Windows will shrink its own partition as needed to create a recovery partition (type 0x27 in gdisk), which is just a NTFS partition.

It depends on it to boot when bitlocker encryption is on: \EFI\Microsoft\Boot\bootmgfw.efi => bootmgr.efi => boot.sdi IIRC

You can store other things in this 0x27 partition if you make it larger, like full ISO images like for Ubuntu Live: just place grubfmx64 in your \EFI partition, add it with efibootmgr and you can boot a baremetal Linux when WSL2 doesn't cut it.

Personally, I'm considering keeping a copy of the old bootloader and not updating the revocation DB as chainloading from bootmg to a Linux EKI with an entry when you press F8 could be a fun thing to add (I've read it could be done with Windows 7 and grub.efi but I have no experience with that)

What I've done on a pc that needs to dual boot and has a single drive is create a bigger /efi partition and store a unified kernel image that I boot directly with the uefi. No grub or shim or systemd-boot or whatever extra moving part. I can use the integrated uefi boot selector to switch to the non-default os.

I've had this setup for a while now, and the multiple windows updates never bothered to make windows the default boot entry.

I do the same! My EFI partitions are always a few gigs, because I even stuff .isos into it for easy reinstall/rescue operations:)

For people who are stuck with a 260 (or 100M) EFI, repurposing the 0x27 partition is easier: just shrink the end of your windows partition, and add what you gained to the 0x27 partition after backing up its content - no need to touch the other partitions!

Shrinking a partition from the beginning (as what would be needed to get a larger EFI) can be harder

> No grub or shim or systemd-boot or whatever extra moving part.

Same, the arch way is just better! FYI you may want to add a grubfmx64.efi in there, to be able to select entries more easily for rescue ops. You also get a grub commandline.

I don't like grub as a normal bootloader, but I like having its flexibility when I want to.

Ha, sticking a rescue ISO on a partition is actually a nice touch, never thought of that.

> you may want to add a grubfmx64.efi in there, to be able to select entries more easily for rescue ops

I hate having to deal with bootloaders with a passion. But it could come in handy if my efi can't boot directly from the iso. It does have the option to browse local drives and boot random files, but I've never tried an iso.

Although my rescue iso is custom-made with archlive so that it supports zfs. I could probably just write it to some extra partition and boot it directly.

> my rescue iso is custom-made with archlive so that it supports zfs. I could probably just write it to some extra partition and boot it directly.

Interesting! Would you like to share it somewhere (or at least the build instrunctions?

It would be faster than a ubuntu live, which needs to start Gnome, while I often only need gdisk, dd, efibootmgr and zfs!

It's pretty basic, really. Follow the Arch Wiki guide to build an ISO and add the packages from the archzfs repo. One unrelated tip is to also bake your ssh pubkey in the ISO, it comes in handy.

https://wiki.archlinux.org/title/ZFS#Create_an_Archiso_image...