シャットダウン時の後処理 （shutdown）

# vi /etc/systemd/system/drop.service
[Unit]
Description= stop httpgwd

DefaultDependencies=no
Before=shutdown.target
RefuseManualStart=true

[Service]
Type=oneshot
ExecStart= /usr/local/sbin/httpgwd  stop
[Install]
WantedBy=shutdown.target

# systemctl daemon-reload

# systemctl enable drop.service