public synchronized static String id(String trackingCode, Context context) {
      if (sID == null) {  
          System.out.println("file creating");
          File installation = new File(context.getFilesDir(), INSTALLATION + "-" + trackingCode);
          try {
              if (!installation.exists())
                  writeInstallationFile(installation);
              sID = readInstallationFile(installation);
          } catch (Exception e) {
              throw new RuntimeException(e);
          }
      } else {
        System.out.println("file exists");
      }
      return sID;
  }