yum安装epel-release扩展源后yum 安装其他包报错：One of the configured repositories failed (unKnown)

yum 安装epel-release扩展源后报错：One of the configured repositories failed (unKnown)

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报错分析：

1、错误提示一：（虚假原因）

One of the configured repositories failed (Unknown),and yum doesn't have enough cached data to continue.

中文翻译

其中一个已配置的存储库失败（未知），并且yum没有足够的缓存数据可以继续。

2、错误提示二：（真实原因）（出问题的根本）

Cannot retrieve metalink for repository: epel/x86_64. Please verify its path and try again

中文翻译

无法检索存储库的metalink：epel / x86_64。 请验证其路径，然后重试

3.完整错误

One of the configured repositories failed (unKnown),
 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 ge
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