- better make a backup of source list first

sudo cp /etc/apt/sources.list /etc/apt/sources.list_backup

- add such text to the end of souces.list as follows:

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

快速设置指南／FeistyFawn-Ubuntu

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