centos7.9yum安装报错Cannot find a valid baseurl for repo

注意: centos7.9 因为已经停止维护,所以安装程序的时候,可能会报各种错误.
遇到下面错误时的参考解决方案,已成功于霖磐服务器操作通过:
安装 google-chrome 时显示报错:

```
-->正在解决依赖关系 ***** , 它被软件包 google-chrome-*** 需要

 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=<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: centos-sclo-sclo
```

解决方案一（推荐）:

替换镜像源为阿里云（推荐）
适用场景：希望长期稳定使用，且无需手动维护仓库配置。
步骤：

备份并清空原仓库配置：
cd /etc/yum.repos.d
sudo mkdir backup && sudo mv *.repo backup/  # 备份原文件
sudo rm -f *.repo  # 清理旧配置

下载阿里云镜像源：
sudo curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo
sudo curl -o /etc/yum.repos.d/epel.repo https://mirrors.aliyun.com/repo/epel-7.repo

更新缓存：
sudo yum clean all
sudo yum makecache
优点：阿里云镜像长期稳定，适合生产环境

 解决方案二：

临时忽略
yum --disablerepo=<报错 Cannot find a valid for repo:后面的那个repoid> install <要安装的rpm>