"Dual Booting Windows and CachyOS" section's systemd-boot guide is misleading

[BombasticBooger]

The guide explains about copying Window's EFI binaries to CachyOS's ESP, despite the fact that it's implied beforehand that they should both be on one ESP:

"The EFI partition may need to be resized, depending on the recommended minimum size on the target boot manager. Refer to Manual Partitioning"

2 ESPs on the same drive is also from what I know also against UEFI spec; I apologize if I'm misinformed

[1Naim]

"The EFI partition may need to be resized, depending on the recommended minimum size on the target boot manager. Refer to Manual Partitioning"

This part confuses me. The dual boot section was always meant to be a post-install setup, and I was not aware that the text beforehand existed. Either it should be removed or the actual steps need to be rewritten.

2 ESPs on the same drive is also from what I know also against UEFI spec; I apologize if I'm misinformed

Do you have a source for this? Windows's ESP is too small sadly to be used alongside Linux for any boot manager except probably GRUB. Resizing is usually a hassle and creating another ESP is just easy to do.

[BombasticBooger]

Don't have a specific quote from the UEFI, but it's said in the Arch wiki (although in a section you usually wouldn't pay attention to), along with the Arch wiki generally recommending a single ESP setup on a single drive

along with EasyBCD author saying in a HN thread about how it shouldn't be done: https://news.ycombinator.com/item?id=16261237

could maybe get parts from the official Arch wiki page about dualbooting? https://wiki.archlinux.org/title/Dual_boot_with_Windows#

apologies if these aren't great sources, I'm not very computer-science savvy and I'm also tired right now

[1Naim]

After doing a little bit of reading, the two main problems I see when doing this are:

1. Multiple boot entries in the UEFI firmware
2. Booting into one ESP rather than the other

(2) is not really a problem. The solution is to change the boot order in the UEFI firmware. The issue seems more overblown than it actually is because Windows users aren't used to doing that I assume, but likewise I would also assume Linux users are already used to this :). (1) is a little more tricky.

For the systemd-boot case specifically, no duplicate entries are created because we're not running efibootmgr to create a new UEFI boot entry, so whatever is copied is only known to systemd-boot, not the UEFI. So to adhere to the spec and best practices for this case, we can:

1. Add the efibootmgr command to create a new Windows boot entry to the UEFI from the Linux ESP.
2. After sanity checking, delete the original Windows ESP.

For other boot managers (Limine, GRUB, rEFInd), I'm not too sure about it sadly. I know that Limine has Windows in its boot menu out of the box, and I vaguely remember it has duplicate Windows boot entries in the UEFI so that might be a problem. I'm not sure about os-prober at GRUB or whatever rEFInd is doing though. We will need to investigate.