There used to be a prompt that while worded poorly, did give you the ability to switch to a bios mode install even though you booted the installer in UEFI mode, but it was removed in 18.04. Unfortunately, instead of making it switch to a bios mode install by default, it keeps with the UEFI install and crashes. This mistake is being tracked in bug #1668148. Hopefully this will be fixed in 18.04.1, but until then, you just have to get your system to boot the installer in bios mode. If you are using a USB stick you can delete the EFI directory to make sure it can't boot in UEFI mode.
** Changed in: grub-installer (Ubuntu) Status: Incomplete => Invalid -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1767703 Title: Calling 'apt-install grub-efi-amd64-signed' failed To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/grub-installer/+bug/1767703/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs