CentOS yum有时出现“Could not retrieve mirrorlist ”的解决办法

安装报错如下： 

[root@centos-02 ~]# yum -y install vim lrzsz 
已加载插件：fastestmirror
Loading mirror speeds from cached hostfile
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= ...

     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 
        or
            subscription-manager repos --disable=

     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=.skip_if_unavailable=true

Cannot find a valid baseurl for repo: base/7/x86_64

原因：没有配置resolv.conf

解决方法:

到/etc目录下配置resolv.conf加入nameserver IP,如： 
nameserver 8.8.8.8 
nameserver 8.8.4.4 
search localdomain 
保存再次运行上面的命令就可以。

如果以上方法没解决，可尝试如下方法：

出现此问题，最根本的原因是“/etc/yum.repos.d/epel.repo”里面的镜像源路径不对。

具体步骤如下：
1、打开 /etc/yum.repos.d/epel.repo；
/etc/yum.repos.d/epel.repo

2、注释掉mirrorlist，取消注释baseurl；
将
[epel]
name=Extra Packages for Enterprise Linux 7 - $basearch
#baseurl=http://download.fedoraproject.org/pub/epel/7/$basearch
mirrorlist=https://mirrors.fedoraproject.org/metalink?repo=epel-7&arch=$basearch
修改为
[epel]
name=Extra Packages for Enterprise Linux 7 - $basearch
baseurl=http://download.fedoraproject.org/pub/epel/7/$basearch
#mirrorlist=https://mirrors.fedoraproject.org/metalink?repo=epel-7&arch=$basearch

3、再次使用yum命令即正常！
yum clean all
yum makecache
yum update