Introduction
Get the kernel sources
Prepare a reproducible build shell
Configure and build the kernel
Wrap the kernel as a Nix package
Configure NixOS to use the custom kernel
Test and rollback
Short tips and safety notes

Introduction

Compiling a Linux kernel on NixOS follows the familiar configure/build steps, but the integration step should use Nix so the kernel lives in the Nix store and is managed by nixos-rebuild. This short guide keeps to the essentials: fetch sources, build (using gcc), wrap as a Nix package, and activate with nixos-rebuild.

Get the kernel sources

git clone https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
cd linux
git checkout v5.x.y    # pick the tag/commit you need

Prepare a reproducible build shell

Enter a nix-shell from the kernel tree (or your development shell that contains required tools). The examples below assume you prefer gcc over clang.

# from the kernel source dir
nix-shell .

If you want to ensure the build uses system gcc (and not clang/LLVM), start a clean env:

env -u CC -u LD -u LLVM -u LLVM_IAS bash
which gcc
gcc --version

Configure and build the kernel

Use an out-of-tree build to keep the source tree clean and reuse /proc/config.gz as a starting point.

# cleanup and prepare
make O=build mrproper
mkdir -p build
zcat /proc/config.gz > build/.config
make O=build olddefconfig

# build with parallel jobs
make O=build -j$(nproc)

This produces the kernel image and modules under build/. You can test by loading the vmlinuz from the build tree (VM) or proceed to wrap the kernel as a Nix package.

Wrap the kernel as a Nix package

Create a small override that points kernelPackages at your source/commit. Example (conceptual):

{ pkgs, lib, stdenv }:

pkgs.linuxPackages.overrideAttrs (old: {
  src = pkgs.fetchFromGitHub {
    owner = "torvalds";
    repo  = "linux";
    rev   = "v5.x.y";
    sha256 = "<hash>";
  };
  # optional: add patches or config fragments via postPatch / configureFlags
})

Save this as e.g. /path/to/my-kernel.nix.

Configure NixOS to use the custom kernel

In /etc/nixos/configuration.nix point boot.kernelPackages to your package:

{ config, pkgs, ... }:
{
  boot.kernelPackages = pkgs.callPackage /path/to/my-kernel.nix { };
}

Then build and switch:

# without flakes
sudo nixos-rebuild switch

# with flakes (example)
sudo nixos-rebuild switch --flake .#yourSystem

nixos-rebuild will build the kernel in the Nix store and update boot entries.

Test and rollback

Reboot and select the new kernel.
If it fails, choose an older generation from the boot menu or run:

sudo nixos-rebuild switch –rollback

Short tips and safety notes

Do not use sudo make install on a running NixOS system — it bypasses the Nix store and system configuration.
For quick tests use a VM or boot the vmlinuz directly (non-Nix bootloader).
Prefer flakes and pinned nixpkgs for reproducible builds.
Keep a known-good configuration.nix before experimenting.

Wrap-up: fetch sources, build reproducibly (use nix-shell + out-of-tree build), package the kernel as a Nix package, set boot.kernelPackages, then nixos-rebuild switch and reboot. This keeps kernels managed, reproducible, and rollbackable under Nix.

Building a Linux Kernel on NixOS

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