The Nix Flake

flake.nix is the entry point for everything. It is large and written by hand, so this page is a map. The file itself is the reference.

Inputs

Input	What it provides
`nixpkgs` (nixos-26.05)	The host side: build tools, unmodified upstream sources that ports reuse
`iig-tools`	`iig`, Apple’s IOKit interface generator, needed to build modern kexts
`kc-tools`	`kc-builder` and `prelink-builder`, which link kernel collections
`xnu-loader`	The bootloader that loads the kernel collection
`pd-sb-key`	The key pair that signs Secure Boot images. It defaults to a keyless placeholder, and builds that sign override it

iig-tools, kc-tools and xnu-loader are PureDarwin repositories. When you are changing one of them alongside the main tree, use --override-input, and remember that a build may need the override on more than one input at once.

How the Outputs Are Put Together

mkSystem is evaluated per system and composes four package sets:

packages = commonPackages // arm64Packages // probePackages
           // (linuxPackages, only when the host is Linux)

linuxPackages is where images, kernel collections and runner apps live, which is why a macOS host builds components, the kernel and libSystem included, but no bootable output.

The supporting files:

File	Role
`build.nix`	The single generic derivation that builds the in-tree CMake sources
`image.nix`	Assembles a partitioned, bootable disk image
`nix/sources.nix`	Pins the component source trees
`nix/image-contents.nix`	Decides what goes into each image flavour, and defines the runners
`nix/arm64.nix`	The arm64 and armv6 kernels, kexts and userland
`nix/lib/kc-kexts.nix`	The shared x86_64 kernel collection kext list
`nix/lib/target-info.nix`	Maps a target triple to meson and clang settings
`nix/pkgs/**`	Every ported third-party package

Package Naming

A bare name is the x86_64 build: kernel, kexts, userland, zsh, mesa.
-arm64 is the arm64 build of the same thing: kernel-arm64, zsh-arm64.
-arm32 or -armv6 is the 32-bit ARM build: kernel-arm32-bcm2835.
A board suffix pins a machine: -virt, -t8010, -bcm2837, -bcm2835.
-debug is the DEVELOPMENT kernel configuration, or a debug image built on it.

So kc-arm64-t8010-debug is the debug kernel collection for the iPad 6 target, and image-minimal-debug is the small x86_64 image built against the debug kernel.

nix flake show prints the full list. It is long, with several hundred outputs.

Apps

Apps are the QEMU runners. nix run .#vm, .#kvm, .#arm64-virt, .#arm64-uefi, .#arm64-uboot. They are documented in Running in QEMU.

The Dev Shell

nix develop gives you the toolchain, the cached native ld, migcom and unifdef, and sets CMAKE_TOOLCHAIN_FILE to cmake/nix-toolchain.cmake. devShells.kernel and devShells.default are the same shell.

The shell is for working on one component at a time. It does not produce a system. See The CMake Tree.