Configuration file '/etc/sudoers'
 ==> Modified (by you or by a script) since installation.
 ==> Package distributor has shipped an updated version.
   What would you like to do about it ?  Your options are:
    Y or I  : install the package maintainer's version
    N or O  : keep your currently-installed version
      D     : show the differences between the versions
      Z     : start a shell to examine the situation
 The default action is to keep your current version.
*** sudoers (Y/I/N/O/D/Z) [default=N] ? Y

Installing new version of config file /etc/sudoers ...

sudo apt-get upgrade時遇到這個選項，這裡千萬千萬不要選擇Y，選擇了Y意味著所有sudo使用者都會被覆蓋掉，之前的配置都沒有了。我選擇這個Y之後，現在已經沒有人有我們伺服器的sudo許可權了。。。大坑啊。。。