1.备份原有的yum库

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

2.下载新的CentOS-Base.repo 到/etc/yum.repos.d/

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

3.添加EPEL

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

4.清理缓存并生成新的缓存

yum clean all

yum makecache

5.这样就安装完成了