Hi!
I tried to install grub2 to a mounted virtual box vdi image, but when I started the virtual machine it didn't work.
I used the following commands for compile and installation:
(in decompressed folder: )
./configure --prefix=/mnt/ --exec-prefix=/mnt/
make
make install
(in /mnt/sbin folder: )
./grub-install --boot-directory=/mnt/boot /dev/nbd0

The error massage was: „no such device: xxx”

The grub.cfg file doesn't load.

Please someone help me what should I do.

I think this thread should be in Hardware. Anyway, paste the outputs of the following command:

What is this? /dev/nbd0

/dev/nbd0 is the virtual disk, where I connected the vdi image with this:
sudo qemu-nbd -c /dev/nbd0 /home/mappa/proba_gep.vdi

The output of the cat fstab:

# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point> <type> <options> <dump> <pass>
proc /proc proc nodev,noexec,nosuid 0 0
# / was on /dev/sda1 during installation
UUID=0dcb9a83-9f35-4ce8-85aa-e8477bd3c84a / ext4 errors=remount-ro 0 1
# swap was on /dev/sda5 during installation
UUID=e8f53a65-6564-4b0c-b3aa-03b09d535f5a none swap sw 0 0