1. 进入到yum源相应的目录

cd /etc/yum.repos.d/

2. 备份

sudo mkdir bak
sudo mv ./* bak

3. 创建CentOS-Base.repo

   sudo vim CentOS-Base.repo
   

   添加：

   # file: /etc/yum.repos.d/CentOS-AppStream.repo
   [aliyun-AppStream]
   name=CentOS-$releasever - AppStream
   baseurl=http://mirrors.aliyun.com/centos/$releasever/AppStream/$basearch/os/
   gpgcheck=1
   enabled=1
   gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-centosofficial
   # file: /etc/yum.repos.d/CentOS-Base.repo
   [aliyun-BaseOS]
   name=CentOS-$releasever - Base
   baseurl=http://mirrors.aliyun.com/centos/$releasever/BaseOS/$basearch/os/
   gpgcheck=1
   enabled=1
   gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-centosofficial
   
   [aliyun-extras]
   name=CentOS-$releasever - Extras
   baseurl=https://mirrors.aliyun.com/centos/8.0.1905/extras/x86_64/os/
   enabled=1
   gpgcheck=1
   

4. 安装epel-release源

dnf -y install epel-release

5. 清yum缓存，重新加载

dnf clear all
dnf makecache
dnf repolist