How to disable boot output to uart0?

Hi guys,

I tried to disable console output on uart0 using this guide https://docs.armbian.com/User-Guide_Fine-Tuning/#how-to-toggle-boot-output

But I still get boot output on uart0.

Problem is, that I'm using uart0 for a java application. Java application crashes a few seconds after starting. I got the hint, that I should disable console output on this port, to make it working. See here: http://pi4j.com/example/serial.html

I think that's the problem, because if I unplug my serial device from uart0, java app doesn't crash.

I'm using Banana Pi.

Kernel is Verison 4.8.12.

Armbian is Jessie 5.24 with desktop.

How can I disable the output?

Yours,

Martin