Hitchhiker's Guide to Openbsd

Do not edit the 
GENERIC
 configuration file!! The only kernel configuration which is supported by the 
OpenBSD team is the GENERIC kernel, the combination of the options in 
/usr/src/sys/arch/
<arch>/conf/GENERIC
and 
/usr/src/sys/conf/GENERIC
as shipped by the OpenBSD team 
(i.e., NOT edited). Reporting a problem on a customized kernel will almost always result in you being 
told to try to reproduce the problem with a GENERIC kernel. Not all options are compatible with each 
other, and many options are required for the system to work. There is no guarantee that just because you 
manage to get a custom kernel compiled that it will actually run. There is no guarantee that a kernel that 
can be "config(8)ed" can be built. 
You can see the platform-specific configuration files here: 
●
alpha Kernel Configuration Files 
●
i386 Kernel Configuration Files
 
http://www.openbsd.org/faq/faq5.html (16 of 26)9/4/2011 10:02:02 AM

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5 - Building the System from Source
●
macppc Kernel Configuration Files
 
●
sparc Kernel Configuration Files
 
●
sparc64 Kernel Configuration Files
 
●
vax Kernel Configuration Files
 
●
hppa Kernel Configuration Files
●
Other Arch's
 
Look closely at these files and you will notice a line near the top similar to: 
include "../../../conf/GENERIC"
This means that it is referencing another configuration file, one that stores platform-independent options. 
When creating your kernel configuration, be sure to look through 
sys/conf/GENERIC
. 
Kernel configuration options should be placed in your kernel configuration file in the format of: 
option
name 
or 
option name=value 
For example, to place option "DEBUG" in the kernel, add a line like this: 
option DEBUG
Options in the OpenBSD kernel are translated into compiler preprocessor options, therefore an option 
like DEBUG would have the source compiled with option -DDEBUG, which is equivalent to doing a 
#define DEBUG
throughout the kernel. 
Sometimes, you may wish to disable an option that is already defined, typically in the "
src/sys/
conf/GENERIC
" file. While you could modify a copy of that file, a better choice would be to use the 
rmoption statement. For example, if you really wanted to disable the in-kernel debugger (not 
recommended!), you would add a line such as: 
rmoption DDB
in your kernel configuration file. 
option DDB
is defined in 
src/sys/conf/GENERIC
, but the 
above 
rmoption
line deactivates it. 
http://www.openbsd.org/faq/faq5.html (17 of 26)9/4/2011 10:02:02 AM

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5 - Building the System from Source
Once again, please see 
options(4)
 for more information about the specifics of these options. Also note 
that many of the options also have their own manual pages -- always read everything available about an 
option before adding or removing it from your kernel.