Building your own kernel with the Fedora kernel configuration
There are a number of situations where you might want to do something like build a stock kernel.org kernel with the same configuration options as a normal Fedora RPM-installed kernel. Alternately, you want to compile a Fedora kernel with a slightly different set of options. These days, how to do this is slightly less than obvious and there is a gotcha or two.
First, you need kernel source. Fedora no longer ships an RPM with their kernel source all set up for you, so you have two options:
- just download the version you want from kernel.org and unpack it somewhere convenient, or
- fetch the kernel
.src.rpmand set up to build it, which requires an RPM build environment. Once you have a kernel source RPM in your RPM build environment, you can get the source tree all patched up and ready to go with
rpmbuild -bp kernel-2.6.spec.
Next, you need a kernel config file. The config file for a particular
kernel RPM that you have installed is
(among other, less convenient places). However, if you are building
by hand you don't want to use this configuration as it is, because if
you try you will discover you wind up with a huge kernel image. The
culprit is the
CONFIG_DEBUG_INFO option, which causes the kernel
to get compiled with
-g; take it out following the directions in
(The kernels in the RPMs are not this big because the RPM build process then strips the debugging info out and puts it in the kernel debuginfo RPM.)
If you are building a kernel.org kernel using a Fedora config file, there are two things to watch out for:
- if you are upgrading kernel versions,
make oldconfigwill probably ask you about a number of new options.
- make sure that you are using a base kernel version at least as recent
as the Fedora kernel RPM. Fedora's current build practices do not
put the subminor kernel version number in the RPM version (eg, the
18.104.22.168-based and 22.214.171.124-based kernel RPMs will both have an RPM
version of just 2.6.20 plus a build sequence number), so you need to
either inspect the kernel source RPM or the kernel RPM's changelog
for the kernel you are running. You do the latter with:
rpm -q --changelog kernel-`uname -r` | less
After that you are pretty much home free, assuming you are not rebuilding a kernel RPM. Doing that does not in any way fit into the margins of this entry.