GNU GRUB (GRand Unified Bootloader) is a bootloader. It was originally intended as a common bootloader for various new operating systems conforming to the multiboot specification. Nowadays, many Linux distributions have adopted GRUB as their default bootloader.
There are two major versions of GRUB, with incompatible configuration files:
- GRUB1, now known as GRUB Legacy, with version numbers up to 0.97;
- GRUB2, with version numbers 1.90 and above.