code: protected void reportFatalError(TaskAttemptID id, Throwable throwable, 
                                    String logMsg) {
      LOG.fatal(logMsg);
      Throwable tCause = throwable.getCause();
      String cause = tCause == null 
                     ? StringUtils.stringifyException(throwable)
                     : StringUtils.stringifyException(tCause);
      try {
        umbilical.fatalError(id, cause);
      } catch (IOException ioe) {
        LOG.fatal("Failed to contact the tasktracker", ioe);
        System.exit(-1);
      }
    }
docs: Report a fatal error to the parent (task) tracker.