How to restore the MBR after do-release-upgrade?

[Tom H]

On Sat, Jul 9, 2016 at 11:03 AM, Ralf Mardorf <silver.bullet at zoho.com> wrote:
> On Sat, 9 Jul 2016 15:05:11 +0200, Liam Proven wrote:
>> On 8 July 2016 at 21:18, Ralf Mardorf <silver.bullet at zoho.com> wrote:
>>>
>>> The do-release-upgrade only offers /dev/sda and /dev/sdb. Assumed
>>> it's installed to the root fs (?partition of the root fs?), then a
>>> do-release-upgrade recognises this?
>>
>> Well, if, for example, your root FS is /dev/sda1, then all you need to
>> do is:
>>
>> sudo grub-install /dev/sda1
>>
>> ... and that should be it. It should write the location into its
>> config file and so remember it from then on.
>
> So there will be a pointer within the 512 bytes of the MBR, but no
> entry beyond those 512 bytes, the GRUB image that might need additional
> bytes, is written to some space, that belongs to the partition? It's
> somewhere on the disk, but definitively not attached to the 512 bytes
> of the MBR?

The boot.img file that in the VBR has to have the block list of
core.img in order to load it because it cannot read a filesystem.