code: public void shutdown() {
      shouldRun = false;
      try {
        if (infoServer != null) infoServer.stop();
      } catch (Exception e) {
        LOG.warn("Exception shutting down SecondaryNameNode", e);
      }
      try {
        if (checkpointImage != null) checkpointImage.close();
      } catch(IOException e) {
        LOG.warn(StringUtils.stringifyException(e));
      }
    }
docs: Shut down this instance of the datanode.
  Returns only after shutdown is complete.