Exception #0 (Staempfli\Pdf\Adapter\WkPdfException): sh: 1: /usr/bin/xvfb-run: not found

[lmuestak]

Hi there,
I'm using the following System in a docker container:

Distributor ID: Ubuntu
Description: Ubuntu 18.04.3 LTS
Release: 18.04
Codename: bionic

We have installed on the machine a magento application to produce PDF documents.

However, we are getting the folling error regardless of the confuguration information.
Exception #0 (Staempfli\Pdf\Adapter\WkPdfException): sh: 1: /usr/bin/xvfb-run: not found
Exception #0 (Staempfli\Pdf\Adapter\WkPdfException): sh: 1: /usr/bin/wkhtmltopdf: not found

wkhtmltox is already installed on the system and it's working from the bash correctly.

What I'm missing? The paths to the exec file are all correct.

Thanks in Advance.