Log error message if allowed-users in nix.conf does not allow to read store

[SuperSandro2000]

Right now if the allowed-users setting does not allow the harmonia user to connect to the nix-daemon only missed hash is returned.
It would be better for debugging if at least an error would be logged.

[Mic92]

What would be the nix command to check that?

[SuperSandro2000]

To check what? If allowed-users is set? That can be read with nix show-config.

[kristoff3r]

I'm hitting the exact same issue, except even more severe. The cause seems to be NixOS/nix#9071, and the only workaround I found was to set nix.settings.allowed-users = ["*"].

I suggest adding a service user until that issue is fixed (or a documented workaround is found), adding some logging for file permission errors that are printed by default, and returning a slightly better error.

[Mic92]

Yeah, we should disable dynamic user than.

[Mic92]

This one disables DynamicUser now in nixpkgs: NixOS/nixpkgs#268303

[Mic92]

Consider this solution good enough for now.

[SuperSandro2000]

But we still don't display a proper error message and instead pretend that the store entry doesn't exist which is rather confusing.

[Mic92]

Ok, but when using the nixos module, how does one get into this situation in the first place?

[SuperSandro2000]

Then it's probably not happening but in case anyone runs into that bug again, maybe because of something different off with their nix-daemon, then they are probably as confused as me and take longer than necessary to find the issue.

[Mic92]

I am open to accept a patch that implement this.

[SuperSandro2000]

Can you just re-open the issue? I have no idea how to properly implement this.