添加国内源有个好处，比如下载软件时直接时国内的服务器，速度有保证。
以下是操作方法：
1、备份
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
2、编辑
sudo gedit /etc/apt/sources.list
提示：可以使用vi、vim这些
3、覆盖源文件的所有内容
# deb cdrom:[Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)]/ xenial main restricted deb-src http://archive.ubuntu.com/ubuntu xenial main restricted
#Added by software-properties deb http://mirrors.aliyun.com/ubuntu/ xenial main restricted deb-src http://mirrors.aliyun.com/ubuntu/ xenial main restricted multiverse universe
#Added by software-properties deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted multiverse universe
#Added by software-properties deb http://mirrors.aliyun.com/ubuntu/ xenial universe deb http://mirrors.aliyun.com/ubuntu/ xenial-updates universe deb http://mirrors.aliyun.com/ubuntu/ xenial multiverse deb http://mirrors.aliyun.com/ubuntu/ xenial-updates multiverse deb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse
#Added by software-properties deb http://archive.canonical.com/ubuntu xenial partner deb-src http://archive.canonical.com/ubuntu xenial partner deb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted multiverse universe
#Added by software-properties deb http://mirrors.aliyun.com/ubuntu/ xenial-security universe deb http://mirrors.aliyun.com/ubuntu/ xenial-security multiverse
4、更新
#升级软件列表
sudo apt-get update
#系统将现有的Package升级,如果有相依性的问题，而此相依性需要安装其它新的Package或影响到其它Package的相依性时，此Package就不会被升级，会保留下来。
#还有种说法时更新软件，但是会更新系统内核，大版本不变，不完全可靠的消息，没经过测试
sudo apt-get upgrade
#可以聪明的解决相依性的问题，如果有相依性问题，需要安装/移除新的Package，就会试着去安装/移除它。会识别出当依赖关系改变的情形并作出处理，而upgrade对此情形不处理。
sudo apt-get dist-upgrade
提示：通常更新源之后只需要升级软件列表即可。其余两项小心使用。
163源：
可以尝试以下163的源，可能会意想不到的的快。
deb http://mirrors.163.com/ubuntu/ wily main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ wily-security main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ wily-updates main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ wily-proposed main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ wily-backports main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ wily main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ wily-security main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ wily-updates main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ wily-proposed main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ wily-backports main restricted universe multiverse
参考：
http://mirrors.aliyun.com/（更多源参考阿里云官方提供的源列表）
http://mirrors.163.com/（更多源参考163官方提供的源列表）
http://blog.csdn.net/paincupid/article/details/52895676