据说国内163的更新源速度很快。 今天换上。 其他源全部丢弃！
测试一下。 效果真的明显。
deb http://mirrors.163.com/ubuntu/ natty main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ natty-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ natty-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ natty-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ natty-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ natty main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ natty-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ natty-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ natty-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ natty-backports main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ natty main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ natty-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ natty-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ natty-proposed main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ natty-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ natty main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ natty-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ natty-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ natty-proposed main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ natty-backports main restricted universe multiverse