首先，rhel5系统安装的时候其实已经有yum了，只是因为如果用官方的网站更新的话除非你是用钱买的rhel5.否则它会提示注册之类的。所以只要把 yum的更新地址改成开源的就行了。而限定yum更新地址的文件在/etc/yum.repos.d/里。先把它们改成备份文件，即在后面加.bak。 
[root@killgoogle ~]# mv /etc/yum.repos.d/rhel-debuginfo.repo /etc/yum.repos.d/rhel-debuginfo.repo.bak 
[root@killgoogle ~]# mv /etc/yum.repos.d/rpmforge.repo.rpmnew /etc/yum.repos.d/rpmforge.repo.rpmnew.bak 
建立新的配置文件： 
[root@killgoogle ~]# cd /etc/yum.repos.d 
[root@killgoogle ~]# touch rhel-debuginfo.repo 
[root@killgoogle ~]# touch mirrors-rpmforge 
[root@killgoogle ~]# touch rpmforge.repo 
往新的配置文件写东西： 
[root@killgoogle ~]#vi rhel-debuginfo.repo 
[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/$basearch/dag/
enabled=1 
gpgcheck=1 
gpgkey=http://ftp.riken.jp/Linux/dag/packages/RPM-GPG-KEY.dag.txt
修改第二个配置文件： 
[root@killgoogle ~]vi mirrors-rpmforge 
http://apt.sw.be/redhat/el5/en/$ARCH/dag
http://archive.cs.uu.nl/mirror/dag.wieers/redhat/el5/en/$ARCH/dag
http://ftp2.lcpe.uni-sofia.bg/freshrpms/pub/dag/redhat/el5/en/$ARCH/dag
#http://ftp.heanet.ie/pub/freshrpms/pub/dag/redhat/el5/en/$ARCH/dag
http://ftp-stud.fht-esslingen.de/dag/redhat/el5/en/$ARCH/dag
http://mirror.cpsc.ucalgary.ca/mirror/dag/redhat/el5/en/$ARCH/dag
http://mirrors.ircam.fr/pub/dag/redhat/el5/en/$ARCH/dag
http://rh-mirror.linux.iastate.edu/pub/dag/redhat/el5/en/$ARCH/dag
http://rpmfind.net/linux/dag/redhat/el5/en/$ARCH/dag
http://wftp.tu-chemnitz.de/pub/linux/dag/redhat/el5/en/$ARCH/dag
http://www.mirrorservice.org/sites/apt.sw.be/redhat/el5/en/$ARCH/dag
修改第三个配置文件： 
[root@killgoogle ~]# vi rpmforge.repo 
# Name: RPMforge RPM Repository for Red Hat Enterprise 5 - dag 
# URL: http://rpmforge.net/
[rpmforge] 
name = Red Hat Enterprise $releasever - RPMforge.net - dag 
#baseurl = http://apt.sw.be/redhat/el5/en/$basearch/dag
mirrorlist = http://apt.sw.be/redhat/el5/en/mirrors-rpmforge
#mirrorlist = file:///etc/yum.repos.d/mirrors-rpmforge 
enabled = 1 
protect = 0 
gpgkey = file:///etc/pki/rpm-gpg/RPM-GPG-KEY-rpmforge-dag 
gpgcheck = 1 

如果风速慢的话可以通过增加yum的超时时间，这样就不会总是因为超时而退出。 
[root@killgoogle ~]vi /etc/yum.conf 
加上这么一句：timeout=120 
到这里配置差不多就完了。还有一个包需要安装：rpmforge-release-0.3.6-1.el5.rf.i386.rpm 
如果不安装的话有可能会出现以下错误：GPG key retrieval failed: [Errno 5] OSError: [Errno 2] 没有那个文件或目录: '/etc/pki/rpm-gpg/RPM-GPG-KEY-rpmforge-dag' 
到http://rpmfind.net/linux/RPM/找到这个包，然后 
[root@killgoogle ~]rpm -ivh rpmforge-release-0.3.6-1.el5.rf.i386.rpm 
接下来就是输入KEY了。 
[root@killgoogle ~] rpm --import http://mirror.be10.com/centos/RPM-GPG-KEY-CentOS-5
这样基本上yum就可以用了。不过如果觉得不爽的话还可以优化： 
加速yum 
[root@killgoogle ~]yum install yum-fastestmirror yum-presto 
指定或去掉软件源的mirror: 
可以在baseurl中将比较慢的mirror去掉 
你的yum镜像的速度测试记录文件： 
/var/cache/yum/timedhosts.txt 
yum Existing lock 错误的解决办法 
如果系统启动的时候， yum 出现Existing lock /var/run/yum.pid: another copy is running as pid 3380. Aborting. 可以用下面的办法解决： 
[root@killgoogle ~]/etc/init.d/yum-updatesd stop 
也可以用以下方法： 
[root@killgoogle ~]rm -f /var/run/yum.pid 
主要原因就是yum在自动更新只要关掉它就可以了 

完了。现在就可以测试能不能用了哦： 
[root@killgoogle ~]yum install mplayer 
这是安装mplayer如果要删除则是： 
[root@killgoogle ~]yum remove mplayer