紀念以下，耗時一整天連不上外網自己出現的一系列錯誤

案例：安裝好虛擬機器進行yum操作時出現：

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; Unknown error"


 One of the configured repositories failed (Unknown),
 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

於是從網上查詢各種資料，方法很多

方法1.   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

儲存再次執行上面命令就可以   

試了試，不行

方法2

使用vi開啟DNS的配置檔案進行修改:

      在命令提示符中輸入: vi  /etc/sysconfig/network-scripts/ifcfg-eth33

用vi 開啟這個檔案後，接下來會出現截圖的內容, 其中要注意兩個配置(按下面的值去設定)，如果不會使用vi的同學，請自行google或者百度用法。

              ONBOOT=yes

               MM_CONTROLLED=no

設定好後。

重啟CentOS後一切就正常了。

試了試，不行。

終於重灌了好多次發現了錯誤

在安裝centos7 的時候，開啟：NETWORK&HOST NAME中的連線時沒有連線上

IP資訊就是不出來，查看了好多帖子，用了好多辦法仍然出現下面的情況，很絕望

最後發現原來是虛擬機器沒有配好造成的錯誤，一定要勾選上！！！！！

勾選之後就可以啦

進入之後，yum指令也能夠正常運行了