First, let us take a quick tour of the kernel build
directory. All directories mentioned will be relative to
the main /usr/src/sys
directory, which is also
accessible through /sys
. There are a number of
subdirectories here representing different parts of the
kernel, but the most important, for our purposes, are
i386/conf
, where you will edit your custom
kernel configuration, and compile
, which is the
staging area where your kernel will be built. Notice the
logical organization of the directory tree, with each
supported device, filesystem, and option in its own
subdirectory. Also, anything inside the i386
directory deals with PC hardware only, while everything
outside the i386
directory is common to all
platforms which FreeBSD could potentially be ported to.
Note: If there is not a
/usr/src/sys
directory on your system, then the
kernel source has not been been installed. The easiest
way to do this is by running /stand/sysinstall (as root),
choosing Configure, then Distributions, then src, then sys.
Next, move to the i386/conf
directory and copy
the GENERIC configuration file to the name you want to
give your kernel. For example:
# cd /usr/src/sys/i386/conf
# cp GENERIC MYKERNEL
Traditionally, this name is in all capital letters and,
if you are maintaining multiple FreeBSD machines with
different hardware, it is a good idea to name it after
your machine's hostname. We will call it MYKERNEL for
the purpose of this example.
Note: You must execute these and all of the following commands under the root account or you will get ``permission denied'' errors.
Now, edit MYKERNEL with your favorite text editor. If
you are just starting out, the only editor available will
probably be vi
, which is too complex to explain
here, but is covered well in many books in the
bibliography. Feel free to change the
comment lines at the top to reflect your configuration or the
changes you have made to differentiate it from GENERIC.
If you have build a kernel under SunOS or some other BSD operating system, much of this file will be very familiar to you. If you are coming from some other operating system such as DOS, on the other hand, the GENERIC configuration file might seem overwhelming to you, so follow the descriptions in the Configuration File section slowly and carefully.
Note: If you are trying to upgrade your kernel from an older version of FreeBSD, you will probably have to get a new version ofconfig(8)
from the same place you got the new kernel sources. It is located in/usr/src/usr.sbin
, so you will need to download those sources as well. Re-build and install it before running the next commands.
When you are finished, type the following to compile and install your kernel:
# /usr/sbin/config MYKERNEL
# cd ../../compile/MYKERNEL
# make depend
# make
# make install
The new kernel will be copied to the root directory as
/kernel
and the old kernel will be moved to
/kernel.old
. Now, shutdown the system and
reboot to use your kernel. In case something goes wrong,
there are some
troubleshooting instructions at the end of this
document. Be sure to read the section which explains how
to recover in case your new kernel
does not boot.
Note: If you have added any new devices (such
as sound cards) you may have to add some
device nodes to your
/dev
directory before you can use them.