[CentOS] Upgrading (?) from legacy boot to UEFI [SOLVED]

Sun Aug 29 03:04:12 UTC 2021
Rob Kampen <rkampen at kampensonline.com>

On 29/08/21 1:03 am, Jonathan Billings wrote:
> On Aug 28, 2021, at 05:58, Rob Kampen <rkampen at kampensonline.com> wrote:
>> Yeah, it is astounding to me that RH does not define their implementation of the grub2 grub.cfg file with particular focus on the things that are different between legacy boot and UEFI. Also what (if any) differences there may be in the initramfs and vmlinuz files between the two boot options. then we have the various .efi files with little or no documentation. So we are left with anaconda ....
> I don’t think migrating from a legacy bootloader to UEFI (on the same hardware) is a common enough process to document.
> I do notice you have a kernel listed with a .efi extension, and I’ve never seen that before.
> Typically on a UEFI C7 system, all the kernels and initrds are in /boot.  Only the EFI executables and supplementary grub files are in the /boot/efi volume (normally /boot/efi/EFI/CentOS). I don’t know where you got that kernel efi file.
>> Jonathan Billings

Thanks all, for your comments.

Jonathan, you are correct about the kernel placement and extension - I 
placed it there early in the process based upon someone's recipe - it 
didn't work but I hadn't got around to cleaning it up.

I have now got it working!

I was close with all the bits I had done, but the final piece is that I 
hand edited the grub.cfg in the ESP in my case /boot/efi/EFI/centos/ and 
/boot/efi2/EFI/centos/ and changed the linux16 to linuxefi and the 
initrd16 to initrdefi.

Then I used the server's UEFI boot manager app (part of this machine's 
setup arsenal) to manually add a UEFI boot on a specific drive with 
arguments pointing at shimx64.efi

Then a reboot and some online grub edits of the linuxefi line and CTRL-X 
and it finally booted up in UEFI mode.

At this point /sys/firmware/efi exists and efibootmgr -v finally gave 
some appropriate output

Then I was able to login, run grub2-mkcfg and get a proper grub.cfg 
file, and finally use efibootmgr  to create the desired default boot and 
backup boot entries in the UEFI.

ALL DONE. Lost some more hair and some sleep, but also much more 
knowledgeable and comfortable with UEFI.

Possibly not a common scenario, but it feels good having finally beaten 
it into submission.


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