Hardware

The blue LED can be controlled with via the sysfs (/sys/devices/platform/leds/leds/power/brightness):

To turn off the blue LED: echo 0 | sudo tee /sys/devices/platform/leds/leds/power/brightness

To turn on the blue LED: echo 1 | sudo tee /sys/devices/platform/leds/leds/power/brightness

Note: the maximum brightness is defined as 255, it doesn’t support dimming however, so 0 and 1 as brightness is sufficient. Turning off the blue LED will turn on a weak red LED. Trigger can be changed via /sys/devices/platform/leds/leds/power/trigger.