- The storage format of the server key has changed and the key must be converted before running the new release.

  - When updating multiple database servers, turn off the database servers from the highest IP down to the lowest with resting periods in between. Start up in reverse order. Do not concurrently run database servers working with different OpenAFS releases!

  - Update servers first, then clients.

- Radicale's default package has changed from 2.x to 3.x. An upgrade checklist can be found [here](https://github.com/Kozea/Radicale/blob/3.0.x/NEWS.md#upgrade-checklist). You can use the newer version in the NixOS service by setting the `package` to `radicale3`, which is done automatically if `stateVersion` is 20.09 or higher.

- `udpt` experienced a complete rewrite from C++ to rust. The configuration format changed from ini to toml. The new configuration documentation can be found at [the official website](https://naim94a.github.io/udpt/config.html) and example configuration is packaged in `${udpt}/share/udpt/udpt.toml`.

- We now have a unified [services.xserver.displayManager.autoLogin](options.html#opt-services.xserver.displayManager.autoLogin) option interface to be used for every display-manager in NixOS.

- The `bitcoind` module has changed to multi-instance, using submodules. Therefore, it is now mandatory to name each instance. To use this new multi-instance config with an existing bitcoind data directory and user, you have to adjust the original config, e.g.:

  ```nix
  {
    services.bitcoind = {
      enable = true;
      extraConfig = "...";
      # ...
    };
  }
  ```

  To something similar:

  ```nix
  {
    services.bitcoind.mainnet = {
      enable = true;
      dataDir = "/var/lib/bitcoind";
      user = "bitcoin";
      extraConfig = "...";
      # ...
    };
  }
  ```

  The key settings are:

  - `dataDir` - to continue using the same data directory.

  - `user` - to continue using the same user so that bitcoind maintains access to its files.

- Graylog introduced a change in the LDAP server certificate validation behaviour for version 3.3.3 which might break existing setups. When updating Graylog from a version before 3.3.3 make sure to check the Graylog [release info](https://www.graylog.org/post/announcing-graylog-v3-3-3) for information on how to avoid the issue.

- The `dokuwiki` module has changed to multi-instance, using submodules. Therefore, it is now mandatory to name each instance. Moreover, forcing SSL by default has been dropped, so `nginx.forceSSL` and `nginx.enableACME` are no longer set to `true`. To continue using your service with the original SSL settings, you have to adjust the original config, e.g.:

  ```nix
  {
    services.dokuwiki = {
      enable = true;
      # ...
    };
  }
  ```

  To something similar:

  ```nix
  {
    services.dokuwiki."mywiki" = {
      enable = true;
      nginx = {
        forceSSL = true;
        enableACME = true;
      };
      # ...
    };
  }
  ```

  The base package has also been upgraded to the 2020-07-29 "Hogfather" release. Plugins might be incompatible or require upgrading.

- The [services.postgresql.dataDir](options.html#opt-services.postgresql.dataDir) option is now set to `"/var/lib/postgresql/${cfg.package.psqlSchema}"` regardless of your [system.stateVersion](options.html#opt-system.stateVersion). Users with an existing postgresql install that have a [system.stateVersion](options.html#opt-system.stateVersion) of `17.03` or below should double check what the value of their [services.postgresql.dataDir](options.html#opt-services.postgresql.dataDir) option is (`/var/db/postgresql`) and then explicitly set this value to maintain compatibility:

  ```nix
  {
    services.postgresql.dataDir = "/var/db/postgresql";
  }
  ```

  The postgresql module now expects there to be a database super user account called `postgres` regardless of your [system.stateVersion](options.html#opt-system.stateVersion). Users with an existing postgresql install that have a [system.stateVersion](options.html#opt-system.stateVersion) of `17.03` or below should run the following SQL statements as a database super admin user before upgrading: