http://www.opennaru.com/linux/%eb%a0%88%eb%93%9c%ed%96%87-%eb%a6%ac%eb%88%85%ec%8a%a4-%ec%9b%8c%ed%81%ac%ec%8a%a4%ed%85%8c%ec%9d%b4%ec%85%98-%ec%b0%a8%ec%9d%b4%ec%a0%90/