Ever since Symless (company behind Synergy product) has published “cloud based Synergy 2 service” I had nothing but problems and headaches with it. The major issue that I have had was that it simply wouldn’t pass the mouse/keyboard control to other configured screen. THIS IS THE SOLE PURPOSE FOR THIS PIECE OF SOFTWARE BTW!.
Anyhow, after I stopped whining and decided to look into issue I’ve found that bot laptop and desktop were “Unable to open display :0:0”. Well, no wonder as THAT ISN’T THE RIGHT DISPLAY. Correct display is, at least for me on Ubuntu, :1.
So, to resolve the issue:
Create systemd service override: systemctl edit synergy.service
Add following thingie in that file: [Service] Environment=DISPLAY=:1
Restart the service.
Voila, you should now have working setup.
BTW, to detect DISPLAY variable you can simply run:
echo $DISPLAY :1