Failed to load platform plugin xcb while launching qt5 app on linux without qt installed

Question

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

User · Answer

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

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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   quot 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  quot   quot 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  quot  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  quot arch quot  gave a different and unhelpful result   dpkg --print-architecture  result for me  amd64  I then googled  quot libxkbcommon-x11 so 0 ubuntu 18 04 amd64 quot   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

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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

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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

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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

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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

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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

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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

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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  quot satisfied quot  all  quot not found quot  dependencies  Then this notorious This application failed to start because it could not find or load the Qt platform plugin  quot xcb quot  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  quot satisfied quot    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  quot  media sf Qt Package platforms quot      QFactoryLoader  QFactoryLoader   looking at  quot  media sf Qt Package platforms libqxcb so quot  Found metadata in lib  media sf Qt Package platforms libqxcb so  metadata         quot IID quot    quot org qt-project Qt QPA QPlatformIntegrationFactoryInterface 5 3 quot        quot MetaData quot              quot Keys quot                  quot xcb quot                        quot className quot    quot QXcbIntegrationPlugin quot        quot debug quot   false       quot version quot   329472     Got keys from plugin meta data   quot xcb quot   loaded library  quot  media sf Qt Package platforms libqxcb so quot  QLibraryPrivate  loadPlugin failed on  quot  media sf Qt Package platforms libqxcb so quot     quot 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   quot  This application failed to start because it could not find or load the Qt platform plugin  quot xcb quot  in  quot  quot    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

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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

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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

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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

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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

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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

User · Answer

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

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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

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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  quot xcb quot  in  quot  quot   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  quot xcb quot  to load properly  So  the solution will be install the  libxcb-xinerama so 0 quot  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

[linux] "Failed to load platform plugin "xcb" " while launching qt5 app on linux without qt installed

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