说明

由于centos8 在2022年停止服务，后继版本为8-steam。在使用阿里云的 centos8 的 yum 时报错。
错误如下所示：

Cannot download repomd.xml: Cannot download repodata/repomd.xml

解决方法

删除 /etc/yum.repos.d 目录中的所有文件，替换 /etc/yum.repos.d 目录中的 CentOS-Base.repo 内容。
新内容如下：

[base]
name=CentOS-8-stream - Base - mirrors.aliyun.com
baseurl=https://mirrors.aliyun.com/centos/8-stream/BaseOS/$basearch/os/
gpgcheck=1
gpgkey=https://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official
#additional packages that may be useful
[extras]
name=CentOS-8-stream - Extras - mirrors.aliyun.com
baseurl=https://mirrors.aliyun.com/centos/8-stream/extras/$basearch/os/
gpgcheck=1
gpgkey=https://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-8-stream - Plus - mirrors.aliyun.com
baseurl=https://mirrors.aliyun.com/centos/8-stream/centosplus/$basearch/os/
gpgcheck=1
enabled=0
gpgkey=https://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official
[PowerTools]
name=CentOS-8-stream - PowerTools - mirrors.aliyun.com
baseurl=https://mirrors.aliyun.com/centos/8-stream/PowerTools/$basearch/os/
gpgcheck=1
enabled=0
gpgkey=https://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official
[AppStream]
name=CentOS-8-stream - AppStream - mirrors.aliyun.com
baseurl=https://mirrors.aliyun.com/centos/8-stream/AppStream/$basearch/os/
gpgcheck=1
gpgkey=https://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official

然后执行下面的命令

yum clean all
yum makecache

执行完成后，即可正常使用 YUM。