对源安装时，要先知道系统的版本，以免安装错的版本
使用命令：lsb_release -c
备份原先的配置文件
cd /etc/apt
sudo cp sources.list sources.list.backup
修改源文件的内容
sudo vim sources.list # 在 /etc/apt 目录下
阿里源的源文件如下：
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
将阿里源文件复制到 sources.list下，用vim的相应操作
全部删除：按esc键后，先按gg（到达顶部），然后dG
全部复制：按esc键后，先按gg，然后ggyG
全选高亮显示：按esc键后，先按gg，然后ggvG或者ggVG
单行复制：按esc键后, 然后yy
单行删除：按esc键后, 然后dd
粘贴：按esc键后, 然后p
复制到粘贴板: 全选高亮显示之后，ctrl+shift+c
参考：
原文：https://blog.csdn.net/vivian_wanjin/article/details/82804884
更新源
sudo apt-get update
更新软件
sudo apt-get upgrade