[Wylug-help] Baffled by Grub2 and GPT

[Dave Fisher]

Needless to say, I've googled like crazy and read the grub manual back
to front, but I'm still baffled, hence this stab in the dark.

I recently did an ubuntu dist-upgrade.

Afterwards the kernel booted, but couldn't mount the root filesystem.

After several manual grub edits, I used a live CD to update and
reinstall grub ...  after which, the system booted fine.

Just to make sure, I immediately rebooted again and it failed consistently.

After several more manual grub edits, grub updates and grub reinstalls
I now get nothing but a grub prompt.

I'm fairly sure that the most recent problem (i.e. nothing but a grub
prompt) is a result of using a GPT partition table and a bios_grub
partition.

I vaguely remember having a similar problem when I originally built the system.

On that occasion, the whole GPT appeared to traditional partition
editors as a single DOS partition, and booting worked fine after I
made the whole GPT bootable/active in fdisk.

Now, fdisk appears to inaccurately recognise the separate GPT
partitions (saying none of them match cyclinder boundaries), so that
trick probably can't work ... and I don't want to try it anyway, just
in case fdisk screws up the whole GPT partition table.

The GPT boot sector has an MBR protective mode, so grub-install should
work properly whether or not it's GPT aware.

I am beginning to think that the latest Ubuntu version of grub2 *is*
fully GPT aware and is installing the grub menu to my bios_grub
partition (rather than the DOS-compatible MBR) but for some reason the
initial part of grub isn't chainloading it.

Under grub1 you could use a 'find' command in the grub shell to locate
the various bits of the boot chain, but that doesn't seem to be their
in my version of grub2.

Any ideas on how I could usefully proceed? i.e. without trashing the
partition table.

Dave