Ubuntu安装完毕后，默认使用的是官方的源，在国内访问速度很慢，这里介绍更换为阿里云的源方法。
步骤如下：
1.备份源配置文件
sudo cp /etc/apt/sources.list /etc/apt/sources.list_backup
2.用编辑器打开源配置文件
sudo vim /etc/apt/sources.list
3.删除文件内容，更换为以下内容（也可使用其他源）
deb http://mirrors.aliyun.com/ubuntu trusty main restricted deb-src http://mirrors.aliyun.com/ubuntu trusty main restricted ## Major bug fix updates produced after the final release of the ## distribution. deb http://mirrors.aliyun.com/ubuntu trusty-updates main restricted deb-src http://mirrors.aliyun.com/ubuntu trusty-updates main restricted ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu ## team. Also, please note that software in universe WILL NOT receive any ## review or updates from the Ubuntu security team. deb http://mirrors.aliyun.com/ubuntu trusty universe deb-src http://mirrors.aliyun.com/ubuntu trusty universe deb http://mirrors.aliyun.com/ubuntu trusty-updates universe deb-src http://mirrors.aliyun.com/ubuntu trusty-updates universe ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu ## team, and may not be under a free licence. Please satisfy yourself as to ## your rights to use the software. Also, please note that software in ## multiverse WILL NOT receive any review or updates from the Ubuntu ## security team. deb http://mirrors.aliyun.com/ubuntu trusty multiverse deb-src http://mirrors.aliyun.com/ubuntu trusty multiverse deb http://mirrors.aliyun.com/ubuntu trusty-updates multiverse deb-src http://mirrors.aliyun.com/ubuntu trusty-updates multiverse ## N.B. software from this repository may not have been tested as ## extensively as that contained in the main release, although it includes ## newer versions of some applications which may provide useful features. ## Also, please note that software in backports WILL NOT receive any review ## or updates from the Ubuntu security team. deb http://mirrors.aliyun.com/ubuntu trusty-backports main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu trusty-backports main restricted universe multiverse deb http://security.ubuntu.com/ubuntu trusty-security main restricted deb-src http://security.ubuntu.com/ubuntu trusty-security main restricted deb http://security.ubuntu.com/ubuntu trusty-security universe deb-src http://security.ubuntu.com/ubuntu trusty-security universe deb http://security.ubuntu.com/ubuntu trusty-security multiverse deb-src http://security.ubuntu.com/ubuntu trusty-security multiverse
4.执行以下命令，刷新
sudo apt-get clean sudo apt-get update