how to integrate an old installation in Grub and startmenu

[Robert Heller]

Os-prober and the Grub config builder scripts are rather limited, and really
cannot properly build a grub menu for older installs of Linux. They are
especially bad if you have a "shared" /boot FS (which you really should have if
you are multibooting Linuxes) and really bad when the "other" Linuxes are for
a completely different distro (eg RedHat / CentOS). It also gets confused if
you are using LVM and have Linux VMs using LVM volumns for their disk space.

The only thing you can do is to hack the Grub config builder scripts and add 
custom ones to handle the "other" Linuxes.  It is in the documentation for the 
Grub config builder that the scripts are limited and should not be considered 
able to work in all cases as distributed.  


At Mon, 13 Sep 2021 13:07:35 +0200 "Ubuntu user technical support,? not for general discussions" <ubuntu-users at lists.ubuntu.com> wrote:

> 
> On Mon, 13 Sept 2021 at 12:30, Lentes, Bernd
> <bernd.lentes at helmholtz-muenchen.de> wrote:
> >
> > Yes. I think that comes from the fact that the PV and VG has been created with Ubuntu 16.04,
> > but the os-prober is started from 20.04, so PV and VG are old for him.
> > I don't think that this is related with my problem.
> 
> I do not *know* but I think they might be.
> 
> Your modern GRUB must be able to "see" into your old OS's /boot and
> root filesystems in order to boot what is in them.
> 
> 

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