<code>前提：xshell能连接到centos，但是yum时就报错

[root@localhost ~]# yum install -y vim

已加载插件：fastestmirror

Determining fastest mirrors

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

一步解决：

直接复制下面的地址去本地网站搜索，就会自动下载源

CentOS 5： http://mirrors.aliyun.com/repo/Centos-5.repo

CentOS 6： http://mirrors.aliyun.com/repo/Centos-6.repo

CentOS 7： http://mirrors.aliyun.com/repo/Centos-7.repo备份centos原本源

#cp /etc/yum.repos.d

#mv CentOS-Base.repo CentOS-Base.repo.bak将下载好的Centos-7.repo文件，通过xshell中的文件传输工具导入到 /etc/yum.repos.d下清空并生成缓存

#yum clean all

#yum makecache测试下载

#yum install -y vim