Error downloading packages:
  vsftpd-3.0.2-25.el7.x86_64: [Errno 256] No more mirrors to try

错误如上

我在网上搜方法 说是

# 清理缓存
$ yum clean all
$ yum makecache
#顺便更新一下
$ yum update

结果又出现了新的错误

Loaded plugins: langpacks, product-id, search-disabled-repos, subscription-manager
This system is not registered with an entitlement server. You can use subscription-manager to register.
file:///media/repodata/repomd.xml: [Errno 14] curl#37 - "Couldn't open file /media/repodata/repomd.xml"
Trying other mirror.


 One of the configured repositories failed (local),
 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=local ...

     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 local
        or
            subscription-manager repos --disable=local

     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=local.skip_if_unavailable=true

failure: repodata/repomd.xml from local: [Errno 256] No more mirrors to try.
file:///media/repodata/repomd.xml: [Errno 14] curl#37 - "Couldn't open file /media/repodata/repomd.xml"

呜呜呜呜哭了
然后又去搜，改了网络配置等等方法，全都不行！！！

最后，我发现，是因为他们都是centos，而我是Redhat。

打扰了……

所以我首先最应该做的！！就是！！挂载！！！

$ mount /dev/cdrom /media

挂载成功了之后，
我再进行

$ yum clean all
$ yum makecache
$ yum update

然后……我就成功了。。

这件事情告诉我们，即使发现错误在网上搜索看见你以为的“相同”的错误，其实也可能不太一样
因为这个，我一整节课都没听呜呜呜，全在搞这个。。
一个生信菜鸡在学习Linux的辛酸路qaq