Syncthing is a great tool for keeping machines in sync. This is quick write-up on how to configure automatic start with systemd on server. Important: This is different from setting it up on a client machine. In this case you would run it as the user logged in.

On Debian systems I recommend to install the deb packages. These will also copy appropriate service files in /lib/systemd/system. Further I recommend to use a dedicated user for running the syncthing server.

$ adduser --system --group syncthing

To enable the service in systemd, run the following code:

$ systemctl enable syncthing@syncthing.service
$ systemctl enable syncthing-resume.service  # to restart syncthing after resume

You can start syncthing with the following line:

$ systemctl start syncthing@synching.service

Afterwards the server listens on localhost:8384. Most probably you want it to listen on all interfaces to get remote access. This needs further configuration in /home/syncthing/.config/syncthing/config.xml. Change the following line removing localhost:

<address>:8384</address>