1.ln功能很强大，在于如果系统中重复安装了一些东西，而又找不到的话，ln过去就有了，比如mysql socket问题
2if you want sudo without prompt password,

edit /etc/sudoers

and add:

username ALL=(ALL) NOPASSWD: ALL

save and that’s it.

the username is the user you want to give doing sudo without password.