以下内容为reed个人见解，不保证内容的准确性，仅供参考讨论，如有错误之处，万望提出！由于工作需要，Linux下经常在各个用户之间切换，所以经常用到这个命令:su -，因为一直用这个命令，所以也没留意su后面为什么要加一个横杠，不加的话有什么区别。今天脑海里一直浮现su和su – 有什么区别，既然有疑问，就要解决之，哪怕是最基本最简单的问题。
————————————————————————————-A.用info su命令查看帮助如下（不用翻译啦，大概看的明白吧）:1）默认的su，也就是不加参数By default, `su’ does not change the current directory. It sets theenvironment variables `HOME’ and `SHELL’ from the password entry forUSER, and if USER is not the super-user, sets `USER’ and `LOGNAME’ toUSER. By default, the shell is not a login shell.2）su加’-‘/’-l’/’–login’参数`-‘`-l’`–login’Make the shell a login shell. This means the following. Unset allenvironment variables except `TERM’, `HOME’, and `SHELL’ (whichare set as described above), and `USER’ and `LOGNAME’ (which areset, even for the super-user, as described above), and set `PATH’to a compiled-in default value. Change to USER’s home directory.Prepend `-‘ to the shell’s name, intended to make it read itslogin startup file(s). Additionaly `DISPLAY’ and `XAUTHORITY’environment variables are preserved as well for PAM functionality.
B.再看看2个例子：1.例子1，现有reed普通用户，，用su切换root用户。
例子1用[su]命令切换root用户，从例子看出的确是切换到root用户了，但是工作目录和环境变量竟然还是reed的，用useradd命令竟然提示找不到。
不求与人相比，但求超越自己，要哭就哭出激动的泪水，要笑就笑出成长的性格。
