报错信息Error: Failed to download metadata for repo ‘appstream’: Cannot prepare internal mirrorlist: No URLs in mirrorlist
解决：
wget 'http://mirror.centos.org/centos/8-stream/baseOS/x86_64/os/Packages/centos-gpg-keys-8-3.el8.noarch.rpm'sudo rpm -i 'centos-gpg-keys-8-3.el8.noarch.rpm'
dnf --disablerepo '*' --enablerepo=extras swap centos-linux-repos centos-stream-repos
sudo dnf distro-sync