Centos7 replaces yum source with Alibaba yum source

#Step1: Download the repository. If there is no wget command, use curl 
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo` 

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

#Step2: Install epel basic component source without wget command. Use curl 
wget -O /etc/ yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-7.repo 

curl -o /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com /repo/epel-7.repo 

yum clean all 

yum makecache