使用redhat系统在线安装时提示This system is not registered with RHN.如下：
[root@localhost chenqi]# yum install httpd
Loaded plugins: rhnplugin, security
This system is not registered with RHN.
RHN support will be disabled.
Setting up Install Process
No package httpd available.
Nothing to do
解决方案：
首先声明一下：我用的是redhat5.0，不同的版本可能不同，需要做适当的调整。
步骤一：卸载redhat自带的yum组件
[root@localhost chenqi]# rpm -qa|grep yum|xargs rpm -e --nodeps
步骤二：安装centos的yum包（依次安装）
[root@localhost chenqi]# wget http://mirrors.ustc.edu.cn/centos/5/os/i386/CentOS/yum-3.2.22-39.el5.centos.noarch.rpm
[root@localhost chenqi]# wget http://centos.ustc.edu.cn/centos/5/os/i386/CentOS/yum-metadata-parser-1.1.2-3.el5.centos.i386.rpm
[root@localhost chenqi]# wget http://mirror.centos.org/centos-5/5/os/i386/CentOS/python-iniparse-0.2.3-4.el5.noarch.rpm
[root@localhost chenqi]# wget http://mirrors.ustc.edu.cn/centos/5/os/i386/CentOS/yum-fastestmirror-1.1.16-21.el5.centos.noarch.rpm
步骤三：安装rpm包
安装顺序
[root@localhost chenqi]# rpm -ivh python-iniparse-0.2.3-4.el5.noarch.rpm
[root@localhost chenqi]# rpm -ivh yum-metadata-parser-1.1.2-3.el5.centos.i386.rpm.4
[root@localhost chenqi]# rpm -ivh yum-3.2.22-39.el5.centos.noarch.rpm.4 yum-fastestmirror-1.1.16-21.el5.centos.noarch.rpm.3
注意：在这个地方第三步一定要两个一起安装，要不然会出现下面的错误：
错误一：warning: yum-3.2.19-18.el5.centos.noarch.rpm: Header V3 DSA signature: NOKEY, key ID e8562897
error: Failed dependencies:
yum-fastestmirror is needed by yum-3.2.19-18.el5.centos.noarch
错误二：warning: yum-fastestmirror-1.1.16-13.el5.centos.noarch.rpm: Header V3 DSA signature: NOKEY, key ID e8562897
error: Failed dependencies:
yum >= 3.0 is needed by yum-fastestmirror-1.1.16-13.el5.centos.noarch
步骤四：下载更新源，并存放在系统目录中
[root@localhost chenqi]# wget http://docs.linuxtone.org/soft/lemp/CentOS-Base.repo
[root@localhost chenqi]# mv CentOS_Base.repo /etc/yum.repos.d/CentOS-Base.repo
到此为止yum就安装成功了。