I am building a multiboot isohybrid image using the following command:
xorriso -as mkisofs -iso-level 3 -full-iso9660-filenames -volid "MULTIBOOT" -eltorito-boot boot/isolinux/isolinux.bin -eltorito-catalog boot/isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table -isohybrid-mbr ${isodir}boot/isolinux/isohdpfx.bin -eltorito-alt-boot -e boot/isolinux/efiboot.img -no-emul-boot -isohybrid-gpt-basdat -output ~/output.iso ${isodir}
This loads the isolinux bootloader as expected when booting in BIOS mode, but as I want to use GRUB, I chain load it using this configuration file:
Default Grub2
LABEL Grub2
SAY Switching to Grub2...
Linux /boot/grub/lnxboot.img
INITRD /boot/grub/core.img
GRUB loads, but instead of displaying the main menu, it drops to the rescue console claiming it can't recognize the filesystem. Interestingly, this happens when if I load the ISO image from a CD, but not if I burn it to a USB drive. I this case, GRUB finds the file system and works as expected.
Here is the start of my current grub.cfg file (without the menu entries):
insmod iso9660
insmod gfxmenu
insmod png
insmod part_msdos
insmod part_gpt
insmod fat
insmod ntfs
insmod ext2
insmod efi_gop
insmod efi_uga
if [ "${grub_platform}" != "efi" ]; then
insmod vbe
insmod vga
fi
insmod gfxterm
terminal_output gfxterm
set gfxmode=800x600
search --file --no-floppy --set=root /multiboot/menu/main_menu.cfg
#set root='hd0,msdos1'
set timeout=30
set theme="/boot/grub/themes/multiboot/theme.txt"
loadfont /boot/grub/fonts/unifont-bold-16.pf2
loadfont /boot/grub/fonts/unifont-regular-16.pf2
loadfont /boot/grub/fonts/unifont-regular-14.pf2
loadfont /boot/grub/fonts/unifont-regular-32.pf2
set default=1
My guess is that my core.img file is missing some module to make things works when booting from CD, but I have already specifically included the ISO 9660 module on my core.img without success.
I came up with the solution. I had to create a core.img file using the following command:
grub-mkimage -O i386-pc -c common.cfg -p /boot/grub biosdisk part_msdos part_gpt fat ntfs exfat iso9660 search -o core.img
With the common.cfg file containing this:
search --file --no-floppy --set=root /multiboot/menu/main_menu.cfg
set cmdpath=($root)
set prefix=($root)/boot/grub