redhat6.5.安装后，登录系统，使用yum update 更新系统。提示：This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.无法更新。redhat 默认自带的 yum 源需要注册，才能更新。我们想不花钱也可以更新，需要替换掉redhat的yum源。
1.检查是否安装yum包
查看RHEL是否安装了yum，若是安装了，那么又有哪些yum包：
[root@localhost ~]# rpm -qa |grep yum
yum-metadata-parser-1.0-8.fc6
yum-3.0.1-5.el5
yum-rhn-plugin-0.4.3-1.el5
yum-updatesd-3.0.1-5.el5
2 删除redhat自带的yum包
卸载上面显示的所有yum包：
[root@localhost ~]# rpm -qa|grep yum|xargs rpm -e --nodeps（不检查依赖，直接删除rpm包）
再用
[root@localhost ~]# rpm -qa |grep yum
[root@localhost ~]#
查看，无信息显示表示已经卸载完成。
3.下载新的yum包。使用Centos6.5的yum包
wget http://mirror.centos.org/centos/6/os/x86_64/Packages/yum-3.2.29-81.el6.centos.noarch.rpm
wget http://mirror.centos.org/centos/6/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.30-40.el6.noarch.rpm
wget http://mirror.centos.org/centos/6/os/x86_64/Packages/yum-metadata-parser-1.1.2-16.el6.x86_64.rpm
安装yum软件包
注意:单个的安装包可能会依赖其它包（例如yum和yum-fastestmirror会相互依赖），所以我们可以把所有这些包放在一起，用一行命令将它们同时安装即可：
rpm -ivh yum-metadata-parser-1.1.2-16.el6.x86_64.rpm yum-plugin-fastestmirror-1.1.30-40.el6.noarch.rpm yum-3.2.29-81.el6.centos.noarch.rpm
4.更换yum源。使用163的源
# 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$releasever全部替换为版本号，即6.5 最后保存！或者直接把下面的内存拷贝到CentOS6-Base-163.repo文件中即可（已经修改好）
# CentOS-Base.repo
#
# The mirror system uses the connecting IP address of the client and the
# update status of each mirror to pick mirrors that are updated to and
# geographically close to the client. You should use this for CentOS updates
# unless you are manually picking other mirrors.
#
# If the mirrorlist= does not work for you, as a fall back you can try the
# remarked out baseurl= line instead.
#
#
[base]
name=CentOS-6 - Base - 163.com
baseurl=http://mirrors.163.com/centos/6/os/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6.5&arch=$basearch&repo=os
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#released updates
[updates]
name=CentOS-6 - Updates - 163.com
baseurl=http://mirrors.163.com/centos/6/updates/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6.5&arch=$basearch&repo=updates
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#additional packages that may be useful
[extras]
name=CentOS-6 - Extras - 163.com
baseurl=http://mirrors.163.com/centos/6/extras/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6.5&arch=$basearch&repo=extras
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-6 - Plus - 163.com
baseurl=http://mirrors.163.com/centos/6/centosplus/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6.5&arch=$basearch&repo=centosplus
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#contrib - packages by Centos Users
[contrib]
name=CentOS-6 - Contrib - 163.com
baseurl=http://mirrors.163.com/centos/6/contrib/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6.5&arch=$basearch&repo=contrib
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
5.清除原有缓存
# yum clean all
重建缓存，以提高搜索安装软件的速度
# yum makecache
6.更新系统
# yum update