Prerequisite Knowledge#

WSL with NixOS running

Basic understanding of:

1. Virtualization
2. Linux
3. Nix/NixOS

Introduction#

I wanted to rice my laptop without turning it on. I thought, “Hey, I can just make a VM in Hyper-V”. “I already use NixOS on WSL2, so I can reuse the VHDX for the VM!” — or so I thought. Then, I quickly found out I can’t just reuse it.

Why Hyper-V?

Hyper-V is a type 1 hypervisor made by Microsoft for Windows machines. WSL’s v2 runs on Hyper-V.

I wanted to use what I already had on my machine, that means I get the privilege of using Hyper-V (yay /s).

I didn’t want to install VMWare or god forbid Oracle VirtualBox.

Software Programming Mantra#

NOTE

I journaled the journey on Bluesky!

Check it out here: https://bsky.app/profile/sakurakat.systems/post/3llnz5asyms2c

trying to make a Hyper-V VM with NixOS so i can rice my laptop without turning it on

— Kathryn<'u1f338> (@sakurakat.systems) March 31, 2025 at 2:39 PM

You can also read the skeets as an article here: https://skywriter.blue/pages/did:plc:rwi65xn77uzhgyewkfbuuziz/post/3llnz5asyms2c

Enter github:nix-community/nixos-generators#

nixos-generators is a project based on the Nix ecosystem, which makes it easy to create VM images, ISOs, cloud images, and a plethora of other formats.

I started by invoking nixos-generator and passed my NixOS config by using the --flake option. However, it kept saying nixos/modules/virtualisation/disk-size-option.nix is missing. Even though I passed the options through the CLI args?

Now, I’m new to flakes and Nix in general, so I couldn’t figure out why it can’t find the option.

NOTE

If you’re also new to Nix, check ¹ to find resources to learn more about them.

So, I figured the best course of action would be copying the example from website, and then incrementally make changes. That is, create a minimal working config, and then adapt it to my needs.

Getting the minimal working config to work#

I just copied the example from the repo.

And it worked! But then I realized I used the wrong config, I used WSL’s config instead of my laptop’s config 🤦. Well, at least I know it works now ².

Then I made a stupid mistake.

See, NixOS allows you to have configuration for multiple… Let’s say… environments. When you do nixos-rebuild test --flake . --use-remote-sudo, the config gets selected depending on the machine’s hostname. You can also specify the config you want to build by doing nixos-rebuild test --flake .#<hostname> --use-remote-sudo.

My laptop’s hostname is kats-laptop, however, the hostname for WSL is nixos (default). So, the flake thought ³ I wanted to build the target using nixos’s config, but, there was no config for nixos. So, I just had to mention the hostname ⁴.

Also, the #<hostname> part isn’t limited to NixOS configs. In general, you use it to select a target. If you’ve used the nix shell nixpkgs#<app> command, you’re selecting a target to build and expose to the shell. Another place you might’ve chosen is when you run nix build github:<owner>/<repo>#<branch>.

The thing after # is the output from the flake.

Recently, I had to update github:MarceColl/zen-browser-flake, so it builds the latest version of the Zen browser. In the flake, you can select if you want to use the build optimized for newer systems, or the compatibility one. The way you chose is by either using #specific, or #generic. If you don’t specify, the flake defaults to specific. (You can read the short thread about the process on Bluesky ⁵)

While trying to get the VM image to build, at some point, I went from trying to build the hyperv target to trying to build the install-iso-hyperv. As the name suggests, install-iso-hyperv builds an ISO instead of a Hyper-V image. (btw, the size of the ISO was ~2.6 GiB). I can’t just load the ISO in the Hyper-V manager. So, it’s time to remake it with the hyperv target.

I was also unsure if 20 GiB would be enough for the VM, so I bumped it up to 40 GiB (changing multiple variables at once is bad, I know).

Back to failing to build#

I thought that changing the image size to 40 GiB was the problem, so I changed it back to 20 GiB. I can just increase the disk size in Hyper-V Manager.

The build failed again. I checked the logs and found this:

Model: (file) Disk /build/nixos.raw: 4295MB Sector size (logical/physical): 512B/512B Partition Table: gpt Disk Flags: Number Start End Size File system Name Flags 1 8389kB 269MB 261MB fat32 ESP boot, esp 2 269MB 4294MB 4024MB ext4 primary

— Kathryn<'u1f338> (@sakurakat.systems) March 31, 2025 at 6:05 PM

Lead astray#

Let’s talk about the assumptions I made that turned out to be wrong.

error: builder for '/nix/store/viir73fa9wxrbp4y18yad03nzp82bhjr-hwdb.bin.drv' failed with exit code 1
error: 1 dependencies of derivation '/nix/store/6g53c6j7nhs4ngy4fs1hk8sgi3hkli2i-etc.drv' failed to build
note: keeping build directory '/mnt/d/build-dir/nix-build-initrd-linux-6.12.21.drv-0/build'
error: 1 dependencies of derivation '/nix/store/xlfbh71qyiwbb00k9xg6bmimqqmip75q-nixos-system-kats-laptop-hyperv-25.05.20250330.52faf48.drv' failed to build
error: 1 dependencies of derivation '/nix/store/bk0kb7mp9kswp6kvnrlqqnmd7fxb1cvh-nixos-hyperv-hyperv-25.05.20250330.52faf48-x86_64-linux.drv' failed to build

{
  virtualisation.diskSize = 20 * 1024;
}

Build success#

I copied the successful build from the Nix store to Windows.

When I tried to load it as a VM

Let’s read this error.

• VM failed to start.
• Something about limitations
• “disk file must be uncompressed and unencrypted and must not be sparse”
  • uncompressed: I compress my disks, so I know how to solve that.
  • unencrypted: I don’t think this should be a problem. I don’t have BitLocker on.
  • sparse: I’m not even sure how I’d solve it, maybe the Hyper-V Manager has some tool I can use.

OK, let’s decompress it first.
right click file > properties > advanced > uncheck Compress contents to save disk space

Next error:

• “No operating system was loaded. Your virtual machine may be configured incorrectly. Exit and re-configure your VM or click restart to retry the current boot sequence again.”
  • Hm, that doesn’t tell much; let’s read the earlier stuff.
• “The unsigned image's hash is not allowed (DB)”
  • Oh, I think I know what’s wrong: secure boot!

right click vm > settings > Security > uncheck 'Enable Secure Boot'

VM booted successfully#

I checked the VHDX file NixOS Generators created and saw it was 4 GiB.

Then, the realization hit me. The error I saw in the #lead-astray section was telling me that the VHDX file was 4 GiB, and not all the various things I thought it was.

Struggles with logging in as ksakura#

A meme about NixOS is that, everything is declarative, except the installation process.

(src: https://youtu.be/nLwbNhSxLd4?list=TLPQMTQwNDIwMjVqtjGiwPFIvg&t=759)

Part of the answer is on mynixos.com/nixpkgs/option/users.users.<name>.initialPassword,
“If none of the password options are set, then no password is assigned to the user, and the user will not be able to do password-based logins.”

And the rest is on mynixos.com/nixpkgs/option/users.users.<name>.hashedPassword
”To generate a hashed password run mkpasswd.”

mkpasswd <password>

$y$j9T$MxmF8OTQHxbHHSRiBN6x5.$l4pf7mt76eBt6NWeyW1t4fM0fdQlWRovwtuwS43kYXB

Successfully logged in#

HELL YEAH

[image or embed]

— Kathryn<'u1f338> (@sakurakat.systems) April 1, 2025 at 2:25 PM

No config files#

ls /etc/nixos/

Empty List

Huh, that’s concerning. I didn’t run the installer, so I guess the config files weren’t generated.

But, at this point, I just want to get done with this project. Also, I’m pretty sure there’s already a way to copy over those files, I just don’t want to learn about it right now.

Final stretch#

1. Reboot the VM
2. nixos-rebuild test --flake . --use-remote-sudo

Success!

The glitchiness is because Hyperland doesn’t like being run in a VM.
Reason: “YMMV, this is not officially supported.”
From: wiki.hyprland.org:Getting-Started/Installation | Section: Running In a VM
Taken on 2025-04-24.

The End (for now)#

I now have a working VM where I can experiment.

But was it worth it? Not really.
Do I regret going through all this effort? Not at all.

I actually tried to rice my laptop when I had nothing else I wanted to do. But it just didn’t feel worth it. It takes so much time, and while I don’t like using Hyprland (due to the author), it is just not worth it to switch to Niri, at least for me.

I do eventually want to update to newer packages but that’s a thing for later.

I can also use the VM to modularize my config.

The flake.nix File#

This is not perfect or good, but I got it to work, it’s good enough for now.

{
  inputs = {
    # NOTE: Replace "nixos-23.11" with that which is in system.stateVersion of
    # configuration.nix. You can also use latter versions if you wish to
    # upgrade.
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    home-manager = {
      url = "github:nix-community/home-manager";
      inputs.nixpkgs.follows = "nixpkgs";
    };
    nixos-generators = {
      url = "github:nix-community/nixos-generators";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };
  outputs = inputs @ {
    self,
    nixpkgs,
    home-manager,
    nixos-generators,
    ...
  }: let
    system = "x86_64-linux";
    pkgs = nixpkgs.legacyPackages.${system};
  in {
    # NOTE: 'nixos' is the default hostname set by the installer
    nixosConfigurations.kats-laptop = nixpkgs.lib.nixosSystem {
      # NOTE: Change this to aarch64-linux if you are on ARM
      system = "x86_64-linux";
      # extraSpecialArgs = {inherit inputs;};
      modules = [
        ./configuration.nix

        {
          nix.settings.experimental-features = [
            "nix-command"
            "flakes"
          ];
        }

        home-manager.nixosModules.home-manager
        {
          home-manager.useGlobalPkgs = true;
          # home-manager.useUserPkgs = true;
          home-manager.users.ksakura = import ./home.nix;
          home-manager.backupFileExtension = "bak";
        }

        {
          virtualisation.diskSize = 20 * 1024;
        }
      ];
    };

    formatter.${system} = pkgs.alejandra;
    devShell = with pkgs;
      mkShell {
        buildInputs = [nil self.formatter.${system}];
      };
  };
}

Questions people have asked me#

Proofreaders#

Divyesh Patil

• https://www.linkedin.com/in/divyesh-patil-525808257/

Andrew

• https://codeberg.org/Andrew15-5

Garnet

• Opted out of sharing socials

Updates#

Footnotes#