https://developer.aliyun.com/mirror/centos?spm=a2c6h.13651102.0.0.3e221b11WaK1yM  --阿里yum源地址

[root@linux-server ~]# cd /etc/yum.repo.d
[root@linux-server yum.repos.d]# mkdir back
[root@linux-server yum.repos.d]# mv *.repo back
[root@linux-server yum.repos.d]# wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo  #下载aliyun的yum源
参数解释
curl -o  指定存放路径
或者
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

安装扩展源--epel.repo
[root@linux-server ~]# wget -O /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-7.repo
[root@linux-server ~]# cd /etc/yum.repos.d/
[root@linux-server yum.repos.d]# ls
CentOS-Base.repo  epel.repo