# /etc/systemd/system/sim800.service

[Unit]
Description=SIM800C PPP Connection
After=rc-local.service

[Service]
Type=forking
PIDFile=/run/ppp0.pid
ExecStart=/etc/init.d/sim800c start
ExecStop=/etc/init.d/sim800c stop
Restart=on-failure
RestartSec=5s

[Install]
WantedBy=multi-user.target