为了从本地镜像中安装一些安装包，我把 yum 玩残了

/etc/yum.repos.d

对yum进行初始化操作

    yum clean all  //清除缓存
    yum makecache   //建立新缓存
    yum -y update  //更新本地yum

反正就是报错了， 各种解决都死命报错后，我一气之下，就都删了，干脆配置成 国内的yum 源了

cd /etc/yum.repos.d/
rm -rf *

# 在CentOS中配置使用网易和阿里的开源镜像
wget http://mirrors.aliyun.com/repo/Centos-7.repo
wget http://mirrors.163.com/.help/CentOS7-Base-163.repo

# 下载阿里开源镜像的epel源文件'
wget -O /etc/yum.repos.d/epel-7.repo http://mirrors.aliyun.com/repo/epel-7.repo    
 
yum clean all  //清除缓存
yum makecache   //建立新缓存
yum -y update  //更新本地yum

# 查看所有的yum源

额， 居然出现了 版本冲突， 算了，不管了

参考链接 ： https://www.cnblogs.com/renpingsheng/p/7845096.html

yum clean all

[root@aimaster yum.repos.d]# yum clean all

已加载插件：fastestmirror, langpacks
Determining fastest mirrors
There are no enabled repos.
 Run "yum repolist all" to see the repos you have.
 To enable Red Hat Subscription Management repositories:
     subscription-manager repos --enable <repo>
 To enable custom repositories:
    yum-config-manager --enable <repo>

yum repolist all

Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was
14: curl#6 - "Could not resolve host: mirrorlist.centos.org; 未知的错误"


 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: base/7/x86_64

解决方式：

vim /etc/resolv.conf
    nameserver 8.8.8.8
    nameserver 8.8.4.4