参考
https://serverfault.com/questions/1161816/mirrorlist-centos-org-no-longer-resolve
修改 Centos 的 yum 源为阿里云
去阿里云 yum 镜像源官网：
https://developer.aliyun.com/mirror/
选择自己对应的操作系统，这里以 centos7 演示：
先备份原 yum 配置文件：
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
下载了阿里云提供的 CentOS 7 的 Yum 源配置文件，并将其覆盖到系统中的 /etc/yum.repos.d/CentOS-Base.repo 文件：
wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo# 或使用 curl 下载文件
curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo
清除旧缓存：
sudo yum clean all
生成新缓存：
sudo yum makecache
检验新配置是否生效：
yum repolist
提示不能解析 mirrorlist.centos.org
Could not retrieve mirrorlist http://mirrorlist.centos.org?arch=x86_64&release=7&repo=sclo-rh 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 onlysafe 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 workingupstream. This is most often useful if you are using a newerdistribution release than is supported by the repository (and thepackages for the previous distribution release still work).3. Run the command with the repository temporarily disabledyum --disablerepo=<repoid> ...4. Disable the repository permanently, so yum won't use it by default. Yumwill then just ignore the repository until you permanently enable itagain or use --enablerepo for temporary usage:yum-config-manager --disable <repoid>orsubscription-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 muchslower). If it is a very temporary problem though, this is often a nicecompromise:yum-config-manager --save --setopt=<repoid>.skip_if_unavailable=true
执行如下命令：
sudo sed -i s/mirror.centos.org/vault.centos.org/g /etc/yum.repos.d/CentOS-*.repo
sudo sed -i s/^#.*baseurl=http/baseurl=http/g /etc/yum.repos.d/CentOS-*.repo
sudo sed -i s/^mirrorlist=http/#mirrorlist=http/g /etc/yum.repos.d/CentOS-*.repo