一、先验证是否有网络
root@localhost:~# ping www.baidu.com
ping: www.baidu.com: Temporary failure in name resolution
root@localhost:~#
说明没有网，参考：https://blog.csdn.net/qq_43445867/article/details/132384031
sudo vim /etc/resolv.conf
二、如果有网络，就更换源
参考：https://blog.csdn.net/calculate23/article/details/126675452
sudo vim /etc/apt/sources.list
