ubuntu@ubuntu:~$ sudo grub-install --recheck --root-directory=/mnt/ /dev/sda
Probing devices to guess BIOS drives. This may take a long time.
Due to a bug in xfs_freeze, the following command might produce a segmentation
fault when /mnt//boot/grub is not in an XFS filesystem. This error is harmless and
can be ignored.
xfs_freeze: specified file ["/mnt//boot/grub"] is not on an XFS filesystem
Installation finished. No error reported.
This is the contents of the device map /mnt//boot/grub/device.map.
Check if this is correct or not. If any of the lines is incorrect,
fix it and re-run the script `grub-install'.

(fd0)   /dev/fd0
(hd0)   /dev/sda
(hd1)   /dev/sdb
ubuntu@ubuntu:~$