GRUB is configured using grub.cfg, usually located under /boot/grub. This file is quite flexible, but most users will not need to write the whole thing by hand.
|• Simple configuration:||Recommended for most users|
|• Shell-like scripting:||For power users and developers|
|• Multi-boot manual config:||For non-standard multi-OS scenarios|
|• Embedded configuration:||Embedding a configuration file into GRUB|