virtualisation.proxmox.iso is constantly erroring (on every option)

[SpiderUnderUrBed]

[spiderunderurbed@daspidercave:~/nixnuc/nixmoxer]$ nix run ~/projects/proxmox-nixos/#nixmoxer -- --flake myvm
warning: ignoring untrusted substituter 'https://cache.saumon.network/proxmox-nixos', you are not a trusted user.
Run `man nix.conf` for more information on the `substituters` configuration option.
warning: ignoring the client-specified setting 'trusted-public-keys', because it is a restricted setting and you are not a trusted user
2025-08-07 22:03:35,646 - INFO - Loading configuration from /home/spiderunderurbed/nixnuc/nixmoxer/nixmoxer.conf...
2025-08-07 22:03:35,646 - INFO - Configuration parsed successfully.
2025-08-07 22:03:35,647 - INFO - Authenticating with password...
2025-08-07 22:03:35,800 - INFO - Authentication successful.
2025-08-07 22:03:35,802 - INFO - Evaluating configuration...
2025-08-07 22:03:59,135 - ERROR - Machine evaluation failed:
2025-08-07 22:03:59,138 - ERROR - warning: Git tree '/home/spiderunderurbed/nixnuc/nixmoxer' is dirty
error:
       … while evaluating attribute 'iso'

       … while evaluating the attribute 'value'
         at /nix/store/a40gkgcry8a1s9gjr2z52f02gn0808bl-source/lib/modules.nix:1085:7:
         1084|     // {
         1085|       value = addErrorContext "while evaluating the option `${showOption loc}':" value;
             |       ^
         1086|       inherit (res.defsFinal') highestPrio;

       … while evaluating the option `virtualisation.proxmox.iso':

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: A definition for option `virtualisation.proxmox.iso' is not of type `package'. Definition values:
       - In `/nix/store/a40gkgcry8a1s9gjr2z52f02gn0808bl-source/flake.nix': null

[ble: exit 1][ble: elapsed 24.966s (CPU 43.5%)] nix run ~/projects/proxmox-nixos/#nixmoxer -- --flake myvm

By the way ~/projects/proxmox-nixos/ is this project freshly cloned, I just have it there for other reasons (like if i need to test changes), but this is the latest version of this repo.

I tried not setting iso, I also tried:
iso = "../nixos-minimal.iso";
and:

iso = pkgs.runCommand "custom-iso" {
  src = ../nixos-minimal.iso;
} ''
  mkdir -p $out
  cp $src $out/
'';

which once worked

Full config:

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

{
  networking.hostName = "myvm";

  virtualisation.proxmox = {
    node = "hostnuc";

    #iso = "../nixos-minimal.iso";
iso = pkgs.runCommand "custom-iso" {
  src = ../nixos-minimal.iso;
} ''
  mkdir -p $out
  cp $src $out/
'';


    vmid = 100;
    memory = 12288;
    cores = 3;
    sockets = 1;

    boot.order = [ "scsi0" ];

    net = [
      {
        model = "virtio";
        bridge = "vmbr0";
      }
    ];

    scsi = [
      {
        file = "local:0,format=qcow2,import-from=/home/spiderunderurbed/hdd/vms/vm-2/nixos.qcow2";
        # size = "20G";  # Optional: only needed if creating disk from scratch
        # format = "none";  # Optional if already qcow2
      }
    ];
  };


  # Optional: uncomment to force image base name
  # image.baseName = lib.mkForce "nixos-custom";
}

My flake if it has any relevence:
https://pastebin.com/dXJYTUNx

[SpiderUnderUrBed]

Fixed, i dont know how, i just uncommented and recommented the iso, maybe its a onetime error, but ill re-open this if i get the error again.

[SpiderUnderUrBed]

I still get this issue.

[Zorgosto]

I also have this issue. I'm not sure what to actually set for this value. What would a typical value to use for this option be? I've tried different things but none have worked.

[JulienMalka]

The option is not easy to use correctly, it should be something that evaluates to an iso image. Usually it's a NixOS configuration that loads the installer/cd-dvd/installation-cd-minimal.nix module.

Maybe look at how it's done in the modules/declarative-vms folder.

[Zorgosto]

Thank you for the tip. I think I understand it better now with the example but I can't replicate it quite yet.
This is my configuration.nix file for the vm:

{config, lib, pkgs, modulesPath, ...}:
{
  imports = [
    ../../disko-config.nix

    ../../../modules/server
    ../../../secrets
  ];

  networking.hostName = "vm";
  networking.domain = "example.domain";

  virtualisation.proxmox = {
    node = "nodename";
    iso = ./iso.nix; # use iso build or autoInstall
    #autoInstall = true; # Auto builds the iso from configuration and adds to proxmox
    memory = 4096;
    cores = 4;
    sockets = 1;
    net = [
      {
        model = "virtio";
        bridge = "vmbr0";
      }
    ];
    bios = "ovmf";
    scsi = [ { file = "crypt:32"; } ]; # This will create a 32GB volume in 'crypt'
    efidisk0 = {
    file = "crypt:1"; # Note storage size is ignored and defualt EFI vars are copied instead
      pre-enrolled-keys = false;
    };
    tpmstate0 = {
      file = "crypt:1"; # Note storage size is ignored and set to 4MiB
      version = "v2.0";
    };
  };
}

And this is nix.iso:

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

{
  imports = [
    #(modulesPath + "/profiles/qemu-guest.nix")
    (modulesPath + "/installer/cd-dvd/installation-cd-minimal.nix")
  ];

  boot.initrd.kernelModules = [ ];
  boot.kernelModules = [ "kvm-amd" ];
  boot.extraModulePackages = [ ];

  isoImage.compressImage = false;
  isoImage.squashfsCompression = null;

  # Enables DHCP on each ethernet and wireless interface. In case of scripted networking
  # (the default) this is the recommended approach. When using systemd-networkd it's
  # still possible to use this option, but it's recommended to use it in conjunction
  # with explicit per-interface declarations with `networking.interfaces.<interface>.useDHCP`.
  networking.useDHCP = lib.mkDefault true;
}

I've also tried setting virtualisation.proxmox.iso directly to '(modulesPath + "/installer/cd-dvd/installation-cd-minimal.nix"' but that also does not seem to work.

This is the command I run and output I get:

nix run github:SaumonNet/proxmox-nixos#nixmoxer -- --flake safe
warning: ignoring untrusted flake configuration setting 'extra-substituters'.
Pass '--accept-flake-config' to trust it
warning: ignoring untrusted flake configuration setting 'extra-trusted-public-keys'.
Pass '--accept-flake-config' to trust it
2025-12-08 15:18:00,014 - INFO - Loading configuration from /srv/christian/asta-nixos/nixmoxer.conf...
2025-12-08 15:18:00,015 - INFO - Configuration parsed successfully.
2025-12-08 15:18:00,015 - INFO - Authenticating with token...
2025-12-08 15:18:00,016 - INFO - Authentication successful.
2025-12-08 15:18:00,016 - INFO - Evaluating configuration...
2025-12-08 15:18:01,258 - ERROR - Machine evaluation failed:
2025-12-08 15:18:01,258 - ERROR - warning: Git tree '/srv/christian/asta-nixos' is dirty
error:
       … while evaluating attribute 'iso'

       … while evaluating the attribute 'value'
         at /nix/store/mmbrs76ksccdn0bvvqs4plivwh6xlcs5-source/lib/modules.nix:1118:7:
         1117|     // {
         1118|       value = addErrorContext "while evaluating the option `${showOption loc}':" value;
             |       ^
         1119|       inherit (res.defsFinal') highestPrio;

       … while evaluating the option `virtualisation.proxmox.iso':

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: A definition for option `virtualisation.proxmox.iso' is not of type `package'. Definition values:
       - In `/nix/store/xcbsw94m6l6vcy7mn9nrwyprlydlm57n-source/hosts/server/safe/configuration.nix': <function>

(PS: using autoInstall generally works but doesn't quite yield the result I need)