yum命令失败：
Errors during downloading metadata for repository 'epel':
- Status code: 404 for http://archives.fedoraproject.org/pub/archive/epel/8/Everything/x86_64/repodata/repomd.xml (IP: 38.145.60.24)
Error: Failed to download metadata for repo 'epel': Cannot download repomd.xml: Cannot download repodata/repomd.xml: All mirrors were tried
1、备份之前的repo文件，命令：
mv /etc/yum.repos.d /etc/yum.repos.d.bak
2、创建源文件目录，命令：
mkdir -p /etc/yum.repos.d
3、下载新的yum源，分别执行以下2条命令：
先输入
curl https://mirrors.aliyun.com/repo/Centos-vault-8.5.2111.repo > /etc/yum.repos.d/Centos-vault-8.5.2111.repo
后输入即可
curl https://mirrors.aliyun.com/repo/epel-archive-8.repo > /etc/yum.repos.d/epel-archive-8.repo