由于Redhat的yum在线更新是收费的，如果没有注册的话是不能使用的，即不能在线安装软件。所以yum install 命令每次都安装失败
下面介绍一种更改yum源的方式：
系统说明：
系统：Red Hat Enterprise Linux Server 6.3
内核：Linux 2.6.32-279.el6.x86_64
1、删除RHEL原有的yum
rpm
-aq|grep yum|xargs rpm -e --nodeps #删除
2、下载新的yum安装包 #这里我们使用CentOS的yum源
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-3.2.29-60.el6.centos.noarch.rpm
wget
http://mirrors.163.com/centos/6/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.30-30.el6.noarch.rpm
(提示：如果下载时提示404找不到错误，请访问http://mirrors.163.com/centos/6/os/x86_64/Packages/，手动查找上面四个包，有时候版本会有点小偏差)
3、安装yum软件包
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-3.2.29-60.el6.centos.noarch.rpm yum-plugin-fastestmirror-1.1.30-30.el6.noarch.rpm
(这里要注意的是：最后两个安装包要放在一起同时安装，否则会提示相互依赖，安装失败。)
4、更改yum源 #我们使用网易的CentOS镜像源
cd /etc/yum.repos.d/
wget http://mirrors.163.com/.help/CentOS6-Base-163.repo
vi CentOS6-Base-163.repo #编辑文件
把文件里面的$releasever全部替换为版本号，即6 最后保存！
或者直接把下面的内存拷贝到CentOS6-Base-163.repo文件中即可
（已经修改好，不用下载直接新建CentOS6-Base-163.repo 也 可以）
# CentOS-Base.repo
#
# The mirror system uses the connecting IP address of the client and the
# update status of each mirror to pick mirrors that are updated to and
# geographically close to the client. You should use this for CentOS updates
# unless you are manually picking other mirrors.
#
# If the mirrorlist= does not work for you, as a fall back you can try the
# remarked out baseurl= line instead.
#
#
[base]
name=CentOS-6 - Base - 163.com
baseurl=http://mirrors.163.com/centos/6/os/$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
5、收尾，测试YUM 是否可用
yum clean all #清理yum缓存
yum makecache #将服务器上的软件包信息缓存到本地,以提高搜索安装软件的速度
yum install vim* #测试yum是否可用