Have you ever encountered this error? is so here is the solution.... :)
This may happen if there are many http request, or forgetting to close the open connection in time so for this what you can do is you can increase the number of open file in linux machine, as it is related to os issue mostly.
Open /etc/sysctl.conf and add the following :
fs.file-max = <65535> <-- keep this number as you need
And for changing the effect of this use following command
sudo sysctl -p /etc/sysctl.conf
