CentOS8 修改国内镜像源

# 1. 备份
cd /etc/yum.repos.d/
mkdir bak
mv * bak/

# 2. 下载阿里云源的文件
curl -O https://mirrors.aliyun.com/repo/Centos-vault-8.5.2111.repo
curl -O https://mirrors.aliyun.com/repo/epel-archive-8.repo

# 3. 清除缓存
yum clean all && yum makecache