Ubuntu 安装后，软件源默认为国外源，下载速度很慢，替换国内阿里巴巴软件源
一、备份原来的源文件
1、首先，进入源文件 sources.list 所在的目录：
cd /etc/apt/
2、对源文件进行备份，以防万一
sudo cp sources.list sources.list.bak
二、修改源文件内容
1、 Gedit 编辑源文件
sudo gedit sources.list
2、复制如下内容到源文件
deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
三、更新源和软件
1、更新获取 阿里云软件源 提供的软件列表
sudo apt-get update
2、更新软件
sudo apt-get upgrade
