1.卸载rhel的yum相关的包

[root@virhost ~]# rpm -qa|grep yum
yum-updatesd-3.0.1-5.el5
yum-3.0.1-5.el5
yum-rhn-plugin-0.5.2-3.el5
yum-metadata-parser-1.0-8.fc6
yum-security-1.0.4-3.el5
[root@virhost ~]# yum update
Loading "rhnplugin" plugin
Loading "installonlyn" plugin
Loading "security" plugin
This system is not registered with RHN.
RHN support will be disabled.
Setting up Update Process
Setting up repositories
No Repositories Available to Set Up
Reading repository metadata in from local files
Skipping security plugin, no data
No Packages marked for Update/Obsoletion
[root@virhost ~]# rpm -e yum-3.0.1-5.el5 --nodeps
[root@virhost ~]# rpm -qa|grep yum
yum-metadata-parser-1.0-8.fc6
yum-updatesd-3.0.1-5.el5
yum-rhn-plugin-0.5.2-3.el5
yum-security-1.0.4-3.el5
[root@virhost ~]# rpm -e yum-updatesd-3.0.1-5.el5
[root@virhost ~]# rpm -e yum-rhn-plugin-0.5.2-3.el5
[root@virhost ~]# rpm -e yum-metadata-parser-1.0-8.fc6(后来测试这个不应该卸载)
[root@virhost ~]# rpm -e yum-security-1.0.4-3.el5


2.安装centos的源

http://centos.ustc.edu.cn/centos/5/os/i386/CentOS/yum-3.0.5-1.el5.centos.5.noarch.rpm
rpm -ivh yum-3.0.5-1.el5.centos.5.noarch.rpm

[root@virhost ~]# wget http://centos.ustc.edu.cn/centos/5/os/i386/CentOS/yum-3.0.5-

1.el5.centos.5.noarch.rpm
[root@virhost ~]# rpm -ivh yum-3.0.5-1.el5.centos.5.noarch.rpm
warning: yum-3.0.5-1.el5.centos.5.noarch.rpm: Header V3 DSA signature: NOKEY, key ID e8562897
error: Failed dependencies:
        yum-metadata-parser is needed by yum-3.0.5-1.el5.centos.5.noarch
[root@virhost ~]# wget http://192.168.1.250/yum-metadata-parser-1.0-8.fc6.i386.rpm
--07:48:55-- http://192.168.1.250/yum-metadata-parser-1.0-8.fc6.i386.rpm
Connecting to 192.168.1.250:80... 已连接。
已发出 HTTP 请求，正在等待回应... 200 OK
长度：22950 (22K) [text/plain]
Saving to: `yum-metadata-parser-1.0-8.fc6.i386.rpm'

100%[==================================================================>] 22,950      --.-K/s   in

0.003s

07:48:55 (8.57 MB/s) - `yum-metadata-parser-1.0-8.fc6.i386.rpm' saved [22950/22950]

[root@virhost ~]# rpm -ivh yum-metadata-parser-1.0-8.fc6.i386.rpm
warning: yum-metadata-parser-1.0-8.fc6.i386.rpm: Header V3 DSA signature: NOKEY, key ID 37017186
Preparing...                ########################################### [100%]
   1:yum-metadata-parser    ########################################### [100%]
[root@virhost ~]# rpm -ivh yum-3.0.5-1.el5.centos.5.noarch.rpm
warning: yum-3.0.5-1.el5.centos.5.noarch.rpm: Header V3 DSA signature: NOKEY, key ID e8562897
Preparing...                ########################################### [100%]
   1:yum                    ########################################### [100%]
由此看来yum-metadata-parser-1.0-8.fc6.i386.rpm这个包不应该删除那


[root@virhost ~]# cd /etc/yum.repos.d/
[root@virhost yum.repos.d]# ls
rhel-debuginfo.repo
[root@virhost yum.repos.d]# vi CentOS-Base.repo这个文件内如是下面的

[base]
name=CentOS-5.1 - Base
baseurl=http://mirror.tini4u.net/centos/5.1/os/$basearch/
http://centos.ustc.edu.cn/centos/5.1/os/$basearch/
gpgcheck=0
gpgkey=http://centos.ustc.edu.cn/centos/5.1/os/i386/RPM-GPG-KEY-CentOS-5

#released updates
[updates]
name=CentOS-5.1 - Updates
baseurl=http://centos.ustc.edu.cn/centos/5.1/os/$basearch/
http://centos.ustc.edu.cn/centos/5.1/os/$basearch/
gpgcheck=0
gpgkey=http://centos.ustc.edu.cn/centos/5.1/os/i386/RPM-GPG-KEY-CentOS-5


#packages used/produced in the build but not released
[addons]
name=CentOS-5.1 - Addons
baseurl=http://centos.ustc.edu.cn/centos/5.1/os/$basearch/
http://centos.ustc.edu.cn/centos/5.1/os/$basearch/
gpgcheck=0
gpgkey=http://centos.ustc.edu.cn/centos/5.1/os/i386/RPM-GPG-KEY-CentOS-5


#additional packages that may be useful
[extras]
name=CentOS-5.1 - Extras
baseurl=http://centos.ustc.edu.cn/centos/5.1/os/$basearch/
http://centos.ustc.edu.cn/centos/5.1/os/$basearch/
gpgcheck=0
gpgkey=http://centos.ustc.edu.cn/centos/5.1/os/i386/RPM-GPG-KEY-CentOS-5

#additional packages that extend functionality of existing packages

[centosplus]
name=CentOS-5.1 ¨C Plus
baseurl=http://centos.ustc.edu.cn/centos/5.1/os/$basearch/
http://centos.ustc.edu.cn/centos/5.1/os/$basearch/
gpgcheck=0
gpgkey=http://centos.ustc.edu.cn/centos/5.1/os/i386/RPM-GPG-KEY-CentOS-5

#contrib - packages by Centos Users
[contrib]
name=CentOS-5.1 - Contrib
baseurl=http://centos.ustc.edu.cn/centos/5.1/os/$basearch/
http://centos.ustc.edu.cn/centos/5.1/os/$basearch/
gpgcheck=0
gpgkey=http://centos.ustc.edu.cn/centos/5.1/os/i386/RPM-GPG-KEY-CentOS-5
然后随便测试了一个命令
[root@virhost yum.repos.d]# rpm -qa|grep postfix
刚好系统没有装这个包
[root@virhost yum.repos.d]# yum install postfix
Loading "installonlyn" plugin
Setting up Install Process
Setting up repositories
updates                   100% |=========================| 1.1 kB    00:00   
contrib                   100% |=========================| 1.1 kB    00:00   
centosplus                100% |=========================| 1.1 kB    00:01   
addons                    100% |=========================| 1.1 kB    00:00   
extras                    100% |=========================| 1.1 kB    00:00   
Reading repository metadata in from local files
primary.xml.gz            100% |=========================| 834 kB    00:03   
################################################## 2400/2400
primary.xml.gz            100% |=========================| 834 kB    00:08   
################################################## 2400/2400
primary.xml.gz            100% |=========================| 834 kB    00:08   
################################################## 2400/2400
primary.xml.gz            100% |=========================| 834 kB    00:04   
################################################## 2400/2400
primary.xml.gz            100% |=========================| 834 kB    00:08   
################################################## 2400/2400
Parsing package install arguments
Resolving Dependencies
--> Populating transaction set with selected packages. Please wait.
---> Downloading header for postfix to pack into transaction set.
postfix-2.3.3-2.i386.rpm 100% |=========================| 41 kB    00:00   
---> Package postfix.i386 2:2.3.3-2 set to be updated
--> Running transaction check

Dependencies Resolved

=============================================================================
Package                 Arch       Version          Repository        Size
=============================================================================
Installing:
postfix                 i386       2:2.3.3-2        extras            3.6 M

Transaction Summary
=============================================================================
Install      1 Package(s)       
Update       0 Package(s)       
Remove       0 Package(s)       

Total download size: 3.6 M
Downloading Packages:
(1/1): postfix-2.3.3-2.i3 100% |=========================| 3.6 MB    00:43   
Running Transaction Test
warning: postfix-2.3.3-2: Header V3 DSA signature: NOKEY, key ID e8562897
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
Installing: postfix                      ######################### [1/1]

Installed: postfix.i386 2:2.3.3-2
Complete!

===========================================================================================================================

1。14.el5.centos.1.noarch.rpm

当你安装yum的时候提示依赖yum-fastestmirror,同时当你安装yum-fastestmirror的时候提示你依赖yum,相互依赖呀.没办法,只能两个一起安装了
[root@blinux ~]# rpm -ivh yum-fastestmirror-1.1.16-14.el5.centos.1.noarch.rpm yum-3.2.22-26.el5.centos.noarch.rpm
2。包的下载地址：
http://centos.ustc.edu.cn/centos/5/os/i386/CentOS/