I thought I was safe from this if I installed windows on a completely separate harddrive... I clearly overestimated Microsoft's ability to make on operating system that does not act like literal malware. Oh well! I guess I'm 100% linux now.
You likely have secure boot and a Microsoft package key installed in UEFI. They likely did what they are supposed to do and removed the unsigned software.
You must either sign your own UEFI keys using the options in your bootloader that may or may not be present, or you must use a distro that has the m$ signed secure boot shim key. These are the only ways for both m$ and Linux to coexist. Indeed, with a shim key (Fedora/Ubuntu) you can easily have a windows partition on the same drive without issues.
Secure boot is a scheme to steal hardware ownership. Of course they say it is not because the standard specifies a mechanism to sign your own keys. However the standard specification is only a guideline and most consumer grade implementations do not allow custom key generation and signing.
If you need to do your own keys, search for the US defense department's guide on the subject. It is by far the most comprehensive explanation of the system and how to set it up correctly. They have a big motivation to prevent corporate data stalking type nonsense and make this kind of documentation accessible publicly.
If your bootloader does not allow custom keys, there is a little known tool called Keytool that allows you to boot directly into UEFI and supposedly change the keys regardless of the implemented utility in the bootloader. I have never tried this myself. The only documentation I have found was from Gentoo, but their documentation assumes a very high level of competence.
Windows went a step further on my machine. I thought it had just screwed up my bootloader, but when I went to restore it my Linux partition was completely gone. Windows Update had deleted the partition.
How else would one motivate itself to learn about grub, boot partitions, UEFI, MBR and all the other wonderful crufty technologies involved in starting operating systems?
Is it just me or does no one actually know how any of it works, and everyone relies on a mixture of grub-install, os-prober, Boot Repair, bootcfg, and random internet guides to make it all work? I dual boot windows and linux and I don't understand where any of the boot files actually live or how they function. It feels like the deeper I dig, the more nondeterministic it all is.
Not having to ever touch Windows again has made my life infinitely better.
I can handle setting it up for a buddy on their new PC I'll build. Getting to build a new PC is worth it. These fools don't even realize how much I enjoy building their PCs. They don't even charge me for it.
UEFI or legacy BIOS? I recently installed Windows 11 on a machine with Proxmox on NVME but installed Windows on a SATA SSD. Windows added its boot entry to the NVME SSD but did not get rid of the Proxmox boot entry.
I’ve definitely had the same issue as you on in the past on legacy BIOS and when I worked in a computer shop 2014-2015 we always removed any extra drives before installing Windows to avoid this issue (not like the other drives had an OS anyway).
It’s a gaming machine. I mainly use a gaming VM with GPU passthrough under Proxmox, but the anti-cheat is some games (Fortnite and The Finals) don’t allow you to run them in VMs. So I run those games in Windows directly under a standard user account as a compromise.
the partition was still there, but if i tried to boot from it would just kick me back to the bios. unless there's some obscure grub bug that happened to trigger exactly after i booted into windows i guess...
the fix was pretty simple, i just reinstalled grub from a live environment.
This happens often. There's a lot of documentation on line on this topic. You can probably fix it with a bootable Linux USB key, mount your Linux partition, chroot into it and run grub to reinstall it in your efi partition.
I always had trouble with running dual boot, mostly because I don't really have a clue about all this stuff. So the consequence was to ditch Windows. Never going back.