1.下载wget

• yum wget install -y

2.备份源yum仓库

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

3.下载阿里云yum仓库

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

4.清空以前的yum缓存

• yum clean all

5.获取阿里云的缓存

• yum makecache