how does freebsd know which kernel to boot ?

[Polytropon]

On Sun, 25 Jul 2010 16:21:38 +0200, claudiu vasadi <claudiu.vasadi at gmail.com> wrote:
> hello ppl,
> 
> 
> I was wondering about the following:
> 
> After I do "make build|install kernel" and reboot, the new kernel is
> automatically booted but the old one is still on the disk. Therefore, how
> does FreeBSD know which one to boot ?
> 
> I'm guessing it's writing this info somewhere but I do not know where or
> how.
> 
> 
> 
> Can anyone give me some short description ?

The kernel is booted by the kernel loader. Its configuration is
in /boot/loader.conf and /boot/default/loader.conf. It will default
to "kernel" (the name of the kernel to boot) by default, but you
can specify another name, too. You can also interrupt the boot and
request a different than the default kernel; using the "nextboot"
can achieve similar results.

Upon kernel installation by "make installkernel", the existing
kernel will be moved to kernel.old; the newly installed kernel
will then be kernel, and the loader will load exactly this name
as before.

Interesting man pages are:
	% man loader
	% man loader.conf
	% man nextboot
	% man boot
	% less /boot/defaults/loader.conf





-- 
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...