Grub2 entry to boot Ubuntu live ISO from 2nd GPT partition

40_iso

#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.
menuentry "Ubuntu 20.04 ISO" {
    set root=(hd0,gpt2)
    set isofile="/ubuntu-20.04.3-desktop-amd64.iso"
        loopback loop $isofile
        linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile persistent persistent-path=/ub2004-1/ fsck.mode=skip quiet splash --
        initrd (loop)/casper/initrd
}
# btw, this file is /etc/grub.d/40_iso - run update-grub to install it