grub / grub2 conflicts

Richard W.M. Jones rjones at
Thu Sep 22 18:47:33 UTC 2011

On Thu, Sep 22, 2011 at 11:38:26AM -0700, Adam Williamson wrote:
> On Thu, 2011-09-22 at 17:18 +0100, Mark McLoughlin wrote:
> > You described yourself how libguestfs could check it. And failing
> > libguestfs doing it, the user could be warned to check it.
> 'check' it? And what's the user expected to do if they're incorrect?
> Crowbar Ubuntu's grub2 into Fedora, or vice versa, so the host and the
> guest will be compatible?

We don't pretend to work on Ubuntu grub2, never said we did.

> I hate to say it, but honestly, this thread looks pretty clear-cut to an
> outsider: pjones and mjg59 are correct, and you and rwmj are incorrect.
> Their arguments that it is fundamentally unsafe to use the host's grub
> or, even more so, grub2 in a guest have clear merit, and it honestly
> feels like the counter-arguments so far have been 'we've got away with
> it so far' and 'doing it any other way is hard, and we already wrote all
> this code, so please stop raising inconvenient questions'. Neither of
> those arguments are at all compelling. I haven't seen a single serious
> attempt to refute the central point that there is no guarantee of
> compatibility between any particular two versions or even builds of grub
> or grub2, and there is not even a mechanism for denoting and testing
> compatibility. Given this, it's hard to see how it can possibly be the
> right thing to do to use the host's grub or grub2 in the guest.

The issue here isn't this at all.

Issue #1 is that a conflicts was added to grub2, but no reason is
given.  It was apparently done to work around some problem in grubby,
but again there's no clarity on what the problem(s) were and if there
would be a better way to fix this.

There is a further issue #2, quite orthogonal, which is that grub
(upstream) doesn't support offline installation.  This is a bug in
grub 1 & 2 which really should be taken upstream.  Nevertheless, it's
quite possible to use grub1 offline on compatible guests.  We don't
really need to "prove" this, because we do it, and test the results,
and we publish everything we do in open source code.


Richard Jones, Virtualization Group, Red Hat
virt-p2v converts physical machines to virtual machines.  Boot with a
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