The story so far:
I have been following this guide to produce a customized version of Ubuntu. As of now, the structure of the CD is complete. I have generated an ISO with the command:
sudo grub-mkrescue -o live_cd.iso /path/to/cd/directory
The iso image boots very well in BIOS mode.
Though, it does not boot in UEFI mode, but shows this:
How do I make the ISO image UEFI compatible?
Thanks in advance!
For EFI boot you need to form a specific structure of the image's filesystem, not just bootsector (since it's unused), so have a look at Ubuntu's live-helper scripts (my guess) or examine mki-copy-efiboot script (the part of mkimage which I wrote and use).
In case you just need a custom rescue image, not neccessarily an Ubuntu-based one, you might like my ALT Linux Rescue as the technology behind it is both open and explicitly created for easy derivatives (but is mostly documented in Russian which didn't stop some people) -- it's basically about grabbing live-builder.iso, booting it on a spare VM/host and:
git clone git://git.altlinux.org/people/mike/packages/mkimage-profiles.git
cd mkimage-profiles
make regular-rescue.iso
grep -B6 RESCUE_PACKAGES conf.d/regular.mk
It might also be helpful to read the excellent Rod's book on EFI bootloaders as well as Matthew Garrett's ISO9660/EFI quest report.
Good luck whatever route you take!
PS: grub-mkrescue is not EFI aware as of 2.00 apparently.
