转载地址：http://www.cnblogs.com/rchen98/p/6056469.html
问题：使用 Red Hat Enterprise Linux Server(RHEL) yum安装软件时显示 This system is not registered with RHN. RHN support will be disabled.
原因：
Red Hat Enterprise Linux Server(RHEL) 的yum服务是付费的，因为没有付费，所以无法使用yum安装软件，如RHEL想安装YUM，一种可行的办法是移植使用CentOS的YUM。
解决方法：
步骤一：卸载RHEL的yum，并下载CentOS的对应软件包
执行：rpm -qa|grep yum|xargs rpm -e --nodeps 将yum卸载掉
cat /etc/issue && uname -a 看一下系统版本号和系统位数
到 http://mirrors.kernel.org/centos/ 或 http://mirrors.163.com/centos/ 找对应系统版本号
如果系统是5.* 64位，则打开http://mirrors.kernel.org/centos/5/os/x86_64/CentOS/
如果系统是5.* 32位，则打开http://mirrors.kernel.org/centos/5/os/i386/CentOS/
如果系统是6.* 64位：http://mirrors.kernel.org/centos/6/os/x86_64/Packages/
如果系统是6.* 32位：http://mirrors.kernel.org/centos/6/os/i386/Packages/
下载的文件包括：
python-iniparse-0.3.1-2.1.el6.noarch.rpm
python-urlgrabber-3.9.1-11.el6.noarch.rpm
yum-3.2.29-73.el6.centos.noarch.rpm
yum-metadata-parser-1.1.2-16.el6.i686.rpm
yum-plugin-fastestmirror-1.1.30-37.el6.noarch.rpm
步骤二：安装CentOS的对应软件包
安装步骤：
rpm -ivh python-iniparse-0.3.1-2.1.el6.noarch.rpm
rpm -ivh yum-metadata-parser-1.1.2-16.el6.x86_64.rpm
rpm -ivh python-urlgrabber-3.9.1-11.el6.noarch.rpm
这一步可能出如下错误
warning: python-urlgrabber-3.9.1-11.el6.noarch.rpm: Header V3 RSA/SHA1 Signature, key ID c105b9de: NOKEY
Preparing... ########################################### [100%]
file /usr/lib/python2.6/site-packages/urlgrabber/grabber.py from install of python-urlgrabber-3.9.1-11.el6.noarch conflicts with file from package python-urlgrabber-3.9.1-8.el6.noarch
file /usr/lib/python2.6/site-packages/urlgrabber/grabber.pyc from install of python-urlgrabber-3.9.1-11.el6.noarch conflicts with file from package python-urlgrabber-3.9.1-8.el6.noarch
file /usr/lib/python2.6/site-packages/urlgrabber/grabber.pyo from install of python-urlgrabber-3.9.1-11.el6.noarch conflicts with file from package python-urlgrabber-3.9.1-8.el6.noarch
file /usr/lib/python2.6/site-packages/urlgrabber/progress.pyc from install of python-urlgrabber-3.9.1-11.el6.noarch conflicts with file from package python-urlgrabber-3.9.1-8.el6.noarch
file /usr/lib/python2.6/site-packages/urlgrabber/progress.pyo from install of python-urlgrabber-3.9.1-11.el6.noarch conflicts with file from package python-urlgrabber-3.9.1-8.el6.noarch
原因是包冲突，需要卸载原有的urlgrabber包：
[root@rchen98]# rpm -qa |grep urlgrabber
python-urlgrabber-3.9.1-8.el6.noarch
[root@rchen98]# rpm -e python-urlgrabber-3.9.1-8.el6.noarch
然后再安装。
然后安装yum
rpm -ivh yum-3.2.29-73.el6.centos.noarch.rpm yum-plugin-fastestmirror-1.1.30-37.el6.noarch.rpm
步骤三：生成yum.repos.d文件
到http://mirrors.163.com的 centos帮助文档 中下载CentOS6-Base-163.repo文件，存放到/etc/yum.repos.d中
#wget http://mirrors.163.com/.help/CentOS6-Base-163.repo
改名为：CentOS6-Base.repo
然后把文件里的$releasever都改为你的Linux版本（6或者5），也就是文件修改成如下即可：
# CentOS-Base.repo
#
# The mirror system uses the connecting IP address of the client and the
# update status of each mirror to pick mirrors that are updated to and
# geographically close to the client. You should use this for CentOS updates
# unless you are manually picking other mirrors.
#
# If the mirrorlist= does not work for you, as a fall back you can try the
# remarked out baseurl= line instead.
#
#
[base]
name=CentOS-6 - Base - 163.com
baseurl=http://mirrors.163.com/centos/6/os/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6&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&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&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&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&arch=$basearch&repo=contrib
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
步骤四：重建缓存
yum clean all 清除原有缓存
yum makecache 获取yum列表
等待，大约三分钟后出现下面提示，表示yum更改完成：
Metadata Cache Created。
----------------------------------------------------------------------------------------------------
补充：把文件里的$releasever都改为你的Linux版本6，可使用如下命令：
:1,$s/$releasever/6
注意：无论你的Linux版本是6.5还是6，都需要统一写6，下载yum包时，也需要选择到6版本。