Re: Converting a BIOS (CSM) Debian installation into UEFI
On Tue 15 Feb 2022 at 14:20:55 (-0500), Felix Miata wrote:
> David Wright composed on 2022-02-15 10:11 (UTC-0600):
>
> > Is anything else required for B to become a "native EFI" installation?
>
> > This conversion process will, I think, make the system boot into
> > the EFI-ed B by default. If I want to make E boot by default again,
> > should I boot E and run update-grub and grub-install?³
> > Or should I do this by running efibootmgr?
>
> Without changing GRUB_DISTRIBUTOR= in /etc/default/grub, you'll wind up with only
> /boot/efi/EFI/debian. It will be just like MBR booting, where the last updated
> Grub overwrites what the previous one put in the MBR. I avoid this by changing the
> default
>
> GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
>
> to e.g.
>
> GRUB_DISTRIBUTOR="bookworm"
That was useful — I hadn't realised the connection between that
variable and the directory name in EFI/. It's quite tricky pulling all
the threads together: the directory layout in EFI/, all the stuff
that's in /sys/firmware/efi/efivars, the efibootmgr's listing, and
the contents (and actions) of the EFI menus when you boot into the
firmware interface (reached with Esc F9 here, IIRC).
> Once you have a unique /boot/efi/EFI/ entry for each installation, you /should/ be
> able to switch which has control either in the BIOS directly, or with efibootmgr.
> Likely update-grub and grub-install would do the same thing, but I've never given
> them the opportunity here. I say /should/ because some UEFI BIOS are finicky
> beasts that can't always be trusted to do as expected.
>
> I avoid the issue of priority usurpation in two ways:
> 1-only mount the ESP filesystem to /boot/efi/ on one installation
> 2-don't install any bootloader
I think I've decided to keep mine simple by:
. booting into one primary system from the ESP,
. only that primary system has /boot/efi/EFI/ mounted (your 1),
. no Grub on the non-primary systems (your 2),
. the primary's Grub will choose which system to boot.
I'm used to using grubenv for one-time boot selection, even when
I'm not at the machine, but am happy to use the EFI menus whenever
I need to boot from a stick, etc.
> I actually boot from /boot/grub/custom.cfg, by copying /etc/grub.d/40_custom to
> 06_custom. This causes grub-mkconfig to generate a grub.cfg that displays my
> custom.cfg entries before its auto-generated entries, minimizing need to scroll
> the menu to find a desired selection. My custom.cfg boots via kernel and initrd
> symlinks (and volume LABEL rather than UUID, same as fstab), so infrequently has
> any need to be updated. Note that my use of singular filenames is inaccurate, as I
> have 5 UEFI systems configured this way, and all have 10 or more Linux installations.
I'll probably go through another iteration of my edgrub
script, to reduce even more of the "garbage" in grub.cfg.
Thanks for the suggestions.
Cheers,
David.
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