pyQGIS problem with GUI on linux

Question

I want to run standalone python script in Docker with QGIS and Ubuntu Xenial and there is problem with GUI.

When QgsApplication is qgs = QgsApplication([],True, None) the error is cannot connect to x server. If I set QgsApplication to False qgs = QgsApplication([],False, None),the error is QPixmap: Cannot create a QPixmap when no GUI is being used.

This is my initialization of the script

#!/usr/bin/env python
#import libraries
import sys, os
import qgis
from qgis.core import *
from PyQt4.QtCore import QFileInfo

# supply path to qgis install location
QgsApplication.setPrefixPath("/usr", True)

# create a reference to the QgsApplication
qgs = QgsApplication([],True, None) #preco hadze False chybu, ked nechcem vyuzit GUI ?
#app.setPrefixPath("/usr", True)

# load providers
qgs.initQgis()

# import processing and set system path to processing
sys.path.append('/usr/share/qgis/python/plugins')   
from processing.core.Processing import Processing
Processing.initialize()
from processing.tools import *

How to initialize script to get it running ? I do not need GUI.

Answer 1

We have solved it with this:

Install Xvfb and start it with the following command (and export DISPLAY): 

Xvfb :99 -ac -noreset & 
export DISPLAY=:99
qgs = QgsApplication([], True)
instalacia xvfb:
sudo apt-get install python-pip
sudo apt-get install xvfb xserver-xephyr vnc4server
sudo pip install pyvirtualdisplay