http://blog.sina.com.cn/s/blog_63d8dad80101cn2s.html
1、卸载rhel的默认安装的yum包
查看yum包
rpm -qa|grep yum
卸载之
rpm -qa|grep yum|xargs rpm -e --nodeps
2、下载新的yum包
64位linux系统下载安装包
wget http://centos.ustc.edu.cn/centos/5/os/x86_64/CentOS/yum-3.2.22-40.el5.centos.noarch.rpm
wget http://centos.ustc.edu.cn/centos/5/os/x86_64/CentOS/yum-fastestmirror-1.1.16-21.el5.centos.noarch.rpm
wget http://centos.ustc.edu.cn/centos/5/os/x86_64/CentOS/yum-metadata-parser-1.1.2-4.el5.x86_64.rpm
32位linux系统下载安装包
wget http://centos.ustc.edu.cn/centos/5/os/i386/CentOS/yum-3.2.22-40.el5.centos.noarch.rpm
wget http://centos.ustc.edu.cn/centos/5/os/i386/CentOS/yum-fastestmirror-1.1.16-21.el5.centos.noarch.rpm
wget http://centos.ustc.edu.cn/centos/5/os/i386/CentOS/yum-metadata-parser-1.1.2-4.el5.i386.rpm
注意：安装包可能会升级，最后的文件名可以通过最新路径下查看得到，例如：
http://centos.ustc.edu.cn/centos/5/os/x86_64/CentOS/
http://centos.ustc.edu.cn/centos/5/os/i386/CentOS/
然后进行安装
rpm -ivh yum-*
注意：yum和yum-fastestmirror相互依赖，所以同时安装即可。
3、下载yum的配置源
wget http://docs.linuxtone.org/soft/lemp/CentOS-Base.repo 下载到 /etc/yum.repos.d/ 目录下面
4、运行yum makecache生成缓存