I have a Dell XPS with multiple drives, one for each OS. I can boot Ubuntu 16.04 fine with the G4D code:
Kernel /vmlinuz root=/dev/sda1 ro
I get no errors
With Ubuntu 18.04, I use:
kernel /vmlinuz root=/dev/sdb1 ro
I get a error 13 after the UUID line. It says "Booting Ubuntu 18.04.2 LTS (sdb1). Setting root to (hd1,0). Filetype is ext2fs, partition type 0x83" and stops with error 13.
I've always used G4D quite successfully until Ubuntu 18.04. 18.04 boots okay under native Grub2. I'm very confused. I might point out that the 16.04 drive is a Toshiba 500GB and the 18.04 is a WDC 500GB. Any help will be appresiated!