1. 备份yum源

cd /etc/yum.repos.d
mkdir repo_bak
mv *.repo repo_bak/

2. 下载阿里云repo文件

wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
wget -O /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-7.repo

3. 清空yum缓存,并生成新的yum缓存

yum clean all
yum makecache

4. 安装软件扩展源

yum install -y epel-release