Simple systemd service descriptor for running on raspberry-pi with added self-restart. Pi's don't seem to like long running cameras and the reasons vary. The easiest work around is to just refresh the process on a regular basis.

mjpg-streamer.service

[Unit]
Description=Streams video with Raspberry Pi Camera
After=syslog.target
After=network.target

[Service]
Type=simple
User=root
Group=root
ExecStart=/usr/local/bin/mjpg_streamer -b \
  -i '/usr/local/lib/mjpg-streamer/input_uvc.so -n -f 10 -r 1280x720' \
  -o '/usr/local/lib/mjpg-streamer/output_http.so -p 8085 -w /usr/local/share/mjpg-streamer/www'
Restart=always
RestartSec=5
RuntimeMaxSec=12h
Environment=

[Install]
WantedBy=multi-user.target