doc: add note about trusted users

[Janik-Haag]

Motivation

it took me way too long to figure out why remote builds with just a machine file don't work, esp. since the error message isn't that great and I want to make it easier for other people.

[fricklerhandwerk]

What exactly is the issue you ran into? Judging from the change, you seem to be on NixOS, have written to /etc/nix/machines directly and are running the build from your-user, right? What exactly was the error message?

Why would it be different if you had used the module to specify machines?

I'm trying to filter what we really need fixed in the Nix manual. Because we certainly shouldn't mention NixOS at all, as that will just continue confusing people about what's what, where things are really happening, and where to find the right bits of information.

Apparently some interaction is unclear here. We have a note about substituters and trusted-users, if the behavior is the same there we should have such a note for builders as well.

[Janik-Haag]

If I don't have:

  nix = {
    distributedBuilds = true;
    buildMachines = [
      {
        hostName = "aarch64.nixos.community";
        maxJobs = 64;
        sshKey = "/home/janik/.ssh/nix-community-builder";
        sshUser = "janik";
        system = "aarch64-linux";
        supportedFeatures = [ "big-parallel" ];
      }
    ];
  };

in my config and instead just use a machine file I have to be in the local trusted users, otherwise nix just throws a error about no available builders if I also set --max-jobs 0, I don't have the remote builders file in /etc/nix/machines

The NixOS wiki also has it in the trouble shooting section https://nixos.wiki/wiki/Distributed_build#Troubleshooting and it's there for ~3 years now https://nixos.wiki/index.php?title=Distributed_build&oldid=4005

[fricklerhandwerk]

So what we really need would be adding the same kind of note to buiders configuration setting as we have for substituters? I think the general problem is that this guide has too much reference documentation that should instead be in the config file section.

[Janik-Haag]

Uhm maybe could you send a link to the substituters docs you are referencing, I'm not not familiar.

[fricklerhandwerk]

We have a note about substituters and trusted-users, if the behavior is the same there we should have such a note for builders as well.

#9202 (comment)

[Janik-Haag]

Yeah something like that would be nice. Also sorry I forgot that you linked it above already, it's been a while 🙈

[fricklerhandwerk]

No problem at all. Do you have the time to add that bit in this PR? Should amount to copypaste and fixup.

[Janik-Haag]

fixed.

[fricklerhandwerk]

Closing in favor of #9526, where the note on trusted-users is incorporated.

@Janik-Haag this is not to dismiss your contribution. In fact, thanks for digging out the issue which would otherwise have gone unnoticed. Also it nudged me to finally make a sweep over the whole topic.