NixOS Build Reproducibility: Better Than You Think
NixOS's build reproducibility has long been a point of contention. While its functional package manager model contributes to build reproducibility, it doesn't guarantee bitwise reproducibility for all builds. A new research paper empirically studies Nixpkgs (NixOS's package collection) over six years, revealing a steadily increasing reproducibility rate—from 69% in 2017 to 91% in April 2023. The study also identifies prevalent causes of non-reproducibility, such as embedded dates, uname outputs, environment variables, and build IDs. These findings demonstrate that while Nixpkgs already achieves high reproducibility rates, there's room for improvement by addressing these low-hanging fruits. This research is crucial for increasing trust in the Nix substitution protocol and driving the development of distributed caching solutions based on build reproducibility.