Nixos-rebuild build-vm # option `virtualisation.cores' does not exist

[imincik]

@igel , see Incomplete documentation for "build-vm" options (can be used only inside "virtualisation.vmVariant") · Issue #196755 · NixOS/nixpkgs · GitHub .

You must specify virtualisation.cores inside of virtualisation.vmVariant.

For example:

{
  virtualisation.vmVariant = {
    # following configuration is added only when building VM with build-vm
    virtualisation.cores = 1;
  };
}