In this tutorial we will install a custom kernel on Raspberry Pi. This will allow us to enable monitor mode on the Pi's internal Wi-Fi chip. So, an external monitor-mode supported Wi-Fi dongle is no longer required. The kernel was built by Re4son. As of now, this kernel works only on Raspberry Pi 0/0W/1/2/3 A/B(+). The Pi 4 is not yet supported. I'll update this post once the kernel was released for Pi 4.

I, myself, have a Pi 3B/3B+. I installed the kernel and it works without any issue. Without further a do, let's begin the installation.

First of all, make a fresh install of the latest raspbian. Then execute the below commands to install the kernel.

echo "deb http://http.re4son-kernel.com/re4son/ kali-pi main" > /etc/apt/sources.list.d/re4son.list
wget -O - https://re4son-kernel.com/keys/http/archive-key.asc | apt-key add -
sudo apt update
sudo apt install -y kalipi-kernel kalipi-bootloader kalipi-re4son-firmware kalipi-kernel-headers libraspberrypi0 libraspberrypi-dev libraspberrypi-doc libraspberrypi-bin

After the installation is finished reboot the Pi. Now you can start and stop the monitor mode using mon0up/mon0down.

That's it. Enjoy!

Credits: Re4son, Kernel Source