1.Error: Failed to download metadata for repo 'AppStream': Cannot prepare internal mirrorlist: No URLs in mirrorlist

一.问题：

centos8 yum 报错 yum Failed to download metadata for repo ‘AppStream’ 

二.原因：

cd /etc/yum.repos.d
vim CentOS-Base.repo

base源地址baseurl失效

解决方案：

参考　　https://developer.aliyun.com/mirror/centos?spm=a2c6h.13651102.0.0.3e221b119E38CQ 　　来切换源

同时可以添加EPEL (Extra Packages for Enterprise Linux)额外包，里面包含nginx这些常用包

参考　　https://developer.aliyun.com/mirror/epel?spm=a2c6h.13651102.0.0.3e221b119E38CQ