今天遇到一个奇怪的原因就是运行yum出错如下：
[root@localhost tool]# yum
There was a problem importing one of the Python modules
required to run yum. The error leading to this problem was:
No module named rpm
Please install a package which provides this module, or
verify that the module is installed correctly.
It's possible that the above module doesn't match the
current version of Python, which is:
2.4.3 (#1, Jan 9 2013, 06:49:54)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-54)]
If you cannot solve this problem yourself, please go to
the yum faq at:
http://wiki.linux.duke.edu/Yum
通过网上搜索得知，centos上，yum依赖于python2.4，我由于想升级使用python2.6，于是决定删除python 2.4，结果运行yum出错如上。
于是，只好重新安装yum。没有了yum是一件痛苦的事情，只能使用rpm：rpm -Uvh http://mirror.centos.org/centos-5/5.9/os/i386/CentOS/yum-3.2.22-40.el5.centos.noarch.rpm
结果，又接连爆出依赖很多包，最后通过命令 rpm -Uvh --force --nodeps 将所有的包都强制安装之后，运行yum成功。