Converting Windows without interfering with GRUB

Roken · 2020-07-25 10:06:18

Documented elsewhere, I ended up re-installing Arch, and was able to recover my personal installation owing to having had some forethought and backed up essential files, having /home on a separate drive, and backing up a pacman list of installed packages. Job done.

I also have a (very rarely used) fully licensed install of Windows 10.

Whilst the original Arch installation was built for UEFI boot, I must have done something and it fell back to BIOS boot. When I reinstalled, it is, again UEFI boot. Because it wad previously BIOS, I installed Windows as BIOS boot, too.

Now I'm back to UEFI, I can't chainload Windows from GRUB. I know that Windows can be converted to UEFI boot without re-installing (though not the end of the world if I have to, and not certain I would even bother if this tunrs out to be problematic).

Windows is on a separate drive, and I can boot by selecting the Windows drive as a boot drive in BIOS. BIOS is set up to boot both UEFI or BIOS.

The Windows bootloader is also installed on it's own dedicated drive, separate from the drive where GRUB is installed.

If I convert Windows to UEFI, will this interfere with GRUB in these circumstances, or will it leave GRUB and the EFI partition that resides on my Arch drive alone until I configure GRUB to chainload?

If the latter, I'll go ahead and convert. If the former, not sure I can be bothered.

The only reason I kept Windows around was my other half is a Windows users, and not tech savvy, so I don't want to force her to use Arch if it can be avoided. If I must, she will either use her laptop, or have to learn.

Last edited by Roken (2020-07-25 10:07:41)

Thiago H · 2020-07-25 10:45:34

From what I can gather, as far as maintaining GRUB: Windows loves to rewrite the EFI configuration so its bootloader is the first one in the pecking order. If that happens, use efibootmgr from the Arch iso.

The rest of the issue sounds like it deserves attention from a Windows forum.

Last edited by Thiago H (2020-07-25 10:45:46)

halasz · 2020-07-25 12:03:48

Roken wrote:

Windows is on a separate drive, and I can boot by selecting the Windows drive as a boot drive in BIOS.

You could install https://wiki.archlinux.org/index.php/REFInd - it will autodetect BIOS Windows installs on on external drives if you set it to in refind.conf (scanfor biosexternal).

Roken · 2020-07-25 18:08:08

I'm aware of the workarounds. Specifically, I'm looking for info around Windows being on an entirely different different drive (both bootloader and system) from Arch and GRUB. If I boot the Windows drive and convert to UEFI from that boot, will it interfere with GRUB and my EFI partition on the Linux drive?

V1del · 2020-07-26 11:01:04

Do you have a distinct ESP on your separate drive and do you intend to do one? Otherwise you will have to use the one on your linux drive anyway, but yes this should generally not have a negative effect on GRUB on the ESP per se. Some badly configured UEFIs might only boot /EFI/BOOT/BOOTx64.efi that one will get overriden by most Windows procedures in which case you'd have to reinstall GRUB/copy the GRUB efi binary to that location.

Generally Windows will not touch files not generated by itself on an EFI partition. You can have multiple distinct EFI binaries and they will coexist.

Last edited by V1del (2020-07-26 11:01:30)

Arch Linux

#1 2020-07-25 10:06:18

Converting Windows without interfering with GRUB

#2 2020-07-25 10:45:34

Re: Converting Windows without interfering with GRUB

#3 2020-07-25 12:03:48

Re: Converting Windows without interfering with GRUB

#4 2020-07-25 18:08:08

Re: Converting Windows without interfering with GRUB

#5 2020-07-26 11:01:04

Re: Converting Windows without interfering with GRUB

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