参考问题链接地址
报错如下：
[root@d083463d1d75 /]# yum makecache
Failed to set locale, defaulting to C.UTF-8
CentOS Linux 8 - AppStream 623 B/s | 150 B 00:00
Errors during downloading metadata for repository 'appstream':
- Status code: 404 for https://mirrors.ustc.edu.cn/centos/8/AppStream/x86_64/os/repodata/repomd.xml (IP: 202.141.160.110)
Error: Failed to download metadata for repo 'appstream': Cannot download repomd.xml: Cannot download repodata/repomd.xml: All mirrors were tried
注：大致的原因为官方取消了CentOS 8对 yum安装命令的支持，转而着重发展他们的商业版系统，如果大家日常练习使用的话，可以降低CentOS 的版本，之前的版本还是支持的
