When booting Linux, the boot loader is responsible for loading the kernel image and the initial RAM disk or filesystem (which contains some critical files and device drivers needed to start the system) into memory.įor systems using the BIOS/MBR method, the boot loader resides at the first sector of the hard disk, also known as the Master Boot Record (MBR). Most Linux boot loaders can present a user interface for choosing alternative options for booting Linux, and even other operating systems that might be installed. Thereafter, information on date, time, and the most important peripherals are loaded from the CMOS values (after a technology used for the battery-powered memory store which allows the system to keep track of the date and time even when it is powered off).Ī number of boot loaders exist for Linux the most common ones are GRUB (for GRand Unified Boot loader), ISOLINUX (for booting from removable media), and DAS U-Boot (for booting on embedded devices/appliances). Up to this stage, the machine does not access any mass storage media. The boot loader is usually stored on one of the hard disks in the system, either in the boot sector (for traditional BIOS/MBR systems) or the EFI partition (for more recent (Unified) Extensible Firmware Interface or EFI/UEFI systems). Once the POST is completed, the system control passes from the BIOS to the boot loader. The BIOS software is stored on a ROM chip on the motherboard. After this, the remainder of the boot process is controlled by the operating system (OS).
This process is also called POST (Power On Self Test). When the computer is powered on, the Basic Input/Output System (BIOS) initializes the hardware, including the screen and keyboard, and tests the main memory. Starting an x86-based Linux system involves a number of steps.
Master Boot Record (MBR) and Boot Loader.
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