Basic configuration for a "base nix" VM instance you can deploy changes on top of

configuration.nix

{ config, pkgs, ... }:
{
  imports =
    [ # Include the results of the hardware scan.
      ./hardware-configuration.nix
    ];

  # Use the systemd-boot EFI boot loader.
  boot.loader.systemd-boot.enable = true;
  boot.loader.efi.canTouchEfiVariables = true;

  nix = {
    settings = {
      sandbox = true;
      trusted-users = [ "root" "@wheel" ];
      experimental-features = [ "nix-command" "flakes" ];
    };
  };

  networking.hostName = "nixos-template"; # Define your hostname.
  environment.systemPackages = with pkgs; [
    nixpkgs-fmt
    curl
    neovim
    git
    parted
  ];
  environment.variables = {
    EDITOR = "vim";
  };

    services.openssh = {
      enable = true;
      openFirewall = true;
      settings = {
        #PermitRootLogin = "no";
        PasswordAuthentication = false;
        KexAlgorithms = [
          "curve25519-sha256"
          "curve25519-sha256@libssh.org"
          "diffie-hellman-group-exchange-sha256"
          "ecdh-sha2-nistp256"
        ];
      };
      hostKeys = [
        {
          type = "rsa";
          bits = 4096;
          path = "/etc/ssh/ssh_host_rsa_key";
        }
        {
          type = "ed25519";
          path = "/etc/ssh/ssh_host_ed25519_key";
        }
        {
          type = "ecdsa";
          bits = 256;
          path = "/etc/ssh/ssh_host_ecdsa_key";
        }
      ];
      #ports = [ 2222 ];
    };

  users.users = {
      cmp = {
        isNormalUser = true;
        extraGroups = [ "wheel" ];
        packages = [ ];
        openssh.authorizedKeys.keys = [
          "..."
        ];
      };
};
  security.sudo.wheelNeedsPassword = true;

  system.stateVersion = "23.05"; # Did you read the comment?

}