NixOS:nixos-rebuild build-vm

A virtual machine can be created , it will use your /etc/nixos/configuration.nix to make a 'clone' of your system. Useful for testing new configurations.

nixos-rebuild build-vm

You will that you will not be able to login to this virtual machine, as the passwords are not carried over to the virtual machine you build.

If you have a user called nixosvmtest for example , you can add

users.users.nixosvmtest.initialHashedPassword = "test";

to your /etc/nixos/configuration.nix

you should now be able to login test your system with this user and password.

https://discourse.nixos.org/t/default-login-and-password-for-nixos/4683/2