前言：
当我们安装了RedHat 的机器时，如果不到RedHat网站注册，会导致不能安装其网站上所 host的软件。而CentOS作为Redhat的社区版，与对应版本的RedHat完全兼容（其发行的Binary就是从RedHat编译而来），因此我们可以考虑将RedHat机器的Repository替换为CentOS的Repository
现象： 当用 yum install $softwarePackage时，报如下错误：
This system is not registered with RHN.
RHN support will be disabled.
1.1 编辑 rhnplugin.conf （ vi /etc/yum/pluginconf.d/rhnplugin.conf ） ，使它具有如下内容：
[main]
enabled = 0
gpgcheck = 0
[rhel-i386-server-5]
enabled = 0
#[some-unsigned-custom-channel]
#gpgcheck = 0
1.2 创建/编辑 centOS的repo
解决方案1-使用heanet：
编辑centos.repo [位于/etc/yum.repos.d] （vi /etc/yum.repos.d/centos.repo）,使它具有以下内容（根据你的版本将 6 保持或改为5 ）：
[centos]
name=CentOS $releasever - $basearch
baseurl=http://ftp.heanet.ie/pub/centos/6/os/$basearch/
enabled=1
gpgcheck=0解决方案2：
1. 假设你的Redhat版本是6. 将以下文件内容创建为 CentOS-Base.repo 并置于/etc/yum.repos.d 目录下：
# 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-$releasever - Base
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#released updates
[updates]
name=CentOS-$releasever - Updates
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
#baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
#baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
#baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib
#baseurl=http://mirror.centos.org/centos/$releasever/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
如果装软件时 （yum install）遇到以下错误：
YumRepo Error: All mirror URLs are not using ftp, http[s] or file. Eg. 6Server is not a valid release or hasnt been released yet
请将CentOS-Base.repo文件中的$releasever 替换为6 （vi中用 :%s/$releasever/6/g），然后执行yum update
2. 假设你的Redhat版本是7. 将以下文件内容创建为 CentOS-Base.repo 并置于/etc/yum.repos.d 目录下：
# CentOS-Base.repo
#
# The mirror system uses the connecting IP address of the client and the
# update status of each mirror to pick mirrors that are updated to and
# geographically close to the client. You should use this for CentOS updates
# unless you are manually picking other mirrors.
#
# If the mirrorlist= does not work for you, as a fall back you can try the
# remarked out baseurl= line instead.
#
#
[base]
name=CentOS-7 - Base
mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=os
#baseurl=http://mirror.centos.org/centos/7/os/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-7
#released updates
[updates]
name=CentOS-7 - Updates
mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=updates
#baseurl=http://mirror.centos.org/centos/7/updates/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-7
#additional packages that may be useful
[extras]
name=CentOS-7 - Extras
mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=extras
#baseurl=http://mirror.centos.org/centos/7/extras/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-7
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-7 - Plus
mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=centosplus
#baseurl=http://mirror.centos.org/centos/7/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-7
#contrib - packages by Centos Users
[contrib]
name=CentOS-7 - Contrib
mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=contrib
#baseurl=http://mirror.centos.org/centos/7/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-7