When upgrading from a previous release, please be aware of the following incompatible changes:

- We no longer produce graphical ISO images and VirtualBox images for `i686-linux`. A minimal ISO image is still provided.

- 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.

- `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.

  ```nix
  {
    imports = [ <nixpkgs/nixos/modules/services/misc/gitit.nix> ];
  }
  ```

  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:

  ```nix
  nginx.override {
    modules = [ nginxModules.rtmp nginxModules.dav nginxModules.moreheaders ];
  }
  ```

- `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.

- Filesystem options should now be configured as a list of strings, not a comma-separated string. The old style will continue to work, but print a warning, until the 16.09 release. An example of the new style:

  ```nix
  {
    fileSystems."/example" = {
      device = "/dev/sdc";
      fsType = "btrfs";
      options = [ "noatime" "compress=lzo" "space_cache" "autodefrag" ];
    };
  }
  ```

- CUPS, installed by `services.printing` module, now has its data directory in `/var/lib/cups`. Old configurations from `/etc/cups` are moved there automatically, but there might be problems. Also configuration options `services.printing.cupsdConf` and `services.printing.cupsdFilesConf` were removed because they had been allowing one to override configuration variables required for CUPS to work at all on NixOS. For most use cases, `services.printing.extraConf` and new option `services.printing.extraFilesConf` should be enough; if you encounter a situation when they are not, please file a bug.