A template systemd service contains the @ symbol like the Syncthing service.
/lib/systemd/system/syncthing@.service
NOTE: This kind of service allows you to run multiple instances.
sudo systemctl start syncthing@user1.service sudo systemctl start syncthing@user2.service
Create a folder for each of these services.
sudo mkdir -p /etc/systemd/system/syncthing@user1.service.d sudo mkdir -p /etc/systemd/system/syncthing@user2.service.d
Create the custom configuration file.
sudo vi /etc/systemd/system/syncthing@user1.service.d/custom.conf sudo vi /etc/systemd/system/syncthing@user2.service.d/custom.conf
Reload systemd.
sudo systemctl daemon-reload