RHEL系列是使用最广的Linux服务器系统之一，但是对于未付费用户，却无法通过Redhat网络安装和更新软件，这不能不说是一个遗憾。
其实我们完全可以通过RHEL的同胞兄弟CentOS的源来更新，步骤如下：
1、在 /etc/yum.repos.d/ 目录下新建一个文件 CentOS-Base.repo
#vi CentOS-Base.repo
2、在该文件中录入以下内容并保存（本例的源在撰写本文时是有效的）：
Linux配置代码如下:
[base]
name=CentOS-5 – Base
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever5&arch=$basearch&
repo=os
#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
baseurl=http://ftp.sjtu.edu.cn/centos/5/os/$basearch/
gpgcheck=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5
#released updates
[update]
name=CentOS-5 – Updates
#mirrorlist=http://mirrorlist.centos.org/?release=4&arch=$basearch&repo=updates
baseurl=http://ftp.sjtu.edu.cn/centos/5/updates/$basearch/
gpgcheck=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5
#packages used/produced in the build but not released
[addons]
name=CentOS-5 – Addons
#mirrorlist=http://mirrorlist.centos.org/?release=4&arch=$basearch&repo=addons
baseurl=http://ftp.sjtu.edu.cn/centos/5/addons/$basearch/
gpgcheck=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5
#additional packages that may be useful
[extras]
name=CentOS-5 – Extras
#mirrorlist=http://mirrorlist.centos.org/?release=4&arch=$basearch&repo=extras
baseurl=http://ftp.sjtu.edu.cn/centos/5/extras/$basearch/
gpgcheck=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-5 – Plus
#mirrorlist=http://mirrorlist.centos.org/?release=4&arch=$basearch&repo=centosplus
baseurl=http://ftp.sjtu.edu.cn/centos/5/centosplus/$basearch/
gpgcheck=0
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5
#contrib – packages by Centos Users
[contrib]
name=CentOS-5 – Contrib
#mirrorlist=http://mirrorlist.centos.org/?release=4&arch=$basearch&repo=contrib
baseurl=http://ftp.sjtu.edu.cn/centos/5/contrib/$basearch/
gpgcheck=0
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5
======================================
另外，如果服务器需要通过代理上网，则需要设置一下代理服务器才能进行联网更新：
在 /etc/yum.conf文件加入下面一行内容，指定一下代理服务器参数：
#Set http proxy
proxy=http://192.168.1.100:8000
3、执行更新：
# yum update
