vpnclientの場合

# cat /usr/lib/systemd/system/vpnclient.service 
[Unit]
Description=SoftEther VPN Server
After=network.target

[Service]
Type=forking
ExecStart=/usr/local/vpnclient/vpnclient start
ExecStop=/usr/local/vpnclient/vpnclient stop

[Install]
WantedBy=multi-user.target

# systemctl daemon-reload

リロードすると、デーモンファイルが読み込まれる

# systemctl list-unit-files -t service| grep vpn
vpnclient.service                             disabled

# systemctl enable vpnclient