echo "deb [arch=amd64] http://download.proxmox.com/debian/pve buster pve-no-subscription" > /etc/apt/sources.list.d/pve-install-repo.list

wget http://download.proxmox.com/debian/proxmox-ve-release-6.x.gpg -O /etc/apt/trusted.gpg.d/proxmox-ve-release-6.x.gpg

chmod +r /etc/apt/trusted.gpg.d/proxmox-ve-release-6.x.gpg  # optional, if you have a non-default umask