Grub2 Bootloader
From Free Knowledge Base- The DUCK Project: information for everyone
/boot/grub/grub.cfg - This is the main configuration file that replaces menu.lst. Unlike menu.lst, this file cannot be edited by hand! I strongly advise against trying to tamper with this file, using chattr command or anything of the sort. Let it be.
/etc/grub.d/ - This new directory contains GRUB scripts. These scripts are building blocks from which the grub.cfg file is built. When the relevant GRUB command is executed, the scripts are read in a certain sequence and grub.cfg is created.
/etc/default/grub - This file contains the GRUB menu settings that are read by the GRUB scripts and written into grub.cfg. It is the customization part of the GRUB, similar to the old menu.lst, except the actual boot entries.
Ubuntu and its derived distros have a useful script named update-grub and you can use it to update your grub configuration file by running sudo update-grub.
