Run like Hell

Dec 1, 2019

Linux ser2net: no connection to /dev/ttyUSB0

If you are running some java application on a Linux box (especially ARM architecture) and this application accesses the serial interface (/dev/ttyUSB0, /dev/ttyUSB1 or just /dev/ttyX), then a easy way to do this, is running ser2net.

For all who are not familiar with the serial port:
https://en.wikipedia.org/wiki/Serial_port

But there is one tricky thing, you have to consider when using ser2net:

Inside ser2net.conf you will find some lines like this here:

15000:raw:0:/dev/ttyUSB0:9600 8DATABITS NONE 1STOPBIT

This means: on port tcp 15000 you can access the serial port /dev/ttyUSB0 (if you have a USB to serial adapter in place).

If this does not work, check the ports with

root@ubuntu:/home/ubuntu/dfld# netstat -lntup |grep ser2net
tcp6       0      0 :::15000                :::*                    LISTEN      1361/ser2net

As you can see, it only listens on TCP6. So you have to reconfigure this to

127.0.0.1,15000:raw:0:/dev/ttyUSB0:9600 8DATABITS NONE 1STOPBIT

If you only want to access this on localhost (which is very nice security enhancement ;-) ).
And after a restart of ser2net everything works like expected:

root@ubuntu:/home/ubuntu/dfld# netstat -lntup |grep ser2net

tcp        0      0 127.0.0.1:15000         0.0.0.0:*               LISTEN

Nov 23, 2019

How to run a java software which needs RXTX on a raspberry pi

In my last posting i wrote about migrating my aircraft noise measurement station to alpine linux. There i had some problems with getting the RXTX library for Java running on a linux, which uses musl and not GNU libc6.

Why does my java application require RXTX? As stated on the RXTX page:

RXTX is a Java library, using a native implementation (via JNI), providing serial and parallel communication for the Java Development Toolkit (JDK).

Now i wanted to move to a raspberry pi. But this runs on ARM and the RXTX is only provided for x86/x64 systems.

But there is another way: ser2net

With this proxy /dev/ttyUSB0 can be mapped to a tcp port and java can access this without using RXTX.

Nov 17, 2019

Alpine Linux, Oracle Java JDK and musl?! - why it does not work...

Sometime ago i did some work with Alpine Linux (s. here) and i was impressed how tiny this Linux distro was and how fast it was running.

So i decided after nearly 6 years of running an aircraft noise measuring station (for dfld.de) with Ubuntu to change to Alpine Linux.

This station runs a software on Java and needs RXTX, because the microphone is connected via USB and is read over /dev/ttyUSB0.

What is the problem with this setup?

RXTX needs a Java which is running on glibc
Alpine Linux does not run on glibc

If you are not aware of this problem, you get some errors like

./javaash: java: command not found

and this happens even if you are in the right directory and java got the execute bit configured.

Alpine Linux changed to musl:

There are some other libc implementations (take a look here).
The homepage is https://www.musl-libc.org/:

And a comparison to other libc can be found at http://www.etalabs.net/compare_libcs.html:

There are some workarounds to get applications build with glibc running on Alpine Linux, but i did not get to run my aircraft noise measuring station - i switched to Debian - because i needed a 32bit Linux for my very old UMPC...

Nov 10, 2019

Oracle Cloud: Feature Set

For all readers, who want to get a short overview to the services which can be configured inside Oracle Cloud, here a walkthrough the menus.
The Main menu shows the following items: