https://www.cnblogs.com/zxy/p/9235358.html
허가 거부
https://jingyan.baidu.com/article/90808022fa50dbfd90c80f52.html
LS : 모든 리눅스 명령은 -bash를 표시 할 수 없습니다 명령을 찾을 수 없습니다
https://www.cnblogs.com/cnsdhzzl/p/9625736.html
https://blog.csdn.net/sun_81/article/details/86714128
https://blog.csdn.net/qq_19734597/article/details/94971925
과학에 유래를 사용하는 방법
https://blog.csdn.net/weixin_38233274/article/details/80349534