dockerfile里或者在容器里执行yum，报错，找不到源(invalid baseurl xxx)，但是宿主机上执行yum是没问题的啊，为什么？
因为不论是dockerfile使用RUN关键字执行yum还是直接进入到容器里面执行yum，它们都是使用的docker镜像里面的源(CentOS是在路径/etc/yum.repo.d/CentOS-Base.repo)，所以你要把宿主机上的同路径下的源拷贝到容器里面，然后docker commit一个新的“基础镜像”，这个时候使用docker build xxx(即使用Dockerfile的方式)就不会报错了。
拷贝方法docker cp xxx xxx
内容扩展
dockerfile中执行yum操作报错
我们先看下报错信息：
Sending build context to Docker daemon 9.363 MB
Step 1 : FROM docker.io/centos
---> 196e0ce0c9fb
Step 2 : MAINTAINER liuliangliang
---> Using cache
---> 7d7e06799c20
Step 3 : ADD file/tomcat7.tgz /usr/local/
---> Using cache
---> 10ffdea53a02
Step 4 : RUN yum install java-1.8.0-openjdk -y
---> Running in 7824a339e077
Loaded plugins: fastestmirror, ovl
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
Could not retrieve mirrorlist http://mirrorlist.centos.org/"Could not resolve host: mirrorlist.centos.org; Unknown error"
The command '/bin/sh -c yum install java-1.8.0-openjdk -y' returned a non-zero code: 1
解决方法：
这个你在resolv.conf文件里加上 DNS服务就行了 这个文件在/etc下， 加上
nameserver 8.8.8.8
nameserver 8.8.4.4
search localdomain
就行了