mkdir命令是常用的命令，用來建立空目錄，它還有2個常用參數：
- -m, --mode=模式 設定權限<模式> (類似 chmod)，而不是 rwxrwxrwx 減 umask
- -p, --parents 需要時創建上層目錄，如目錄早已存在則不當作錯誤
下面是英文原版
-m, --mode=MODE set file mode (as in chmod), not a=rwx - umask
-p, --parents no error if existing, make parent directories as needed
-v, --verbose print a message for each created directory
-Z set SELinux security context of each created directory
to the default type
--context[=CTX] like -Z, or if CTX is specified then set the SELinux
or SMACK security context to CTX
--help display this help and exit
--version output version information and exit