Bug#919029: grub-pc: meaningless message "RUB boot loader was previously installed..."

[Colin Watson]

On Sat, Jan 12, 2019 at 02:11:25PM +0100, Vincent Lefevre wrote:
> On 2019-01-12 10:36:02 +0000, Colin Watson wrote:
> > The ID changing is presumably the systemd bug you mentioned, and that
> > seems to be the grave part of this.
> 
> Actually, I think that the fact that grub-pc changes the configuration
> and loses the previous one is a grave bug too (even though it is
> caused by the udev bug). There should have been a way for the user to
> keep the previous configuration so that nothing gets broken due to
> temporary issues.

I'm not at all sure that I agree.  The configuration in question exists
in order to tell the postinst which devices it should run grub-install
on.  If the device does not exist, it obviously isn't possible to run
grub-install on it.

I can see the argument that it might be convenient to have configuration
that effectively says "install to this device if it exists, otherwise
continue anyway"; but such a configuration may mean that the GRUB image
on disk that you might in fact attempt to boot from will end up being
incompatible with the rest of /boot/grub/ and thus cause a failure to
boot even though the postinst pretended everything is fine!
Disregarding this kind of configuration error can have grave
consequences of its own.  In any case, even if it might be convenient to
have such a configuration, I won't accept that part of the issue as a
grave bug.

Note that temporary issues of this kind are extremely rare; this is the
first of its kind that I can recall hearing about.  By contrast, it's
quite common for people to accidentally end up with a boot sector that
they thought was being updated when it in fact wasn't.  It makes a lot
more sense for the GRUB maintainer scripts to prioritise dealing with
the latter situation than the former.  So I'm happy to try to improve
the way the maintainer scripts responded here, but not in a way that
results in silently ignoring missing devices.

If the dialog box hadn't been cut off in a way that made it non-obvious
that GRUB needed you to select devices to install to, I don't think you
would have ended up in this situation.

-- 
Colin Watson                                       [cjwatson at debian.org]