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Container for WSJT-X

Introduction

When running SDRangel in a container some significant delay is introduced in the audio (normally a pulseaudio virtual device). This delay can be as large as ~4s and WSJT-X cannot synchronize its decoders that are based on the system clock. WSJT-X cannot be configured with a specified delay either.

The libfaketime library can tweak the clock as a program sees it by capturing the system calls for time and introducing a delay without affecting your system clock in any way.

To do the magic it uses LD_PRELOAD trick. You can try it from the command line if you have cloned and built libfaketime in say /opt/build/libfaketime and installed WSJT-X in /opt/install/wsjtx:

LD_PRELOAD=/opt/build/libfaketime/src/libfaketime.so.1 FAKETIME="-4s" /opt/install/wsjtx/bin/wsjtx

Here for your convenience we will provide ways to create a container with WSJT-X and libfaketime built from source and used to introduce a specific delay.

Build image

Use the ./build.sh script to build the WSJT-X with libfaketime Docker image. You can specify the WSJT-X version with the -t option (default 2.1.2). With the default WSJT-X version a wsjtx/bionic:v2.1.2 image is created.

Run image

The run.sh script can be used to run the WSJT-X image in a Docker container.

xhost utility should be installed in your system.

A WSJT-X.ini file is created in the .config folder in your home directory that will allow settings to be persistent. It is mapped to /home/wsjtx/.config/WSJT-X.ini in the container.

You can use the following options:

  • -t version: image version if different from latest
  • -d delay: delay in seconds (defaut 2)

Note that the default image version is latest. It is the responsibility of the user to tag the desired image version to version latest. This makes it easy to switch from one version to the other in case of trouble.