【Linux】yum 無法更新

yum update 時, 出現以下錯誤訊息 ----

...
---> Package httpd-manual.i386 0:2.2.3-22.el5.centos.1 set to be updated
Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in ?
    yummain.user_main(sys.argv[1:], exit_code=True)
  File "/usr/share/yum-cli/yummain.py", line 229, in user_main
    errcode = main(args)
...


先 yum clean all

會出現訊息 ----
Loaded plugins: fastestmirror
Cleaning up Everything
Cleaning up list of fastest mirrors

再 yum update

不過還沒搞懂原因 & why, 也不確定是否適用其他情況.