Nix does not have libraries in the dynamic linking library path, they are made available for linking by specifying the library's derivation as a dependency. The

Nix does not have libraries in the dynamic linking library path, they are made available for linking by specifying the library's derivation as a dependency. There is no such thing as e.g. a global glibc or readline. E.g.: % ldd $(which nc) | grep ssl libtls.so.18 => /nix/store/s6j0yd68cnfb4mv76lyrb413qhhac57g-libressl-2.8.3/lib/libtls.so.18 (0x00007f8875f6d000) libssl.so.46 => /nix/store/s6j0yd68cnfb4mv76lyrb413qhhac57g-libressl-2.8.3/lib/libssl.so.46 (0x00007f8875f1a000) libcrypto.so.44 => /nix/store/s6j0yd68cnfb4mv76lyrb413qhhac57g-libressl-2.8.3/lib/libcrypto.so.44 (0x00007f8875d3b000) A binary or library always links against a specific version of a library. This is why in Nix, you can have several versions of a library installed in parallel. The initial part of the path after /nix/store is the hash of the derivation used to build this version of libressl and all of its recursive dependencies. Furthermore, Nix can build packages in a sandbox (which is the default on NixOS) to avoid accidental dependencies. Consequently, a Python derivation that depends on readline would have a different hash than one that does not depend on readline.