https://blog.gongquiz.com/2020/10/13/pstree-%eb%aa%85%eb%a0%b9%ec%96%b4%eb%a5%bc-%eb%8b%a4%ec%9d%8c%ea%b3%bc-%ea%b0%99%ec%9d%b4-%ec%82%ac%ec%9a%a9-%ed%95%98%ec%98%80%ec%9d%84-%eb%95%8c-%ea%b4%84%ed%98%b8-%ec%95%88%ec%97%90-%ec%95%8c/