code: public static void error(String msg, Throwable t) {
          if (quietMode)
              return;
  
          System.err.println(ERR_PREFIX + msg);
          if (t != null) {
              t.printStackTrace();
          }
      }
docs: This method is used to output log4j internal error
  statements. There is no way to disable error statements.
  Output goes to <code>System.err</code>.