1，备份原有yum源

yum -y install yum-utils
yum -y install wget
cd   /etc/yum.repos.d/
mkdir repo_bak
mv *.repo repo_bak/

2，配置阿里yum源

wget  http://mirrors.aliyun.com/repo/Centos-7.repo
yum clean all
yum makecache