nixos/hosts/hardware/vm.nix

#./hosts/hardware/vm.nix
# Stand-in "hardware" for `nixos-rebuild build-vm --flake .#mediaserver-vm`.
#
# Keeps hostName = FredOS-Mediaserver so every hostname-gated module under
# services/ switches on, but throws away the real disks, NICs and GPU. The
# point is watching arr-interconnect wire a *fresh* stack from empty state —
# something the live host can't demonstrate anymore, since its /var/lib is
# already populated and the script is a reconciler, not an installer.
{ lib, ... }:
{
  networking.hostName = "FredOS-Mediaserver";
  system.stateVersion = "25.11";
  nixpkgs.hostPlatform = "x86_64-linux";

  # qemu-vm.nix supplies "/" and the bootloader. Only the media pool has to
  # exist by hand, so the *arr root folders resolve — contents are throwaway.
  fileSystems."/mnt/storage" = {
    device = "tmpfs";
    fsType = "tmpfs";
    options = [ "mode=0777" ];
  };

  # --- Undo router.nix. This VM is not a router. ---
  # Its networkd units match NIC names pinned to the real MACs, so the VM's
  # NIC matches nothing and comes up unconfigured; its nft input chain is
  # policy-drop, which would eat the forwarded ports below. Scripted DHCP on
  # QEMU's user-mode NIC replaces both.
  networking.useNetworkd = lib.mkForce false;
  networking.nftables.tables = lib.mkForce { };
  services.dnsmasq.enable = lib.mkForce false;

  virtualisation.vmVariant.virtualisation = {
    memorySize = 8192;
    cores = 4;
    diskSize = 32768;   # docker images for shelfarr/profilarr are not small
    graphics = false;   # serial console; ctrl-a x to quit
    # Host side is offset by 10000 so the VM can run on the mediaserver
    # itself without fighting the live services for those ports.
    forwardPorts = [
      { from = "host"; host.port = 10022; guest.port = 22; }    # ssh
      { from = "host"; host.port = 18989; guest.port = 8989; }  # sonarr
      { from = "host"; host.port = 17878; guest.port = 7878; }  # radarr
      { from = "host"; host.port = 19696; guest.port = 9696; }  # prowlarr
      { from = "host"; host.port = 16767; guest.port = 6767; }  # bazarr
      { from = "host"; host.port = 18080; guest.port = 8080; }  # qbittorrent
      { from = "host"; host.port = 18096; guest.port = 8096; }  # jellyfin
      { from = "host"; host.port = 15055; guest.port = 5055; }  # seerr
    ];
  };
}