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Starting QT app as a Systemd service

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  • V vmetodiev

    @Pl45m4, @KroMignon

    Well, here is a snippet from my main function:

    int main(int argc, char *argv[])
{
     QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

     QGuiApplication app(argc, argv);
     QQmlApplicationEngine engine;
     ...
}

    I will read a bit more about QCore and QGui... now it is some kind of a Frankenstein :D

    @SGaist

    Yes, I always start the X server before attempting to launch the QT application.
    It also starts correctly as a systemd service.

    About "eglfs" - thanks for mentioning this, I will read about it as well and write another post. I have no idea what you are taking about right now.

    Thank you guys for your support and informative directions!

    JonBJ Offline
    JonBJ Offline
    JonB
    wrote on last edited by
    #6

    @vmetodiev
    I am not an expert, but how can you have a QGuiApplication and/or a QQmlApplicationEngine if you're not going to have any UI or interaction?

    1 Reply Last reply
    0
    • V Offline
      V Offline
      vmetodiev
      wrote on last edited by
      #7

      @JonB

      I agree! My goal is to make the GUI application start as a service with only the X server running beneath it, without LXDE or any other desktop environment.

      I am just struggling how to achieve it no additional overhead...

      KroMignonK 1 Reply Last reply
      0
      • V vmetodiev

        @JonB

        I agree! My goal is to make the GUI application start as a service with only the X server running beneath it, without LXDE or any other desktop environment.

        I am just struggling how to achieve it no additional overhead...

        KroMignonK Offline
        KroMignonK Offline
        KroMignon
        wrote on last edited by KroMignon
        #8

        @vmetodiev said in Starting QT app as a Systemd service:

        I agree! My goal is to make the GUI application start as a service with only the X server running beneath it, without LXDE or any other desktop environment.
        I am just struggling how to achieve it no additional overhead...

        So you want to start you Qt QML/QWidget application with SystemD and X-Server.
        Your error looks very similar to this ==> https://community.toradex.com/t/starting-qt-app-as-a-systemd-service/15954

        So I guess you have to change qtapp.service to setup QT_QPA_PLATFORM.
        Something like this:

        [Unit]
Description=QT Application
After=xserver.service

[Service]
Type=simple
Environment="QT_QPA_PLATFORM=wayland-egl"
ExecStart=/opt/TestQtApp
ExecStop=/bin/bash -c 'pkill TestQtApp'
Restart=always
IgnoreSIGPIPE=no

[Install]
Alias=qtapp.service

        It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

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        • V vmetodiev

          Hello QT Community,

          I need to start my QT application without XFCE, Gnome, KDE, or what-so-ever desktop environment. I have disabled the lxdm.service (on my Toradex board running Angstrom Linux) and created a custom one that starts the X server only.

          xserver.service

          [Unit]
Description=X Server
Conflicts=getty@tty1.service plymouth-quit.service
After=systemd-user-sessions.service getty@tty1.service plymouth-quit.service

[Service]
ExecStart=/usr/bin/X
ExecStop=/usr/bin/killall -9 X
Restart=always
IgnoreSIGPIPE=no

[Install]
Alias=display-manager.service

          This works perfectly. The other service is the QT application itself:

          qtapp.service

          [Unit]
Description=QT Application
After=xserver.service

[Service]
Type=simple
ExecStart=/opt/TestQtApp
ExecStop=/bin/bash -c 'pkill TestQtApp'
Restart=always
IgnoreSIGPIPE=no

[Install]
Alias=qtapp.servic

          However, it won’t start due to some enviroment issue. The log in the journal looks like this:

          Jan 07 14:58:57 apalis-imx6 systemd[1]: Started QT Application.
Jan 07 14:58:57 apalis-imx6 TestQtApp[607]: QML debugging is enabled. Only use this in a safe environment.
Jan 07 14:58:57 apalis-imx6 TestQtApp[607]: QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-root'
Jan 07 14:58:57 apalis-imx6 TestQtApp[607]: qt.qpa.screen: QXcbConnection: Could not connect to display
Jan 07 14:58:57 apalis-imx6 TestQtApp[607]: Could not connect to any X display.
Jan 07 14:58:57 apalis-imx6 systemd[1]: qtapp.service: Main process exited, code=exited, status=1/FAILURE
Jan 07 14:58:57 apalis-imx6 systemd[1]: qtapp.service: Unit entered failed state.
Jan 07 14:58:57 apalis-imx6 systemd[1]: qtapp.service: Failed with result 'exit-code'.
Jan 07 14:58:57 apalis-imx6 systemd[1]: qtapp.service: Service hold-off time over, scheduling restart.
Jan 07 14:58:57 apalis-imx6 systemd[1]: Stopped QT Application.
Jan 07 14:58:57 apalis-imx6 systemd[1]: Started QT Application.

          Merging the commands for starting the X server and the QT application within a single service behaves similarly - I see the X process running, but not the QT application.

          Logging into the Bash shell and executing the "ExecStart" commands manually launches the QT application correctly.

          May someone advise on this?

          Thank you in advance!

          raven-worxR Offline
          raven-worxR Offline
          raven-worx
          Moderators
          wrote on last edited by raven-worx
          #9

          @vmetodiev said in Starting QT app as a Systemd service:

          Jan 07 14:58:57 apalis-imx6 TestQtApp[607]: qt.qpa.screen: QXcbConnection: Could not connect to display
          Jan 07 14:58:57 apalis-imx6 TestQtApp[607]: Could not connect to any X display.

          i think you are just missing the "DISPLAY=:0" env variable?

          try it manually by calling

          DISPLAY=:0 /opt/TestQtApp

          --- SUPPORT REQUESTS VIA CHAT WILL BE IGNORED ---
          If you have a question please use the forum so others can benefit from the solution in the future

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          0
          • V Offline
            V Offline
            vmetodiev
            wrote on last edited by
            #10

            @KroMignon
            Your error looks very similar to this ==> https://community.toradex.com/t/starting-qt-app-as-a-systemd-service/15954
            -> Absolutely :D It was posted by me in the Toradex forum, than I switched here...

            Environment="QT_QPA_PLATFORM=wayland-egl"
            -> As far I understand, in this case the QT app will work with Wayland instead of the X server, correct?

            @raven-worx
            Well, I added it as an enviroment and achived a certain progress.

            root@apalis-imx6:~# cat /lib/systemd/system/qtapp.service
[Unit]
Description=QT Application
After=xserver.service

[Service]
Type=simple
Environment="DISPLAY=:0"
ExecStart=/opt/TestQtApp
ExecStop=/bin/bash -c 'pkill TestQtApp'
Restart=always
IgnoreSIGPIPE=no

[Install]
Alias=qtapp.service

            The service now starts when I manually invoke it by "systemctl start qtapp".
            Nevertheless, it won't start automatically after reboot. The journal log is empty. Maybe the "After=xserver.service" is not quite correct?

            raven-worxR 1 Reply Last reply
            0
            • V vmetodiev

              @KroMignon
              Your error looks very similar to this ==> https://community.toradex.com/t/starting-qt-app-as-a-systemd-service/15954
              -> Absolutely :D It was posted by me in the Toradex forum, than I switched here...

              Environment="QT_QPA_PLATFORM=wayland-egl"
              -> As far I understand, in this case the QT app will work with Wayland instead of the X server, correct?

              @raven-worx
              Well, I added it as an enviroment and achived a certain progress.

              root@apalis-imx6:~# cat /lib/systemd/system/qtapp.service
[Unit]
Description=QT Application
After=xserver.service

[Service]
Type=simple
Environment="DISPLAY=:0"
ExecStart=/opt/TestQtApp
ExecStop=/bin/bash -c 'pkill TestQtApp'
Restart=always
IgnoreSIGPIPE=no

[Install]
Alias=qtapp.service

              The service now starts when I manually invoke it by "systemctl start qtapp".
              Nevertheless, it won't start automatically after reboot. The journal log is empty. Maybe the "After=xserver.service" is not quite correct?

              raven-worxR Offline
              raven-worxR Offline
              raven-worx
              Moderators
              wrote on last edited by raven-worx
              #11

              @vmetodiev
              do you start the xserver service manually?
              if not you are also missing Require=xserver.service so it is ensured that its running when your qt app gets started

              also to start it after reboot, you have to call systemctl enable qtapp

              --- SUPPORT REQUESTS VIA CHAT WILL BE IGNORED ---
              If you have a question please use the forum so others can benefit from the solution in the future

              1 Reply Last reply
              1
              • V Offline
                V Offline
                vmetodiev
                wrote on last edited by
                #12

                @raven-worx

                Yes, the service is enabled. Well, I added "Requires=xserver.service", but still the qtapp.service would not start.

                The xserver is fine upon reboot, visible inside "ps -auxf".

                Invoking " systemctl start qtapp" start the Qt app...

                KroMignonK 1 Reply Last reply
                0
                • SGaistS Offline
                  SGaistS Offline
                  SGaist
                  Lifetime Qt Champion
                  wrote on last edited by
                  #13

                  Maybe this service example might help.

                  Interested in AI ? www.idiap.ch
                  Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                  0
                  • V vmetodiev

                    @raven-worx

                    Yes, the service is enabled. Well, I added "Requires=xserver.service", but still the qtapp.service would not start.

                    The xserver is fine upon reboot, visible inside "ps -auxf".

                    Invoking " systemctl start qtapp" start the Qt app...

                    KroMignonK Offline
                    KroMignonK Offline
                    KroMignon
                    wrote on last edited by
                    #14

                    @vmetodiev said in Starting QT app as a Systemd service:

                    Invoking " systemctl start qtapp" start the Qt app...

                    I am far a way to be a systemd expert, so I may be wrong.
                    But I guess you have to add WantedBy=multi-user.target in the [Install] section to start the service automatically.

                    It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                    raven-worxR 1 Reply Last reply
                    1
                    • KroMignonK KroMignon

                      @vmetodiev said in Starting QT app as a Systemd service:

                      Invoking " systemctl start qtapp" start the Qt app...

                      I am far a way to be a systemd expert, so I may be wrong.
                      But I guess you have to add WantedBy=multi-user.target in the [Install] section to start the service automatically.

                      raven-worxR Offline
                      raven-worxR Offline
                      raven-worx
                      Moderators
                      wrote on last edited by
                      #15

                      @KroMignon said in Starting QT app as a Systemd service:

                      But I guess you have to add WantedBy=multi-user.target in the [Install] section to start the service automatically.

                      yep, thats true, good catch

                      --- SUPPORT REQUESTS VIA CHAT WILL BE IGNORED ---
                      If you have a question please use the forum so others can benefit from the solution in the future

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                      0
                      • V Offline
                        V Offline
                        vmetodiev
                        wrote on last edited by
                        #16

                        @SGaist @KroMignon
                        Yes, your suggestions helped. Now it works perfectly. Thank you so much for your support!!!

                        I am providing the service files below:

                        xserver.service

                        [Unit]
Description=X Server
Conflicts=getty@tty1.service plymouth-quit.service
After=systemd-user-sessions.service getty@tty1.service plymouth-quit.service

[Service]
ExecStart=/usr/bin/X
ExecStop=/usr/bin/killall -9 X
Restart=always
IgnoreSIGPIPE=no

[Install]
Alias=display-manager.service

                        qtapp.service

                        [Unit]
Description=QT Application
Requires=xserver.service
After=xserver.service

[Service]
Type=simple
Environment="DISPLAY=:0"
ExecStart=/opt/TestQtApp
ExecStop=/bin/bash -c 'pkill TestQtApp'
Restart=always
IgnoreSIGPIPE=no

[Install]
WantedBy=multi-user.target
                        1 Reply Last reply
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