I want to create additional files during build, and change permissions. This is an example:

pkgs.dockerTools.buildLayeredImage {
  name = "xtruder/kubepatcher";
  tag = "latest";

  contents = [ pkg pkgs.cacert passwd group ];

  extraCommands = ''
    mkdir tmp
    chmod 1777 tmp
  '';

  config = {
    Entrypoint = "${pkg}/bin/kubepatcher";
    Cmd = [ "--logtostderr" ];
    User = "app";
  };
}

Motivation for this change

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.