How Do I Compile a FreeBSD Kernel?

This is just an introduction into compiling your own FreeBSD kernel. For more detailed information, check out the FreeBSD Handbook.

Procedure

1. Get a fresh kernel source

         root# mkdir [my kernel dir]
         root# cd /usr/src/sys
         root# tar cvf - . | (cd [my kernel dir]; tar xf -)
   

2. Configure your new kernel

   Here, if you want an ALTQ kernel, replace "DIRT" with "ALTQ.1000" or "ALTQ.100" depending upon the clock speed you want.

         root# cd [my kernel dir]/i386/conf/
         root# cp DIRT [my kernel name]
         root# config [my kernel name]
   

3. Make the new kernel

         root# cd ../../compile/[my kernel name]
         root# make depend
         root# make clean
         root# make
   

4. Install the kernel on the appropriate machine (usually NOT on the machine where it was compiled)

         root# cp [my kernel dir]/compile/[my kernel name]/kernel /kernel.[my kernel name]
         root# chflags noschg /kernel
         root# cp /kernel /kernel.prev
         root# cp /kernel.[my kernel name] /kernel
         root# chflags schg /kernel
   

   /usr/dirt/bin/change_kernel follows these steps.

Use uname -a to check that the new kernel is running (after rebooting, obviously.)

Newer Releases

Compiling a 4.10 kernel gave me (Felix) some problems today. The procedure above failed in the make step, so I went back to the FreeBSD handbook and read about a new method (running make buildkernel KERNCONF=MYKERNEL in /usr/src). This worked like a charm (but the kernel binary ended up under /usr/obj).