private static String checkHadoopHome() {

    // first check the Dflag hadoop.home.dir with JVM scope
    String home = System.getProperty("hadoop.home.dir");

    // fall back to the system/user-global env variable
    if (home == null) {
      home = System.getenv("HADOOP_HOME");
    }

    try {
       // couldn't find either setting for hadoop's home directory
       if (home == null) {
         throw new IOException("HADOOP_HOME or hadoop.home.dir are not set.");
       }

       if (home.startsWith("\"") && home.endsWith("\"")) {
         home = home.substring(1, home.length()-1);
       }

       // check that the home setting is actually a directory that exists
       File homedir = new File(home);
       if (!homedir.isAbsolute() || !homedir.exists() || !homedir.isDirectory()) {
         throw new IOException("Hadoop home directory " + homedir
           + " does not exist, is not a directory, or is not an absolute path.");
       }

       home = homedir.getCanonicalPath();

    } catch (IOException ioe) {
      if (LOG.isDebugEnabled()) {
        LOG.debug("Failed to detect a valid hadoop home directory", ioe);
      }
      home = null;
    }
    
    return home;
  }