nixos-generate-config --no-filesystems --show-hardware-config

nixos/modules/installer/tools/tools.nix

# This module generates nixos-install, nixos-rebuild,
# nixos-generate-config, etc.

{ config, lib, pkgs, ... }:

with lib;

let
  makeProg = args: pkgs.substituteAll (args // {
    dir = "bin";
    isExecutable = true;
  });

  nixos-build-vms = makeProg {
    name = "nixos-build-vms";
    src = ./nixos-build-vms/nixos-build-vms.sh;
    inherit (pkgs) runtimeShell;
  };

  nixos-install = makeProg {
    name = "nixos-install";
    src = ./nixos-install.sh;
    inherit (pkgs) runtimeShell;
    nix = config.nix.package.out;
    path = makeBinPath [
      pkgs.jq
      nixos-enter
    ];
  };

  nixos-rebuild = pkgs.nixos-rebuild.override { nix = config.nix.package.out; };

  nixos-generate-config = makeProg {
    name = "nixos-generate-config";
    src = ./nixos-generate-config.pl;
    perl = "${pkgs.perl.withPackages (p: [ p.FileSlurp ])}/bin/perl";
    nixInstantiate = "${pkgs.nix}/bin/nix-instantiate";
    detectvirt = "${config.systemd.package}/bin/systemd-detect-virt"; # !!!
    btrfs = "${pkgs.btrfs-progs}/bin/btrfs";
    inherit (config.system.nixos-generate-config) configuration desktopConfiguration;
    xserverEnabled = config.services.xserver.enable;
  };



installer/tools/nixos-generate-config.pl

    --root ...
    !!!
        --no-filesystems
    !!!
        --show-hardware-config

...
my @attrs = ();
my @kernelModules = ();
my @initrdKernelModules = ();
my @initrdAvailableKernelModules = ();
my @modulePackages = ();
my @imports;
...
my $virt = `/nix/store/xhdxx70inipwzif62dq7m3p3acpq9hcg-systemd-252.5/bin/systemd-detect-virt`;
    # in my case -> kvm