yum install -y wget
进入到yum.repos.d目录
cd /etc/yum.repos.d/
下载Centos-7.repo
wget http://mirrors.aliyun.com/repo/Centos-7.repo
备份CentOS-Base.repo
mv CentOS-Base.repo CentOS-Base.repo.bak
重命名Centos-7.repo
mv Centos-7.repo CentOS-Base.repo
清除缓存
yum clean all
建立缓存
yum makecache
更新yum
yum update