[gentoo-user] [offtopic] dual boot Windows 11 / Linux

[Helmut Jarausch]

Hi,

I have purchased a new Laptop with Windows 11 pre-installed.
I have managed to do (so far)

- shrink the Windows partition (from within Windows since it's
encrypted)
- turned off secure boot to be able to boot a Linux rescue system from
USB
- created new partitions (boot, root and home)
- copied a gentoo system from a similar laptop onto the root partition
- reinstalled grub2 (after doing chroot)

My problem now is that I can't select the Gentoo partition within BIOS
since this partition isn't offered as a boot option.

Many thanks for any hints or pointers,
Helmut

[Wol]

Because, as Windows is installed, BIUS isn't an option?

Look at UEFI boot. You can install grub into UEFI, but probably not here
because Windows will have given you pretty much no space. If you can get
the kernel and initramfs into the UEFI partition you should hopefully be
okay. Your problem will be squeezing ANYthing into the space Windows has
left.

As for helping you do it, sorry I haven't. My two laptops that came with
linux, one I've added Windows, the other I have yet to configure. The
one that came with Windows still has no linux ...

Cheers,
Wol

[Серега Филатов]

If it's a similar laptop I assume you have grub2 installed in EFI mode.

Check if you have grubx64.efi in your EFI partition (usually /<mounted EFI partition>/EFI/gentoo/).

Also check if you have efi boot entry for grub with efibootmgr utility. if grub-install with EFI target was used on a new system it should call efibootmgr to add a Gentoo entry in UEFI).

If you are trying to install grub in legacy mode then look in UEFI settings if CSM or legacy boot is enabled. But since you have win11 and you want dual boot I don't think that it's what you want. Os-prober will not pick up EFI win11 installation if grub is installed in legacy and you can't install win11 in legacy since Microsoft made win11 UEFI-only.

[Mark Knecht]

An example:

root@science2:~# ls -al /boot/efi/
total 6
drwx------ 3 root root 1024 Dec 31 1969 .
drwxr-xr-x 4 root root 4096 Mar 29 14:37 ..
drwx------ 5 root root 1024 Feb 13 15:35 EFI
root@science2:~# ls -al /boot/efi/EFI/
total 5
drwx------ 5 root root 1024 Feb 13 15:35 .
drwx------ 3 root root 1024 Dec 31 1969 ..
drwx------ 2 root root 1024 Feb 13 15:35 Boot
drwx------ 4 root root 1024 Dec 1 20:43 Microsoft
drwx------ 2 root root 1024 Feb 13 15:35 ubuntu
root@science2:~# ls -al /boot/efi/EFI/Boot/
total 1857
drwx------ 2 root root 1024 Feb 13 15:35 .
drwx------ 5 root root 1024 Feb 13 15:35 ..
-rwx------ 1 root root 955656 Feb 13 15:35 bootx64.efi
-rwx------ 1 root root 85672 Feb 13 15:35 fbx64.efi
-rwx------ 1 root root 856232 Feb 13 15:35 mmx64.efi
root@science2:~# ls -al /boot/efi/EFI/Microsoft/
total 8
drwx------ 4 root root 1024 Dec 1 20:43 .
drwx------ 5 root root 1024 Feb 13 15:35 ..
drwx------ 40 root root 5120 Dec 1 20:43 Boot
drwx------ 2 root root 1024 Dec 1 20:44 Recovery
root@science2:~# ls -al /boot/efi/EFI/ubuntu/
total 3457
drwx------ 2 root root 1024 Feb 13 15:35 .
drwx------ 5 root root 1024 Feb 13 15:35 ..
-rwx------ 1 root root 108 Feb 13 15:35 BOOTX64.CSV
-rwx------ 1 root root 117 Feb 13 15:35 grub.cfg
-rwx------ 1 root root 1722240 Feb 13 15:35 grubx64.efi
-rwx------ 1 root root 856232 Feb 13 15:35 mmx64.efi
-rwx------ 1 root root 955656 Feb 13 15:35 shimx64.efi
root@science2:~#

[Michael]

On Sunday, 10 April 2022 14:58:26 BST Серега Филатов wrote:
> If it's a similar laptop I assume you have grub2 installed in EFI mode.
> Check if you have grubx64.efi in your EFI partition (usually /<mounted EFI
> partition>/EFI/gentoo/).
> Also check if you have efi boot entry for grub with efibootmgr utility. if
> grub-install with EFI target was used on a new system it should call
> efibootmgr to add a Gentoo entry in UEFI).
>
> If you are trying to install grub in legacy mode then look in UEFI settings
> if CSM or legacy boot is enabled. But since you have win11 and you want
> dual boot I don't think that it's what you want. Os-prober will not pick up
> EFI win11 installation if grub is installed in legacy and you can't install
> win11 in legacy since Microsoft made win11 UEFI-only.

Some UEFI firmware is buggy and may not pick up a new OS bootloader in the ESP,
at least not pick it up initially. In these cases temporarily changing a UEFI
setting to nudge the firmware to parse the ESP for boot menu entries will help.
So /should/ running the efibootmgr to create an entry with grub's efi image.

[Серега Филатов]

Also if you've booted your live media in legacy mode then efibootmgr might not do anything because efivars are not accessible in this mode. That could explain the situation when you have grubx64.efi but no boot entry. So check that you're booting live system in UEFI too.