XDG_RUNTIME_DIR , propagateSizeHints() errors

Question

When I run this script "python3 script.py" everything is alright. (I tried to run the script as a root, and other user too)

import music21
import os

# "qt.qpa.xcb: could not connect to display"
# "qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found." 
os.putenv("QT_QPA_PLATFORM", "offscreen") #handle error above in my case

us = music21.environment.UserSettings()
us['musescoreDirectPNGPath'] = '/usr/bin/musescore3'

score = music21.converter.parse("myfile.musicxml")
score.write('musicxml.pdf', fp='song.pdf')

But when my django backend has to execute this code as a function to respond API call, its not working. I got:

QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-myusername'
This plugin does not support propagateSizeHints()

And if I remove part with "QT_QPA_PLATFORM", I got "qt.qpa.xcb" error. I have not idea what to do. I also tried to add following line in my gunicorn setup script but nothing changed.

export QT_QPA_PLATFORM=offscreen

Any ideas how to fix it ? What can be wrong ?

Server OS: Ubuntu 20.04

Answer 1

You probably need to also set XDG_RUNTIME_DIR. See https://github.com/cuthbertLab/music21/issues/260#issuecomment-834489173