[SOLVED] qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""

PieBru · 11 Feb 2020, 18:20

Hi there,
I'm on Arch Linux X64 Gnome3 and I tried installing urh (https://github.com/jopohl/urh), which is based on python3-pyqt5.
I get the following error, which persists after reinstalling urh, libxcb, and the whole qt:

$ urh
Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.
QFactoryLoader::QFactoryLoader() checking directory path "/usr/lib/python3.8/site-packages/PyQt5/Qt/plugins/platforms" ...
QFactoryLoader::QFactoryLoader() checking directory path "/usr/bin/platforms" ...
qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Aborted (core dumped)

This post didn't help in my case:
https://forum.qt.io/topic/93247/qt-qpa-plugin-could-not-load-the-qt-platform-plugin-xcb-in-even-though-it-was-found

Any hint on how to proceed to sort this out?
Thanks,
Piero

raven-worx · 13 Feb 2020, 10:54

@PieBru
so what is the output of ldd /usr/lib/qt/plugins/platforms/libqxcb.so?

PieBru · 13 Feb 2020, 11:54

Thank you for the reply @raven-worx , here it is:

$ ldd /usr/lib/qt/plugins/platforms/libqxcb.so
	linux-vdso.so.1 (0x00007fff86527000)
	libQt5XcbQpa.so.5 => /usr/lib/libQt5XcbQpa.so.5 (0x00007fec9f498000)
	libQt5Gui.so.5 => /usr/lib/libQt5Gui.so.5 (0x00007fec9edef000)
	libQt5Core.so.5 => /usr/lib/libQt5Core.so.5 (0x00007fec9e8b6000)
	libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x00007fec9e6cd000)
	libc.so.6 => /usr/lib/libc.so.6 (0x00007fec9e507000)
	libfontconfig.so.1 => /usr/lib/libfontconfig.so.1 (0x00007fec9e4bf000)
	libfreetype.so.6 => /usr/lib/libfreetype.so.6 (0x00007fec9e3ef000)
	libQt5DBus.so.5 => /usr/lib/libQt5DBus.so.5 (0x00007fec9e354000)
	libpthread.so.0 => /usr/lib/libpthread.so.0 (0x00007fec9e332000)
	libX11-xcb.so.1 => /usr/lib/libX11-xcb.so.1 (0x00007fec9e32d000)
	libxcb-xinput.so.0 => /usr/lib/libxcb-xinput.so.0 (0x00007fec9e308000)
	libxcb-icccm.so.4 => /usr/lib/libxcb-icccm.so.4 (0x00007fec9e103000)
	libxcb-image.so.0 => /usr/lib/libxcb-image.so.0 (0x00007fec9defc000)
	libxcb-shm.so.0 => /usr/lib/libxcb-shm.so.0 (0x00007fec9def7000)
	libxcb-keysyms.so.1 => /usr/lib/libxcb-keysyms.so.1 (0x00007fec9dcf4000)
	libxcb-randr.so.0 => /usr/lib/libxcb-randr.so.0 (0x00007fec9dce2000)
	libxcb-render-util.so.0 => /usr/lib/libxcb-render-util.so.0 (0x00007fec9dade000)
	libxcb-render.so.0 => /usr/lib/libxcb-render.so.0 (0x00007fec9dace000)
	libxcb-shape.so.0 => /usr/lib/libxcb-shape.so.0 (0x00007fec9dac6000)
	libxcb-sync.so.1 => /usr/lib/libxcb-sync.so.1 (0x00007fec9dabc000)
	libxcb-xfixes.so.0 => /usr/lib/libxcb-xfixes.so.0 (0x00007fec9dab2000)
	libxcb-xinerama.so.0 => /usr/lib/libxcb-xinerama.so.0 (0x00007fec9daad000)
	libxcb-xkb.so.1 => /usr/lib/libxcb-xkb.so.1 (0x00007fec9da8f000)
	libxcb.so.1 => /usr/lib/libxcb.so.1 (0x00007fec9da65000)
	libX11.so.6 => /usr/lib/libX11.so.6 (0x00007fec9d923000)
	libSM.so.6 => /usr/lib/libSM.so.6 (0x00007fec9d918000)
	libICE.so.6 => /usr/lib/libICE.so.6 (0x00007fec9d8fb000)
	libxkbcommon-x11.so.0 => /usr/lib/libxkbcommon-x11.so.0 (0x00007fec9d8f1000)
	libxkbcommon.so.0 => /usr/lib/libxkbcommon.so.0 (0x00007fec9d8b0000)
	libglib-2.0.so.0 => /usr/lib/libglib-2.0.so.0 (0x00007fec9d78b000)
	libm.so.6 => /usr/lib/libm.so.6 (0x00007fec9d643000)
	libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0x00007fec9d629000)
	libmd4c.so.0 => /usr/lib/libmd4c.so.0 (0x00007fec9d613000)
	libGL.so.1 => /usr/lib/libGL.so.1 (0x00007fec9d58d000)
	libpng16.so.16 => /usr/lib/libpng16.so.16 (0x00007fec9d555000)
	libz.so.1 => /usr/lib/libz.so.1 (0x00007fec9d53b000)
	libharfbuzz.so.0 => /usr/lib/libharfbuzz.so.0 (0x00007fec9d435000)
	libsystemd.so.0 => /usr/lib/libsystemd.so.0 (0x00007fec9d38e000)
	libdouble-conversion.so.3 => /usr/lib/libdouble-conversion.so.3 (0x00007fec9d377000)
	libicui18n.so.65 => /usr/lib/libicui18n.so.65 (0x00007fec9d083000)
	libicuuc.so.65 => /usr/lib/libicuuc.so.65 (0x00007fec9cea1000)
	libdl.so.2 => /usr/lib/libdl.so.2 (0x00007fec9ce9c000)
	libpcre2-16.so.0 => /usr/lib/libpcre2-16.so.0 (0x00007fec9ce16000)
	libzstd.so.1 => /usr/lib/libzstd.so.1 (0x00007fec9cd6c000)
	/usr/lib64/ld-linux-x86-64.so.2 (0x00007fec9f636000)
	libexpat.so.1 => /usr/lib/libexpat.so.1 (0x00007fec9cd3c000)
	libbz2.so.1.0 => /usr/lib/libbz2.so.1.0 (0x00007fec9cd29000)
	libdbus-1.so.3 => /usr/lib/libdbus-1.so.3 (0x00007fec9ccdf000)
	libXau.so.6 => /usr/lib/libXau.so.6 (0x00007fec9ccd8000)
	libXdmcp.so.6 => /usr/lib/libXdmcp.so.6 (0x00007fec9ccd0000)
	libxcb-util.so.1 => /usr/lib/libxcb-util.so.1 (0x00007fec9caca000)
	libuuid.so.1 => /usr/lib/libuuid.so.1 (0x00007fec9cac1000)
	libpcre.so.1 => /usr/lib/libpcre.so.1 (0x00007fec9ca4e000)
	libGLdispatch.so.0 => /usr/lib/libGLdispatch.so.0 (0x00007fec9c995000)
	libGLX.so.0 => /usr/lib/libGLX.so.0 (0x00007fec9c962000)
	libgraphite2.so.3 => /usr/lib/libgraphite2.so.3 (0x00007fec9c93d000)
	librt.so.1 => /usr/lib/librt.so.1 (0x00007fec9c932000)
	liblzma.so.5 => /usr/lib/liblzma.so.5 (0x00007fec9c90a000)
	liblz4.so.1 => /usr/lib/liblz4.so.1 (0x00007fec9c8e8000)
	libgcrypt.so.20 => /usr/lib/libgcrypt.so.20 (0x00007fec9c7c8000)
	libicudata.so.65 => /usr/lib/libicudata.so.65 (0x00007fec9ad17000)
	libgpg-error.so.0 => /usr/lib/libgpg-error.so.0 (0x00007fec9acf5000)

raven-worx · 13 Feb 2020, 13:33

@PieBru
so your plugins are located in /usr/lib/qt/plugins but your Qt libs are in /usr/lib??
Is this really correct?!
I never used a installed Qt package on Linux, i always compiled it myself, thats why i am asking.
Or did you even install it via the package manager?

PieBru · wrote on 13 Feb 2020, 13:33

@raven-worx
I installed via the Arch package manager, initially yay but then I tried also with the plain pacman
/usr/lib contains libQt5* files, /usr/lib/qt/plugins/ contains plugins:

$ ls -l /usr/lib/qt/plugins/
total 0
drwxr-xr-x 1 root root  42 11 feb 10.02 assetimporters
drwxr-xr-x 1 root root  74 11 feb 10.02 audio
drwxr-xr-x 1 root root 110 11 feb 10.02 bearer
drwxr-xr-x 1 root root 198 11 feb 10.02 canbus
drwxr-xr-x 1 root root 126 11 feb 18.18 designer
drwxr-xr-x 1 root root 244 11 feb 10.02 egldeviceintegrations
drwxr-xr-x 1 root root  70 11 feb 10.02 gamepads
drwxr-xr-x 1 root root 314 11 feb 10.02 generic
drwxr-xr-x 1 root root 102 11 feb 10.02 geometryloaders
drwxr-xr-x 1 root root 316 11 feb 10.02 geoservices
drwxr-xr-x 1 root root  28 11 feb 10.02 iconengines
drwxr-xr-x 1 root root 230 11 feb 10.02 imageformats
drwxr-xr-x 1 root root 280 11 feb 10.02 lipi_toolkit
drwxr-xr-x 1 root root 160 11 feb 10.02 mediaservice
drwxr-xr-x 1 root root 208 11 feb 10.02 platforminputcontexts
drwxr-xr-x 1 root root 406 11 feb 10.02 platforms
drwxr-xr-x 1 root root  68 11 feb 10.02 platformthemes
drwxr-xr-x 1 root root  44 11 feb 10.02 playlistformats
drwxr-xr-x 1 root root 156 11 feb 10.02 position
drwxr-xr-x 1 root root  48 11 feb 10.02 printsupport
drwxr-xr-x 1 root root  40 11 feb 18.18 PyQt5
drwxr-xr-x 1 root root 460 11 feb 10.02 qmltooling
drwxr-xr-x 1 root root  26 11 feb 10.02 renderplugins
drwxr-xr-x 1 root root 130 11 feb 10.02 sceneparsers
drwxr-xr-x 1 root root 126 11 feb 10.02 sensorgestures
drwxr-xr-x 1 root root 158 11 feb 10.02 sensors
drwxr-xr-x 1 root root 168 11 feb 10.02 sqldrivers
drwxr-xr-x 1 root root 106 11 feb 10.02 texttospeech
drwxr-xr-x 1 root root 416 11 feb 10.02 virtualkeyboard
drwxr-xr-x 1 root root  28 11 feb 10.02 wayland-decoration-client
drwxr-xr-x 1 root root 302 11 feb 10.02 wayland-graphics-integration-client
drwxr-xr-x 1 root root 430 11 feb 10.02 wayland-graphics-integration-server
drwxr-xr-x 1 root root 210 11 feb 10.02 wayland-shell-integration
drwxr-xr-x 1 root root  50 11 feb 10.02 webview
drwxr-xr-x 1 root root 104 11 feb 10.02 xcbglintegrations

hskoglund · 13 Feb 2020, 17:22

Hi, I think @raven-worx is on to something here, there's a problem with the location of Qt's files, but not a problem for libqxb.so for finding the .dlls it needs (that's why the ldd looks good) but rather a problem for your executable file urh to find the location of Qt's plugin files.

I think you need to give urh a helping hand by creating a qt.conf file with this contents:

[Paths]
Plugins=/usr/lib/qt/plugins

and place qt.conf in the same directory as the urh executable file

PieBru · wrote on 13 Feb 2020, 17:22

@hskoglund
I'm on Arch Linux, no luck by placing qt.conf in ~/.config/urh/ (together with urh.ini) and /usr/bin/ (where is located the urh executable).

$ urh
Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.
qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Aborted (core dumped)

hskoglund · 13 Feb 2020, 18:50

No worries, there are other ways of setting the path, for example you could try exporting it as an environment variable, say like this:

export QT_PLUGIN_PATH=/usr/lib/qt/plugins
urh

If that doesn't work, also you can specify the path to libqxcb.so with a command argument to urh, like this:

urh -platformpluginpath /usr/lib/qt/plugins/platforms

(Note: this 2nd example only helps out with locating libqxcb.so, i.e. if urh needs more plugins to be loaded (and the 1st example above doesn't work) your still out of luck.)

PieBru · wrote on 13 Feb 2020, 18:50

@hskoglund
Thank you much, both solutions works here!!!
The urh command now shows only the wayland warning, but it seems not harmful as the app window appears and it seems to work as expected.

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

Thank you again,
Piero

PabloC · wrote on 16 Jun 2020, 20:28

@hskoglund Hi sorry for the question but, what is urh, i try to find information about it but i dont got it, i have te same problem but i cant find the urh thing, thanks!

hskoglund · 16 Jun 2020, 21:05

Hi, look at the first post on this page, urh stands for Universal Radio Hacker...

PabloC · wrote on 16 Jun 2020, 21:05

@hskoglund Thanks!

NoWhereMan1979 · wrote on 5 Jul 2020, 14:06

@hskoglund said in [SOLVED] qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in "":

export QT_PLUGIN_PATH=/usr/lib/qt/plugins

Hi dear @hskoglund
Your efficient advises helped me too. just wanted to thank you.

goksan.isil · wrote on 25 Jul 2020, 11:42

@NoWhereMan1979 said in [SOLVED] qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in "":

@hskoglund

@hskoglund your export QT_PLUGIN_PATH=/usr/lib/qt/plugins advice has helped me too. THank you!

mol_ · 8 Nov 2020, 03:15

@hskoglund thank you, I have tried your mentioned method and it works well.

export QT_PLUGIN_PATH=/usr/lib/qt/plugins

superdummy · 3 Mar 2021, 21:24

Hi,
I experienced this problem on Debian 10 Buster after upgrading my Qt to 5.15.2 and QtCreator to 14.0
In the end the lib libxcb-util.so.1 was missing.

ldd /home/developer/Qt5/5.15.2/gcc_64/plugins/platforms/libqxcb.so
...
libxcb-util.so.1 => not found
...

See here: https://bugreports.qt.io/browse/QTBUG-88688

andreionea · wrote on 3 Mar 2021, 21:24

@superdummy worked for me

LiZheCN · wrote on 29 Jan 2022, 14:03

I stuck at this issue too.

I set the environment variable export QT_PLUGIN_PATH=/usr/lib/qt/plugins.
but not work.

I run a python script use pyqt. Get the error message:

QObject::moveToThread: Current thread (0x55e4e5df2060) is not the object's thread (0x55e4e61624e0).
Cannot move to target thread (0x55e4e5df2060)

qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "/home/lizhe/.local/lib/python3.10/site-packages/cv2/qt/plugins" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: xcb, eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx.

Aborted (core dumped)

There is a file /home/lizhe/.local/lib/python3.10/site-packages/cv2/qt/plugins/platforms/libqxcb.so I move the libqxcb.so in upper dir, not work either.

output of ldd /usr/lib/qt/plugins/platforms/libqxcb.so


	linux-vdso.so.1 (0x00007ffe049cc000)
	libQt5XcbQpa.so.5 => /usr/lib/libQt5XcbQpa.so.5 (0x00007f11af265000)
	libQt5Gui.so.5 => /usr/lib/libQt5Gui.so.5 (0x00007f11aebff000)
	libQt5Core.so.5 => /usr/lib/libQt5Core.so.5 (0x00007f11ae6e1000)
	libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x00007f11ae4cb000)
	libc.so.6 => /usr/lib/libc.so.6 (0x00007f11ae2ff000)
	libfontconfig.so.1 => /usr/lib/libfontconfig.so.1 (0x00007f11ae2b0000)
	libfreetype.so.6 => /usr/lib/libfreetype.so.6 (0x00007f11ae1e3000)
	libQt5DBus.so.5 => /usr/lib/libQt5DBus.so.5 (0x00007f11ae163000)
	libpthread.so.0 => /usr/lib/libpthread.so.0 (0x00007f11ae142000)
	libX11-xcb.so.1 => /usr/lib/libX11-xcb.so.1 (0x00007f11ae13d000)
	libxcb-icccm.so.4 => /usr/lib/libxcb-icccm.so.4 (0x00007f11ae137000)
	libxcb-image.so.0 => /usr/lib/libxcb-image.so.0 (0x00007f11ae131000)
	libxcb-shm.so.0 => /usr/lib/libxcb-shm.so.0 (0x00007f11ae12a000)
	libxcb-keysyms.so.1 => /usr/lib/libxcb-keysyms.so.1 (0x00007f11ae125000)
	libxcb-randr.so.0 => /usr/lib/libxcb-randr.so.0 (0x00007f11ae113000)
	libxcb-render-util.so.0 => /usr/lib/libxcb-render-util.so.0 (0x00007f11ae10d000)
	libxcb-render.so.0 => /usr/lib/libxcb-render.so.0 (0x00007f11ae0fd000)
	libxcb-shape.so.0 => /usr/lib/libxcb-shape.so.0 (0x00007f11ae0f8000)
	libxcb-sync.so.1 => /usr/lib/libxcb-sync.so.1 (0x00007f11ae0ec000)
	libxcb-xfixes.so.0 => /usr/lib/libxcb-xfixes.so.0 (0x00007f11ae0e2000)
	libxcb-xinerama.so.0 => /usr/lib/libxcb-xinerama.so.0 (0x00007f11ae0dd000)
	libxcb-xkb.so.1 => /usr/lib/libxcb-xkb.so.1 (0x00007f11ae0bf000)
	libxcb-xinput.so.0 => /usr/lib/libxcb-xinput.so.0 (0x00007f11ae09a000)
	libxcb.so.1 => /usr/lib/libxcb.so.1 (0x00007f11ae070000)
	libX11.so.6 => /usr/lib/libX11.so.6 (0x00007f11adf2c000)
	libSM.so.6 => /usr/lib/libSM.so.6 (0x00007f11adf22000)
	libICE.so.6 => /usr/lib/libICE.so.6 (0x00007f11adf05000)
	libxkbcommon-x11.so.0 => /usr/lib/libxkbcommon-x11.so.0 (0x00007f11adefb000)
	libxkbcommon.so.0 => /usr/lib/libxkbcommon.so.0 (0x00007f11adeb2000)
	libglib-2.0.so.0 => /usr/lib/libglib-2.0.so.0 (0x00007f11add76000)
	libm.so.6 => /usr/lib/libm.so.6 (0x00007f11adc30000)
	libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0x00007f11adc15000)
	libGL.so.1 => /usr/lib/libGL.so.1 (0x00007f11adb8f000)
	libpng16.so.16 => /usr/lib/libpng16.so.16 (0x00007f11adb58000)
	libz.so.1 => /usr/lib/libz.so.1 (0x00007f11adb3e000)
	libharfbuzz.so.0 => /usr/lib/libharfbuzz.so.0 (0x00007f11ada65000)
	libmd4c.so.0 => /usr/lib/libmd4c.so.0 (0x00007f11ada4d000)
	libsystemd.so.0 => /usr/lib/libsystemd.so.0 (0x00007f11ad971000)
	libdouble-conversion.so.3 => /usr/lib/libdouble-conversion.so.3 (0x00007f11ad95b000)
	libicui18n.so.70 => /usr/lib/libicui18n.so.70 (0x00007f11ad635000)
	libicuuc.so.70 => /usr/lib/libicuuc.so.70 (0x00007f11ad439000)
	libdl.so.2 => /usr/lib/libdl.so.2 (0x00007f11ad432000)
	libpcre2-16.so.0 => /usr/lib/libpcre2-16.so.0 (0x00007f11ad3a3000)
	libzstd.so.1 => /usr/lib/libzstd.so.1 (0x00007f11ad2cc000)
	/usr/lib64/ld-linux-x86-64.so.2 (0x00007f11af3c5000)
	libexpat.so.1 => /usr/lib/libexpat.so.1 (0x00007f11ad29c000)
	libbz2.so.1.0 => /usr/lib/libbz2.so.1.0 (0x00007f11ad289000)
	libbrotlidec.so.1 => /usr/lib/libbrotlidec.so.1 (0x00007f11ad27b000)
	libdbus-1.so.3 => /usr/lib/libdbus-1.so.3 (0x00007f11ad224000)
	libxcb-util.so.1 => /usr/lib/libxcb-util.so.1 (0x00007f11ad21c000)
	libXau.so.6 => /usr/lib/libXau.so.6 (0x00007f11ad217000)
	libXdmcp.so.6 => /usr/lib/libXdmcp.so.6 (0x00007f11ad20f000)
	libuuid.so.1 => /usr/lib/libuuid.so.1 (0x00007f11ad206000)
	libpcre.so.1 => /usr/lib/libpcre.so.1 (0x00007f11ad18d000)
	libGLdispatch.so.0 => /usr/lib/libGLdispatch.so.0 (0x00007f11ad0d5000)
	libGLX.so.0 => /usr/lib/libGLX.so.0 (0x00007f11ad0a2000)
	libgraphite2.so.3 => /usr/lib/libgraphite2.so.3 (0x00007f11ad07d000)
	librt.so.1 => /usr/lib/librt.so.1 (0x00007f11ad072000)
	liblzma.so.5 => /usr/lib/liblzma.so.5 (0x00007f11ad047000)
	liblz4.so.1 => /usr/lib/liblz4.so.1 (0x00007f11ad024000)
	libcap.so.2 => /usr/lib/libcap.so.2 (0x00007f11ad018000)
	libgcrypt.so.20 => /usr/lib/libgcrypt.so.20 (0x00007f11acedc000)
	libicudata.so.70 => /usr/lib/libicudata.so.70 (0x00007f11ab2c0000)
	libbrotlicommon.so.1 => /usr/lib/libbrotlicommon.so.1 (0x00007f11ab29b000)
	libgpg-error.so.0 => /usr/lib/libgpg-error.so.0 (0x00007f11ab273000)

System information:

 OS: Manjaro 21.2.2 Qonos
 Kernel: x86_64 Linux 5.15.16-1-MANJARO
 Uptime: 5h 18m
 Packages: 1396
 Shell: fish 3.3.1
 Resolution: 3840x1080
 DE: KDE5 / Plasma
 WM: KWin
 GTK Theme: Breeze [GTK2/3]
 Icon Theme: breeze-dark
 Disk: 31G / 236G (14%)
 CPU: Intel Core i7-7700K @ 8x 4.5GHz [44.0°C]
 GPU: Intel Corporation HD Graphics 630 (rev 04)
 RAM: 6722MiB / 15866MiB
 Python 3.10.1

hskoglund · 30 Jan 2022, 01:35

Hi, do you get the same error if you try a vanilla Hello World python app?
Say like this:

app = QApplication(sys,argv)
window = QWidget()
window.setWindowTitle('Hello world')
window.setGeometry(100, 100, 640, 480)
window.show()
sys.exit(app.exec_())

LiZheCN · wrote on 30 Jan 2022, 01:35

@hskoglund Without reboot a simple qt hello world project can run. After reboot every thing goes fine. Thank you for you time.