CentOS-7配置阿里YUM源

配置阿里云YUM源：
1,备份 #cd /etc/yum.repo.d/
#mkdir repos
#mv *.repo repos
2，下载 #wget wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

3，#yum install -y epel-release.noarch 按装epel扩展源
4，之后运行yum makecache生成缓存