Upgrading 17.10 to 18.04, no disk format

[Brook Harty]

Tried to upgrade a 17.04 to 18.04 beta 2, without wiping system. I removed all directories on the SSD except home before the install.

Just error aborted on "grub-efi-amd64-signed failed to install"

SSD is formatted as 3 partitions, bios/swap/root

# fdisk -l /dev/sda
Disk /dev/sda: 477 GiB, 512110190592 bytes, 1000215216 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 7E8873B9-CD45-408B-8D2F-C46053AB715B

Device Start End Sectors Size Type
/dev/sda1 2048 4095 2048 1M BIOS boot
/dev/sda2 4096 4225023 4220928 2G Linux swap
/dev/sda3 4225024 1000215182 995990159 474.9G Linux filesystem

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity 18.04.4 [modified: lib/partman/automatically_partition/question]
ProcVersionSignature: Ubuntu 4.15.0-13.14-generic 4.15.10
Uname: Linux 4.15.0-13-generic x86_64
ApportVersion: 2.20.9-0ubuntu2
Architecture: amd64
CasperVersion: 1.392
Date: Fri Apr 13 10:08:02 2018
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi file=/cdrom/preseed/ubuntu-mate.seed boot=casper quiet splash ---
LiveMediaBuild: Ubuntu-MATE 18.04 LTS "Bionic Beaver" - Beta amd64 (20180404)
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)

[Phillip Susi (psusi)]

Your disk is currently partitioned to boot in bios mode, but you booted the installer in EFI mode. A warning message prompted you that this could be a problem and recommended performing a bios mode install instead, but you chose not to. You either need to perform the bios mode install, or partition the disk using GPT and set up an EFI system partition to install in EFI mode. This will be done for you if you choose the "use entire disk" guided install option.