Bootmanagers

Bootmanagers are software components involved in the early stages of a computer’s boot process. They run after the system firmware (BIOS or UEFI) has initialized hardware and located a bootable medium, and they present a selectable interface from which a user can choose an operating system, kernel, or recovery options to boot.

A boot manager differs from a bootloader in that it provides a menu or selection mechanism, and then delegates to a loader for the chosen entry. In UEFI systems, the firmware may load a boot manager directly, while BIOS-era setups often chainload a bootloader. Boot managers support multiple boot entries, default selections, timeouts, and sometimes password protection. They can also influence boot parameters and enable recovery or diagnostic paths.

Common implementations include GRUB (the GNU Grand Unified Bootloader), Windows Boot Manager, Syslinux, and older LILO. In modern systems, GRUB is widely used for Linux distributions, while Windows relies on the Windows Boot Manager. EFISTUB and other UEFI-specific mechanisms interact with firmware tools like efibootmgr to manage boot entries. Configuration is typically via text files or stores: GRUB uses grub.cfg generated from scripts, while Windows uses the BCD (Boot Configuration Data) store.

Boot managers enable multi-boot setups, kernel parameter customization, initial ramdisk options, and recovery paths. They also intersect with security features such as Secure Boot, which requires signed bootloaders and entries. Misconfiguration can render a system unbootable, making recovery and careful management essential.