid --set fd0c6442-dc3d-49ba-8e46-91657460fe52
linux /boot/vmlinuz-2.6.31-17-generic
root=UUID=fd0c6442-dc3d-49ba-8e46-91657460fe52 ro
initrd /boot/initrd.img-2.6.31-17-generic
I have tried a custom entry by creating a file (07_UbuntuUSB) in
etc/grub.d and running as follows:
menuentry "UbuntuUSB, Linux 2.6.31-17-generic" {
recordfail=1
if [ -n ${have_grubenv} ]; then save_env recordfail; fi
set quiet=1
insmod ext4
set root=UUID=fd0c6442-dc3d-49ba-8e46-91657460fe52
search --no-floppy --fs-uuid --set fd0c6442-dc3d-49ba-8e46-91657460fe52
linux /boot/vmlinuz-2.6.31-17-generic
root=UUID=fd0c6442-dc3d-49ba-8e46-91657460fe52 ro
initrd /boot/initrd.img-2.6.31-17-generic
}
It shows in the grub boot menu ok then fails because it it cannot find a
file (but doesn't report which file it cannot find - another enhancement
request please). The UUID refers to the boot partition on the external
drive which contains the grub files and the os.
--
upgrades of the grub-pc package can overwrite wrong MBR
https://bugs.launchpad.net/bugs/496435
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