sudo: unable to resolve host ****
解决：
修改了/etc/hostname之后，还要修改/etc/hosts
参考 http://ubuntuforums.org/showthread.php?t=799896
Yup. If you change the hostname in /etc/hostname, you must also fix up /etc/hosts so the new name resolves to 127.0.0.1. The safest way is to edit hosts and add the new name, then edit hostname, then go back to hosts to remove the old hstname.
