求助：为什么每次使用YUM都出现这样的错误信息？而且每个软件用YUM时都是这样的错误信息。这个fedora-cn是什么？有办法解决吗？我是菜鸟，谢谢！
[root@localhost ~]# yum install yumex
Loading "installonlyn" plugin
Setting up Install Process
Parsing package install arguments
ftp://ftp.fedora.cn/pub/fedora-c ... epodata/repomd.xml: [Errno 4] IOError: [Errno ftp error] 550 Failed to change directory.
Trying other mirror.
Error: Cannot open/read repomd.xml file for repository: fedora-cn
