Make sure you set the `_netdev` option for each of the file systems referring to block devices provided by the autoLuks module. Not doing this might render the system in a state where it doesn't boot anymore.
If you are actively using the `autoLuks` module please let us know in [issue \#62211](https://github.com/NixOS/nixpkgs/issues/62211).
- The setopt declarations will be evaluated at the end of `/etc/zshrc`, so any code in [programs.zsh.interactiveShellInit](options.html#opt-programs.zsh.interactiveShellInit), [programs.zsh.loginShellInit](options.html#opt-programs.zsh.loginShellInit) and [programs.zsh.promptInit](options.html#opt-programs.zsh.promptInit) may break if it relies on those options being set.
- The `prometheus-nginx-exporter` package now uses the official exporter provided by NGINX Inc. Its metrics are differently structured and are incompatible to the old ones. For information about the metrics, have a look at the [official repo](https://github.com/nginxinc/nginx-prometheus-exporter).
- The `shibboleth-sp` package has been updated to version 3. It is largely backward compatible, for further information refer to the [release notes](https://wiki.shibboleth.net/confluence/display/SP3/ReleaseNotes) and [upgrade guide](https://wiki.shibboleth.net/confluence/display/SP3/UpgradingFromV2).
Nodejs 8 is scheduled EOL under the lifetime of 19.09 and has been dropped.
- By default, prometheus exporters are now run with `DynamicUser` enabled. Exporters that need a real user, now run under a separate user and group which follow the pattern `<exporter-name>-exporter`, instead of the previous default `nobody` and `nogroup`. Only some exporters are affected by the latter, namely the exporters `dovecot`, `node`, `postfix` and `varnish`.
- The `ibus-qt` package is not installed by default anymore when [i18n.inputMethod.enabled](options.html#opt-i18n.inputMethod.enabled) is set to `ibus`. If IBus support in Qt 4.x applications is required, add the `ibus-qt` package to your [environment.systemPackages](options.html#opt-environment.systemPackages) manually.
- The CUPS Printing service now uses socket-based activation by default, only starting when needed. The previous behavior can be restored by setting `services.cups.startWhenNeeded` to `false`.
- The `services.systemhealth` module has been removed from nixpkgs due to lack of maintainer.
- The `services.mantisbt` module has been removed from nixpkgs due to lack of maintainer.
- Squid 3 has been removed and the `squid` derivation now refers to Squid 4.
- The `services.pdns-recursor.extraConfig` option has been replaced by `services.pdns-recursor.settings`. The new option allows setting extra configuration while being better type-checked and mergeable.
- No service depends on `keys.target` anymore which is a systemd target that indicates if all [NixOps keys](https://nixos.org/nixops/manual/#idm140737322342384) were successfully uploaded. Instead, `<key-name>-key.service` should be used to define a dependency of a key in a service. The full issue behind the `keys.target` dependency is described at [NixOS/nixpkgs\#67265](https://github.com/NixOS/nixpkgs/issues/67265).
The following services are affected by this:
- [`services.dovecot2`](options.html#opt-services.dovecot2.enable)
- [`services.nsd`](options.html#opt-services.nsd.enable)
- [`services.softether`](options.html#opt-services.softether.enable)
- [`services.strongswan`](options.html#opt-services.strongswan.enable)
- [`services.strongswan-swanctl`](options.html#opt-services.strongswan-swanctl.enable)
- [`services.httpd`](options.html#opt-services.httpd.enable)
- The `security.acme.directory` option has been replaced by a read-only `security.acme.certs.<cert>.directory` option for each certificate you define. This will be a subdirectory of `/var/lib/acme`. You can use this read-only option to figure out where the certificates are stored for a specific certificate. For example, the `services.nginx.virtualhosts.<name>.enableACME` option will use this directory option to find the certs for the virtual host.