Has the behavior of --build-host been changed?

Help
1

I was upgrading an old laptop, that hadn’t seen meaningful update since November 2023. It’s a pretty weak laptop, so I used nixos-rebuild --build-host <local-ip-of-my-desktop> (Nix 2.17.1) and it worked great. Now that my laptop has been updated (Nix 2.28.3), I wanted to build something else, so again I used --build-host, but now it seemed to do nothing. When I put in an IP that wasn’t my desktop, it didn’t care, and did the same thing. When I forced it to not build locally using -j 0, I got the following:

error:
    Unable to start any build;
    either increase '--max-jobs' or enable remote builds.

I’ve looked through the nix configuration. I don’t see anything like remote-builds = true. I’m puzzled as to why this no longer works.

edit: I decided to just go back to the old generation where it worked to build my current config, and it gave me the same error. So now I’m even more confused.

2

can it contact the builder as root ?

3

It can if I specify the user, but I tried that and nixos-rebuild still fails in the same way. To be clear, you’re asking about trying to ssh into a non-root user as root, not about trying to ssh into a root user, correct?

4

okay, so making sure I add the user@ bit to the host did actually fix --builders not working. However --build-host still doesn’t work no matter what I do. I can proceed using --builders, but I’m still curious why --build-host doesn’t work.

5

I warm up the agent on my limited device (rpi4) first with:

sudo ssh <remoteuser>@<snapdragon>

Followed by:

sudo nixos-rebuild --build-host <remoteuser>@<snapdragon> switch

What output do you get with the above commands?

6

sudo ssh <user>@<host> succeeds
(Throwing in a -j0 in there to make sure I don’t get any false positives)
sudo nixos-rebuild --build-host <user>@<host> -j0 build
gives me the error in the original post.

7

What is the output of:

ssh <user>@<host> nixos-option nix.trustedUsers

and:

ssh <user>@<host> id

?

edit: anything in the logs of the remote host btw, if you execute sudo nixos-rebuild --build-host <user>@<host> switch ?

8 
$ ssh mason@192.168.0.105 nixos-option nix.trustedUsers
Value:
  [
    "root"
    "mason"
    "root"
  ]

Type:
  submodule

Description:
  Alias of {option}`nix.settings.trusted-users`.

Declared by:
  /nix/store/vj980b72z6zb0yg6v0a7nzc9rcww3jmn-source/nixos/modules/config/nix.nix

Defined by:

evaluation warning: Obsolete option `nix.trustedUsers' is used. It was renamed to `nix.settings.trusted-users'.

$ ssh mason@192.168.0.105 id
uid=1000(mason) gid=100(users) groups=100(users),1(wheel),57(networkmanager),131(docker)
9

Nothing wrong there afaics.

What does the build host log?

Both hosts are running the same version of nix and nixos? Not that it should matter :thinking:

10

If you’re talking journalctl, nothing gets logged.

They are the same version of nix and nixos. They are different kernels though.