错误信息

docker build yum install Could not retrieve **

 > [2/2] RUN yum install -y wget:                                                                                                                                                                        
#0 0.308 Loaded plugins: fastestmirror, ovl
#0 0.367 Determining fastest mirrors
#0 0.373 
#0 0.373 
#0 0.373  One of the configured repositories failed (Unknown),
#0 0.373  and yum doesn't have enough cached data to continue. At this point the only
#0 0.373  safe thing yum can do is fail. There are a few ways to work "fix" this:
#0 0.373 
#0 0.373      1. Contact the upstream for the repository and get them to fix the problem.
#0 0.373 
#0 0.373      2. Reconfigure the baseurl/etc. for the repository, to point to a working
#0 0.373         upstream. This is most often useful if you are using a newer
#0 0.373         distribution release than is supported by the repository (and the
#0 0.373         packages for the previous distribution release still work).
#0 0.373 
#0 0.373      3. Run the command with the repository temporarily disabled
#0 0.373             yum --disablerepo=<repoid> ...
#0 0.373 
#0 0.373      4. Disable the repository permanently, so yum won't use it by default. Yum
#0 0.373         will then just ignore the repository until you permanently enable it
#0 0.373         again or use --enablerepo for temporary usage:
#0 0.373 
#0 0.373             yum-config-manager --disable <repoid>
#0 0.373         or
#0 0.373             subscription-manager repos --disable=<repoid>
#0 0.373 
#0 0.373      5. Configure the failing repository to be skipped, if it is unavailable.
#0 0.373         Note that yum will try to contact the repo. when it runs most commands,
#0 0.373         so will have to try and fail each time (and thus. yum will be be much
#0 0.373         slower). If it is a very temporary problem though, this is often a nice
#0 0.373         compromise:
#0 0.373 
#0 0.373             yum-config-manager --save --setopt=<repoid>.skip_if_unavailable=true
#0 0.373 
#0 0.373 Cannot find a valid baseurl for repo: base/7/x86_64
#0 0.373 Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=container error was
#0 0.373 14: curl#6 - "Could not resolve host: mirrorlist.centos.org; Unknown error"

昨天刚安装完成docker的时候还是可以使用的，今天再用的时候就出现这个问题了（中间服务器是否重启不太清楚） 。

最后通过以下方法解决：原因是nameserver的问题

解决步骤

1. 修改resolv.conf文件，增加nameserver

vim /etc/resolv.conf 

nameserver 8.8.8.8
nameserver 114.114.114.114

2. 保存后如果重启的话，还会还原的这里需要进行锁定

chattr +i /etc/resolv.conf   //resolv被锁定，即使root也不能修改

3. 如果需要继续修改

chattr -i /etc/resolv.conf

4. 重启network 查看是否还存在(centos8)

systemctl restart NetworkManager