```
error: --- SysError --- nix-daemon
cannot link '/nix/store/.tmp-link-30504-327133527' to '/nix/store/.links/0i0y9b74cx56hxdv150jz527k7lxyjjnz80kpm79svkk6cj9y4l5': File exists
error: --- Error --- nix-daemon
some substitutes for the outputs of derivation '/nix/store/hja0dfcxsni9fili532668kj2b4l22l6-python-2.7.18.drv' failed (usually happens due to networking issues); try '--fallback' to build derivation from source
error: --- Error --- nix-daemon
```