Once the system is up and running, a new kernel may be overlayed on top of the existing one using NFS. This way, you don't have to boot into OpenBSD every time you build a new kernel and want to run it. Just leave your old kernel on the OpenBSD partition, the boot blocks will load this old one, and when the system is up you can reboot it with the new kernel over NFS. Further, the three initial programs discussed above all will check to see if the latest installed kernel is newer than the one that was booted. If so, they will automatically reboot using the newest kernel.
This works by checking /boot/xok.osid in the root NFS partition. If the contents don't match the running kernel then /boot/xok will be reloaded on top of the existing kernel. If the file /boot/.noboot exists then the this step will be skipped.