In computing, booting (booting up) is a bootstrapping process that starts operating systems when the user turns on a computer system. A boot sequence is the set of operations the computer performs when it is switched on that loads an operating system.
GNU GRUB (“GRUB” for short) is a boot loader package from the GNU Project. GRUB is the reference implementation of the Multiboot Specification, which allows a user to have several different operating systems on their computer at once, and to choose which one to run when the computer starts. GRUB can be used to select from different kernel images available on a particular operating system’s partitions, as well as to pass boot-time parameters to such kernels.
GNU GRUB developed from a previous package called the GRand Unified Bootloader (a play on grand unified theory). GRUB can run on any operating system with a Multiboot kernel. It is predominantly used on Unix-like systems; the GNU operating system uses GNU GRUB as its boot loader, as do most general-purpose Linux distributions. Solaris has been able to boot using GRUB since version 10 (1/06 release).