Centos7安装nginx yum报错，yum源报错解决办法：
1、更新epel源后，出现yum报错

[root@hacker117 ~]# yum install epel-release（安装成功）
[root@hacker117 ~]# yum install nginx（安装失败，提示如下：）
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile


 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 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=<repoid> ...

     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 <repoid>
        or
            subscription-manager repos --disable=<repoid>

     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=<repoid>.skip_if_unavailable=true

2、解决办法2种：

（1）更新阿里源或其它源（自行百度）
（2）修改源文件解决（采用这种）
可以执行下的命令，如果正常安装软件可以不用执行（我这里正常能安装）。

yum clean all
yum makecache
yum update

如果还是报错怎么办：
直接改成这样：在后面 添加一行

mirrorlist=https://mirrors.fedoraproject.org/metalink?repo=epel-7&arch=$basearch