不知怎麼了，ubuntu11.04的源這幾天開始不能用了，找了好久才找到可以用的。
先備份一下/etc/apt/sources.list，然後用以下內容替換掉整個文件
deb http://mirrors.163.com/ubuntu/ oneiric main universe restricted multiverse
deb-src http://mirrors.163.com/ubuntu/ oneiric main universe restricted multiverse
deb http://mirrors.163.com/ubuntu/ oneiric-security universe main multiverse restricted
deb-src http://mirrors.163.com/ubuntu/ oneiric-security universe main multiverse restricted
deb http://mirrors.163.com/ubuntu/ oneiric-updates universe main multiverse restricted
deb http://mirrors.163.com/ubuntu/ oneiric-proposed universe main multiverse restricted
deb-src http://mirrors.163.com/ubuntu/ oneiric-proposed universe main multiverse restricted
deb http://mirrors.163.com/ubuntu/ oneiric-backports universe main multiverse restricted
deb-src http://mirrors.163.com/ubuntu/ oneiric-backports universe main multiverse restricted
deb-src http://mirrors.163.com/ubuntu/ oneiric-updates universe main multiverse restricted保存後執行一下sudo apt-get update就可以了。