All credit goes to @jshc1, I only found this info in this post and split it off here so it could more easily be found later.

 

I am not sure if this applies only to ODROID-XU4 or other Odroids as well.

 

4 hours ago, jshc1 said:

Odroid does not behave like PI.

Odroid has one blue diode which signals heartbeat signal. After connecting the power it will light up. If it finds a boot and starts booting, it will start flashing. The blinking speed depends on the load.
The red LED is on all the time when the current reaches the sbc.
The green LED lights up when HDD is connected, blinks when HDD has activity.

 

ODROID XU4, HC2, HC1, C2 and N2 does have the same blinking when turned ON. But you can easyli change the LED behavior with different commands put one of these commands in /etc/rc.local 

 

Blue light off:

echo none > /sys/class/leds/blue\:heartbeat/trigger

 

Orignal state of light, it is called heartbeat.

echo heartbeat > /sys/class/leds/blue\:heartbeat/trigger

 

Constant on:

echo deafult-on > /sys/class/leds/blue\:heartbeat/trigger

 

On SD card access:

echo sd >/sys/class/leds/blue\:heartbeat/trigger

 

There is alot of different blue light settings. You can change blue light behavior to track your emmc and cpu load etc.

cat /sys/class/leds/blue\:heartbeat/trigger

 

 

2 hours ago, soerenderfor said:

ODROID XU4, HC2, HC1, C2 and N2 does have the same blinking when turned ON

 

Thanks for input. Title updated.

I would recommend changes to settings only for advanced users. Changes for fun can only make future diagnostics more difficult when someone changes the heartbeat and then it can only result in unnecessary confusion.

Your right @jshc1 if you turn the blue light off manual. It will not show if the kernel fails, right?

 

@TRS-80 the blue light indicate if the kernel are loaded right, then you will have blue light blinking. But if the kernel fails the blue light will be off.

17 minutes ago, soerenderfor said:

It will not show if the kernel fails, right?

That depends ... You can have such bash script too started /etc/rc.local :

#!/bin/bash

echo none >/sys/class/leds/blue\:heartbeat/trigger

while true; do
	echo 0 > /sys/class/leds/blue\:heartbeat/brightness
	sleep 0.25
	echo 255 > /sys/class/leds/blue\:heartbeat/brightness 
	sleep 0.25
done

Then, it will toogle/flash and will stop if kernel is frozen ...

@martinayotte thanks, nice and profitable feedback 

5 hours ago, soerenderfor said:

if you turn the blue light off manual. It will not show if the kernel fails, right?

More or less. The blue LED can say a lot, especially if the person cannot connect the console.
This was useful not so long ago in the 5.x kernel where after upgrading from 4.14 simply Odroid HC does not boot and the diode just lights up all the time indicating that the sbc is hanging. For example, if the sd card were damaged and the boot partition is missing, the LED would not light up at all, the same effect as without an sd card.
For novice users it is always best to stick to the standards because later unnecessary problems are created especially with headless sbc and no uart.