code: def Run(self, arg):
      
      try:
        if self.grr_worker.client.FleetspeakEnabled():
          raise ValueError("Not supported on Fleetspeak enabled clients.")
      except AttributeError:
        pass
  
      smart_arg = {str(field): value for field, value in iteritems(arg)}
  
      disallowed_fields = [
          field for field in smart_arg
          if field not in UpdateConfiguration.UPDATABLE_FIELDS
      ]
  
      if disallowed_fields:
        raise ValueError("Received an update request for restricted field(s) %s."
                         % ",".join(disallowed_fields))
  
      if platform.system() != "Windows":
        # Check config validity before really applying the changes. This isn't
        # implemented for our Windows clients though, whose configs are stored in
        # the registry, as opposed to in the filesystem.
  
        canary_config = config.CONFIG.CopyConfig()
  
        # Prepare a temporary file we'll write changes to.
        with tempfiles.CreateGRRTempFile(mode="w+") as temp_fd:
          temp_filename = temp_fd.name
  
        # Write canary_config changes to temp_filename.
        canary_config.SetWriteBack(temp_filename)
        self._UpdateConfig(smart_arg, canary_config)
  
        try:
          # Assert temp_filename is usable by loading it.
          canary_config.SetWriteBack(temp_filename)
        # Wide exception handling passed here from config_lib.py...
        except Exception:  # pylint: disable=broad-except
          logging.warning("Updated config file %s is not usable.", temp_filename)
          raise
  
        # If temp_filename works, remove it (if not, it's useful for debugging).
        os.unlink(temp_filename)
  
      # The changes seem to work, so push them to the real config.
      self._UpdateConfig(smart_arg, config.CONFIG)
docs: Does the actual work.