解决方法
vim /etc/apt/sources.list.d/pve-enterprise.list

注释掉

deb https://enterprise.proxmox.com/debian/pve stretch pve-enterprise

也可以直接删除掉

rm -f /etc/apt/sources.list.d/pve-enterprise.list

echo "deb http://download.proxmox.com/debian/pve stretch pve-no-subscription" > /etc/apt/sources.list.d/pve-install-repo.list

wget http://download.proxmox.com/debian/proxmox-ve-release-5.x.gpg -O /etc/apt/trusted.gpg.d/proxmox-ve-release-5.x.gpg

apt update && apt dist-upgrade

官方文档：

https://pve.proxmox.com/wiki/Install_Proxmox_VE_on_Debian_Stretch

之后就可以正常使用

apt update && apt dist-upgrade

升级完成后，可以执行pveversion -v查看下最新的软件版本。然后执行reboot重启物理服务器

pve5.4 测试通过