A cautionary tale - distribution upgrade from 11.04 to 11.10

[Peter Hillier-Brook]

I write this note in case anyone else hits the bug that caught me yesterday.

I have a system with 3 SATA drives that I use to keep operating systems 
isolated as follows:

/dev/sda is given over to Ubuntu 11.10, upgraded from 11.04
/dev/sdb is a redundant (almost) Windows 7 installation
/dev/sdc is for Kubuntu 11.10, also upgraded from 11.04. This is my 
primary choice for day to day operations and the disk in which the 
"working" version of grub is installed in the MBR and which is the 
chosen boot disk in the BIOS.

Until the upgrade of Ubuntu to 11.10, which I performed AFTER I upgraded 
Kubuntu, all was well in the grub world, with the installation in 
/dev/sdc and osprober sorting out grub.cfg for all installed systems on 
all 3 disks. After the upgrade, the MBR on /dev/sdc (or possibly another 
grub component, I'm not sufficiently au fait with the grub code) is now 
pointing to a historically installed version of grub on /dev/sda, 
picking up entirely the wrong version of grub.cfg.

I've no idea which element of the upgrade process caused this corruption 
of the MBR, but I thought I ought to warn others in a similar situation.

Peter HB