- 首先备份源列表：
sudo cp /etc/apt/sources.list /etc/apt/sources.list_backup
- 而后用gedit或其他编辑器打开（也可以复制到Windows下打开，修改后在放回Ubuntu里，方法很多，反正能修改里面的内容就是好方法）：
sudo gedit /etc/apt/sources.list
- 从下面列表中选择合适的源，替换掉文件中所有的内容，保存编辑好的文件:
- 然后刷新列表，注意一定要执行刷新：
- 重要：
sudo apt-get update
源列表
Trusty(14.04)版本
Ubuntu 官方更新服务器（欧洲，此为官方源，国内较慢，但无同步延迟问题，电信、移动/铁通、联通等公网用户可以使用)：
deb http://archive.ubuntu.com/ubuntu/ trusty main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse