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| --- | ||
| feature: uefi_boot_only_for_supported_systems | ||
| start-date: 2023-06-16 | ||
| author: Ryan Lahfa | ||
| co-authors: (find a buddy later to help out with the RFC) | ||
| shepherd-team: (names, to be nominated and accepted by RFC steering committee) | ||
| shepherd-leader: (name to be appointed by RFC steering committee) | ||
| related-issues: (will contain links to implementation PRs) | ||
| --- | ||
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| # Summary | ||
| [summary]: #summary | ||
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| NixOS should drop support for legacy boot and assumes that | ||
| all systems **supported by UEFI** can be booted off UEFI. | ||
| For legacy boot systems, an UEFI-providing environment bootloader should be used to polyfill | ||
| for UEFI features. | ||
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| # Motivation | ||
| [motivation]: #motivation | ||
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| Legacy boot is defined by the BIOS Boot specification, written in 1996: https://www.scs.stanford.edu/nyu/04fa/lab/specsbbs101.pdf. | ||
| Nowadays, computers are defaulting to UEFI more and more for the extended features provided (e.g. SecureBoot, native network boot, etc.). | ||
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| Nevertheless, many legacy boots machines or machines that does not have support for UEFI are used with NixOS: Single Board Computers for example | ||
| on other architectures. | ||
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| In nixpkgs, legacy boot forces a dichotomy between `boot.loader.efi` and... two legacy bootloaders: GRUB and a family of UBoot/extlinux-compatible/etc. | ||
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| In the case of GRUB, there are increasing problems with this bootloader: | ||
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| - Upstream do not do releases anymore: https://github.com/NixOS/nixpkgs/blob/nixos-unstable/pkgs/tools/misc/grub/default.nix#L62-L350 | ||
| - Co-maintenance / release work with other ecosystems such as the kernel is simply not done: https://github.com/NixOS/nixpkgs/blob/nixos-unstable/pkgs/tools/misc/grub/default.nix#L345-L349 causing GRUB's drivers to explode in production for our users: https://github.com/NixOS/nixpkgs/pull/235222 | ||
| - Our own maintenance of GRUB is subpar: https://github.com/NixOS/nixpkgs/pull/227741 https://github.com/NixOS/nixpkgs/pull/226821 https://github.com/NixOS/nixpkgs/pull/195805 https://github.com/NixOS/nixpkgs/pull/95901 https://github.com/NixOS/nixpkgs/pull/236027 | ||
| - GRUB installation procedure uses `install-grub.pl`, one of the remaining Perl script: https://github.com/NixOS/nixpkgs/pull/95901#issuecomment-756702696 offered to rewrite it with sponsoring, but no one took the offer yet, it is also very complicated to integrate with it: https://github.com/nix-community/lanzaboote/pull/96 | ||
| - GRUB installation procedure for UEFI-only is still confusing because our scripts does not handle well UEFI-only (you have to pass `nodev` and this is not very well documented). See https://github.com/NixOS/nixpkgs/issues/222491 | ||
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| The worse about this, is this is our **default** bootloader for our install images **because** of legacy boot. | ||
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| In the case of UBoot/extlinux-compatible/etc. : we should definitely keep it as it is used by other ecosystems. | ||
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| Getting rid of legacy boot opens up the way to get rid of GRUB as a default and enable all our users to benefit from UEFI-in-mind developed abstractions. | ||
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| BIOS also hold back all improvements in the boot story, considering we are not held back by this, is very interesting for NixOS. | ||
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| # Detailed design | ||
| [design]: #detailed-design | ||
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| Legacy boot is booted via UBoot or any bootloader able to provide an UEFI environment. | ||
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| Then, we boot using any usual bootloader, e.g. systemd-boot. | ||
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| # Examples and Interactions | ||
| [examples-and-interactions]: #examples-and-interactions | ||
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| Fedora is considering doing this: https://lists.fedoraproject.org/archives/list/[email protected]/thread/GOETDM5SWINBX5ZDV37SWMHIPRRUVVTT/. | ||
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| Asahi Linux is booting UEFI via UBoot without EFI variables and it has been great for them. | ||
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| People who want to boot off strange partitions at boot-time can exploit UEFI drivers capability to load any filesystem driver and | ||
| open the EFI System Partition in ZFS if they really insist. | ||
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| # Drawbacks | ||
| [drawbacks]: #drawbacks | ||
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| - 2-stage boot for legacy BIOS systems is more than 1-stage boot | ||
| - Increased internal complexity in the boot story of NixOS | ||
| - Increased load and reliance on UBoot | ||
| - The runtime service `SetVariable` will probably stay highly unstable for a while (variable storage) | ||
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| # Alternatives | ||
| [alternatives]: #alternatives | ||
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| - Keeping legacy BIOS and hoping someday it will be a bit more maintained | ||
| - Getting rid of legacy BIOS without other options | ||
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| Then, if we don't do this, we will continue to have users relying on bootloaders with shady maintenance stories and a skewed perception of what a bootloader can do (e.g. boot on a ZFS partition?). | ||
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| # Unresolved questions | ||
| [unresolved]: #unresolved-questions | ||
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| - How to migrate existing installs without any GPT partition table? | ||
| - How to migrate existing installs with a GPT partition table but without a supported EFI System Partition, e.g. LVM | ||
| - NTFS, XFS, exFAT, Amiga FFS/SFS, BFS, UFS, ZFS are handled via https://efi.akeo.ie/ which is an EFI driver that can be loaded | ||
| - Subquestion: how to load EFI drivers for unsupported EFI System Partition? | ||
| - Answer: Build EDK2 or UBoot with https://github.com/pbatard/efifs them. | ||
| - When to do it? | ||
| - What to do about variable storage (Asahi Linux showed this is not that important for a start)? | ||
| - Design architecture in nixpkgs? | ||
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| # Future work | ||
| [future]: #future-work | ||
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| - Improved support for UEFI features on non-UEFI native systems |