Re: [gentoo-user] Dual booting with Windows 10

[Peter Humphrey <peter@prh.myzen.co.uk>]

On Friday, 21 May 2021 20:06:25 BST Michael wrote:
> On Friday, 21 May 2021 15:42:01 BST peter@prh.myzen.co.uk wrote:
> > Hello list,
> > 
> > Mynew machine has Win-10 installedon /dev/nvme0n1 with the ESP as
> > partition
> > 1. I want to install Gentoo on /dev/nvme1n1. So far I haven't found a way
> > to set up a working boot arrangement. I've tried mounting the ESP on /efi,
> > on /EFI and on /boot/EFI. Efibootmgr seems to write a boot entry in some
> > of
> > those cases, and it's still there after a reboot - but it isn't visible to
> > the BIOS.
> > 
> > Can anyone offer some enlightenment, please?
> 
> If your ESP is on /dev/nvme0n1 and you are using vmlinuz symlinks, you can
> use /boot/EFI as the mountpoint for the ESP VFAT partition.  Your
> kernels/config/ System.map/initrd.img files will go into /boot, which will
> be on the same fs as / on /dev/nvme1, using a fs which supports symlinks.
> 
> The efibootmgr '--loader' option should/could be used to specify the path to
> your bootloader image, or if you are not using a bootloader image to
> chainload your kernel with, point it directly to the path of your kernel;
> e.g.
> 
> efibootmgr --create --disk /dev/nvme0n1 --part 1 --label "gentoo-5.10.27" \
> --loader "\EFI\gentoo\gentoo-5.10.27.efi"
> 
> The BIOS/UEFI menu should be able to list entries of bootable *.efi images,
> as long as they are within the subdirectory of /boot/EFI on the ESP, but if
> you are using a bootloader, then it is the bootloader image which will run
> and chainload your OSs and their kernels.

Thanks Michael. I've finally got it booting, by resorting to the same hack as I 
did on my previous machine.

Using efibootmgr to add a UEFI boot record does create it, but selecting it in 
the BIOS fails and it just drops to the next in line: Windows 10. No 
adjustments to the --create command resulted in a bootable system, so I had to 
run bootctl-install as well and then remove the hex-numbered directory and 
restore my own loader.conf. I spent days wrestling with this.

It's clear that I just don't understand UEFI booting. It sounds simple enough, 
but it clearly isn't. I've read everything I could find on the subject, to no 
avail.

-- 
Regards,
Peter.