Re: [Xen-users] Where does PyGrub run?

[Simon Hobson <linux@xxxxxxxxxxxxxxxx>]

eva wrote:

> Thanks for answering. I read that part, but afterwards I read the link
> that Luke posted that says:
>
> "The problem with PyGRUB is that while it's a good simulation of a
> bootloader, it has to mount the domU partition"
>
>
> http://wiki.prgmr.com/mediawiki/index.php/Chapter_7:_Hosting_Untrusted_Users_Under_Xen:_Lessons_from_the_Trenches#PV-GRUB:_A_SAFER_ALTERNATIVE_TO_PYGRUB.3F
>
> ..hence my confusion.
Hmm, yes. One or other of the Wiki entries is wrong then.

In that link I see the answer to your other query. In there, in 
extolling the virtues of pvgrub, the author is hinting (but 
explicitly stating) that he is providing a read-only volume which the 
end user (DomU owner) cannot modify. In that read-only partition, he 
has a basic (rescue) system which the DomU always boots "through" - 
thus the end user can never ever completely trash his DomU to the 
point that it won't boot anything.
My guess is that he has GRUB installed in the rescue partition, with 
two entries - rescue and user. Rescue boots into the rescue system, 
user (the default) chain loads a GRUB config from the user's normal 
partition. In normal operation, the DomU will load the read-only 
GRUB, chainload the user's GRUB, and then boot the user's OS. If the 
user screws it up, he can interrupt the initial GRUB, boot into the 
rescue system, and from there fix his own system.
--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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