Sorry, there was a typo ( /etc <> /etd ) http://www.freedesktop.org/software/systemd/man/systemd.exec.html
[Unit] Description=BZFlag game server Documentation=man:bzfs(6) After=network.target [Service] Environment="OPTIONS=-advertise NONE" EnvironmentFile=-/etc/default/bzflag User=games Group=games ExecStart=/usr/games/bzfs $OPTIONS [Install] WantedBy=multi-user.target