前言

CentOS（Community Enterprise Operating System，中文意思是社区企业操作系统）是Linux发行版之一，是免费的、开源的、可以重新分发的开源操作系统。

遇到问题

产品需要支持ARM架构，但是CentOS ARM版本 装好以后并不能成功安装软件，安装ssh时报错如下：

[root@3f0492e1adc1 /]# yum install openssh-server
Loaded plugins: fastestmirror, ovl
Determining fastest mirrors
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=aarch64&repo=os&infra=container 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/aarch64

原因是因为无法从 CentOS 镜像列表服务器（http://mirrorlist.centos.org/?release=7&arch=aarch64&repo=os&infra=container）检索镜像列表，我们手动访问发现也无法请求。

解决方案

• 首先备份原来的源配置文件

  mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak

• 然后下载新的源配置文件替换旧配置文件

  curl -o /etc/yum.repos.d/CentOS-Base.repo  http://mirrors.aliyun.com/repo/Centos-altarch-7.repo

• 然后执行命令

  yum clean all

• 最后执行安装命令成功安装

  yum install openssh-server