Bug#966575: grub-pc: Bailing out if the boot device from the debconf database does not longer exist might produce a more complicated issue

[Daniel Leidert]

Am Donnerstag, dem 11.02.2021 um 21:09 +0000 schrieb Colin Watson:
> On Thu, Feb 11, 2021 at 09:34:31PM +0100, Daniel Leidert wrote:
> > I recently stumbled into this issue myself. Reading your explanation was
> > very
> > helpful. However the way you fixed it produces another issue as described
> > here:
> > 
> > https://forum.openmediavault.org/index.php?thread/37903-grub-related-error-on-5-5-23-update/
> > 
> > The command suggested by the error message (dpkg-reconfigure) actually
> > doesn't work if grub-pc is not fully installed.
> 
> Hm, it's true that's not entirely ideal, sorry.  I think I'd probably
> meant to recommend an interactive run of "dpkg --configure grub-pc", but
> I'll need to think about how to present that best.  Your reply on that
> thread seems slightly overkill - there should be no reason to drop to
> low priority, since the relevant questions are asked at critical.

I didn't check the priority. But I only see two possible actions to take after
the installation bailed out: either run "apt-get install -f" and enforce a
debconf frontend, or preset the value using debconf tools.

> > I don't have a technical solution myself, but bailing out creates an
> > even worse situation here.
> 
> For context: every single time the GRUB core <-> modules ABI has changed
> in the last ten years or so, we've had multiple critical bugs filed due
> to unbootable systems as a result of incorrect configuration causing the
> boot loader to be only half-upgraded.  I entirely disagree that a failed
> upgrade, even on many systems, is a worse situation than that.

"Worse" in the sense of that the upgrade bails out and the presented command
doesn't work. I wasn't just talking about the bailing-out part.

The user just needs a way to fix things when this issue is detected.

[..]
> > I was also thinking: If this cannot be handled in a technical way this
> > should definitely be mentioned in the release notes.
> 
> I'm not opposed to some kind of mention in the release notes, I suppose,
> but it feels like more of a general operations manual sort of thing (for
> example, it might happen on the next upgrade after a subtly-botched disk
> swap), and I'm not sure where would be best.  This isn't particularly
> specific to any one Debian release.

Large parts of the document are not specific to any one Debian release. Almost
all advice given in section 4 applies to upgrades in general. Maybe add a
section similar to 4.6 and call it "Upgrading grub (and related packages)"?


Regards, Daniel
-- 
Regards,
Daniel Leidert <dleidert at debian.org> | https://www.wgdd.de/
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