xset: unable to open display

[bennyboom38]

Hello
When I push the button I get the following error message :

pi@raspberrypi:~/Smart-Doorbell $ python doorbell.py
Starting Doorbell...
Powering off HDMI
Waiting for doorbell rings...
Powering on HDMI with preferred settings
xset: unable to open display ""
[1088:1088:0611/013447.984641:ERROR:browser_main_loop.cc(584)] Failed to put Xlib into threaded mode.

**(chromium-browser-v7:1088): Gtk-WARNING : 01:34:47.989: cannot open display:

Do you know why display can't be opened?

Thanks for your help !

Regards

Ben

[mroelandts]

Do you have a physical display connected to it?

Otherwise you have to enable vnc through sudo raspi-config
And uncomment the line hdmi_force_hotplug=1 in the file /boot/config.txt
To force a display even if no physical display is connected to the hmdi

[bennyboom38]

hello !
Yes i have a screen on it
I'm goint to check without option : hdmi_force_hotplug=1
Thanks a lot