code: @Override
      public void close() throws IOException {
          isOpen();
          int ret = WDT.close(fd);
          if(ret<0) {
              throw new IOException("Close file " + filename + " got " + ret + " back.");
          }
          fd=-1;
      }
docs: Close a watchdog (file). If close without {@link disable} Raspberry reboot after
  timeout expired.
  
  @throws IOException