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/7/os/i386/Packages/
x86_64 http://mirrors.163.com/centos/7/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：
[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CentOS7-Base-163.repo文件，存放到/etc/yum.repos.d中
wget http://mirrors.163.com/.help/CentOS7-Base-163.repo
5、编辑CentOS7-Base-163.repo文件，
将其中的$releasever更改为centos的版本号，这里修改为7
| # CentOS-Base.repo # # The mirror system uses the connecting IP address of the client and the # update status of each mirror to pick mirrors that are updated to and # geographically close to the client. You should use this for CentOS updates # unless you are manually picking other mirrors. # # If the mirrorlist= does not work for you, as a fall back you can try the # remarked out baseurl= line instead. # #
[base] name=CentOS-7 - Base - 163.com baseurl=http://mirrors.163.com/centos/7/os/$basearch/ #mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=os gpgcheck=1 gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-7
#released updates [updates] name=CentOS-7 - Updates - 163.com baseurl=http://mirrors.163.com/centos/7/updates/$basearch/ #mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=updates gpgcheck=1 gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-7
#additional packages that may be useful [extras] name=CentOS-7 - Extras - 163.com baseurl=http://mirrors.163.com/centos/7/extras/$basearch/ #mirrorlist=http://mirrorlist.centos.org/?release=6&arch=$basearch&repo=extras gpgcheck=1 gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-7
#additional packages that extend functionality of existing packages [centosplus] name=CentOS-7 - Plus - 163.com baseurl=http://mirrors.163.com/centos/7/centosplus/$basearch/ #mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=centosplus gpgcheck=1 enabled=0 gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#contrib - packages by Centos Users [contrib] name=CentOS-7 - Contrib - 163.com baseurl=http://mirrors.163.com/centos/7/contrib/$basearch/ #mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=contrib gpgcheck=1 enabled=0 |
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
