Notice

This is essentially a copy of this Stackexchange post: https://raspberrypi.stackexchange.com/questions/117632/turn-off-external-leds-on-raspberry-pi-3/130495#130495

Post

At first, check if you have the correct Model of the Raspberry Pi 3b:

cat /sys/firmware/devicetree/base/model

The output should be: # Raspberry Pi 3 Model B Rev 1.2

Now, you need to install libusb-1.0-0-dev, make, build-essential and gcc:

sudo apt install libusb-1.0-0-dev make gcc build-essential -y

After that, you clone this repository: https://github.com/dumpsite/lan951x-led-ctl

git clone git@github.com:dumpsite/lan951x-led-ctl.git

Now build the project:

cd lan951x-led-ctl && make && sudo chmod +x ./lan951x-led-ctl

Disable the LEDs

The following command will disable both Ethernet LEDs.

sudo ./lan951x-led-ctl --fdx=0 --lnk=0 --spd=0

You need to apply this on every restart!