Bad remote builder settings are very difficult to revert

[zmitchell]

I made a mistake filling out the configuration for a remote builder (I had the comment part of my SSH key still in there), which now means I can't build my system at all:

error: bad machine specification: failed to convert column #3 in a row: 'ssh-ng://nixbld@fd7a:115c:a1e0::19 aarch64-linux ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAILsj5Gfjmar7Nj38f2bc7riB9CBqOoByzrR2zw4814HF zmitchell@fastmail.com 1 1 kvm,big-parallel,nixos-test,benchmark - c3NoLWVkMjU1MTkgQUFBQUMzTnphQzFsWkRJMU5URTVBQUFBSU93SjIvSGdwL0N4UWFac2Q0ak1oYjhhNUllY1l1Qm00NWltdGJUWlRWS2Ugcm9vdEBidWlsZC1hcm0K' to 'unsigned int'
error:
       … while reading the response from the build hook

       error: unexpected EOF reading a line

I haven't figured out where this setting is or how to delete it so that I can do a fresh build with the correct config.

• Rollbacks don't help because they still run the __build-remote hook, which finds whatever this setting is and fails because of it.
• Doing a build with --offline doesn't work either.

So at this point I'm at a loss how to proceed, I'm completely unable to build the system.

[zmitchell]

I've also ensured that I have nix.distributedBuilds = false.

[zmitchell]

Alright, I managed to get myself unstuck. Here's what I did:

• Clone nix-darwin
• Edit pkgs/darwin-rebuild.sh to include --builders '' in this line: https://github.com/LnL7/nix-darwin/blob/a55b3f1ab41bb6d5025ebeebb4da5fd240b9b3b3/pkgs/nix-tools/darwin-rebuild.sh#L212
• Use this clone of nix-darwin to build my system:

  $ nix run .#darwin-rebuild -- switch --flake <path to my flake>

WOOF, that was scary for a bit, but I figured it out 😅

[zmitchell]

It would be nice if there was a way for the user to pass flags to the underlying nix build/nix-build call.

[emilazy]

Does darwin-rebuild build --option builders '' not work?

[daniel-hope-koan]

The config to use the builder may have been in the /etc/nix/nix.conf file