Custom Kernel questions...

Daniel Bye freebsd-questions at
Sun Apr 23 00:44:54 UTC 2006

On Sat, Apr 22, 2006 at 04:52:45PM -0700, Andrew Carton wrote:
> While I am not exactly new to FreeBSD or other *nix variants, I choose 
> to use FreeBSD because of its blazing performance, especially on older, 
> slower machines. Yet, I also wish to strip that kernel to squeeze out 
> every bit of usable power I can. My delving into kernel customizing 
> with FreeBSD has been realativly short, and for the most part error free,
> but in comparison to Linux, it seems to offer fewer customizing options.
>   More specificly, many of my machines are being setup as servers, and
> thusly have no need of many services such as sound drivers, yet it 
> appears that I see code for them passing by the screen as I configure and
> compile. Has anyone here delved deeper into the configuration of the 
> kernel, are there more options is other files aside from the main 
> configuration file?

By cutting out drivers for devices that you don't need (see the output
of dmesg to check what you've got), you reduce the size of the kernel

However, the default buildkernel target will build all kernel modules,
which is probably why you see sound drivers etc scrolling by.  In order
to avoid compiling modules you don't need, there is the MODULES_OVERRIDE
knob in /etc/make.conf, which you can set to the names of the modules
you actually want. 

The following knobs may be of interest to you, but I have only ever had
cause to use MODULES_OVERRIDE so can't speak with any authority.

#NO_MODULES=            # do not build modules with the kernel
#MODULES_WITH_WORLD=    # do not build modules when building kernel
#MODULES_OVERRIDE=      linux ipfw
# The list of modules to never build, applied *after* MODULES_OVERRIDE.
#WITHOUT_MODULES=       bktr plip



Daniel Bye

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