yum update后无法使用

yum update后出错，提示引用的python模块有问题,以为是yum软件损坏了，差一点就重新安装yum服务。

使用rpm -qa|grep yum指令查看,原有的yum服务还在

yum-3.2.29-69.el6.centos.noarch
yum-plugin-fastestmirror-1.1.30-30.el6.noarch
yum-metadata-parser-1.1.2-16.el6.x86_64

仔细一瞧，原来是python版本升级导致的问题

There was a problem importing one of the Python modules
required to run yum. The error leading to this problem was:

   No module named yum

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:
2.7.10 (default, Aug 23 2016, 18:47:04) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-16)]

If you cannot solve this problem yourself, please go to 
the yum faq at:
  http://yum.baseurl.org/wiki/Faq

yum升级之后，将系统原有的python服务版本由2.6升级到了2.7，使用whereis python指令可以看到有两个版本的python服务

python: /usr/bin/python2.7-config /usr/bin/python /usr/bin/python2.6 /usr/bin/python2.6-config /usr/bin/python2.7 /usr/lib/python2.6 /usr/lib64/python2.6 /usr/include/python2.6 /usr/share/man/man1/python.1.gz

lrwxrwxrwx 1 root root 18 8月  23 2016 /usr/bin/python -> /usr/bin/python2.7

知道问题所在，解决方案也就有了

1.编辑/usr/bin/yum文件

将/usr/bin/yum开头的
#!/usr/bin/python
替换顾
#!/usr/bin/python2.6
注意此处替换为你系统原有的python版本

2.重新建立系统python软链接

rm /usr/bin/python
ln -s /usr/bin/python2.6 /usr/bin/python