edhat默认自带的yum源需要注册，才能更新，报错：
Loaded plugins: product-id, refresh-packagekit, security, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
http://mirrors.163.com/centos/6Server/os/x86_64/repodata/repomd.xml: [Errno 14] PYCURL ERROR 22 - “The requested URL returned error: 404 Not Found”
Trying other mirror.
可替换为centos对应的源。 操作如下：
更换yum源，将原有源删除或备份到别的目下下：#cd /etc/yum.repos.d/#wget http://mirrors.163.com/.help/CentOS6-Base-163.repo#vi CentOS6-Base-163.repo编辑文件，把文件里面的$releasever全部替换为版本号：6（注意，不是6.5！）最后保存！：%s/$releasever/6/g
清除原有缓存，重建缓存：
#yum clean all
#yum makecache
更新系统：
#yum update