1.备用源
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
2.换源
cd /etc/yum.repos.d
wget http://mirrors.aliyun.com/repo/Centos-7.repo
wget http://mirrors.163.com/.help/CentOS7-Base-163.repo
3.清除及生成缓存
yum clean all
yum makecache
结束。