为了优化ubuntu软件安装/更新速度，我测试了国内几家apt源的速度，发现北京交大的apt源速度相对最快，然后可以通过以下步骤更新ubuntu源
1) 备份默认的apt源
$ cd /etc/apt
$ sudo cp sources.list sources.list.backup
2) 编辑
$ sudo gedit sources.list
复制粘贴以下列表：
deb http://archive.ubuntu.com/ubuntu/ raring main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ raring-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ raring-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ raring-proposed main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ raring-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ raring main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ raring-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ raring-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ raring-proposed main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ raring-backports main restricted universe multiverse
3) 注意，每次修改完apt源，一定要执行一下更新
$ sudo apt-get update
大概花了几分钟，更新完成之后，就可以使用apt来安装应用程序了。
备注：ubuntu apt源列表 http://wiki.ubuntu.org.cn/源列表