ubuntu自带的更新源很慢的，大家可以试试这个，速度比较快哦！

deb http://ubuntu.cn99.com/ubuntu/ gutsy main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ gutsy-security main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ gutsy-updates main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ gutsy-proposed main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ gutsy-backports main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ gutsy main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ gutsy-security main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ gutsy-updates main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ gutsy-proposed main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ gutsy-backports main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu-cn/ gutsy main restricted universe multiverse