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Broken UEFI implementations: Difference between revisions
→CDs are wild and crazy
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=== CDs are wild and crazy ===
CDs can be booted through the option key menu if they're set up properly. There are also some caveats.
# On some machines, they need to be Apple Partition Map formatted, i.e. the format Apple has used since they derived it from the format NeXT used when they bought them
# This also means to make a disc that works on EFI+Apple+BIOS as both an ISO image /and/ an image on a USB stick, you need to actually /execute/ the APM header signature on BIOS machines. Thankfully that's pretty safe, but it's a little squicky in your head. [http://www.syslinux.org/wiki/index.php/The_Syslinux_Project syslinux]]'s "isohybrid" utility has had this ability to build this sort of image since version 4.05 .
# On some machines, there needs to be a special El Torito image for an HFS+ formatted ESP that conforms to what's above in [http://wiki.osdev.org/index.php?title=Broken_UEFI_implementations#There.27s_additional_UI_presented_mixed_in_with_BDS There's additional UI presented mixed in with BDS] in order to have it show your UEFI-bootable image as anything other than "Windows". This means there are /three/ El Torito entries - the "Validation Entry" of type 0x00 (80x86), which holds the BIOS code, and then *two* entries of type 0xef - the HFS+ and then the FAT one. The HFS+ one needs to be last one. Tools like mkisofs can make ISOs with multiple images with the several boot images using the "-eltorito-alt-boot" and "-e" options.
# The menus will show the BIOS image as "Windows"
# Unfortunately the menus will also show the FAT-based UEFI image as "Windows".
# Some machines will not correctly boot the FAT-based UEFI image. This means you need to tell your users that when they're trying to boot a CD or USB stick of your product, they need to pick the left-most correctly labeled one with an icon.
It's pretty easy to orchestrate getting all this correct with tools like [https://github.com/rhinstaller/lorax Lorax], which has scripts for doing it on RHEL and Fedora, and can be taught to do it on other things without excessive work.
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