a mesterValahogy így ?
sudo chattr -i /boot/grub/i386-pc/core.img
sudo grub-install --target=i386-pc --debug --force /dev/sdbx
sudo chattr +i /boot/grub/i386-pc/core.img
https://github.com/alberthdev/alberthdev-misc/wiki/Installing-GRUB2-to-a-Partition