问题：大部分yum命令 ，其中包括yum list。都报以下错误：

已加载插件：fastestmirror
Determining fastest mirrors
 * base: mirrors.aliyun.com
 * extras: mirrors.aliyun.com
 * updates: mirrors.aliyun.com
base                                                                                                   | 3.6 kB  00:00:00     
epel-apache-maven                                                                                      | 3.3 kB  00:00:00     
extras                                                                                                 | 3.4 kB  00:00:00     
nginx                                                                                                  | 2.9 kB  00:00:00     
http://nginx.org/packages/centos/7/noarch/RPMS/nginx-release-centos-7-0.el7.ngx.noarch.rpm/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found
正在尝试其它镜像。
To address this issue please refer to the below wiki article 

https://wiki.centos.org/yum-errors

If above article doesn't help to resolve this issue please use https://bugs.centos.org/.



 One of the configured repositories failed (added from: http://nginx.org/packages/centos/7/noarch/RPMS/nginx-release-centos-7-0.el7.ngx.noarch.rpm),
 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=nginx.org_packages_centos_7_noarch_RPMS_nginx-release-centos-7-0.el7.ngx.noarch.rpm ...

     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 nginx.org_packages_centos_7_noarch_RPMS_nginx-release-centos-7-0.el7.ngx.noarch.rpm
        or
            subscription-manager repos --disable=nginx.org_packages_centos_7_noarch_RPMS_nginx-release-centos-7-0.el7.ngx.noarch.rpm

     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=nginx.org_packages_centos_7_noarch_RPMS_nginx-release-centos-7-0.el7.ngx.noarch.rpm.skip_if_unavailable=true

failure: repodata/repomd.xml from nginx.org_packages_centos_7_noarch_RPMS_nginx-release-centos-7-0.el7.ngx.noarch.rpm: [Errno 256] No more mirrors to try.
http://nginx.org/packages/centos/7/noarch/RPMS/nginx-release-centos-7-0.el7.ngx.noarch.rpm/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found

最后翻译了一下，大概的意思是，上一个配置的源安装没有完成，卡住了，要不要跳过。

最后提示运行：

大坑搞了一晚上，真刺激。。。。。。。。。。。。。。。。