Yum不能用...

oo0t0oo

輪入:
yum update

出現以下:
Traceback (most recent call last):
  File "/usr/bin/yum", line 28, in ?
    import yummain
  File "/usr/share/yum-cli/yummain.py", line 25, in ?
    from yum import logginglevels
ImportError: cannot import name logginglevels

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
到底出了什麼問題....plx help
THX