$ sudo /run/current-system/fine-tune/child-1/bin/switch-to-configuration test
  ```

- The Nginx log directory has been moved to `/var/log/nginx`, the cache directory to `/var/cache/nginx`. The option `services.nginx.stateDir` has been removed.

- The httpd web server previously started its main process as root privileged, then ran worker processes as a less privileged identity user. This was changed to start all of httpd as a less privileged user (defined by [services.httpd.user](options.html#opt-services.httpd.user) and [services.httpd.group](options.html#opt-services.httpd.group)). As a consequence, all files that are needed for httpd to run (included configuration fragments, SSL certificates and keys, etc.) must now be readable by this less privileged user/group.

  The default value for [services.httpd.mpm](options.html#opt-services.httpd.mpm) has been changed from `prefork` to `event`. Along with this change the default value for [services.httpd.virtualHosts.\<name\>.http2](options.html#opt-services.httpd.virtualHosts) has been set to `true`.

- The `systemd-networkd` option `systemd.network.networks.<name>.dhcp.CriticalConnection` has been removed following upstream systemd's deprecation of the same. It is recommended to use `systemd.network.networks.<name>.networkConfig.KeepConfiguration` instead. See systemd.network 5 for details.

- The `systemd-networkd` option `systemd.network.networks._name_.dhcpConfig` has been renamed to [systemd.network.networks._name_.dhcpV4Config](options.html#opt-systemd.network.networks._name_.dhcpV4Config) following upstream systemd's documentation change. See systemd.network 5 for details.

- In the `picom` module, several options that accepted floating point numbers encoded as strings (for example [services.picom.activeOpacity](options.html#opt-services.picom.activeOpacity)) have been changed to the (relatively) new native `float` type. To migrate your configuration remove the quotes around the numbers.

- When using `buildBazelPackage` from Nixpkgs, `flat` hash mode is now used for dependencies instead of `recursive`. This is to better allow using hashed mirrors where needed. As a result, these hashes will have changed.

- The syntax of the PostgreSQL configuration file is now checked at build time. If your configuration includes a file inaccessible inside the build sandbox, set `services.postgresql.checkConfig` to `false`.

- The rkt module has been removed, it was archived by upstream.

- The [Bazaar](https://bazaar.canonical.com) VCS is unmaintained and, as consequence of the Python 2 EOL, the packages `bazaar` and `bazaarTools` were removed. Breezy, the backward compatible fork of Bazaar (see the [announcement](https://www.jelmer.uk/breezy-intro.html)), was packaged as `breezy` and can be used instead.

  Regarding Nixpkgs, `fetchbzr`, `nix-prefetch-bzr` and Bazaar support in Hydra will continue to work through Breezy.

- In addition to the hostname, the fully qualified domain name (FQDN), which consists of `${networking.hostName}` and `${networking.domain}` is now added to `/etc/hosts`, to allow local FQDN resolution, as used by the `hostname --fqdn` command and other applications that try to determine the FQDN. These new entries take precedence over entries from the DNS which could cause regressions in some very specific setups. Additionally the hostname is now resolved to `127.0.0.2` instead of `127.0.1.1` to be consistent with what `nss-myhostname` (from systemd) returns. The old behaviour can e.g. be restored by using `networking.hosts = lib.mkForce { "127.0.1.1" = [ config.networking.hostName ]; };`.

- The hostname (`networking.hostName`) must now be a valid DNS label (see RFC 1035, RFC 1123) and as such must not contain the domain part. This means that the hostname must start with a letter or digit, end with a letter or digit, and have as interior characters only letters, digits, and hyphen. The maximum length is 63 characters. Additionally it is recommended to only use lower-case characters. If (e.g. for legacy reasons) a FQDN is required as the Linux kernel network node hostname (`uname --nodename`) the option `boot.kernel.sysctl."kernel.hostname"` can be used as a workaround (but be aware of the 64 character limit).