redhat默认自带的yum源需要注册，才能更新，报错：
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
今天试了一下，替换为centos对应的源。
先看了一下yum所有的包，其中提供yum命令的是yum-3.2.29-81.el6.centos.noarch包。
[root@localhost ~]# rpm -qf /usr/bin/yum
yum-3.2.29-81.el6.centos.noarch网上说只删除subscription-manager这个包就可以了，本次没有验证。本次是把yum和subscription-manager包同时删除了，顺便试试自己能否修复。^^
[root@localhost ~]# rpm -e yum
error: Failed dependencies:
yum is needed by (installed) rhn-client-tools-1.0.0.1-16.el6.noarch
yum >= 3.0 is needed by (installed) PackageKit-yum-plugin-0.5.8-21.el6.x86_64
yum >= 3.2.19 is needed by (installed) PackageKit-yum-0.5.8-21.el6.x86_64
yum >= 3.2.19-15 is needed by (installed) yum-rhn-plugin-0.9.1-48.el6.noarch
yum is needed by (installed) python-meh-0.12.1-3.el6.noarch
yum >= 3.2.19-15 is needed by (installed) subscription-manager-1.9.11-1.el6.x86_64
yum >= 3.2.18 is needed by (installed) yum-plugin-security-1.1.30-14.el6.noarch
yum >= 3.2.29 is needed by (installed) yum-utils-1.1.30-14.el6.noarch
[root@localhost ~]# rpm -e subscription-manager
error: Failed dependencies:
subscription-manager = 1.9.11-1.el6 is needed by (installed) subscription-manager-gui-1.9.11-1.el6.x86_64[root@localhost ~]# rpm -e yum --nodeps各种依赖关系，只能强制删除yum了，删除之后再测试，果然没有yum命令了。
[root@localhost ~]# yum repolist
-bash: /usr/bin/yum: No such file or directory对于subscription-manager，简单粗暴的一删到底。对不起了，redhat……^^
[root@localhost ~]# rpm -e subscription-manager
error: Failed dependencies:
subscription-manager = 1.9.11-1.el6 is needed by (installed) subscription-manager-gui-1.9.11-1.el6.x86_64
You have new mail in /var/spool/mail/root
[root@localhost ~]# rpm -e subscription-manager-gui-1.9.11-1.el6.x86_64
error: Failed dependencies:
subscription-manager-gui = 1.9.11-1.el6 is needed by (installed) subscription-manager-firstboot-1.9.11-1.el6.x86_64
[root@localhost ~]# rpm -e subscription-manager-firstboot-1.9.11-1.el6.x86_64
[root@localhost ~]# rpm -e subscription-manager-gui-1.9.11-1.el6.x86_64
You have new mail in /var/spool/mail/root
[root@localhost ~]# rpm -e subscription-manager
You have new mail in /var/spool/mail/root都删完了就开始安装了。我选择上163镜像源下载软件包。
http://mirrors.163.com/centos/6/os/x86_64/Packages/
yum相关的包很多，只有yum-3.2.29-81.el6.centos.noarch.rpm是主程序包，我把它下载下来，通过xftp或者xshell自带的ftp工具传到centos6.5系统上。
chmod修改权限之后，检查依赖关系，发现还需要python-urlgrabber和yum-plugin-fastestmirror包，同时需要KEY。
[root@localhost ~]# rpm -ivh --test yum-3.2.29-81.el6.centos.noarch.rpm
warning: yum-3.2.29-81.el6.centos.noarch.rpm: Header V3 RSA/SHA1 Signature, key ID c105b9de: NOKEY
error: Failed dependencies:
python-urlgrabber >= 3.9.1-10 is needed by yum-3.2.29-81.el6.centos.noarch
yum-plugin-fastestmirror is needed by yum-3.2.29-81.el6.centos.noarch
You have new mail in /var/spool/mail/root在http://mirrors.163.com/centos/6/os/x86_64 的页面下载RPM-GPG-KEY-CentOS-6文件，传到服务器上，并导入操作系统。
[root@localhost ~]# rpm --import RPM-GPG-KEY-CentOS-6下载python-urlgrabber和yum-plugin-fastestmirror包。开始安装，结果新下载的包与系统已经安装的包冲突，那就强制卸载掉。
[root@localhost ~]# rpm -ivh python-urlgrabber-3.9.1-11.el6.noarch.rpm
Preparing... ########################################### [100%]
file /usr/lib/python2.6/site-packages/urlgrabber/grabber.py from install of python-urlgrabber-3.9.1-11.el6.noarch conflicts with file from package python-urlgrabber-3.9.1-9.el6.noarch
file /usr/lib/python2.6/site-packages/urlgrabber/grabber.pyc from install of python-urlgrabber-3.9.1-11.el6.noarch conflicts with file from package python-urlgrabber-3.9.1-9.el6.noarch
file /usr/lib/python2.6/site-packages/urlgrabber/grabber.pyo from install of python-urlgrabber-3.9.1-11.el6.noarch conflicts with file from package python-urlgrabber-3.9.1-9.el6.noarch
file /usr/lib/python2.6/site-packages/urlgrabber/progress.pyc from install of python-urlgrabber-3.9.1-11.el6.noarch conflicts with file from package python-urlgrabber-3.9.1-9.el6.noarch
file /usr/lib/python2.6/site-packages/urlgrabber/progress.pyo from install of python-urlgrabber-3.9.1-11.el6.noarch conflicts with file from package python-urlgrabber-3.9.1-9.el6.noarch
You have new mail in /var/spool/mail/root
[root@localhost ~]# rpm -e python-urlgrabber-3.9.1-9.el6.noarch
error: Failed dependencies:
urlgrabber is needed by (installed) python-virtinst-0.600.0-18.el6.noarch
python-urlgrabber is needed by (installed) python-virtinst-0.600.0-18.el6.noarch[root@localhost ~]# rpm -e python-urlgrabber-3.9.1-9.el6.noarch --nodeps
You have new mail in /var/spool/mail/root然后重新安装，成功。
[root@localhost ~]# rpm -ivh python-urlgrabber-3.9.1-11.el6.noarch.rpm
Preparing... ########################################### [100%]
1:python-urlgrabber ########################################### [100%][root@localhost ~]# rpm -ivh yum-plugin-fastestmirror-1.1.30-40.el6.noarch.rpm
error: Failed dependencies:
yum >= 3.0 is needed by yum-plugin-fastestmirror-1.1.30-40.el6.noarch
[root@localhost ~]# rpm -ivh yum-plugin-fastestmirror-1.1.30-40.el6.noarch.rpm yum-3.2.29-81.el6.centos.noarch.rpm
Preparing... ########################################### [100%]
1:yum ########################################### [ 50%]
2:yum-plugin-fastestmirro########################################### [100%]最后试试yum，没问题了。