$ sudo grub-install /dev/sda

$ sudo grub-install /dev/sda
Installing for i386-pc platform.
Installation finished. No error reported.

$ sudo update-grub
Generating grub configuration file ...
Found background image: /usr/share/images/desktop-base/desktop-grub.png
Found linux image: /boot/vmlinuz-5.10.0-15-amd64
Found initrd image: /boot/initrd.img-5.10.0-15-amd64
Found linux image: /boot/vmlinuz-5.10.0-11-amd64
Found initrd image: /boot/initrd.img-5.10.0-11-amd64
Found linux image: /boot/vmlinuz-5.10.0-10-amd64
Found initrd image: /boot/initrd.img-5.10.0-10-amd64
Found linux image: /boot/vmlinuz-5.10.0-9-amd64
Found initrd image: /boot/initrd.img-5.10.0-9-amd64
Found linux image: /boot/vmlinuz-5.10.0-8-amd64
Found initrd image: /boot/initrd.img-5.10.0-8-amd64
Found memtest86+ image: /boot/memtest86+.bin
Found memtest86+ multiboot image: /boot/memtest86+_multiboot.bin
Found linux image: /boot/vmlinuz-5.10.0-15-amd64
Found initrd image: /boot/initrd.img-5.10.0-15-amd64
Found linux image: /boot/vmlinuz-5.10.0-11-amd64
Found initrd image: /boot/initrd.img-5.10.0-11-amd64
Found linux image: /boot/vmlinuz-5.10.0-10-amd64
Found initrd image: /boot/initrd.img-5.10.0-10-amd64
Found linux image: /boot/vmlinuz-5.10.0-9-amd64
Found initrd image: /boot/initrd.img-5.10.0-9-amd64
Found linux image: /boot/vmlinuz-5.10.0-8-amd64
Found initrd image: /boot/initrd.img-5.10.0-8-amd64
Found Debian GNU/Linux bookworm/sid on /dev/sda2
Found Kona Linux 6.0 MATE/x86_64 (11) on /dev/sda3
Found Debian GNU/Linux bookworm/sid on /dev/sda5
Found Kona Linux 6.0 MATE/x86_64 (11) on /dev/sda6
Found Debian GNU/Linux bookworm/sid on /dev/sda2
Found Kona Linux 6.0 MATE/x86_64 (11) on /dev/sda3
Found Debian GNU/Linux bookworm/sid on /dev/sda5
Found Kona Linux 6.0 MATE/x86_64 (11) on /dev/sda6
Found linux image: /boot/vmlinuz-5.10.0-15-amd64
Found initrd image: /boot/initrd.img-5.10.0-15-amd64
Found linux image: /boot/vmlinuz-5.10.0-11-amd64
Found initrd image: /boot/initrd.img-5.10.0-11-amd64
Found linux image: /boot/vmlinuz-5.10.0-10-amd64
Found initrd image: /boot/initrd.img-5.10.0-10-amd64
Found linux image: /boot/vmlinuz-5.10.0-9-amd64
Found initrd image: /boot/initrd.img-5.10.0-9-amd64
Found linux image: /boot/vmlinuz-5.10.0-8-amd64
Found initrd image: /boot/initrd.img-5.10.0-8-amd64
Found Debian GNU/Linux bookworm/sid on /dev/sda2
Found Kona Linux 6.0 MATE/x86_64 (11) on /dev/sda3
Found Debian GNU/Linux bookworm/sid on /dev/sda5
Found Kona Linux 6.0 MATE/x86_64 (11) on /dev/sda6
Found Debian GNU/Linux bookworm/sid on /dev/sda2
Found Kona Linux 6.0 MATE/x86_64 (11) on /dev/sda3
Found Debian GNU/Linux bookworm/sid on /dev/sda5
Found Kona Linux 6.0 MATE/x86_64 (11) on /dev/sda6
Found Debian GNU/Linux bookworm/sid on /dev/sda2
Found Kona Linux 6.0 MATE/x86_64 (11) on /dev/sda3
Found Debian GNU/Linux bookworm/sid on /dev/sda5
Found Kona Linux 6.0 MATE/x86_64 (11) on /dev/sda6
done