Warnings when starting QGIS (on linux)

[rduivenvoorde]

What is the bug or the crash?

When starting (self compiled) QGIS master OR 3.22 I get the following warning in my terminal:

Info: Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.

From https://forum.qt.io/topic/126731/what-is-this-warning I concluded that I had to change my start script and added:

export QT_QPA_PLATFORM=wayland
export XDG_SESSION_TYPE=

Which 'solved' it. I'm not sure if this is some relict of my (older) desktop setup or if others also encounter this (apparently safe) warning.

Another warning I only have with master, NOT with 3.22 is:

Warning: QSocketNotifier: Can only be used with threads started with QThread
Stacktrace (piped through c++filt):
/home/richard/bin/qgis_/master/debug/bin/qgis(+0xe24c)[0x55f7ac69e24c]

Googling brought me: https://forum.qt.io/topic/29587/solved-qsocketnotifier-can-only-be-used-with-threads-started-with-qthread
which tells me it has something todo with QFileSystemWatcher and with not using 'start' on a Thread...

Not sure if this is only me, or if this is a potential issue?

Steps to reproduce the issue

Start QGIS from command line, setting some environment vars in bash like below:

#!/usr/bin/env bash

export QT_QPA_PLATFORM=wayland
export XDG_SESSION_TYPE=
export QGIS_PREFIX_PATH=/home/richard/bin/qgis_/master/debug
# see https://qtibia.com/how-to-setup-pycharm-for-qgis-development-under-linux-and-windows/
export PYTHONPATH=$QGIS_PREFIX_PATH/share/qgis/python/plugins:$QGIS_PREFIX_PATH/share/qgis/python:/home/richard/bin/pycharm_/debug-eggs/pydevd-pycharm.egg

export LD_LIBRARY_PATH=$QGIS_PREFIX_PATH/lib:/usr/lib:/usr/lib/grass78/lib
# with Oracle
LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/opt/oracle/instantclient_19_9/

# from https://www.qtcentre.org/threads/70250-QMYSQL-Driver-not-Loaded-there-are-no-driver-Available-on-the-QSqlDatabase
# show debug for qt plugins
QT_DEBUG_PLUGINS=0

export QGIS_DEBUG=0
# passing ALL parameters to qgis bin
# eg to be able to call a certain translation
# qgis --lang nl
#gdb /home/richard/bin/qgis_/master/debug/bin/qgis "$@"
/home/richard/bin/qgis_/master/debug/bin/qgis "$@"

Versions

QGIS version	3.23.0-Master	QGIS code revision	637e5ca
Qt version	5.15.2
Python version	3.9.8
GDAL/OGR version	3.3.3
PROJ version	8.2.0
EPSG Registry database version	v10.038 (2021-10-21)
GEOS version	3.10.1-CAPI-1.16.0
SQLite version	3.36.0
PostgreSQL client version	unknown
SpatiaLite version	5.0.1
QWT version	6.1.4
QScintilla2 version	2.11.6
OS version	Debian GNU/Linux bookworm/sid

and

QGIS version	3.22.0-Białowieża	QGIS code revision	95f7829
Qt version	5.15.2
Python version	3.9.7
Compiled against GDAL/OGR	3.3.2	Running against GDAL/OGR	3.3.3
Compiled against PROJ	8.1.1.%3.%4	Running against PROJ	8.2.0
EPSG Registry database version	v10.038 (2021-10-21)
Compiled against GEOS	3.10.0-CAPI-1.16.0	Running against GEOS	3.10.1-CAPI-1.16.0
SQLite version	3.36.0
PostgreSQL client version	14.0 (Debian 14.0-1)
SpatiaLite version	5.0.1
QWT version	6.1.4
QScintilla2 version	2.11.6
OS version	Debian GNU/Linux bookworm/sid
This copy of QGIS writes debugging output.

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

No response

[nyalldawson]

I wouldn't recommend running qgis under a Wayland session at all. Qt 5 doesn't have great support for Wayland sessions.

[rduivenvoorde]

Are you sure? https://doc.qt.io/qt-5/wayland-and-qt.html does not mention that we should not, and in most Distro's I think Wayland/Gnome is more or less mainstream?

$ apt search wayland | grep qt

fcitx5-frontend-qt5/testing,testing,now 5.0.7-2 amd64 [installed,automatic]
gambas3-gb-qt5-wayland/testing,testing 3.16.3-2 amd64
layer-shell-qt/testing,testing 5.23.2-1 amd64
libfcitx5-qt-data/testing,testing,now 5.0.7-2 all [installed,automatic]
libfcitx5-qt-dev/testing,testing 5.0.7-2 amd64
libfcitx5-qt1/testing,testing,now 5.0.7-2 amd64 [installed,automatic]
liblayershellqtinterface-dev/testing,testing 5.23.2-1 amd64
liblayershellqtinterface5/testing,testing 5.23.2-1 amd64
libqt5waylandclient5/testing,testing,now 5.15.2-4 amd64 [installed,automatic]
libqt5waylandclient5-dev/testing,testing 5.15.2-4 amd64
libqt5waylandcompositor5/testing,testing,now 5.15.2-4 amd64 [installed,automatic]
libqt5waylandcompositor5-dev/testing,testing 5.15.2-4 amd64
qml-module-qtwayland-client-texturesharing/testing,testing 5.15.2-4 amd64
qml-module-qtwayland-compositor/testing,testing 5.15.2-4 amd64
qtwayland5/testing,testing,now 5.15.2-4 amd64 [installed,automatic]
qtwayland5-dev-tools/testing,testing 5.15.2-4 amd64
qtwayland5-doc/testing,testing,now 5.15.2-4 all [installed,automatic]
qtwayland5-doc-html/testing,testing 5.15.2-4 all
qtwayland5-examples/testing,testing 5.15.2-4 amd64
qtwayland5-private-dev/testing,testing 5.15.2-4 amd64

[nyalldawson]

Yep -- there's a lot of unsolved issues, even on current Qt versions. Just scroll through https://pointieststick.com/category/this-week-in-kde/ and you'll see that KDE is STILL working to a usable version under Wayland, and a lot of the issues they work on are upstream.

[Paltis96]

Looks like Xorg is going to be removed from the codebase in some distributions. Red hut is going to remove it in the 40 Fedora release...

[firefoxlover]

I wouldn't recommend running qgis under a Wayland session at all. Qt 5 doesn't have great support for Wayland sessions.

I use Fedora KDE with Wayland only since a year or so. Qt perfectly works in Wayland.

Yes @Paltis96 this is important. To be fair, Xwayland will still be there, which is what QGis currently runs in (on Fedora it does not, but displays a warning about incomplete features).

Is there some documentation about what is actually missing? As a beginner I would have no idea, forcing XWayland currently to avoid any issues though.

[nyalldawson]

Qt perfectly works in Wayland.

As an example: try dragging a panel or a toolbar -- you'll end up with a broken application state that can't be fixed on Wayland.

This particular one is fixed in qt6/KDE plasma 6 Wayland sessions, but not qt5 or qt6/gnome yet.

[agiudiceandrea]

See also https://github.com/qgis/QGIS-Website/pull/1196/files#diff-b1cadc89d24da7a18e53486f114d4097fdf7ef22f9ae7d045b2c24f2d6bc9f02R122-R128