Cannot download repomd.xml解决CentOS8 yum安装AppStream报错

# 腾云yum源
# sudo mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup.3
# sudo wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.cloud.tencent.com/repo/centos8_base.repo
# 阿里yum源
sudo mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
sudo wget -O/etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-8.5.2111.repo

# 清理yum缓存
yum clean all
# 建立新的缓存
yum makecache
# dnf makecache