当我运行yum install时，它显示在此错误下方：
yum install -y --setopt = obsoletes = 0 docker-ce-17.03.1.ce-1.el7.centos docker-ce-selinux-17.03.1.ce-1.el7.centos 加载的插件：最快的镜像 基地3.6 kB 00:00:00 https://download./repodata/repomd.xml：[Errno 14] curl＃6-“无法解析主机：下载。；名称或服务未知” 尝试其他镜子。
其中一个已配置的存储库发生故障（从https://download添加）。 并且yum没有足够的缓存数据来继续。在这一点上唯一 yum可以做的安全的事情是失败。有几种方法可以“解决”此问题：
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=download ...
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 download
or
subscription-manager repos --disable=download
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=download.skip_if_unavailable=true
失败：从下载的repodata / repomd.xml：[Errno 256]没有更多尝试的镜像。 https://download./repodata/repomd.xml：[Errno 14] curl＃6-“无法解析主机：下载。；名称或服务未知”