What is the limit on this?
You'll probably get rate-limited by the whois servers before you get limited by the OS. If you really need access to tons of whois records Google for "bulk whois". Here's how to request bulk whois records from ARIN: https://www.arin.net/resources/request/bulkwhois.html
Registries install packet-shapers to rate limit the traffic on whois servers. I think the default whois command goes to networksolutions, I think. Try this:
whois -h whois.publicinterestregistry.net jboss.org
Keep running this command and see how many times you succeed. It will throw 'limit exceeded' warning. The warning is stored in whois cache servers for a few mins and then the cache is cleared, and if you run the above command it will work again.