新安装centOS7,无法YUM，原来是没有设DNS。没经验。

虚拟机安装，直接桥接，在安装过程中配置了IP，设DHCP。
进系统后要YUM更新，不行。
输：#yum update。提示如下：
Repository base is listed more than once in the configuration
Repository updates is listed more than once in the configuration
Repository extras is listed more than once in the configuration
Repository centosplus is listed more than once in the configuration
Loading mirror speeds from cached hostfile
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was
14: curl#6 - “Could not resolve host: mirrorlist.centos.org; 未知的错误”

输：#yum install wget.。提示如下：
The remote SSH server rejected X11 forwarding request.
Last login: Sat Aug 31 23:01:01 2019 from 192.168.1.11
[root@live66-centOS7 ~]# yum install wget
已加载插件：fastestmirror
Repository base is listed more than once in the configuration
Repository updates is listed more than once in the configuration
Repository extras is listed more than once in the configuration
Repository centosplus is listed more than once in the configuration
Loading mirror speeds from cached hostfile
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was

英语不行，硬伤。
后增加DNS，正常。