code: private static String[] adjustConf(String[] argv, Configuration conf) {
      String[] serviceId = new String[] { "" };
      String[] filteredArgv = DFSUtil.getServiceName(argv, serviceId);
      
      if (!serviceId[0].equals("")) {
        NameNode.checkServiceName(conf, serviceId[0]);
        DFSUtil.setGenericConf(conf, serviceId[0],
            NameNode.NAMESERVICE_SPECIFIC_KEYS);
        NameNode.setupDefaultURI(conf);
      }
      
      // make it avatar aware (manual option)
      if (optionExist(argv, "-one")) {
        updateConfKeys(conf, "1", serviceId[0]);
      } else {
        updateConfKeys(conf, "0", serviceId[0]);
      }
      return filteredArgv;
    }
docs: Adjusts configuration for nameservice keys. Also uses avatar-aware trick,
  so we can use fsck without ZK, also during failover, manually by specifying
  zero/one option.