Re: [gentoo-user] Duel boot - How to verify boot loader updates?

[Mark Knecht]

On Fri, Dec 9, 2022 at 4:07 AM Arve Barsnes <arve.barsnes@×××××.com> wrote:
>
> On Fri, 9 Dec 2022 at 11:55, Michael <confabulate@××××××××.com> wrote:
> > To check the GRUB version of the second OS without booting into it, you
can
> > grep for grub in its /var/log/emerge.log
>
> Or see what version is named in the /usr/share/doc/grub-2.?? folder name.
>
> On the other hand, if the question is *really* about knowing if
> grub-install has been run on one of the machines, I don't know if
> there is a way. Probably look at change dates on the files in
> /boot/grub/?
>
> Regards,
> Arve

Thanks to both of you for your responses. I appreciate them, although I
don't think they get as far down in the weeds as I was wondering about.

My understanding of the boot loader - and maybe I'm using the wrong
terminology so if I am someone please correct me - is that at the start
of boot BIOS tells the processor to read some part of the disk and it is
the code read there that gets the whole process kicked off and
out of BIOS's control.

I'm wondering about that first bit of code being written by installation
#2's update into the initial section of installation #1's disk.

Rethink the picture a bit and make installation #1 Windows and
installation #2 Linux. Assume that after updating each install, and
further assume both installs made some very minor change to their
own first bits of code on the disk, and assume everything still
boots correctly, BUT assume that one of the updates actually
wrote into the other install's initial boot code and replaced it with
their own because it was confused about which disk it was
supposed to put this on. How would I be able to determine that
this happened?

It's not totally a thought experiment. One machine I have which
is dual boot recently complained that the original disk grub was
installed on had changed when in fact there hadn't been any
hardware changes and I had to carefully figure out how to
answer a couple of questions. After the fact I started to wonder
about this edge case.

I think it comes down to reading what's on the disk with a
hex editor possibly but I know nothing about what to expect
there.

Thanks,
Mark