yum 报错3

 . Contact the upstream for the repository and get them to fix the problem.

     . 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).

     . Disable the repository, 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 epel

     . 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=epel.skip_if_unavailable=true

failure: repodata/repomd.xml from epel: [Errno ] No more mirrors to try.
http://mirrors.cloud.aliyuncs.com/epel/7/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: mirrors.cloud.aliyuncs.com

解决方法：

vi /etc/yum.repos.d/epel.repo

修改前
[epel]
name=Extra Packages for Enterprise Linux  - $basearch
baseurl=http://mirrors.cloud.aliyuncs.com/epel/7/$basearch
failovermethod=priority
enabled=
gpgcheck=

修改后
[epel]
name=Extra Packages for Enterprise Linux  - $basearch
#baseurl=http://mirrors.cloud.aliyuncs.com/epel/7/$basearch
failovermethod=priority
enabled=
gpgcheck=