This appendix covers enabling DTrace on FreeBSD and includes an e-mail from John Birrell.
DTrace is not available in FreeBSD 7.1/8.0 following an installation. A kernel build is required after editing the kernel configuration file. The DTrace modules must also explicitly be loaded after the new kernel is booted.
You can reference the online FreeBSD documentation for enabling DTrace here:
Information on the kernel configuration file and building kernels can be found here: