Disable onboard Wifi and Bluetooth on Raspberry Pi 3 device.
Disable onboard WiFi on boot.
$ echo "dtoverlay=pi3-disable-wifi" | sudo tee -a /boot/config.txt
Disable Bluetooth boot.
$ echo "dtoverlay=pi3-disable-bt" | sudo tee -a /boot/config.txt
Disable systemd service that initializez Bluetooth Modems connected by UART.
$ sudo systemctl disable hciuart
Reboot Raspberry Pi device.
$ sudo reboot
You can directly edit
config.txt file located on the boot partition before inserting SD card into the Raspberry Pi 3 device, but remember to create
ssh file on the same partion. It will execute
sshswitch service to start
OpenBSD Secure Shell server then remove created file, so you can connect and enable
ssh service persistently.
Device Tree overlays are extensively described in GitHub repository.