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:

  1. Create systemd service override: systemctl edit synergy.service

  2. Add following thingie in that file: [Service] Environment=DISPLAY=:1

  3. Restart the service.

Voila, you should now have working setup.

BTW, to detect DISPLAY variable you can simply run: