Restart the network-manager if no network connection is found on the Raspberry Pi 2/3.

wifi_rebooter.sh

#!/bin/bash
#see: http://alexba.in/blog/2015/01/14/automatically-reconnecting-wifi-on-a-raspberrypi/

# The IP for the server you wish to ping (8.8.8.8 is a public Google DNS server)
SERVER=8.8.8.8
#specify wlan interface
INTERFACE=wlan0

# Only send two pings, sending output to /dev/null
ping -I ${INTERFACE} -c2 ${SERVER} > /dev/null

# If the return code from ping ($?) is not 0 (meaning there was an error)
if [ $? != 0 ];
then
    # Restart the Network Manager
    sudo service network-manager restart 
fi