1.为了方便起见，先切换到root用户
2.先删除rhel6自带的yum
rpm -aq|grep yum|xargs rpm -e --nodeps
3.下载CentOS 6的yum
wget http://mirrors.163.com/centos/6.0/os/x86_64/Packages/python-iniparse-0.3.1-2.1.el6.noarch.rpm
wget http://mirrors.163.com/centos/6.0/os/x86_64/Packages/yum-metadata-parser-1.1.2-14.1.el6.x86_64.rpm
wget http://mirrors.163.com/centos/6.0/os/x86_64/Packages/yum-3.2.27-14.el6.centos.noarch.rpm
wget http://mirrors.163.com/centos/6.0/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.26-11.el6.noarch.rpm
4.安装这几个rpm包,安装的时候可能有依赖问题，多试几次就可以了。
rpm -ivh python-iniparse-0.3.1-2.1.el6.noarch.rpm
rpm -ivh yum-metadata-parser-1.1.2-14.1.el6.x86_64.rpm
rpm -ivh yum-3.2.27-14.el6.centos.noarch.rpm yum-plugin-fastestmirror-1.1.26-11.el6.noarch.rpm
5.下载CentOS的repo源配置文件，我下载到的是CentOS 5的配置，需要做些修改才能用在CentOS6上面。我已经改好了，用的是国内163的源镜像。
[base]
name=CentOS-6 - Base
repo=os
baseurl=http://mirrors.163.com/centos/6/os/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#released updates
[update]
name=CentOS-6 - Updates
baseurl=http://mirrors.163.com/centos/6/updates/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#packages used/produced in the build but not released
#[addons]
#name=CentOS-6 - Addons
#baseurl=http://mirrors.163.com/centos/5/addons/$basearch/
#gpgcheck=1
#gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
#additional packages that may be useful
[extras]
name=CentOS-6 - Extras
baseurl=http://mirrors.163.com/centos/6/extras/$basearch/
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
baseurl=http://mirrors.163.com/centos/6/centosplus/$basearch/
gpgcheck=1
enabled=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#contrib - packages by Centos Users
[contrib]
name=CentOS-6 - Contrib
baseurl=http://mirrors.163.com/centos/6/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
6.然后把CentOS-Base.repo放到/etc/yum.repos.d/目录下面
mv ./CentOS-Base.rep /etc/yum.repos.d/
7.清除yum的缓存
yum clean all
8.现在应该就可以用了
试试：yum search nginx