#place in /etc/systemd/system/factorio.service
# systemctl start factorio.service
# systemctl enable factorio.service   #autostarts the server
# systemctl stop factorio.service

[Unit]
Descritpion=Factorio Headless Server
After=network.target
After=systemd-user-sessions.service
After=network-online.target

[Service]
Type=simple
User=root
ExecStart=/opt/factorio/bin/x64/factorio --start-server /opt/factorio/saves/my-save.zip --server-settings /opt/factorio/server-settings.json

[Install]
WantedBy=multi-user.target