pi@raspberrypi ~ $ sudo su
root@raspberrypi:/home/pi# cd /usr/src
root@raspberrypi:/usr/src# git clone \
  https://github.com/raspberrypi/linux.git\
  -b rpi-3.9.y
root@raspberrypi:# cd linux
root@raspberrypi:# make bcmrpi-defconfig
root@raspberrypi:# make menuconfig
root@raspberrypi:# make
root@raspberrypi:# make modules_install
root@raspberrypi:# cp arch/arm/boot/zImage\
   /boot/linux-3.9.y
root@raspberrypi:# echo "kernel=linux-3.9.y"\
   >>config.txt