One of the configured repositories failed（yum配置存储库失败）

在进行本地yum的基本配置时出现错误

错误代码：

One of the configured repositories failed (CentOS-7 - Media),
and yum doesn’t have enough cached data to continue. At this point the only
safe thing yum can do is fail. There are a few ways to work “fix” this:

 1. Contact the upstream for the repository and get them to fix the problem.

 2. Reconfigure the baseurl/etc. for the repository, to point to a working
    upstream. This is most often useful if you are using a newer
    distribution release than is supported by the repository (and the
    packages for the previous distribution release still work).

 3. Run the command with the repository temporarily disabled
        yum --disablerepo=c7-media ...

 4. Disable the repository permanently, so yum won't use it by default. Yum
    will then just ignore the repository until you permanently enable it
    again or use --enablerepo for temporary usage:

        yum-config-manager --disable c7-media
    or
        subscription-manager repos --disable=c7-media

 5. Configure the failing repository to be skipped, if it is unavailable.
    Note that yum will try to contact the repo. when it runs most commands,
    so will have to try and fail each time (and thus. yum will be be much
    slower). If it is a very temporary problem though, this is often a nice
    compromise:

        yum-config-manager --save --setopt=c7-media.skip_if_unavailable=true

这段错误信息指的是“其中一个配置的存储库失败（CentOS-7-媒体），
并且yum没有足够的缓存数据继续。在这一点上，唯一可以做的安全的事情就是失败。”

这个问题出现的原因可能是你之前修改过yum的源，然后你又对CentOS-Media.repo文件进行了修改，导致上一个yum库产生冲突

解决办法

1. 下载一个新的源（这里我选择下载阿里云的源）

wget http://mirrors.aliyun.com/repo/Centos-7.repo

2. 将下载的源替换原来的repo文件

mv Centos-7.repo CentOS-Media.repo

(如果没有CentOS-Media.repo可能为CentOS-Base.repo)

3. 清理旧缓存数据，缓存新数据

yum clean all

yum makecache

(yum makecache的作用就是把服务器的包信息下载到本地电脑缓存起来)

4. 最后出现metadata cache created（中文下显示为“元数据缓存已建立”）即已完成配置