nixpkgs/nixos/doc/manual/development/bootspec.chapter.md

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Experimental feature: Bootspec

Bootspec is a experimental feature, introduced in the RFC-0125 proposal, the reference implementation can be found there in order to standardize bootloader support and advanced boot workflows such as SecureBoot and potentially more.

You can enable the creation of bootspec documents through boot.bootspec.enable = true, which will prompt a warning until RFC-0125 is officially merged.

Schema

The bootspec schema is versioned and validated against a CUE schema file which should considered as the source of truth for your applications.

You will find the current version here.

Extensions mechanism

Bootspec cannot account for all usecases.

For this purpose, Bootspec offers a generic extension facility boot.bootspec.extensions which can be used to inject any data needed for your usecases.

An example for SecureBoot is to get the Nix store path to /etc/os-release in order to bake it into a unified kernel image:

{ config, lib, ... }: {
  boot.bootspec.extensions = {
    "org.secureboot.osRelease" = config.environment.etc."os-release".source;
  };
}

To reduce incompatibility and prevent names from clashing between applications, it is highly recommended to use a unique namespace for your extensions.

External bootloaders

It is possible to enable your own bootloader through boot.loader.external.installHook which can wrap an existing bootloader.

Currently, there is no good story to compose existing bootloaders to enrich their features, e.g. SecureBoot, etc. It will be necessary to reimplement or reuse existing parts.