cd /etc/yum.repos.d
sudo mv CentOS-Base.repo CentOS-Base.repo.bak
sudo wget -O CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
sudo wget -P /etc/yum.repos.d/ http://mirrors.aliyun.com/repo/epel-7.repo ;
yum clean all
yum makecache
