On Mon, 16 Nov 2015 20:55:58 +0900
janpenguin@??? wrote:

> Below is the error message.
>
> Install the GRUB boot loader on a hard disk
>
> Unable to install GRUB in /dev/sda
> Executing 'grub-install /dev/sda' failed.
>
> This is a fatal error.

Hi,
I was having the same problem.
I found that my hdd had some old fs data/label (UFS to be correct).
It seemed Devuan installer was unable to clear it.
I solved by zeroing the first hdd megabyte, then restarting the
installer.

Hope it helps.
Bye

--
BL