1.备份原来的源文件
cd /etc/apt/
ls
sudo cp sources.list sources.list.bak
2.替换源
sudo gedit sources
阿里源：
deb http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse
3.更新源和软件
sudo apt-get update
sudo apt-get upgrade
