备份自带yum源
[root@localhost ~]# cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.default
[root@localhost ~]# cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak
下载阿里云yum源（也可使用其它国内yum源）
[root@localhost ~]# curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
刷新yum缓存，确保使用新的源
[root@localhost ~]# yum clean all
[root@localhost ~]# yum makecache
查看当前使用yum源
[root@localhost ~]# yum repolist