Sun. Jan 19th, 2020

NixOS 19.09 released, GNU/Linux distribution

4 min read

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. NixOS has many innovative features:



  • Declarative system configuration model In NixOS, the entire operating system — the kernel, applications, system packages, configuration files, and so on — is built by the Nix package manager from a description in a purely functional build language. The fact that it’s purely functional essentially means that building a new configuration cannot overwrite previous configurations. Most of the other features follow from this.You configure a NixOS system by writing a specification of the functionality that you want on your machine in /etc/nixos/configuration.nix.
  • Reliable upgrades

    Another advantage of purely functional package management is that nixos-rebuild switch will always produce the same result, regardless of what packages or configuration files you already had on your system. Thus, upgrading a system is as reliable as reinstalling from scratch.

  • Atomic upgrades

    NixOS has a transactional approach to configuration management: configuration changes such as upgrades are atomic. This means that if the upgrade to a new configuration is interrupted — say, the power fails half-way through — the system will still be in a consistent state: it will either boot in the old or the new configuration. In most other systems, you’ll end up in an inconsistent state, and your machine may not even boot anymore.

  • Rollbacks

    Because the files of a new configuration don’t overwrite old ones, you can (atomically) roll back to a previous configuration. For instance, if after a nixos-rebuild switch you discover that you don’t like the new configuration, you can just go back: $ nixos-rebuild switch –rollback

  • Reproducible system configurations

    NixOS’s declarative configuration model makes it easy to reproduce a system configuration on another machine (for instance, to test a change in a test environment before doing it on the production server). You just copy the configuration.nix file to the target NixOS machine and run nixos-rebuild switch. This will give you the same configuration (kernel, applications, system services, and so on) except for ‘mutable state’ (such as the stuff that lives in /var).

  • Safe to test changesNixOS makes it safe to test potentially dangerous changes to the system because you can always roll back. (Unless you screw up the bootloader, that is…) For instance, whether the change is as simple as enabling a system service, or as large as rebuilding the entire system with a new version of Glibc, you can test it by doing: $ nixos-rebuild test
  • Source-based model, with binaries. The Nix build language used by NixOS specifies how to build packages from source. This makes it easy to adapt the system — just edit any of the ‘Nix expressions’ for NixOS or Nixpkgs in/etc/nixos, and run nixos-rebuild. However, building from source is also slow. Therefore Nix automatically downloads pre-built binaries from if they are available. This gives the flexibility of a source-based package management model with the efficiency of a binary model.
  • Consistency The Nix package manager ensures that the running system is ‘consistent’ with the logical specification of the system, meaning that it will rebuild all packages that need to be rebuilt. For instance, if you change the kernel, Nix will ensure that external kernel modules such as the NVIDIA driver will be rebuilt as well — so you never run into an X server that mysteriously fails to start after a kernel security upgrade. And if you update the OpenSSL library, Nix ensures that all packages in the system use the new version, even packages that statically link against OpenSSL.
  • Multi-user package management On NixOS, you do not need to be root to install the software. In addition to the system-wide ‘profile’ (set of installed packages), all users have their own profile in which they can install packages. Nix allows multiple versions of a package to coexist, so different users can have different versions of the same package installed in their respective profiles. If two users install the same version of a package, only one copy will be built or downloaded, and Nix’s security model ensures that this is secure. Users cannot install setuid binaries.

NixOS 19.09 released.


  • End of support is planned for end of April 2020, handing over to 20.03.
  • PHP now defaults to PHP 7.3, updated from 7.2.
  • PHP 7.1 is no longer supported due to upstream not supporting this version for the entire lifecycle of the 19.09 release.
  • The binfmt module is now easier to use. Additional systems can be added through boot.binfmt.emulatedSystems. For instance, boot.binfmt.emulatedSystems = [ "wasm32-wasi" "x86_64-windows" "aarch64-linux" ]; will set up binfmt interpreters for each of those listed systems.
  • The installer now uses a less privileged nixos user whereas before we logged in as root. To gain root privileges use sudo -i without a password.
  • We’ve updated to Xfce 4.14, which brings a new module services.xserver.desktopManager.xfce4-14. If you’d like to upgrade, please switch from the services.xserver.desktopManager.xfce module as it will be deprecated in a future release. They’re incompatibilities with the current Xfce module; it doesn’t support thunarPlugins and it isn’t recommended to use services.xserver.desktopManager.xfce and services.xserver.desktopManager.xfce4-14 simultaneously or to downgrade from Xfce 4.14 after upgrading.
  • The GNOME 3 desktop manager module sports an interface to enable/disable core services, applications, and optional GNOME packages like games.