Run Qt widget app on linux with no GUI

Bremenpl · wrote on 19 Oct 2016, 22:41

Hello there,
I am using latest QT 5.7 on Debian x64. I was wondering either it is possible to somehow run the QT widget app on the system where the GUI environment is off? I remember that there was a QT embedded version with own framebuffer. But here the gui is installed it is just off (console mode). So could a Qt 5.7 widget app open on top of console instead of graphical user interface? This is needed for a PC that has only one task- to run the Qt app and nothing else, thats why I want to turn the whole system background off.
I would appreciate all help regarding this topic.

p3c0 · wrote on 20 Oct 2016, 06:16

Hi @Bremenpl
If the X Server and the Window manager is running in the background I dont see any problem in running the application provided all the Qt application dependencies are satisfied.

Bremenpl · 20 Oct 2016, 06:56

Do you know how to keep the X server and window manager running while in console mode on Linux?

jsulm · wrote on 20 Oct 2016, 06:56

@Bremenpl Usually you can switch to text console from X server pressing Strg-Alt-F1 (or F2-F6). To go back to the X server you then press Alt-F7.

p3c0 · wrote on 20 Oct 2016, 06:57

@Bremenpl Since you said you have installed "GUI" I hope the X is already running in the background.
Fire this at your console:

ps ax | grep -i "/usr/bin/X"

Bremenpl · wrote on 20 Oct 2016, 07:02

Output:

  872 tty7     Ssl+   0:01 /usr/bin/X :0 -seat seat0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch
 1692 ?        S      0:00 /usr/bin/xprop -root -spy
 1722 pts/0    S+     0:00 grep -i /usr/bin/X

Yes when I switch to text mode with ctrl alt F1 and run the app I get "aborted" in return.

p3c0 · wrote on 20 Oct 2016, 07:09

@Bremenpl Tt says X server is using tty7 (it is by default) so you can run applications only on tty7 and not tty1 (which you did by pressing CTRL+ALT+F1 and launching the app)

Now the question is what is running at tty7 ? What does it display when you press CTRL+ALT+F7 ? Since you have disabled GUI is it blank ?

Bremenpl · 20 Oct 2016, 07:26

Ok now I understand. Yes on F7 there is my regular gui and on F1 pure console. My question is- How can I qun qt application being in pure console? I havent disabled anything by hand yet, I just switched context F1-F7

tomma · wrote on 20 Oct 2016, 07:22

You can try to run using minimal or offscreen platform-plugin. http://doc.qt.io/qt-5/qguiapplication.html#platformName-prop .

m.sue · wrote on 20 Oct 2016, 07:23

Hi,

if the GUI app does not need user interaction you can try to run it with option --platform offscreen on the command line. Then the app will run without visible GUI. You will need to have the offscreen platform plugin in-place, of course.
-Michael.

Bremenpl · wrote on 20 Oct 2016, 07:25

No, no thats not the case. I Need full GUI Widget functionality with user interaction. I Just want the whole operating system GUI background to be gone. So the user can only use the QT app when using a the PC. When PC starts there should be just command line without gui and after a while script would turn on my Qt application (thats graphical and needs user interaction).

I Recall in Qt embedded I had to add -qws parameter to do this, but there was no GUI at all from the system. The app itself had GUI.

p3c0 · wrote on 20 Oct 2016, 07:26

Or you can just disable the fancy items loaded by the GUI and directly boot to your application by putting it into a startup script.
Also disable the extra unwanted tty's and keep tty7 default

Bremenpl · wrote on 20 Oct 2016, 07:30

Yes thats exacly what I need, and by disabling fancy stuff I wanted to disable whole OS gui. tty7 is default for now. So the scenario is like this:

PC starts with only console mode
Script turns on the QT GUI application in full screen mode.

Would this be possible: http://doc.qt.io/qt-5/embedded-linux.html#linuxfb ?

p3c0 · wrote on 20 Oct 2016, 07:35

@Bremenpl Usually for these kind of applications (can say kiosk mode) people start with a minimal OS and a minimal light weight window manager so that OS customizations become easier.

Bremenpl · wrote on 20 Oct 2016, 07:38

Thats exaclt what i mean- Kiosk mode. But my os is quite lightweight. I can make it lighter even, but the point is I dont know how to turn the app on in console mode in any OS for now :P.

p3c0 · wrote on 20 Oct 2016, 07:47

@Bremenpl

but the point is I dont know how to turn the app on in console mode in any OS

As said earlier boot to default tty where X is running, launch the app in fullscreen mode through startup scripts.
Or you can try the linuxfb mode so that you own the framebuffer but then you get no window manager functionalities for eg. alt-tab switch or window decorations

Bremenpl · wrote on 20 Oct 2016, 07:52

So in short words, there is no way in linux to hide the whole OS GUI but still be able to run selected apps with GUI? One has to use own frame buffer?

p3c0 · 20 Oct 2016, 08:05

@Bremenpl

So in short words, there is no way in linux to hide the whole OS GUI but still be able to run selected apps with GUI?

Yes there is. The most easiest is to use the minimal OS so customizations becomes easy. Donot install anything else but a bare minimal window manager so that the user gets a feel that only your application is running on top.

Bremenpl · P p3c0 20 Oct 2016, 08:00

@p3c0 So lets say I install Debian without any GUI and then I just install lightDM or OpenBox?

p3c0 · wrote on 20 Oct 2016, 08:07

@Bremenpl Right. Or Fluxbox.