Monitor DNS resolution and internet connectivity script

 while true; do
    date
    echo "DNS check:"
    host google.com
    echo "Ping check:"
    ping -c 1 google.com | grep "time="
    echo "---"
    sleep 5
done

See ping for more details on what this is doing.

The host command contacts a DNS server and does a reverse lookup for the IP-address of the human-readable domain name.