my machine happed also, add a user script to restart nginx automaticly, hope it decrease problem.
```
#!/bin/bash
pid=$(cat /var/run/nginx.pid)
if [[ $(ps -ef | awk "\$3==$pid" | wc -l) -eq 0 ]]; then
/etc/rc.d/rc.nginx start
sleep 5
exit 0;
fi
ps -ef | awk "\$3==$pid" | grep '<defunct>' > /dev/null
if [[ $? -eq 0 ]]; then
kill -9 $pid
sleep 1
/etc/rc.d/rc.nginx start
sleep 5
fi
```