Hendrik Boom <hendrik@???> wrote:

> Do I understand correctly that grub-install will scan my only hard
> drive looking for (at least) bootable Linux systems? And that as a
> result, running grub-install on the old system will detect both and
> create a grub menu that contains both?
>
> (of course, using the grub files on the old system, which I'd better
> not delete if I still want to boot)

grub-install will install the first stage.
update-grub will update the grub menu, and depending on how you've set options, it will scan all filesystems looking for OSs to put in the menu.

So one option would be to copy your files, then update-grub to add the newly copied version to the grub menu. That would allow you to boot into your new copy, after which you could run update-grub again to correctly set the menu for that system.

There is a slight complication though - where you have multiple systems on one physical drive, I'm not sure how grub gets to select which set of files to use. My guess is that the location of the filesystem containing the files is hardcoded into the first stage when it's installed.

Alternatively, try http://www.supergrubdisk.org and save a lot of hassle !