linux下yum无法安装lrzsz，Error: Failed to download metadata for repo ‘appstream‘: Cannot prepare internal

linux虚拟机上准备安装一下rz sz，执行yum命令后提示如下：

[root@tony001 ~]# yum install lrzsz
CentOS Linux 8 - AppStream 53 B/s | 38 B 00:00
Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: No URLs in mirrorlist

百度查询，有的说是关闭防火墙，有的说是网络问题，验证防火墙已关闭，网络可ping通百度，经查询发现其他linux虚拟机原来可以yum安装现在也不能执行yum

linux下yum无法安装lrzsz，Error: Failed to download metadata for repo ‘appstream‘: Cannot prepare internal最先出现在Python成神之路。