问题：
[root@cloud-all-in-one home]# yum list
Loaded plugins: fastestmirror, refresh-packagekit, security
Loading mirror speeds from cached hostfile
YumRepo Error: All mirror URLs are not using ftp, http[s] or file.
Eg. </html>/
removing mirrorlist with no valid mirrors: /var/cache/yum/x86_64/6/base/mirrorlist.txt
Error: Cannot find a valid baseurl for repo: base
解决办法：
这是 yum源出问题了，先ping外网，/etc/yum.repos.d/目录下面的文件编写可能有错误
# ping www.baidu.com ping一下外网是不是通
# yum clean all
# yum list