更换yum源地址

cd /etc/yum.repos.d/
mv CentOS-Base.repo CentOS-Base.repo.backup

mv CentOS-Base.repo CentOS-Base.repo.back
下载163的镜像源
wget http://mirrors.163.com/.help/CentOS7-Base-163.repo
mv CentOS-Base.repo.back CentOS-Base.repo

mv CentOS-Base.repo CentOS-Base.repo.back
mv CentOS7-Base-163.repo CentOS-Base.repo

　　

下载阿里yum配置到该目录中，选择对应版本
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos7.repo

　　

重建缓存
yum clean all
yum makecache
看一下yum仓库有多少包
yum repolist