Nixos VM to build x86_64 targets from Apple silicon

This guide is based on the great nixos-utm helper.

Before starting ensure you have UTM installed with nix or homebrew.

Installation on MacOS

sed is different in different platforms. Following steps only work on MacOS.

# Create new nix configuration for UTM vm
$ nix flake new -t github:ciderale/nixos-utm my-utm-vm

$ cd my-utm-vm

# Generate new passwordless ssh key to be used just for this VM
$ ssh-keygen -t ed25519 -f ~/.ssh/utm-vm-nixos-builder -P "" -C "$USER@utm-vm-nixos-builder"

# Replace the VM ssh key
$ sed -i'' -e "/ssh-ed25519/ s/.*/    \"$(cat ~/.ssh/utm-vm-nixos-builder.pub)\"/" configuration.nix

# Enable rosetta in the VM
$ sed -i '' '/services.openssh.enable = true;/i\
\ \ virtualisation.rosetta.enable = true;\
' configuration.nix

# Run the UTM installer
VM_NAME=nixos nix run github:ciderale/nixos-utm#nixosCreate .#utm

.local address instead of 192.168.64.X ip-address

Avahi enables you want your host machine to find the VM with utm-vm-nixos-builder.local address. You can enable it by adding following lines to the configuration.nix

{
  networking.hostName = "utm-vm-nixos-builder";

  services = {
      avahi = {
          enable = true;
          nssmdns4 = true;
          openFirewall = true;
          publish = {
              enable = true;
              userServices = true;
              addresses = true;
          };
      };
  };
}

Local setup to your MacOS host

According to this great guide nix will use root user for the remote builds and thus the root user needs to trust the builder VM.

It's probably easiest to just symlink your own ssh known hosts to the root user:

sudo mkdir /var/root/.ssh
sudo ln -s ~/.ssh/known_hosts /var/root/.ssh/

Then add the x86_64-linux capable remote builder to your nix config

mkdir -p ~/.config/nix/

echo -e "\nbuilders = ssh://root@utm-vm-nixos-builder.local?ssh-key=$HOME/.ssh/utm-vm-nixos-builder x86_64-linux" >> ~/.config/nix/nix.conf

After you have done all of this steps you should be able to use the remote builder in VM:

nix build --impure --expr '(with import <nixpkgs> { system = "x86_64-linux"; }; runCommand "foo" {} "uname > $out")'
cat result

If the file outputs Linux everything is working properly.

Getting the IP address of the VM

VM_NAME=nixos nixos nix run github:ciderale/nixos-utm#nixosIP

Logging to the nixos VM

ssh root@$(VM_NAME=nixos nix run github:ciderale/nixos-utm#nixosIP)

Deploying new configuration for the VM

nix run nixpkgs#nixos-rebuild -- switch --fast --flake .#utm --target-host root@utm-vm-nixos-builder.local --build-host root@utm-vm-nixos-builder.local

License

ISC