On Tue, Jun 30, 2020 at 12:36:58AM +1000, terryc wrote:
> On Mon, 29 Jun 2020 08:18:24 -0400
> Hendrik Boom <hendrik@???> wrote:
>
>
> > Does it determine which MBRs to update by looking at the BIOS 'boot'
> > flags?
>
> As I understand it, the boxen looks at the UEFI(?) for the pointer to
> which piece of HW carries the initial loader, which then loads "grub"
> and its configuration files and the modules it needs to access the
> basic system to build up the OS to the final system.

My hardware does not do UEFI. It is a BIOS system.

Two of the drives are smallish, and have the old-style partitioning,
with four primary partitions, one of which is subdivided into secondary
partitions, One of these drives is the problem.

I have two large EFI-partitioned disks, starting of course with
"protective MBR"s. These are working properly.
/boot is on these drives. Well, actually in one partition on each of
them, these partitions paired off as a software RAID.

>
> The only file that I can find that points to any articular piece of
> hardware is /boot/grub/grub.cfg, which shoud list the various boot
> menu options. which points to hd0 with a device-id.

Looked through that. It contains descriptions of all the operating
systems on my disk drives, identified by some kind of UUID. It does not
seem to have anything describing where boot from initially to load grub
stage 1 or grub stage 1.5. This is what I expected, because the
early stages of Grup already have to be loaded and running before it
can even understand the /boot file system.
Grub stage 1.5 presumably looks through the menu and figures out what
partition contains the /boot it si supposed to look for.

>
> > Or is there some configuration file somewhere?
>
> So when (for me) sudo apt-get dist-upgrade loads newer images and runs
> grub-update/update-grub/?? is runs it probably checks what is in the
> existing grub.cfg and just adjust the various boot menu options(add
> newest, drops oldest).
>
> If you can get the machine to boot, there is a method to
> copy the grub config to a floppy or I guess a usb stick
> these days.

Machine boots fine. Just won't upgrade.

>
> At one stage, writing a spare boot floppy and keeping it up todate was
> recommended.

I used to do that, but no loger have a floppy drive. I'd have to use a
USB stick, or perhaps even a Devuan installer used as a rescue disk.

-- hendrik

>
> Remember the reference to the hardware wll be 'primative' as t only has
> a basic system at first.
> _______________________________________________
> Dng mailing list
> Dng@???
> https://mailinglists.dyne.org/cgi-bin/mailman/listinfo/dng