思路:

rm -fr /etc/yum.repo.d/*  #删除下面内容


wget http://mirrors.aliyun.com/repo/Centos-7.repo

wget http://mirrors.aliyun.com/repo/Centos-6.repo   #从三个任一选择一个下载

wget http://mirrors.aliyun.com/repo/Centos-5.repo


yum clean all  #清除

yum makecache  #重新加载缓存