On Thu, Dec 02, 2021 at 10:37:38AM +0100, frantal@libero.it wrote: > How to install os-prober? apt install os-prober > I think I have to be able to boot Debian first to be able to install it later. > > Right? Yes. Either boot Debian natively, or boot some sort of rescue system, mount the Debian root partition (and /boot if you have a separate /boot), chroot into the Debian system, and then install os-prober there.