NixOS is a GNU/Linux distribution that aims to improve the state of the art in system configuration management. In existing distributions, actions such as upgrades are dangerous: upgrading a package can cause other packages to break, upgrading an entire system is much less reliable than reinstalling from scratch, you can’t safely test what the results of a configuration change will be, you cannot easily undo changes to the system, and so on. We want to change that. NixOS has many innovative features: