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.

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

> 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.

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

Remember the reference to the hardware wll be 'primative' as t only has
a basic system at first.