Dual boot problem - Vista disappeared from Grub menu

[Colin Law]

On 19 September 2010 17:18, Goh Lip <g.lip at gmx.com> wrote:
> On Sunday 19,September,2010 11:14 PM, Colin Law wrote:
>> Hi
>>
>> On a machine with dual boot Ubuntu 10.04 and Vista which has been
>> working fine for many months, suddenly Vista no longer appears in the
>> boot menu (GRUB2).  I have not used Vista for a week so am not sure
>> exactly when it happened.  I am not aware of any problems in the
>> meantime apart from an update (don't know what to) which complained of
>> a download not being available, but this seemed ok when the update was
>> run again later.
>>
>> I have checked /etc/default/grub and run
>> sudo update-grub
>> which does not report the Vista partition.
>> I am able to access the files on the vista partition from Ubuntu and
>> it looks ok in gparted (showing the boot flag).
>>
> Colin, try the following
> sudo grub-mkdevicemap
> sudo update-grub

Thanks for the help.
OK, did that, no change.

>
> You should check if you can boot up windows if you do the following at
> the grub prompt (press 'c' at grub menu)
> set root=(hd0,x)
> chainloader +1
> boot
>
> where (hd0,x) is /dev/sdax of the windows partition, (usually x=1)

This boots into Vista ok.  So that means that Vista is ok, but for
some reason grub does not see it.
I see from the grub docs that I can manually include the relevant boot
option, but it would be better if I could persuade grub to work it out
for itself.   Any ideas where to go next?

Colin