(Spelled by the program itself as "DiG", but I have no idea where this sudden burst of l33tness has come...)
Short for domain information groper (though this smells like a backronym).
It's a command-line tool used to fetch information from DNS servers. It can query all sorts of stuff from the DNS servers with various criteria.
For example, it's useful for finding out for whom some specific IP address belongs to:
holt:~$ dig -x 220.127.116.11
; <<>> DiG 8.2 <<>> -x
;; res options: init recurs defnam dnsrch
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2
;; QUERY SECTION:
;; 18.104.22.168.in-addr.arpa, type = ANY, class = IN
;; ANSWER SECTION:
22.214.171.124.in-addr.arpa. 23h58m42s IN PTR everything2.com.
;; AUTHORITY SECTION:
14.170.206.in-addr.arpa. 23h58m42s IN NS ns1.upn.net.
14.170.206.in-addr.arpa. 23h58m42s IN NS ns2.upn.net.
;; ADDITIONAL SECTION:
ns1.upn.net. 18h34m51s IN A 126.96.36.199
ns2.upn.net. 18h34m51s IN A 188.8.131.52
;; Total query time: 34 msec
;; FROM: holt to SERVER: default -- 184.108.40.206
;; WHEN: Tue Sep 18 15:42:14 2001
;; MSG SIZE sent: 45 rcvd: 172
Of course, it's not exactly human-readable - for most needs, you probably want to use
- The host(1) program - this will return the DNS name based on IP, and IP based on DNS.
- Use whois(1) to find out who owns the IP block (ARIN's whois server knows.)