A good guide is this Debian web page.
An image that boots only on UEFI can be created with xorriso
like this:
xorriso -as mkisofs \
-iso-level 3 \
-r -V <ISO_LABEL> \
-J -joliet-long \
-append_partition 2 0xef <BOOT_IMG> \
-partition_cyl_align all \
-o <OUTPUT_IMAGE> \
<ISO_DIRECTORY>
The UEFI_BOOT_IMAGE
is an ESP ([U]EFI System Partition) image file. That means that it should be formatted as a FAT32
partition. You can generate it with:
BOOT_IMG_DATA=$(mktemp -d)
BOOT_IMG=$(mktemp -d)/efi.img
mkdir -p $(dirname $BOOT_IMG)
truncate -s 8M $BOOT_IMG
mkfs.vfat $BOOT_IMG
mount $BOOT_IMG $BOOT_IMG_DATA
mkdir -p $BOOT_IMG_DATA/efi/boot
grub-mkimage \
-C xz \
-O x86_64-efi \
-p /boot/grub \
-o $BOOT_IMG_DATA/efi/boot/bootx64.efi \
boot linux search normal configfile \
part_gpt btrfs ext2 fat iso9660 loopback \
test keystatus gfxmenu regexp probe \
efi_gop efi_uga all_video gfxterm font \
echo read ls cat png jpeg halt reboot
umount $BOOT_IMG_DATA
rm -rf $BOOT_IMG_DATA
That will create the ESP image in $(mktemp -d)/efi.img
, so you must replace the placeholder with the actual file path.
This answer was based on a coment by @ThomasSchmitt.