centos8安装阿里云源和epel

1. 备份
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup

2.下载
wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-8.5.2111.repo

3.生成缓存
yum clean all
yum makecache

4.安装epel
yum install epel-release