Barebone kernel options request

samir.otmane at samir.otmane at
Mon Mar 11 09:36:27 UTC 2019

Hi Kevin, Thanks for the answer.
Actually my ISP webmail is kinda buggy, i apologize for multiple mail sending.
I'm already aware of kernel compilation options through NOTES file, and yeah i'm using amd64 arch.
As peoples told me and as i'm actually thinking of it is i might be a little exaggerating about overhead stuff, but yet i'd like to choose what i want to.


---- Message d'origine ----
De : "Kevin P. Neal" <kpn at>
À : samir.otmane at
Objet : Re: Barebone kernel options request
Date : 11/03/2019 03:31:30 CET
Copie à : freebsd-questions at

On Sun, Mar 10, 2019 at 02:09:37PM +0100, samir.otmane at wrote:
> Hello everyone,
> For my purpose, i would like to get a very barebone FreeBSD kernel ( For instance i don't want jaling, i'll want to get rid of unwanted overhead ), but i don't know how to do so.
> IRC chatters told me that it would be very challenging to do so.
> I found that page ( ) but it only disables user-land program building, not kernel-land code.

Three emails to the same list is two email too many. Just one email would
be sufficient, and if you get no response another single email a reasonable
period of time later. I don't know if this community has a definition of
"reasonable period of time", though. The LLVM community's is roughly "a
week or so".

Anyway. On to business:

What you want is to build a custom kernel. The GENERIC kernel config file
is, for the 64-bit amd64 host, located at:

You didn't say what host, but the other hosts are at guessable locations
based on that path, and the filename to look for is "GENERIC".

You'll need to copy that file and edit out the stuff you don't want. This
will probably take some research and trial and error.

Note that this may not be granular enough. I don't know if you can remove
jailing, for example. But I don't know that jailing actually increases the
overhead in a measureable way if you aren't using it. So it may not be
worth your time to bother with it. This goes double if it requires special
patches to the kernel that you have to maintain forever and incur the
cost forever. You'll need to do the cost/benefit analysis yourself.

I don't know the current correct method of building custom kernels. It's
no doubt docuemented, and maybe someone will chime in here.

"A method for inducing cats to exercise consists of directing a beam of
invisible light produced by a hand-held laser apparatus onto the floor ...
in the vicinity of the cat, then moving the laser ... in an irregular way
fascinating to cats,..." -- US patent 5443036, "Method of exercising a cat"
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