http://mirrors.ustc.edu.cn/centos/7.2.1511/os/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: mirrors.ustc.edu.cn; Unknown error"
Trying other mirror.
网卡配置问题，
进入 cd /etc/sysconfig/network-scripts
打开vi ifcfg-ens33
更改BOOTPROTO=dhcp
ONBOOT=yes
启用激活网卡
执行命令
service network restart