-hda vdisk.img -cdrom bionic-server-amd64.iso -append 'console=ttyS0 locale=en_US.UTF-8 priority=critical'. 5. Proceed with the install by 1) enter user info and 2) select disk. 6. Eventually the “Ubuntu installer main menu” will appear. Even if you click on “Install the system” the installation step will fail.

Ubuntu VPS Hosting via debian-installer/main-menu changes priority.