QEMU

QEMU is a generic and open source machine emulator and virtualizer.

Setup

To install the main QEMU program system-wide, add the following to your configuration.nix:

  environment = {
    systemPackages = [ pkgs.qemu ];
  };

Tip

In order to affect your NixOS system by your nix-language-specific changes you must first evaluate it:

$ nixos-rebuild switch --use-remote-sudo

Quick EMU

Quickly create and run highly optimised desktop virtual machines for Linux, macOS and Windows; with just two commands.

https://github.com/quickemu-project/quickemu

quickget windows 11
quickemu --vm windows-11.conf

Configuration

Booting UEFI

To boot UEFI systems using QEMU, the UEFI firmware replacing the BIOS implementation needs to be provided while starting QEMU.

The following installs a script, that always starts QEMU with OVMF firmware implementing UEFI support.

 environment = {
   systemPackages = [
     (pkgs.writeShellScriptBin "qemu-system-x86_64-uefi" ''
       qemu-system-x86_64 \
         -bios ${pkgs.OVMF.fd}/FV/OVMF.fd \
         "$@"
     '')
   ];
 };

qcow-efi images generated from nixos-generators require more RAM than the default 128MB. Failing to provide enough RAM results in grub reporting "error: start_image() returned 0x800000000000009." or systemd-boot reporting "Failed to execute NixOS: Out of resources".

Run binaries of different architecture

Following configuration will enable the emulation of different architectures. For example to run aarch64 and riscv64 binaries on an native x86_64 host, add following part to your system configuration, apply it and reboot your system.

boot.binfmt.emulatedSystems = [
  "aarch64-linux"
  "riscv64-linux"
];

Tips and tricks

Emulate different architecture

The following Flake file constructs and executes a NixOS virtual machine with an architecture distinct from that of the host system; in this example, it utilizes aarch64.

Save the snippet as flake.nix and run nix run in the same directory to bootup the VM.

{
  description = "Nix flake to build and run a NixOS VM for aarch64";

  inputs = {
    nixpkgs.url = "nixpkgs/nixos-24.05";
  };

  outputs = { self, nixpkgs }:
  let
    pkgs = import nixpkgs { system = "x86_64-linux"; };
    pkgsAarch64 = import nixpkgs { system = "aarch64-linux"; };

    iso = (pkgsAarch64.nixos {
      imports = [ "${nixpkgs}/nixos/modules/installer/cd-dvd/installation-cd-base.nix" ];
    }).config.system.build.isoImage;

    vmScript = pkgs.writeScriptBin "run-nixos-vm" ''
      #!${pkgs.runtimeShell}
      ${pkgs.qemu}/bin/qemu-system-aarch64 \
        -machine virt,gic-version=max \
        -cpu max \
        -m 2G \
        -smp 4 \
        -drive file=$(echo ${iso}/iso/*.iso),format=raw,readonly=on \
        -nographic \
        -bios ${pkgsAarch64.OVMF.fd}/FV/QEMU_EFI.fd
    '';

  in {
    defaultPackage.x86_64-linux = vmScript;
  };
}

Alternatively a different iso file can be specified in the drive-parameter, for example for Ubuntu Server ARM64.