GNU GRUB (or just GRUB) is a boot loader package that supports multiple operating systems on a computer.

During boot-up, the user can select the operating system to run.

GNU GRUB is based on an earlier multiboot package, GRUB (GRand Unified Bootloader).

What is grub and how does it work?

22. Basically, GRUB bootloader is the software that loads the Linux kernel. (It has other uses as well). It is the first software that starts at a system boot. When the computer starts, BIOS first run a Power-on self-test (POST) to check hardware like memory, disk drives and that it works properly.

How do I start Linux from Grub?

The second line tells GRUB the location of the kernel you want to use. Start typing /boot/vmli , and then use tab-completion to fill in the rest. Type root=/dev/sdX to set the location of the root filesystem.