錯誤如下：

[[email protected] svn]# yum install gcc-c++.x86_64
已載入外掛：fastestmirror, langpacks
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; 未知的錯誤"


 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

原因：沒有配置resolv.conf
解決方法:
到/etc目錄下配置resolv.conf加入nameserver IP,如：
nameserver 8.8.8.8
nameserver 8.8.4.4
search localdomain
儲存再次執行上面的命令就可以。

/etc/resolv.conf 配置DNS 客戶
檔案/etc/resolv.conf 配置DNS 客戶，它包含了主機的域名搜尋順序和DNS伺服器的地址，每一行應包含一個關鍵字和一個或多個的由空格隔開的引數。
下面是一個例子檔案：
**nameserver 8.8.8.8
nameserver 8.8.4.4
search localdomain**
合法的引數及其意義如下：
nameserver 表明DNS 伺服器的IP 地址。可以有很多行的nameserver，每一個帶一個I P 地址。在查詢時就按nameserver 在本檔案中的順序進行，且只有當第一個nameserver 沒有反應時才查詢下面的nameserver.
domain 宣告主機的域名。很多程式用到它，如郵件系統；當為沒有域名的主
機進行DNS 查詢時，也要用到。如果沒有域名，主機名將被使用，刪除所有在第一個點( . )前面的內容。
search 它的多個引數指明域名查詢順序。當要查詢沒有域名的主機，主機將在由search 宣告的域中分別查詢。domain 和search 不能共存；如果同時存在，後面出現的將會被使用。
sortlist 允許將得到域名結果進行特定的排序。它的引數為網路/掩碼對。允許任意的排列順序。Red Hat 中沒有提供預設的/ e t c / r e s o l v. c o n f 檔案，它的內容是根據在安裝時給出的選項動態建立的。