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GNU GRUB (short for GNU GRand Unified Bootloader, commonly referred to as GRUB) is a boot loader package from the GNU Project.GRUB is the reference implementation of the Free Software Foundation's Multiboot Specification, which provides a user the choice to boot one of multiple operating systems installed on a computer or select a specific kernel configuration available on a particular ...
systemd-boot is a free and open-source boot manager created by obsoleting the gummiboot project and merging it into systemd in May 2015. [1] [2] [3] [4]gummiboot was developed by the Red Hat employees Kay Sievers and Harald Hoyer and designed as a minimal alternative to GNU GRUB for systems using the Unified Extensible Firmware Interface (UEFI).
In UEFI systems, the Linux kernel can be executed directly by UEFI firmware via the EFI boot stub, [8] but usually uses GRUB 2 or systemd-boot as a bootloader. [9] [10] If UEFI Secure Boot is supported, a "shim" or "Preloader" is often booted by the UEFI before the bootloader or EFI-stub-bearing kernel. [11]
Note: The column MBR (Master Boot Record) refers to whether or not the boot loader can be stored in the first sector of a mass storage device. The column VBR (Volume Boot Record) refers to the ability of the boot loader to be stored in the first sector of any partition on a mass storage device.
systemd is a software suite that provides an array of system components for Linux [7] operating systems. The main aim is to unify service configuration and behavior across Linux distributions. [8] Its primary component is a "system and service manager" — an init system used to bootstrap user space and manage user processes.
GRUB 2, elilo and systemd-boot serve as conventional, full-fledged standalone UEFI boot managers (a.k.a. bootloader managers) for Linux. Once loaded by a UEFI firmware, they can access and boot kernel images from all devices, partitions and file systems they support, without being limited to the EFI system partition.
In the example 2 above, GRUB 2 stores its core.img in a BIOS boot partition. When used, the BIOS boot partition contains the second stage of the boot loader program, such as the GRUB 2; the first stage is the code that is contained within the Master Boot Record (MBR). Use of this partition is not the only way BIOS-based boot can be performed ...
Microsoft boot sectors, therefore, traditionally imposed certain restrictions on the boot process. For example, the boot file had to be located at a fixed position in the root directory of the file system and stored within consecutive sectors, [6] [7] conditions taken care of by the SYS command and slightly relaxed in later versions of DOS.