gistfile1.txt

[root@nas:/etc/nixos/nixcfg]# nix-build '<nixpkgs>' --arg config '{}' --arg overlays '[]' -A hydra
these derivations will be built:
  /nix/store/z1wcic2l41wwsi8klqqayx13myw0hbr3-graphviz-2999.20.0.1.drv
  /nix/store/1jk4qbs1mhxp133b73l8j6j4wvyl37v3-darcs-2.14.0.drv
  /nix/store/57nml2s1bbfwnzpwfj6lrhrncrqb803c-hydra-2017-11-21.drv
building '/nix/store/z1wcic2l41wwsi8klqqayx13myw0hbr3-graphviz-2999.20.0.1.drv' on 'ssh://builder@system76.localnet'...
setupCompilerEnvironmentPhase
...
Data/GraphViz/Printing.hs:348:37: error:
    Ambiguous occurrence ‘<>’
    It could refer to either ‘PP.<>’,
                             imported from ‘Text.PrettyPrint.Leijen.Text.Monadic’ at Data/GraphViz/Printing.hs:(79,1)-(85,68)
                          or ‘Data.Semigroup.<>’,
                             imported from ‘Data.Semigroup’ at Data/GraphViz/Printing.hs:105:24-36
builder for '/nix/store/z1wcic2l41wwsi8klqqayx13myw0hbr3-graphviz-2999.20.0.1.drv' failed with exit code 1
error: build of '/nix/store/z1wcic2l41wwsi8klqqayx13myw0hbr3-graphviz-2999.20.0.1.drv' on 'ssh://builder@system76.localnet' failed: builder for '/nix/store/z1wcic2l41wwsi8klqqayx13myw0hbr3-graphviz-2999.20.0.1.drv' failed with exit code 1
builder for '/nix/store/z1wcic2l41wwsi8klqqayx13myw0hbr3-graphviz-2999.20.0.1.drv' failed with exit code 1
cannot build derivation '/nix/store/1jk4qbs1mhxp133b73l8j6j4wvyl37v3-darcs-2.14.0.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/57nml2s1bbfwnzpwfj6lrhrncrqb803c-hydra-2017-11-21.drv': 1 dependencies couldn't be built
error: build of '/nix/store/57nml2s1bbfwnzpwfj6lrhrncrqb803c-hydra-2017-11-21.drv' failed
[root@nas:/etc/nixos/nixcfg]# nix-instantiate --eval '<nixpkgs>' -A lib.nixpkgsVersion
trace: `lib.nixpkgsVersion` is deprecated, use `lib.version` instead!
"18.09pre140920.5b468ea6b1d"