阿里云ESC云主机centos系统yum更新时，会遇到类似如下404等错误：
http://mirrors.aliyun.com/centos/6/os/x86_64/repodata/repomd.xml: [Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 404 Not Found" Trying other mirror.
http://mirrors.aliyuncs.com/centos/6/os/x86_64/repodata/repomd.xml: [Errno 14] PYCURL ERROR 7 - "Couldn't connect to host" Trying other mirror.
Error: Cannot retrieve repository Metadata (repomd.xml) for repository: base. Please verify its path and try again
蓝叶经过研究发现阿里云的yum源好多都不完善，才会出现以上错误导致yum源无法更新，解决方法只需要按照以下步骤修改文件就可以解决阿里云centos系统yum源错误，如果懂命令就登陆ssh使用命令修改，如果是新手可以使用winscp登陆后下载/etc/yum.repos.d/目录下的CentOS-Base.repo、epel.repo文件进行修改。
