Error when launching rqt

[John.M T]

hi guys,
I am running ubuntu20.04 server with ROS2 foxy desktop on raspberry pi 4.
Using window10 putty SSH accessing raspberry pi 4 and login to its ubuntu.
When launching "rqt", the following error showed up:

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could not connect to display
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb.

---

Please advise.
Thanks

[JonB]

@John-M-T
I don't know what "rqt" is. But as you can when so many people ask the same question as you with the error message you show, you should set an environment variable QT_DEBUG_PLUGINS=1 and then look at the end of detailed diagnostic messages you will get.

[John.M T]

@JonB Thanks for your reply. Have used "export qt_debug_plugins=1", but no other error messages except those I mentioned above. :(

[Pl45m4]

@John-M-T

You are not coding something with Qt, aren't you?! You've started a program and this message showed up?!

rqt is RosQt or something like that?

Have you used capital letters for QT_DEBUG_PLUGINS?

This error is very common and could come from different sources.
Maybe this helps

• https://askubuntu.com/questions/308128/failed-to-load-platform-plugin-xcb-while-launching-qt5-app-on-linux-without

Like @JonB also said, you should see at least some more lines when you start the program that causes this error in your console.

[jsulm]

@John-M-T You're trying to start a GUI application through SSH. This is not going to work like this.
You need to use VNC for example to forward the graphical output to your Windows machine.

[John.M T]

@Pl45m4 Thanks for your reply. You are right, I am launching rqt for ROS application development. I hope Qt experts here can help to give some hints on what needs to pay attention to. Yes, i used capital letters for QT_DEBUG_PLUGINS. Meanwhile, I also looking around for solutions. Thanks for the link provided. Appreciate that.

[John.M T]

@jsulm hi there, thanks for your reply. Yes, you are right. I am trying to launch a GUI application via SSH. May be the remote x-client was not launched and that caused the "could not connect to display" error. Thanks for the prompt ... will look into that direction for solution. Appreciate that.

[JonB]

@John-M-T
The QT_DEBUG_PLUGINS variable needs to be in the environment of the running Qt program. My guess is your way is not passing that through to the final program running?

[John.M T]

@JonB , @jsulm , @Pl45m4 Thanks everyone. I managed to have the problem resolved based on your suggestion and advices.

1. "could not connect to display" error
Because the x-server was trying to connect the remote x-client. But the x-client was not launched. After launching VcXsrv, connection was established and the GUI app appeared on the remote PC (i.e. x-client side).

2. however, still have some error message
Although the connection was successful, x-server reported the following error:
libGL error: No matching fbConfigs or visuals found
libGL error: failed to load driver: swrast

Managed to find the solution posted at
https://itectec.com/ubuntu/ubuntu-win10-linux-subsystem-libgl-error-no-matching-fbconfigs-or-visuals-found-libgl-error-failed-to-load-driver-swrast/

All error messages are gone by now. Hope this post benefit those who are having the same problem as mine.

Thank you very much guys!