Contributed by &a.phk;. v1.1, April 26th.
+
+ Booting FreeBSD is essentially a three step: Load the kernel,
+ determine the root filesystem and initialize user-land things. This
+ leads to some interesting possibilities shown below.
We presently have three basic mechanisms for loading the kernel:
Biosboot is our ``bootblocks'', it consists of two files, which
will be installed in the first 8Kbytes of the floppy or hard-disk
slice to be booted from.
Biosboot can load a kernel from a FreeBSD filesystem.
Dosboot was written by DI. Christian Gusenbauer, and is
unfortunately at this time one of the few pieces of code that
isn't compilable under FreeBSD itself because it is written for
MicroSoft compilers.
Dosboot will boot the kernel from a MS-DOS file or from a FreeBSD
filesystem partition on the disk. It attempts to negotiate with
the various and strange kinds of memory manglers that lurk in
high memory on MS/DOS systems and usually wins them for it's
case.
Netboot will try to find a supported ethernet card, and use
BOOTP, TFTP and NFS to find a kernel file to boot.
Once the kernel is loaded and the boot-code jumps to it, the kernel
will initialize itself, trying to determine what hardware is
present and so on, and then it needs to find a root filesystem.
Presently we support the following types of rootfilesystems:
This is the most normal type of root filesystem. It can reside on
a floppy or on harddisk.
While this is technically possible, it isn't particular useful,
because of ``FAT'' filesystems inability to make links, device
nodes and such ``UNIXisms''.
This is actually a UFS filesystem which has been compiled into
the kernel. That means that the kernel does not really need any
disks/floppies or other HW to function.
This is for using a CD-ROM as root filesystem.
This is for using a fileserver as root filesystem, basically
making it a diskless machine.
To get the user-land going, when the kernel has finished
initialization, it will create a with ``/sbin/init''.
You can substitute any program for /sbin/init, as long as you keep
in mind that:
there is no stdin/out/err unless you open it yourself, if you exit,
the machine panics signal handling is special for ``Interesting combinations
Boot a kernel with a MFS in it with a special /sbin/init
which...