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Redhat 安装安装免费yum源
服务器默认装的是rehl5版本，而且还没在红帽官网上注册，虽然系统也默认装了yum，但是不能从其源地址进行软件的下载安装。
使用yum安装会出现：
This system is not registered with RHN.
RHN support will be disabled.
下面是安装方法：
1.首先推荐一个开源的镜像网站地址http://mirrors.ustc.edu.cn/。我们直接换CentOS的yum源，具体地址是：http://mirrors.ustc.edu.cn/centos/5/os/i386/CentOS/。首先我们要下载安装yum需要的各种安装文件。
先cd /usr/local/
#wget http://mirrors.ustc.edu.cn/centos/5/os/i386/CentOS/yum-3.2.22-33.el5.centos.noarch.rpm
#wget http://mirrors.ustc.edu.cn/centos/5/os/i386/CentOS/yum-downloadonly-1.1.16-14.el5.centos.1.noarch.rpm
#wget http://mirrors.ustc.edu.cn/centos/5/os/i386/CentOS/yum-fastestmirror-1.1.16-14.el5.centos.1.noarch.rpm
#wget http://mirrors.ustc.edu.cn/centos/5/os/i386/CentOS/yum-metadata-parser-1.1.2-3.el5.centos.i386.rpm
#wget http://mirrors.ustc.edu.cn/centos/5/os/i386/CentOS/yum-utils-1.1.16-14.el5.centos.1.noarch.rpm
2.rpm -ivh yum*.rpm。若遇到冲突问题，直接--replacepkgs。安装成功后，就可以通过yum指令来查看了，但是这个时候的源地址配置还是原来的，需要修改。
3.RHEL5 配置YUM源 。
cd /etc/yum.repos.d/
cp rhel-debuginfo.repo rhel-debuginfo.repo.bak
Vi rhel-debuginfo.repo
先删除rhel-debuginfo.repo文件中所有内容，然后添加以下内容：
cd /etc/yum.repos.d/
cp rhel-debuginfo.repo rhel-debuginfo.repo.bak
先删除rhel-debuginfo.repo文件中所有内容，然后添加以下内容：
[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/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5
#released updates
[update]
name=CentOS-5 - Updates
#mirrorlist=http://mirrorlist.centos.org/?release=4&arch=$basearch&repo=updates
baseurl=http://ftp.sjtu.edu.cn/centos/5/updates/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5
#packages used/produced in the build but not released
[addons]
name=CentOS-5 - Addons
#mirrorlist=http://mirrorlist.centos.org/?release=4&arch=$basearch&repo=addons
baseurl=http://ftp.sjtu.edu.cn/centos/5/addons/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5
#additional packages that may be useful
[extras]
name=CentOS-5 - Extras
#mirrorlist=http://mirrorlist.centos.org/?release=4&arch=$basearch&repo=extras
baseurl=http://ftp.sjtu.edu.cn/centos/5/extras/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-5 - Plus
#mirrorlist=http://mirrorlist.centos.org/?release=4&arch=$basearch&repo=centosplus
baseurl=http://ftp.sjtu.edu.cn/centos/5/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5
#contrib - packages by Centos Users
[contrib]
name=CentOS-5 - Contrib
#mirrorlist=http://mirrorlist.centos.org/?release=4&arch=$basearch&repo=contrib
baseurl=http://ftp.sjtu.edu.cn/centos/5/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5
# vi dag.repo
[dag]
name=Dag RPM Repository for RHEL5
baseurl=http://ftp.riken.jp/Linux/dag/redhat/el5/en/$basearch/dag/
enabled=1
gpgcheck=1
gpgkey=http://ftp.riken.jp/Linux/dag/packages/RPM-GPG-KEY.dag.txt
4.导入key
rpm --import http://ftp.sjtu.edu.cn/centos/5/os/i386/RPM-GPG-KEY-CentOS-5 。