centos7无法安装求帮忙怎么解决。

1. <p>Loaded plugins: fastestmirror</p><p>Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infr</p><p>a=stock error was14: curl#6 - "Could not resolve host: mirrorlist.centos.org; Unknown error"</p><p>
   
2. </p><p>
   
3. </p><p> One of the configured repositories failed (Unknown),</p><p> and yum doesn't have enough cached data to continue. At this point the only</p><p> safe thing yum can do is fail. There are a few ways to work "fix" this:</p><p>
   
4. </p><p>     1. Contact the upstream for the repository and get them to fix the problem.</p><p>
   
5. </p><p>     2. Reconfigure the baseurl/etc. for the repository, to point to a working</p><p>        upstream. This is most often useful if you are using a newer</p><p>        distribution release than is supported by the repository (and the</p><p>        packages for the previous distribution release still work).</p><p>
   
6. </p><p>     3. Disable the repository, so yum won't use it by default. Yum will then</p><p>        just ignore the repository until you permanently enable it again or use</p><p>        --enablerepo for temporary usage:</p><p>
   
7. </p><p>            yum-config-manager --disable <repoid></p><p>
   
8. </p><p>     4. Configure the failing repository to be skipped, if it is unavailable.</p><p>        Note that yum will try to contact the repo. when it runs most commands,</p><p>        so will have to try and fail each time (and thus. yum will be be much</p><p>        slower). If it is a very temporary problem though, this is often a nice</p><p>        compromise:</p><p>
   
9. </p><p>            yum-config-manager --save --setopt=<repoid>.skip_if_unavailable=true</p><p>
   
10. </p><p>Cannot find a valid baseurl for repo: base/7/x86_64</p>

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请问大师如何解决呢？

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