In addition to numerous new and upgraded packages, this release has the following highlights: You can now pin a specific version of NixOS in your configuration.nix by setting: nixos.path = ./nixpkgs-unstable-2015-12-06/nixos; This will make NixOS re-evaluate your configuration with the modules of the specified NixOS version at the given path. For more details, see Firefox and similar browsers are now wrapped by default. The package and attribute names are plain firefox or midori, etc. Backward-compatibility attributes were set up, but note that nix-env -u will not update your current firefox-with-plugins; you have to uninstall it and install firefox instead. More discussion is on the PR. The following new services were added since the last release: services/monitoring/longview.nix services/web-apps/pump.io.nix When upgrading from a previous release, please be aware of the following incompatible changes: wmiiSnap has been replaced with wmii_hg, but services.xserver.windowManager.wmii.enable has been updated respectively so this only affects you if you have explicitly installed wmiiSnap. jobs NixOS option has been removed. It served as compatibility layer between Upstart jobs and SystemD services. All services have been rewritten to use systemd.services wmiimenu is removed, as it has been removed by the developers upstream. Use wimenu from the wmii-hg package. Gitit is no longer automatically added to the module list in NixOS and as such there will not be any manual entries for it. You will need to add an import statement to your NixOS configuration in order to use it, e.g. ]; } ]]> will include the Gitit service configuration options. nginx does not accept flags for enabling and disabling modules anymore. Instead it accepts modules argument, which is a list of modules to be built in. All modules now reside in nginxModules set. Example configuration: s3sync is removed, as it hasn't been developed by upstream for 4 years and only runs with ruby 1.8. For an actively-developer alternative look at tarsnap and others. ruby_1_8 has been removed as it's not supported from upstream anymore and probably contains security issues. tidy-html5 package is removed. Upstream only provided (lib)tidy5 during development, and now they went back to (lib)tidy to work as a drop-in replacement of the original package that has been unmaintained for years. You can (still) use the html-tidy package, which got updated to a stable release from this new upstream. extraDeviceOptions argument is removed from bumblebee package. Instead there are now two separate arguments: extraNvidiaDeviceOptions and extraNouveauDeviceOptions for setting extra X11 options for nvidia and nouveau drivers, respectively. The Ctrl+Alt+Backspace key combination no longer kills the X server by default. There's a new option services.xserver.enableCtrlAltBackspace allowing to enable the combination again. emacsPackagesNg now contains all packages from the ELPA, MELPA, and MELPA Stable repositories. Data directory for Postfix MTA server is moved from /var/postfix to /var/lib/postfix. Old configurations are migrated automatically. service.postfix module has also received many improvements, such as correct directories' access rights, new aliasFiles and mapFiles options and more. Other notable improvements: The command-not-found hook was extended. Apart from $NIX_AUTO_INSTALL variable, it newly also checks for $NIX_AUTO_RUN which causes it to directly run the missing commands via nix-shell (without installing anything). ejabberd module is brought back and now works on NixOS.