Method 1:
> grub --> recovery mode --> e
> ro single <--> rw single init=/bin/bash
> ctrl + x
> chmod 0440 /etc/sudoers
Method 2:
> pkexec chmod 0440 /etc/sudoers
Change Sudoers Mod 777 To 0440
原文：http://blog.csdn.net/kallen_ding/article/details/40108279
