A systemd service has to be located in
/etc/systemd/system/<service_name>.service
[Unit]
Description=System Logging Service
Requires=syslog.socket
Documentation=man:rsyslogd(8)
Documentation=http://www.rsyslog.com/doc/
[Service]
Type=notify
ExecStart=/usr/sbin/rsyslogd -n
StandardOutput=null
Restart=on-failure
[Install]
WantedBy=multi-user.target
Alias=syslog.service