1.)输入：sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup //此为保存当前的源列表
2.)输入：sudo gedit /etc/apt/sources.list //此为编辑源列表
此时会用gedit打开源列表，全选后，复制以下横线之间的内容覆盖原有的全部内容：
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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
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做好这一步之后，保存好编辑过的源后关闭sources.list，然后回到终端，继续输入以下命令：
3.)输入：sudo apt-get update
4.)输入：sudo apt-get dist-upgrade
呵呵，只要以上没出错的话，源已经成功换成了cn99的源了，这时接下来要做的就是要配置好中文环境了，这里就不多说了哦。^_^