Install GRUB boot-blocks

Install

from source

slack150+

slack150 now has the package available

slackpkg search grub-2

GPT

define your target disk

fdisk -l
disk=/dev/sda
disk=/dev/nvme0n1

in case it is a GPT table, do this first (BIOS BOOT PARTITION)

cgdisk $disk

(about 1M free space is more than enough)
(it does not matter what partition number / slot you take)
type --> ef02
name --> bios-boot

partprobe $disk
fdisk -l $disk
ls -lF ${disk}*

Ready to go

in any case, you can then proceed anyway

grub-install --no-floppy --boot-directory=/boot $disk

SETUP

see grub