Ytdyklly

I've noted that the Ubuntu ISO file is bootable on systems with BIOS and with UEFI. I've remastered Ubuntu from scratch and I'd like my ISO file to be bootable in both cases.

My remastering of Ubuntu is done by first installing debootstrap into a chroot jail, and then gradually adding files until I have all desired programs. However, the resulting ISO file is only bootable on a system with BIOS.

I believe I need some different magic with mkisofs, but what about the files in EFI/BOOT? What is the origin of those files? Is there anything else I need?

Thanks!

AndyS

You can generate an ESP (EFI System Partition) image suitable for booting on UEFI with:

#! /bin/sh



BOOT_IMG_DATA=$(mktemp -d)

BOOT_IMG=efi.img



mkdir -p $(dirname $BOOT_IMG)



truncate -s 4M $BOOT_IMG

mkfs.vfat $BOOT_IMG

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 fat iso9660 loopback 

    test keystatus gfxmenu regexp probe 

    efi_gop efi_uga all_video gfxterm font 

    echo read ls cat png jpeg halt reboot



mcopy -i $BOOT_IMG -s $BOOT_IMG_DATA/efi ::

That will generate a FAT-formatted file (change the location of the file by changing the $BOOT_IMG variable), which is, in turn, an ESP image.

You can use the generated image by adding the flag -append_partition 2 0xef efi.img to the xorriso command.

The resulting xorriso command may be something like this:

xorriso -as mkisofs 

    -r -V <ISO_LABEL> 

    -o <OUTPUT_ISO_IMAGE> 

    -J -J -joliet-long -cache-inodes 

    -isohybrid-mbr /usr/lib/ISOLINUX/isohdpfx.bin 

    -b isolinux/isolinux.bin 

    -c isolinux/boot.cat 

    -boot-load-size 4 -boot-info-table -no-emul-boot 

    -eltorito-alt-boot 

    -e --interval:appended_partition_2:all:: 

    -append_partition 2 0xef efi.img 

    -no-emul-boot -isohybrid-gpt-basdat 

    <ISO_DIRECTORY>

Bear in mind that you also need to use ISOLINUX if you want your image to boot on BIOS systems. GRUB2 is for UEFI.

Also, you should use a recent version of xorriso (the flag --interval:appended_partition_2:all:: was added a couple years ago, so old versions doesn't support it).

For further guidance, also take a look to this question.