public void stop() throws Exception {
    if (server == null) {
      throw new AmbariException("Error stopping the server");
    } else {
      try {
        server.stop();
      } catch (Exception e) {
        LOG.error("Error stopping the server", e);
      }
    }
  }
Creates default users if in-memory database is used
ambari-server/src/main/java/org/apache/ambari/server/controller/AmbariServer.java