ubuntu 11.04版本，在sources.list里面填写以下源：
deb https://archive.ubuntu.com/ubuntu/ natty main restricted universe multiverse
deb https://archive.ubuntu.com/ubuntu/ natty-security main restricted universe multiverse
deb https://archive.ubuntu.com/ubuntu/ natty-updates main restricted universe multiverse
deb https://archive.ubuntu.com/ubuntu/ natty-proposed main restricted universe multiverse
deb https://archive.ubuntu.com/ubuntu/ natty-backports main restricted universe multiverse
deb-src https://archive.ubuntu.com/ubuntu/ natty main restricted universe multiverse
deb-src https://archive.ubuntu.com/ubuntu/ natty-security main restricted universe multiverse
deb-src https://archive.ubuntu.com/ubuntu/ natty-updates main restricted universe multiverse
deb-src https://archive.ubuntu.com/ubuntu/ natty-proposed main restricted universe multiverse
deb-src https://archive.ubuntu.com/ubuntu/ natty-backports main restricted universe multiversedeb htt
