1.备份原来的源文件

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

2.修改源

sudo vi /etc/apt/sources.list
##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  
  
##Ubuntu官方提供的其他软件（第三方闭源软件等）：  
  
  
  
deb http://archive.canonical.com/ubuntu/ trusty partner  
  
deb http://extras.ubuntu.com/ubuntu/ trusty main

　　

保存！

sudo apt-get update