Linux and Unix-like system uses Internet address (in dot notation) of a name server that the resolver should query to convert host names to IP address and vice versa. The resolver reads a configuration file called /etc/resolv.conf. The name server IP address are stored in /etc/resolv.conf file. Up to three name servers may be listed per line using the following syntax:
nameserver ISP-DNS-IP1
nameserver DNS-IP2
nameserver DNS-IP3
How do I see my DNS server IP address?
Type the following cat command:
cat /etc/resolv.conf |
Or use grep command as follows:
grep nameserver /etc/resolv.conf |
Sample outputs:
How do I change or update my DNS nameservers IP address?
Use a text editor such as vi, ee, emacs, joe and co to edit the file /etc/resolv.conf as root user:
$ sudo vi /etc/resolv.conf
DNS lookup on a Linux and Unix systems
Now, you know your DNS name server IP address. It is time to use command such as host command and dig command to find out more information about domains or IP address.
dig command examples
Type the following command to resolve domain name called cyberciti.biz
dig cyberciti.biz |
Sample outputs:
; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.30.rc1.el6_6.1 <<>> cyberciti.biz ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 9933 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;cyberciti.biz. IN A ;; ANSWER SECTION: cyberciti.biz. 300 IN A 75.126.153.206 ;; Query time: 47 msec ;; SERVER: 10.0.80.11#53(10.0.80.11) ;; WHEN: Mon Jan 12 11:00:20 2015 ;; MSG SIZE rcvd: 47 |
To see just IP address, type:
dig +short cyberciti.biz |
Sample outputs:
75.126.153.206
To see an IPv6 address for www.cyberciti.biz, enter:
dig aaaa www.cyberciti.biz dig +short aaaa www.cyberciti.biz |
Sample outputs:
2607:f0d0:1002:51::4
A few more examples using the dig command:
# list authoritative dns server ## dig ns cyberciti.biz ## show mx (mail server) info/ip for cyberciti.biz domain## dig mx cyberciti.biz ## Reverse lookups — mapping addresses to dns names # dig -x ip dig -x 75.126.153.206 |
host command examples
The syntax is:
## Get an IPv4 address for cyberciti.biz ## host cyberciti.biz ## Get mail server info for cyberciti.biz ## host -t mx cyberciti.biz ## Get nameserver info for cyberciti.biz ## host -t ns cyberciti.biz ## Get an IPv6 address ## host -t aaaa cyberciti.biz ## Use specific (Google) dns server ip # 8.8.8.8 to query www.cyberciti.biz ## host www.cyberciti.biz 8.8.8.8 ## Get all info about cyberciti.biz ## host -a -v cyberciti.biz |
Sample outputs: