I wrote application for linux which uses Qt5.
But when I am trying to launch it on the linux without Qt SDK installed, the output in console is:
Failed to load platform plugin "xcb". Available platforms are:
How can I fix this? May be I need to copy some plugin file?
When I use ubuntu with Qt5 installed, but I rename Qt directory, the same problem occurs. So, it uses some file from Qt directory...
UPDATE:
when I create in the app dir "platforms" folder with the file libqxcb.so, the app still doesnot start, but the error message changes:
Failed to load platform plugin "xcb". Available platforms are:
xcb
How can this happen? How can platform plugin be available but can't be loaded?
Use ldd (man ldd) to show shared library dependencies. Running this on libqxcb.so
.../platforms$ ldd libqxcb.so
shows that xcb depends on libQt5DBus.so.5 in addition to libQt5Core.so.5 and libQt5Gui.so.5 (and many other system libs). Add libQt5DBus.so.5 to your collection of shared libs and you should be ready to move on.
As was posted earlier, you need to make sure you install the platform plugins when you deploy your application. Depending on how you want to deploy things, there are two methods to tell your application where the platform plugins (e.g. platforms/plugins/libqxcb.so) are at runtime which may work for you.
The first is to export the path to the directory through the QT_QPA_PLATFORM_PLUGIN_PATH variable.
QT_QPA_PLATFORM_PLUGIN_PATH=path/to/plugins ./my_qt_app
or
export QT_QPA_PLATFORM_PLUGIN_PATH=path/to/plugins
./my_qt_app
The other option, which I prefer is to create a qt.conf file in the same directory as your executable. The contents of which would be:
[Paths]
Plugins=/path/to/plugins
More information regarding this can be found here and at using qt.conf
I tried to start my binary, compiled with Qt 5.7, on Ubuntu 16.04 LTS where Qt 5.5 is preinstalled. It didn't work.
At first, I inspected the binary itself with ldd as was suggested here, and satisfied all "not found" dependencies. Then this notorious This application failed to start because it could not find or load the Qt platform plugin "xcb" error was thrown.
How to resolve this in Linux
Firstly you should create platforms directory where your binary is, because it is the place where Qt looks for XCB library. Copy libqxcb.so there. I wonder why authors of other answers didn't mention this.
Then you may want to run your binary with QT_DEBUG_PLUGINS=1 environment variable set to check which dependencies of libqxcb.so are not satisfied. (You may also use ldd for this as suggested in the accepted answer).
The command output may look like this:
me#xerus:/media/sf_Qt/Package$ LD_LIBRARY_PATH=. QT_DEBUG_PLUGINS=1 ./Binary
QFactoryLoader::QFactoryLoader() checking directory path "/media/sf_Qt/Package/platforms" ...
QFactoryLoader::QFactoryLoader() looking at "/media/sf_Qt/Package/platforms/libqxcb.so"
Found metadata in lib /media/sf_Qt/Package/platforms/libqxcb.so, metadata=
{
"IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
"MetaData": {
"Keys": [
"xcb"
]
},
"className": "QXcbIntegrationPlugin",
"debug": false,
"version": 329472
}
Got keys from plugin meta data ("xcb")
loaded library "/media/sf_Qt/Package/platforms/libqxcb.so"
QLibraryPrivate::loadPlugin failed on "/media/sf_Qt/Package/platforms/libqxcb.so" : "Cannot load library /media/sf_Qt/Package/platforms/libqxcb.so: (/usr/lib/x86_64-linux-gnu/libQt5DBus.so.5: version `Qt_5' not found (required by ./libQt5XcbQpa.so.5))"
This application failed to start because it could not find or load the Qt platform plugin "xcb"
in "".
Available platform plugins are: xcb.
Reinstalling the application may fix this problem.
Aborted (core dumped)
Note the failing libQt5DBus.so.5 library. Copy it to your libraries path, in my case it was the same directory where my binary is (hence LD_LIBRARY_PATH=.). Repeat this process until all dependencies are satisfied.
P.S. thanks to the author of this answer for QT_DEBUG_PLUGINS=1.
I tried the main parts of each answer, to no avail. What finally fixed it for me was to export the following environment variables:
LD_LIBRARY_PATH=/usr/local/lib:~/Qt/5.9.1/gcc_64/lib
QT_QPA_PLATFORM_PLUGIN_PATH=~/Qt/5.9.1/gcc_64/plugins/
Ubuntu 16.04 64bit.
I got the problem for apparently no reasons. The night before I watched a movie on my VideoLan instance, that night I would like to watch another one with VideoLan. VLC just didn't want to run because of the error into the question.
I google a bit and I found the solution it solved my problem: from now on, VLC is runnable just like before. The solution is this comand:
sudo ln -sf /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/ /usr/bin/
I am not able to explain what are its consequencies, but I know it creates some missing symbolic link.
Since version 5, Qt uses a platform abstraction system (QPA) to abstract from the underlying platform.
The implementation for each platform is provided by plugins. For X11 it is the XCB plugin. See Qt for X11 requirements for more information about the dependencies.
There might be many causes to this problem. The key is to use
export QT_DEBUG_PLUGINS=1
before you run your Qt application. Then, inspect the output, which will point you to the direction of the error. In my case it was:
Cannot load library /opt/nao/plugins/platforms/libqxcb.so: (/opt/nao/bin/../lib/libz.so.1: version `ZLIB_1.2.9' not found (required by /usr/lib/x86_64-linux-gnu/libpng16.so.16))
But that is solved in different threads. See for instance https://stackoverflow.com/a/50097275/2408964.
Probably this information will help. I was on Ubuntu 18.04 and when I tried to install Krita, using the ppa method, I got this error:
This application failed to start because it could not find or load the Qt platform plugin "xcb" in "".
Available platform plugins are: linuxfb, minimal, minimalegl, offscreen, wayland-egl, wayland, xcb.
Reinstalling the application may fix this problem.
Aborted
I tried all the solutions that I found in this thread and other webs without any success.
Finally, I found a post where the author mention that is possible to activate the debugging tool of qt5 using this simple command:
export QT_DEBUG_PLUGINS=1
After adding this command I run again krita I got the same error, however this time I knew the cause of that error.
libxcb-xinerama.so.0: cannot open shared object file: No such file or directory.
This error prevents to the "xcb" to load properly. So, the solution will be install the `libxcb-xinerama.so.0" right? However, when I run the command:
sudo apt install libxcb-xinerama
The lib was already installed. Now what Teo? Well, then I used an old trick :) Yeah, that one --reinstall
sudo apt install --reinstall libxcb-xinerama
TLDR: This last command solved my problem.
I ran into a very similar problem with the same error message. First, debug some by turning on the Qt Debug printer with the command line command:
export QT_DEBUG_PLUGINS=1
and rerun the application. For me this revealed the following:
"Cannot load library /home/.../miniconda3/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqxcb.so: (libxkbcommon-x11.so.0: cannot open shared object file: No such file or directory)"
"Cannot load library /home/.../miniconda3/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqxcb.so: (libxkbcommon-x11.so.0: cannot open shared object file: No such file or directory)"
Indeed, I was missing libxkbcommon-x11.so.0 and libxkbcommon-x11.so.0. Next, check your architecture using dpkg from the linux command line. (For me, the command "arch" gave a different and unhelpful result)
dpkg --print-architecture #result for me: amd64
I then googled "libxkbcommon-x11.so.0 ubuntu 18.04 amd64", and likewise for libxkbcommon-x11.so.0, which yields those packages on packages.ubuntu.com. That told me, in retrospect unsurprisingly, I'm missing packages called libxkbcommon-x11-0 and libxkbcommon0, and that installing those packages will include the needed files, but the dev versions will not. Then the solution:
sudo apt-get update
sudo apt-get install libxkbcommon0
sudo apt-get install libxkbcommon-x11-0
So, I spent about a day trying to figure out what was the issue; tried all the proposed solutions, but none of that worked like installing xcb libs or exporting Qt plugins folder. The solution that suggested to use QT_DEBUG_PLUGINS=1 to debug the issue didn't provide me a direct insight like in the answer - instead I was getting something about unresolved symbols within Qt5Core.
That gave me a hint, though: what if it's trying to use different files from different Qt installations? On my machine I had standard version installed in /home/username/Qt/ and some local builds within my project that I compiled by myself (I have other custom built kits as well in other locations). Whenever I tried to use any of the kits (installed by Qt maintenance tool or built by myself), I would get an "xcb error".
The solution was simple: provide the Qt path through CMAKE_PREFIX_PATH and not though Qt5_DIR as I did, and it solved the problem. Example:
cmake .. -DCMAKE_PREFIX_PATH=/home/username/Qt/5.11.1/gcc_64
I faced the same problem when after installing Viber. It had all required qt libraries in /opt/viber/plugins/.
I checked dependencies of /opt/viber/plugins/platforms/libqxcb.so and found missing dependencies. They were libxcb-render.so.0, libxcb-image.so.0, libxcb-icccm.so.4, libxcb-xkb.so.1
So I resolved my issue by installing missing packages with this libraries:
apt-get install libxcb-xkb1 libxcb-icccm4 libxcb-image0 libxcb-render-util0
I like the solution with qt.conf.
Put qt.conf near to the executable with next lines:
[Paths]
Prefix = /path/to/qtbase
And it works like a charm :^)
For a working example:
[Paths]
Prefix = /home/user/SDKS/Qt/5.6.2/5.6/gcc_64/
The documentation on this is here: https://doc.qt.io/qt-5/qt-conf.html
All you need to do is
pip uninstall PyQt5
and
conda install pyqt
Most of the problem of pyqt can be fixed by this simplest solution.
In my case, I needed to deploy two Qt apps on an Ubuntu virtualbox guest. One was command-line ("app"), the other GUI_based ("app_GUI").
I used "ldd app" to find out what the required libs are, and copied them
to the Ubuntu guest.
While the command-line executable "app" worked ok, the GUI-based executable crashed, giving
the "Failed to load platform plugin "xcb" error. I checked ldd for libxcb.so, but this too had no missing dependencies.
The problem seemed to be that while I did copy all the right libraries I accidentally had copied also libraries that were already present at the guest system.. meaning that (a) they were unnecessary to copy them in the first place and (b) worse, copying them produced incompatibilities between the install libraries.
Worse still, they were undetectable by ldd like I said..
The solution? Make sure that you copy libraries shown as missing by ldd and absolutely no extra libraries.
In my case missing header files were the reason libxcb was not built by Qt. Installing them according to https://wiki.qt.io/Building_Qt_5_from_Git#Linux.2FX11 resolved the issue:
yum install libxcb libxcb-devel xcb-util xcb-util-devel mesa-libGL-devel libxkbcommon-devel
Folks trying to get this started on Ubuntu 20.04 please try to run this and see if this solves the problem. This worked for me
sudo apt-get update -y
sudo apt-get install -y libxcb-xinerama0
I link all Qt stuff statically to the generic Linux builds of my open source projects. It makes life a bit easier. You just need to build static versions of Qt libraries first. Of course this cannot be applied to closed source software due to licensing issues. The deployment of Qt5 apps on Linux is currently a bit problematic, because Ubuntu 12.04, for example, doesn't have Qt5 libraries in the package repositories.
I had this problem, and on a hunch I removed the Qt Configs from my environment. I.e.,
rm -rf ~/.config/Qt*
Then I started qtcreator and it reconfigured itself with the existing state of the machine. It no longer remembered where my projects were, but that just meant I had to browse to them "for the first time" again.
But more importantly it built itself a coherent set of library paths, so I could rebuild and run my project executables again without the xcb or qxcb libraries going missing.
I faced the same situation, but on a Ubuntu 20.04 VM.
TL;DR: Check file permissions.
What I did:
I copied the Qt libs required to /usr/local/lib/x86_64-linux-gnu/ and added it to LD_LIBRARY_PATH
I copied the platforms folder from Qt to my application directory and added it to QT_PLUGIN_PATH
I ran ldd on the executable and in the offending libqxcb.so (ldd libqxcb.so), and it complains about some dependencies although ldconfig listed them as found.
linux-vdso.so.1 (0x00007ffee19af000)
libQt5XcbQpa.so.5 => not found
libfontconfig.so.1 => /lib/x86_64-linux-gnu/libfontconfig.so.1 (0x00007f7cb18fb000)
libfreetype.so.6 => /lib/x86_64-linux-gnu/libfreetype.so.6 (0x00007f7cb183c000)
libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f7cb1820000)
libQt5Gui.so.5 => /usr/local/lib/x86_64-linux-gnu/libQt5Gui.so.5 (0x00007f7cb0fd4000)
libQt5DBus.so.5 => not found
I used export QT_DEBUG_PLUGINS=1 for further info. It complains about missing files, although they are there.
What I found:
For some reason, when copying to the VM through the shared folder the files permissions were not the correct ones.
Thus, I ran: sudo chmod 775 * on the libs and voilà.
I solved the issue through this https://github.com/NVlabs/instant-ngp/discussions/300
pip uninstall opencv-python
pip install opencv-python-headless
This seems to have been a problem with the cv2 Python package and how it loops in Qt
sudo ln -sf /usr/lib/...."adapt-it"..../qt5/plugins/platforms/ /usr/bin/
It creates the symbolic link it's missed. Good for QT ! Good for VLC !!
I followed these instructions in the configuration of OpenCV SDK for using it in Qt Creator IDE, but I couldn't conclude point 6.5, due to configuration errors in Cmake-GUI. I setup the configuration in CMake of the compilers gcc and g++ contained in Qt folder for MinGW32, and all looks Ok. But when Cmake-GUI starts the process of build configuration it ends up saying
"Error in configuration process, project files may be invalid".
It can't find the following:
QT_QMAKE_EXECUTABLE;
Qt5Concurrent_DIR;
QT5Core_DIR;
QT5Gui_DIR;
QT5Test_DIR;
QT5Widgets_DIR.
After this issue I tried to go on with following points of configuration tutorial, without reaching the final instruction of mingw32-make install. I'm using the following versions of softwares: Qt 5.3.0, OpenCV 2.4.9, CMake 2.8.12.2. My OS is Windows 7.
How can I recover the missing Qt files in CMake configuration?
Is there an alternative way for configuring OpenCV with Qt (like using precompiled build of OpenCV libraries)?
You just need to indicate CMake the correct paths to each one. Click oh the path to browse and set each one individually:
QT_QMAKE_EXECUTABLE;
For this one, you need to search inside the Qt installation folder for the /bin directory. On it, you' ll find the qmake.exe. In my case it was C:/Qt/5.3/winrt_x64/bin/qmake.exe
All the following ones are in the Qt's /lib/cmake directory. In my case: C:/Qt/5.3/winrt_x64/lib/cmake :
Qt5Concurrent_DIR;
C:/Qt/5.3/winrt_x64/lib/cmake/Qt5Concurrent
QT5Core_DIR;
C:/Qt/5.3/winrt_x64/lib/cmake/Qt5Core
QT5Gui_DIR;
C:/Qt/5.3/winrt_x64/lib/cmake/Qt5Gui
QT5Test_DIR;
C:/Qt/5.3/winrt_x64/lib/cmake/Qt5Test
QT5Widgets_DIR.
C:/Qt/5.3/winrt_x64/lib/cmake/Qt5Widgets
Then click generate. It' ll show a new error and ask you for the QT5OpenGL_DIR. Just as before, show CMake the correct directory. In my case: C:/Qt/5.3/winrt_x64/lib/cmake/Qt5OpenGL. Finally, click Configure again, and then Generate, and now you're done creating the build files.
You have to specify the location of Qt manually by passing it as an argument for QT5Core_DIR. Qt5_DIR or CMAKE_PREFIX_PATH does also the trick.
Example
Given your Qt 5 is installed at /opt/selfcompiled/Qt5. When calling cmake, add the flag from above:
cmake -DQt5_DIR=/opt/selfcompiled/Qt5 <pathToSourceDir>
Once the Qt 5 directory is set and found by CMake, all the other variables related to Qt 5 should be found from there, too.
I am attempting to compile a software that I have built using Qt, ITK, VTK, using mingw32 on Windows 7. I have successfully done this on many computers, but I am having trouble on my laptop.
I made a mistake when I first installed Qt on this machine, in that I installed the "msvc2010" or visual studio verision of Qt. I had VS installed, and this is what it defaulted to, and I did not change it. Realizing my mistake, I uninstalled all traces of this Qt, and installed the Mingw32 version. The exact version I downloaded was: Qt libraries 4.8.3 for Windows (minGW 4.4, 317 MB)
I installed mingw32, installed qt, all nice and dandy, and now I am compiling my software. It builds beautifully, but during the linking stage I get the following nasty error:
mingw32-make[2]: *** No rule to make target 'C:/QtSDK/Desktop/Qt/4.8.1/msvc2010/
lib/QtOpenGL4.dll', needed by 'x.exe'. Stop.
CMakeFiles\Makefile2:62: recipe for target 'CMakeFiles/x.dir/all' failed
mingw32-make[1]: *** [CMakeFiles/x.dir/all] Error 2
Makefile:74: recipe for target 'all' failed
mingw32-make: *** [all] Error 2
Where x is the name of my project.
Note the make target: C:/QtSDK/Desktop/Qt/4.8.1/msvc2010/lib/QtOpenGL4.dll. This is NOT the correct place to look for the DLLs. It is looking at the lib location of my first installation of Qt. The QtSDK folder does not even exist anymore, the new version is under a different folder.
This is sadly also reflected in the link.txt under CMakeFiles that is generated in the build folder by cmake. One of the entries is:
C:\QtSDK\Desktop\Qt\4.8.1\msvc2010\lib\QtGui4.dll
along with many other DLLs.
Clearly, the problem is that Cmake is generating targets for the previous version of Qt.
How can I erase whatever ridiculous cache this is originating from, so that it does not do this? I have reinstalled Cmake, I have reinstalled Qt, I have done everything I can think of. I have verified that the Cmake variable are all pointing to the correct Qt folder (the other one does not exist, so no way we could get to the linking stage if they were incorrect).
Thank you so much.
EDIT:
I get this very pertinent warning, that has the wretched file path in it:
CMake Warning (dev) at CMakeLists.txt:22 (ADD_EXECUTABLE):
Policy CMP0003 should be set before this line. Add code such as
if(COMMAND cmake_policy)
cmake_policy(SET CMP0003 NEW)
endif(COMMAND cmake_policy)
as early as possible but after the most recent call to
cmake_minimum_required or cmake_policy(VERSION). This warning appears
because target "x" links to some libraries for which the linker must
search:
comctl32, vfw32, ws2_32, wsock32, -lgdi32, opengl32
and other libraries with known full path:
C:/Qt/4.8.3/lib/libQtGui4.a
C:/ITK/lib/libitksys-4.1.dll.a
C:/VTK/bin/libQVTK.a
C:/QtSDK/Desktop/Qt/4.8.1/msvc2010/lib/QtOpenGL4.dll
CMake is adding directories in the second list to the linker search path in
case they are needed to find libraries from the first list (for backwards
compatibility with CMake 2.4). Set policy CMP0003 to OLD or NEW to enable
or disable this behavior explicitly. Run "cmake --help-policy CMP0003" for
more information.
This warning is for project developers. Use -Wno-dev to suppress it.
I added the "NEW" policy, and the warning went away, but I still have the same problem.
The problem turned out to be that I had installed VTK while I had the old Qt (configured for VS2010 installed). When I included VTK's libraries, it also included DLLs from Qt--but it was still pointing to the old Qt.
I reinstalled VTK, and we got past this step.
Try to regenerate cmake files, :
mingw32-make clean
cmake .
Short version: You need to delete your CMakeCache.txt file in your build directory.
Long version: Whenever CMake searches for external libraries/programes etc (eg. by FIND_LIBRARY which is called when searching for Qt, for example), it saves the result in the cache. On subsequent runs, it simply uses the cached value (if any) instead of searching for the libraries again. Therefore, you need to remove these cache entries so that CMake really searches for the libraries again. Simply delete the CMakeCache.txt and start over. If both versions are installed in parallel, make sure that QTDIR environment variable is set correctly and the path includes <QTDIR>/bin, as CMake relies on qmake to find the relevant libraries.
Note: If you don't want to delete the whole cache, deleting the Qt relevant variables should work, too.
cmake -U *QT_* .
should do the trick.
However, deleting the whole cache is the cleanest solution.
I'm compiling Qt from source, but I don't want to extract the source each time I want to build it.
How can I clean previous configuration with the configure tool?
For Qt4 and earlier, try this:
nmake confclean
You can then re-configure and re-compile QT.
As noted in the comments, this no longer works in QT 5. This is due to the fact that the Qt project now uses separate sub-modules for different parts. If you have a local clone of the Qt git repos, you can try calling this from the main Qt directory:
git submodule foreach --recursive "git clean -dfx"
As noted here, there may be some problems if you have a downloaded source archive. The link I posted suggests using a shadow build instead so the process of making a clean configuration is as simple as configuring to build at a new shadow build destination.
As of today (Qt 5.9.0 beta2) there is no confclean target in Linux, and you need to manually remove .config.cache file to reconfigure.
Note that make distclean doesn't help at all.
For the latest versions, use a shadow build, then you can just nuke your directory. My batch file for configuring effectively creates a new folder, moves into it, then calls configure.
Then you just go into the shadow directory and run 'jom'.
When you want to make a different configuration, just use a different shadow directory.
This effectively means that your source tree doesn't get filled with build artifacts, which are impossible to remove when you want a different configuration. Trust me, this is the thing to do....
mkdir shadow_dir
cd shadow_dir
%~dp0\src\configure.bat ....
On Ubuntu:
make confclean
BTW, the following text displayed after run configure:
Qt is now configured for building. Just run 'make'.
Once everything is built, you must run 'make install'.
Qt will be installed into /home/ben/qt/qt-everywhere-opensource-4.7.4-debug
To reconfigure, run 'make confclean' and 'configure'.