Remote builders: operation 'addToStore' is not supported by store

After having to run several builds this afternoon on my machine, I finally decided to be serious about setting up remote builders. I’ve setup my nix.buildMachines and for now set nix.distributedBuilds = false; because I want to build on remote builders only when I explicitly decide it. While trying, I triggered an unhelpful error "operation not supported by store ". Luckily, nix master generates better messages, hence I tried the same command with nix master

/nix/store/1w96sgqwv5aabhk68av84h9yhlmnz98q-nix-2.3pre6628_25722bd/bin/nix-build --store ssh://myRemoteBuilder -A python3Packages.pandas ~/nixpkgs                                                                                                       
error: while evaluating the attribute 'args' of the derivation 'python3.7-pandas-0.24.1' at /home/teto/nixpkgs/pkgs/development/interpreters/python/mk-python-derivation.nix:73:3:
operation 'addToStore' is not supported by store 'ssh://myRemoteBuilder'

This is a bit more precise yet I don’t know how to solve this problem.

Here is a bunch of answer I got on irc. Thanks to them :slight_smile:

teto: `--store ssh://foo` requires that $USER (the remote user by the same name as local) be trusted on the remote box, or it cant add things to its /nix/store/
teto: i think you want --option builders ssh://foo

teto: it only works with ssh-ng, not with ssh
teto: so if you just replace ssh with ssh-ng in the command it should work.