GRUB (Grand Unified Bootloader) is a bootloader available from the GNU project, and it is the first program that runs when a computer starts. It is responsible for loading and managing the boot process in Linux operating systems. GRUB is the default bootloader for many Linux distributions, and it is better than many of the previous versions of bootloaders. Some of its features include:
- GRUB supports LBA (Logical Block Addressing Mode) which puts the addressing conversion used to find files into the firmware of the hard drive.
- GRUB provides maximum flexibility in loading the operating systems with required options using a command-based, pre-operating system environment.
When a Linux operating system starts up, GRUB is the first program that runs. It loads the kernel of the operating system, and then the kernel loads the rest of the operating system, including the shell, the desktop environment, and other operating system features. GRUB is also a boot manager, and the boot loader is the part of GRUB that loads the kernel of the operating system into memory. The boot manager part of GRUB is the menu that allows you to select different operating system kernels to load.
GRUB has three interfaces that provide different levels of functionality, and the Linux kernel can be booted by the users with the help of these interfaces. The interfaces are:
- Menu Interface: This is the usual GRUB screen that allows you to choose which operating systems to boot, if there is more than one on your machine. You can also choose to load a different kernel if your Linux distribution has more than one installed.
- Command-line Interface: This interface is used to execute commands manually.
- Rescue Interface: This interface is used when something goes wrong, or your boot entries are invalid.
Many distributions of Linux, like Ubuntu, automatically install GRUB when you install the operating system.
