进入apt目录，备份原来的源地址
cd /etc/apt
mv ./source.list ./source.list.bak
修改源文件source.list
vim source.list
更换阿里云源
deb http://mirrors.aliyun.com/ubuntu/ trusty main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ trusty-backports main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ trusty-proposed main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ trusty-security main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ trusty-updates main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ trusty main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-backports main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-proposed main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-security main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-updates main multiverse restricted universe
:wq 保存退出即可
更新源
sudo apt-get update
也可以全局更新
sudo apt-get upgrade
但这个很耗时，执行上面那一条就可以了