Mark Fletcher <mark2...@gmail.com> writes > The question is, what values are config_directory and prefix set to?
Grub sets config_directory to point to the directory where it's reading it's config from. In other words, /boot. But why not just use 40_custom? It copies whatever is in the file (after the header) to your grub.cfg. Don't need to figure out what file goes in what directory. It also keeps configuration in /etc instead of moving it to /boot.
