Find out what DNS requests are made in real time via command line

Since all DNS requests are over port 53, we can use the raw tcpdump utility and just look at the packets on that port:

tcpdump -vvv -s 0 -l -n port 53

Someone took the extra step to write a php script to massage that data, so that it is easier to read as well as focusing on those queries that either do not resolve or take a long time to resolve:

http://jontai.me/blog/2011/11/monitoring-dns-queries-with-tcpdump/