1. wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-6.repo
    1. sed -i -e '/mirrors.cloud.aliyuncs.com/d' -e '/mirrors.aliyuncs.com/d' /etc/yum.repos.d/CentOS-Base.repo
    1. yum clean all
    1. yum makecache
    1. rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7