Building iso for digital ocean

Help
1

NixOS version: 23.11

I am trying to build an iso for digital ocean. I followed a similar path from this question
But a simpler version. See below
nix-build image.nix

{ pkgs ? import <nixpkgs> { } }:
let config = {
  imports = [ <nixpkgs/nixos/modules/virtualisation/digital-ocean-image.nix> ];
};
in
(pkgs.nixos config).digitalOceanImage

With the following result. How can I make this work?

Booting from ROM...
loading kernel modules...isable)... ock
mounting Nix store...
mounting host's temporary directory...
starting stage 2 (/nix/store/qp1a67s1cv4s538qnrwh4s0mxw31rfsk-vm-run-stage2)
tune2fs 1.47.0 (5-Feb-2023)
Setting maximal mount count to -1
Setting interval between checks to 0 seconds
Setting time filesystem last checked to Thu Apr 24 19:26:19 2025

dirname: missing operand
Try 'dirname --help' for more information.
mkdir: missing operand
Try 'mkdir --help' for more information.
[    1.401166] reboot: Power down
error: builder for '/nix/store/6x5rlrnd8ik0gz906zqww6rqqr1g0hq8-digital-ocean-image.drv' failed with exit code 1;
       last 25 log lines:
       > WARNING: Image format was not specified for 'nixos.raw' and probing guessed raw.
       >          Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted.
       >          Specify the 'raw' format explicitly to remove the restrictions.
       > cSeaBIOS (version rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org)
       >
       >
       > iPXE (http://ipxe.org) 00:03.0 CA00 PCI2.10 PnP PMM+3EFD0C20+3EF30C20 CA00
       >
       >
       >
       > Booting from ROM...
       > loading kernel modules...isable)... ock
       > mounting Nix store...
       > mounting host's temporary directory...
       > starting stage 2 (/nix/store/qp1a67s1cv4s538qnrwh4s0mxw31rfsk-vm-run-stage2)
       > tune2fs 1.47.0 (5-Feb-2023)
       > Setting maximal mount count to -1
       > Setting interval between checks to 0 seconds
       > Setting time filesystem last checked to Thu Apr 24 19:26:19 2025
       >
       > dirname: missing operand
       > Try 'dirname --help' for more information.
       > mkdir: missing operand
       > Try 'mkdir --help' for more information.
       > [    1.401166] reboot: Power down
       For full logs, run 'nix log /nix/store/6x5rlrnd8ik0gz906zqww6rqqr1g0hq8-digital-ocean-image.drv'.
2

I tried a different set of instructions and was able to build an image. we’ll see if I can progress further