lan951x-led-ctl is a command line tool to control the LEDs connected to a LAN9512 or LAN9514 ethernet controller. Usually those LEDs show the ethernet status like "Link/Activity", "Speed" and "Duplex" mode. Using this tool you can turn them off, if you don't like a disco in your room at night ;-) Or you can turn them on/off from any shell script to show whatever status you wish. These ethernet and USB controllers are used on many embedded computers like Raspberry Pi (until Version 3 B - but not 3 B Plus), Olinuxino and many more. Further info can be found at: https://familie-radermacher.ch/dominic/computer/raspberry-pi/lan951x-led-ctl/