#  验证网络
ping mirrors.aliyun.com

# 备份CentOS 7系统自带yum源配置文件/etc/yum.repos.d/CentOS-Base.repo命令：
cp /etc/yum.repos.d/CentOS-Base.repo.backup /etc/yum.repos.d/CentOS-Base.repo
# 安装wget
yum install -y wget

# 下载CentOS 7的repo文件
wget -O /etc/yum.repos.d/CentOS-Base.repo  <http://mirrors.aliyun.com/repo/Centos-7.repo>
# 清理
yum clean all

# 缓存
yum makecache

# 更新
yum update