Note: I am reporting this based on the Debian package version 2.04-19, but the relevant code appears present in upstream git.

If I run a verbose-grub-install, that reports a grub-mkimage command:

$ sudo grub-install -v /dev/sda 2>&1 | grep grub-mkimage
grub-install: info: grub-mkimage --directory '/usr/lib/grub/i386-pc' --prefix '(mduuid/90aa34c17bd7b3502690763c289ebaf1)/boot/grub' --output '/boot/grub/i386-pc/core.img'  --dtb '' --sbat '' --format 'i386-pc' --compression 'auto'  'ext2' 'part_msdos' 'part_msdos' 'diskfilter' 'mdraid1x' 'biosdisk'


...yet that command cannot be run:

$ sudo grub-mkimage --directory '/usr/lib/grub/i386-pc' --prefix '(mduuid/90aa34c17bd7b3502690763c289ebaf1)/boot/grub' --output '/boot/grub/i386-pc/core.img'  --dtb '' --sbat '' --format 'i386-pc' --compression 'auto'  'ext2' 'part_msdos' 'part_msdos' 'diskfilter' 'mdraid1x' 'biosdisk'
grub-mkimage: error: cannot open `': No such file or directory.


The problem is the "--dtb ''" and "--sbat ''" parts. When grub-install runs, it calls grub_install_generate_image() directly and passes NULL pointers for those options, yet when grub-mkimage is run from the command line, those options are pointers to empty strings. grub_install_generate_image() checks for NULL pointers, but not for empty strings.

I do not know the best solution; either grub-install should omit those options when they are unset or grub-mkimage should accept them and consider empty strings to mean "disabled".

Thanks,
Corey