FreeBSD boot process

MrMoo

In order to understand things a bit clearer I like diagrams, here's a diagram I have made outlining the FreeBSD boot process. Corrections welcome.

Stage zero of boot process

A small 446 byte long program is loaded by the BIOS when switched on. In FreeBSD the usual
boot manager is called boot0 and is setup via boot0cfg or fdisk. This program presents a
menu of which operating systems the user can load, e.g. FreeBSD, Linux, Windows, etc.

Example install:

# fdisk -B -b /boot/boot0

or

# boot0cfg -B -b /boot/boot0

Example screen:


F1 FreeBSD

Default: F1

references:

http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/boot-blocks.html
http://www.freebsd.org/cgi/man.cgi?query=boot0cfg
http://www.freebsd.org/cgi/man.cgi?query=fdisk

Stage one of boot process

A small 512 byte program to locate and load boot2, the second stage. This program is
managed together with stage two as a single entity.

Stage two of boot process

Provides an interface to choose the boot loader / kernel.

Example install of stage one and two:

# bsdlabel -B

Example screen:


>> FreeBSD/i386 BOOT
Default: 0:ad(0,a)/boot/loader
boot:

Stage three of boot process

An interface to choose kernel and set boot options.

Example screen:


BTX loader 1.00 BTX version is 1.01
Console: internal video/keyboard
BIOS drive A: is disk0
BIOS drive B: is disk1
BIOS drive C: is disk2
BIOS drive D: is disk3
BIOS 639kB/261120kB available memory

FreeBSD/i386 bootstrap loader, Revision 0.8

/kernel text=0x277391 data=0x3268c+0x332a8 |

|
Hit [Enter] to boot immediately, or any other key for command prompt.
Booting [kernel] in 9 seconds... _

references:

http://www.freebsd.org/cgi/man.cgi?query=loader&sektion=8