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Troubleshooting---Slow Control

qt.qpa.plugin

When you try to start the slow control and have an error message similar to this one 

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
try the following:

  1. add 
    export QT_PLUGIN_PATH=/home/USERNAME/Qt5.12.9/5.12.9/gcc_64/plugins
    to your .bashrc and reinstall the Slow Control via make clean, qmake vmmdcs.pro and make in the build-directory of the Slow Control folder.
  2. alternatively, it may also be an error in your $DISPLAY environment variable. It should be set to your network IP, with :0 at the end. For instance, if your IP is 10.0.0.5, you should write: export DISPLAY=10.0.0.5:0 You can try it by running xeyes or any QT GUI app. You can also automatise it by adding this to your .bashrc: 
    export DISPLAY=$(ip route list default | awk '{print $3}'):0

Slow control is not working

  • Remove firewall blocking of UDP
  • An MTU value of 9000 (jumbo frames) is needed in the network card settings
  • Check the firmware combination