So I've been banging my head against the wall trying to figure out what I'm doing wrong.
I have 2 different machines I'm trying to get this to work on. A Dell Precision 5820 & a Dell Precision 5810. I take the standard ISO of Ubuntu 18.04.1 LTS Desktop (from here: https://www.ubuntu.com/download/desktop), burn it to a DVD using Brasero (from an Ubuntu 16.04 machine), and use that DVD to install Ubuntu on both machines just fine (UEFI). Two things to note. Both machines are using a RAID controller and the 5820 has an NVMe M.2 drive while the 5810 has an SSD.
Now what I want to do is customize the ISO to make it an unattended install with the latest package updates. I was able to successfully do this with Ubuntu 16.04 (BIOS/Legacy boot) using a preseed file and following the instructions here (Live CD Customization), here (preseeding), and here.
So now I'm taking the 18.04 ISO, doing the same thing I did with 16.04 and following instructions here to make it UEFI bootable. This seems to work when I boot to a VM in VirtualBox (and enabling EFI), but not on the Dell computers I have. The same computers were able to boot the default Ubuntu 18.04 image, but not my custom one. I'm sure I'm doing something wrong.
When I check the file system of both ISO's with fdisk like this:
$ sudo fdisk -l ubuntu-18.04.1-desktop-amd64.iso
Disk ubuntu-18.04.1-desktop-amd64.iso: 1.8 GiB, 1953349632 bytes, 3815136 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: dos
Disk identifier: 0x663eb4c4
Device Boot Start End Sectors Size Id Type
ubuntu-18.04.1-desktop-amd64.iso1 * 0 3815135 3815136 1.8G 0 Empty
ubuntu-18.04.1-desktop-amd64.iso2 3737268 3741939 4672 2.3M ef EFI (FAT-12/16/32)
They both look identical, with the exception of the size of the first partition. The custom ISO is a little bigger since I installed some updates.
