Richard Owlett composed on 2025-12-28 09:10 (UTC-0600):
> I've been a computer _user_ since early 60's [undergrad E.E. student].
> I have used multi-boot since the days of Squeeze.
> I wish to grok multi-boot.
> I currently default to Debian 12 , other options are available.
> After doing some years overdue disk housekeeping, I wish to *ADD* a
> clean install of Trixie.
> Some of the housekeeping will be for re-purposing some existing disk
> partitions.
> To safely do that, I need to know the details of the power on boot
> sequence and what files are used.
> I'm carefully not asking specific questions as decades of tech support
> (in another field) has taught me that "wrong questions" can cause as
> much grief as "wrong answers" ;{
As in cat skinning, there are multiple ways to multiboot.
To start:
dual-boot = exactly two bootable operating systems installed on a computer
multiboot = more than one bootable operating system installed on a computer
BBS menu = BIOS Boot Service. Most PCs made in the past 20 or more years provide
this service that on striking the appropriate hotkey during POST, will present a
menu comprised of bootable devices from which to choose. Older PCs supporting
only
legacy/MBR type booting present more limited selections, among them HDD, floppy,
CD/DVD drive, PXE, and various storage alternatives if present. UEFI BBS menus
add
selections for UEFI entries, which facilitate use of more than one ESP per
system
when desired, or when ESP sharing among installations is problematic or
bootloader(s) specific to any individual OS is/are preferred or necessary. BBS
menu entries may be administered either from within firmware setup, or an OS
utility, such as efibootmgr on Linux.
Traditional booting from MBR partitioned media is limited to one bootloader per
storage device that is usable by the BIOS, beginning at the first device sector,
then either continued on immediately following sectors, or jumping to some
partition's first sector. Additional bootloaders may be present on OS system
partitions or boot-specific partitions, but these are not addressable by the
BIOS,
only useable via chainloading. This legacy/MBR system is famously subject to
multiple OS installations' bootloaders usurping control from other OS
installations at either installation time, or when bootloaders are updated
following installation of a new OS kernel.
With the advent of GPT partitioning, usurpation potential is reduced due to the
use of (U)EFI, which utilizes one or more ESP partitions having directories for
IPL use by the firmware taking the place of code in an MBR. Usurpation is
reduced
to the priorities assigned to the directories on the ESP(s), with priorities
readily altered either via firmware setup, or OS utility, again, such as
efibootmgr in Linux distros; or simply bypassed using the BBS menu.
How best to add Trixie to a computer having only Bookworm installed depends on
whether legacy or UEFI booting will be employed.
--
Evolution as taught in public schools is, like religion,
based on faith, not based on science.
Team OS/2 ** Reg. Linux User #211409 ** a11y rocks!
Felix Miata
