One of the configured repositories failed，yum在下载httpd时出错

最近在使用虚拟机时，遇到了如下的问题

One of the configured repositories failed (未知),
 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

Cannot find a valid baseurl for repo: cm-repo

查找了很多资料，最后解决问题
方法一：
将/etc/yum.repos.d/epel.repo中的mirrorlist改为baseurl

vim /etc/yum.repos.d/epel.repo
[epel]
name=Extra Packages for Enterprise Linux 7 - $basearch
baseurl=http://download.fedoraproject.org/pub/epel/7/$basearch
#mirrorlist=https://mirrors.fedoraproject.org/metalink?repo=epel-7&arch=$basearch
failovermethod=priority
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7

epel-debuginfo]
name=Extra Packages for Enterprise Linux 7 - $basearch - Debug
baseurl=http://download.fedoraproject.org/pub/epel/7/$basearch/debug
#mirrorlist=https://mirrors.fedoraproject.org/metalink?repo=epel-debug-7&arch=$basearch
failovermethod=priority
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7
gpgcheck=1

[epel-source]
name=Extra Packages for Enterprise Linux 7 - $basearch - Source
baseurl=http://download.fedoraproject.org/pub/epel/7/SRPMS
#mirrorlist=https://mirrors.fedoraproject.org/metalink?repo=epel-source-7&arch=$basearch
failovermethod=priority
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7
gpgcheck=1

然后/etc/resolv.conf文件中增加nameserver 144.144.144.144
vim /etc/resolv.conf

nameserver 192.168.1.2
nameserver 144.144.144.144

大多数搜到的方法都是这个，修改镜像
网上说还要执行下面几个命令：

yum clean all 
yum makecache
yum update
yum install -y lsof

意思大概就是释放一下缓存

点击查看代码

方法二：（也是我最后解决的办法） 首先能ping通百度，（网络可用） ping www.baidu.com

删除yum.repos.d目录下所有文件

rm -f /etc/yum.repos.d/*
然后执行下边的命令，重新下载阿里的这个文件（需要外网）

wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
执行下边的命令，清理缓存

yum clean all

最后问题解决，可以下载。