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Re: Converting a BIOS (CSM) Debian installation into UEFI

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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"

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 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.
-- 
Evolution as taught in public schools is, like religion,
	based on faith, not based on science.

 Team OS/2 ** Reg. Linux User #211409 ** a11y rocks!

Felix Miata

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Thread

Converting a BIOS (CSM) Debian installation into UEFI David Wright <deblis@lionunicorn.co.uk> - 2022-02-15 17:20 +0100
  Re: Converting a BIOS (CSM) Debian installation into UEFI Felix Miata <mrmazda@earthlink.net> - 2022-02-15 20:30 +0100
    Re: Converting a BIOS (CSM) Debian installation into UEFI David Wright <deblis@lionunicorn.co.uk> - 2022-02-22 16:20 +0100

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