访问地址为:http://mirrors.163.com/.help/centos.html
首先备份源:
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
备份之前的源BASE，进入对应目录。
cd /etc/yum.repos.d/ wget http://mirrors.163.com/.help/CentOS7-Base-163.repo mv CentOS7-Base-163.repo CentOS-Base.repo
刷新YUM的缓存状态：
yum clean all
yum makecache