Re: What does grub-install do?

[Goh Lip]

On Friday 01,October,2010 11:32 PM, Dennis Cao wrote:
> Now, I find another confusing problem. If I choose to boot from USB
> Hard Disk(/dev/sdb1), the screen will show the welcome message of Grub
> 1.97 beta, then it quickly show the grub menu which is configured in
> the hard disk (/dev/sda8).
>
> I wonder whether this is caused by the command 'grub-install'? Because
> I still do not very understand what '--root-directory' does in the
> grub-install command.  According to Goh's explanation, I guess it
> installs the boot.img and core.img to specified device and tried to
> load 'grub.cfg' from {boot-device}:{root-directory}. Is it right?

Cao, when you just do a "grub-install /dev/sda" it 'sets' the grub to 
the mbr. Similarly, when you do a "grub-install /dev/sdb" it sets the 
grub to that disk's (sdb) mbr section. So when you boot from sdb 
directly, it uses the grub from where it was set from. That's what 
exactly it does.

When you do a "grub-install --root-directory=/media/something /dev/sda", 
it creates a /boot and /boot/grub/ (without any grub.cfg) from the OS to 
that /media/something and sets the /media/something's grub to the mbr.

Hope that is clear. Good luck again.

Regards - Goh Lip