思路：卸载redhat自带yum，然后下载centos的yum，安装后修改配置文件

1、首先到http://mirrors.163.com/centos下载软件包

x86 地址：http://mirrors.163.com/centos/6/os/i386/Packages/

x86_64 地址：http://mirrors.163.com/centos/6/os/x86_64/Packages/

必要下载的软件包有（以64位系统为例）：

a python-iniparse-0.3.1-2.1.el6.noarch.rpm

b yum-3.2.29-40.el6.centos.noarch.rpm

c yum-metadata-parser-1.1.2-16.el6.x86_64.rpm

d yum-plugin-fastestmirror-1.1.30-14.el6.noarch.rpm

下载命令：

wget http://mirrors.163.com/centos/6/os/x86_64/Packages/python-iniparse-0.3.1-2.1.el6.noarch.rpm

wget http://mirrors.163.com/centos/6/os/x86_64/Packages/yum-metadata-parser-1.1.2-16.el6.x86_64.rpm

wget http://mirrors.163.com/centos/6/os/x86_64/Packages/yum-3.2.29-40.el6.centos.noarch.rpm

wget http://mirrors.163.com/centos/6/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.30-14.el6.noarch.rpm
 

[注] :版本不一定要最新的

2、卸载RedHat自带的yum

 rpm -qa | grep yum | xargs rpm -e --nodeps

注：a、xargs是一条Unix和类Unix操作系统的常用命令。它的作用是将参数列表转换成小块分段传递给其他命令，以避免参数列表过长的问题

 b、--nodeps 强制卸载,不管依赖性

3、安装下载的centos的yum包：

rpm -ivh python-iniparse-0.3.1-2.1.el6.noarch.rpm

rpm -ivh yum-metadata-parser-1.1.2-16.el6.x86_64.rpm

rpm -ivh yum-3.2.29-40.el6.centos.noarch.rpm yum-plugin-fastestmirror-1.1.30-14.el6.noarch.rpm

[注] :最后2个需要一起安装，否则会出现依赖性错误

4、到http://mirrors.163.com的centos帮助文档中下载CentOS6-Base-163.repo文件，存放到/etc/yum.repo.d中

wget http://mirrors.163.com/.help/CentOS6-Base-163.repo

5、编辑CentOS6-Base-163.repo文件，将其中的$releasever更改为centos的版本号

下面是修改好的：

# 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-6 - Base - 163.com

baseurl=http://mirrors.163.com/centos/6/os/$basearch/

#mirrorlist=http://mirrorlist.centos.org/?release=6&arch=$basearch&repo=os

gpgcheck=1

gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6

#released updates

[updates]

name=CentOS-6 - Updates - 163.com

baseurl=http://mirrors.163.com/centos/6/updates/$basearch/

#mirrorlist=http://mirrorlist.centos.org/?release=6&arch=$basearch&repo=updates

gpgcheck=1

gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6

#additional packages that may be useful

[extras]

name=CentOS-6 - Extras - 163.com

baseurl=http://mirrors.163.com/centos/6/extras/$basearch/

#mirrorlist=http://mirrorlist.centos.org/?release=6&arch=$basearch&repo=extras

gpgcheck=1

gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6

#additional packages that extend functionality of existing packages

[centosplus]

name=CentOS-6 - Plus - 163.com

baseurl=http://mirrors.163.com/centos/6/centosplus/$basearch/

#mirrorlist=http://mirrorlist.centos.org/?release=6&arch=$basearch&repo=centosplus

gpgcheck=1

enabled=0

gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6

#contrib - packages by Centos Users

[contrib]

name=CentOS-6 - Contrib - 163.com

baseurl=http://mirrors.163.com/centos/6/contrib/$basearch/

#mirrorlist=http://mirrorlist.centos.org/?release=6&arch=$basearch&repo=contrib

gpgcheck=1

enabled=0

gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6

CentOS-Base.repo文件，这是centos的源文件，需将其重命名为rhel-debuginfo.repo  复制到/etc/yum.repos.d/下

6、yum clean all清除原有缓存

7、yum makecache 获取yum列表

出现下面提示，表示yum更改完成：

Metadata Cache Created