cd /usr/src
sudo make buildworld
sudo make buildkernel
sudo make installkernel
mount -u /
(To mount your fs as rw) cd /usr/src
make installworld
reboot
make installworld
is better to run it on Single User Mode and why or why not, but on me worked and on Single User Mode and just after make installkernel
without rebooting my system. Perhaps someone here can give you more informations.