設置Ubuntu源
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup
sudo gedit /etc/apt/sources.list
Ubuntu 官方源：
deb http://archive.ubuntu.com/ubuntu/ feisty main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ feisty-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ feisty-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ feisty-proposed main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ feisty-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ feisty main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ feisty-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ feisty-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ feisty-proposed main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ feisty-backports main restricted universe multiverse
sudo apt-get update
sudo apt-get dist-upgrade
