I can't boot to the Ubuntu 14.10 ISO I have on my drive (running Ubuntu 14.04 as my main OS btw). I added these lines to the bottom of /etc/grub.d/40_custom:
menuentry 'ubuntu-iso' {
set isofile="/boot/ubuntu-14.10-desktop-amd64.iso"
loopback loop (hd0,1)$isofile
linux (loop)/casper/vmlinuz.efi boot=casper iso-scan/filename=$isofile noprompt noeject
initrd (loop)/casper/initrd.lz
}
The Ubuntu ISO is at /boot/ubuntu-14.10-desktop-amd64.iso, and I've verified its checksum. /dev/sda1 is mounted at /boot, which is why I've done (hd0,1)$isofile above.
Then I run sudo update-grub. The new menu entries show up in the grub menu screen, but when I select it and try to boot it just boots to my existing OS instead of the ISO.