How to use "dig" Command in Linux

How to use "dig" Command in Linux

Dig (Domain Information Groper) is a powerful command-line tool for querying name servers. The dig command, allows you to query information about various DNS records. This tutorial explains how to use the dig utility through  examples and detailed explanations of the most common dig options.

How to Install dig

If dig is not present on your system, please follow these procedures to install it.

Ubuntu and Debian

# apt update &&  apt install dnsutils

Install dig on CentOS and Fedora

# yum install bind-utils

Once the package has been installed now let's dig it.

[root@k8smaster ~]# dig centos.org

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-9.P2.el7 <<>> centos.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 22632
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;centos.org.                    IN      A

;; ANSWER SECTION:
centos.org.             600     IN      A       81.171.33.202
centos.org.             600     IN      A       81.171.33.201

;; Query time: 186 msec
;; SERVER: 10.0.0.2#53(10.0.0.2)
;; WHEN: Thu Mar 26 17:13:14 UTC 2020
;; MSG SIZE  rcvd: 60

[root@k8smaster ~]#

The first line of the output prints the installed dig version, and the queried domain name. The second line shows the global options (by default, only cmd).

In this example, the status is NOERROR, which means that the requested authority served the query without any issue.

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 22632

In the “QUESTION” section dig shows the query . By default, dig requests the A record. In ANSWER it shows the results of this query.

The last section of the dig output includes statistics about the query.

;; Query time: 186 msec
;; SERVER: 10.0.0.2#53(10.0.0.2)
;; WHEN: Thu Mar 26 17:13:14 UTC 2020
;; MSG SIZE  rcvd: 60

IF you are interested in short answer to your query then run dig with  +short option

[root@k8smaster ~]# dig centos.org +short
81.171.33.201
81.171.33.202
[root@k8smaster ~]#

Query Specific Name Server

By default, if no name server is specified, dig uses the servers listed in /etc/resolv.conf file.

To specify a name server against which the query will be executed, use the "@" symbol followed by the name server IP address or hostname.

[root@k8smaster ~]# dig centos.org @8.8.8.8

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-9.P2.el7 <<>> centos.org @8.8.8.8
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 27739
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;centos.org.                    IN      A

;; ANSWER SECTION:
centos.org.             599     IN      A       81.171.33.202
centos.org.             599     IN      A       81.171.33.201

;; Query time: 361 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Thu Mar 26 17:25:40 UTC 2020
;; MSG SIZE  rcvd: 71

[root@k8smaster ~]#

We will see how to query spefic type of records, such as   A (the IP address), CNAME (canonical name), TXT (text record), MX (mail exchanger), and NS (name servers).

1. Querying A records
To get a list of all the address(es) for a domain name, use the "a" option:

dig +nocmd centos.org a +noall +answer

[root@k8smaster ~]# dig +nocmd centos.org a +noall +answer
centos.org.             600     IN      A       81.171.33.201
centos.org.             600     IN      A       81.171.33.202
[root@k8smaster ~]#

2.  Querying NS records
dig +nocmd centos.org ns +noall +answer

[root@k8smaster ~]# dig +nocmd centos.org ns +noall +answer
centos.org.             14400   IN      NS      ns1.centos.org.
centos.org.             14400   IN      NS      ns4.centos.org.
centos.org.             14400   IN      NS      ns3.centos.org.
[root@k8smaster ~]#

3. Querying CNAME records
To find the alias domain name use the cname option:

dig +nocmd mail.google.com cname +noall +answer

[root@k8smaster ~]# dig +nocmd mail.google.com cname +noall +answer
mail.google.com.        589202  IN      CNAME   googlemail.l.google.com.
[root@k8smaster ~]#

4. Querying MX records
To get a list of all the mail servers for a specific domain use the mx option:

[root@k8smaster ~]# dig +nocmd yahoo.com mx +noall +answer
yahoo.com.              1544    IN      MX      1 mta5.am0.yahoodns.net.
yahoo.com.              1544    IN      MX      1 mta6.am0.yahoodns.net.
yahoo.com.              1544    IN      MX      1 mta7.am0.yahoodns.net.
[root@k8smaster ~]#

5. Querying All Records
Use the any option to get a list of all DNS records for a specific domain:

dig +nocmd yahoo.com any +noall +answer

[root@k8smaster ~]# dig +nocmd yahoo.com any +noall +answer
yahoo.com.              735     IN      A       72.30.35.9
yahoo.com.              735     IN      A       98.137.246.8
yahoo.com.              735     IN      A       72.30.35.10
yahoo.com.              735     IN      A       98.138.219.232
yahoo.com.              735     IN      A       98.138.219.231
yahoo.com.              735     IN      A       98.137.246.7
yahoo.com.              490     IN      AAAA    2001:4998:58:1836::10
yahoo.com.              490     IN      AAAA    2001:4998:c:1023::4
yahoo.com.              490     IN      AAAA    2001:4998:44:41d::3
yahoo.com.              490     IN      AAAA    2001:4998:c:1023::5
yahoo.com.              490     IN      AAAA    2001:4998:58:1836::11
yahoo.com.              490     IN      AAAA    2001:4998:44:41d::4
yahoo.com.              741     IN      MX      1 mta7.am0.yahoodns.net.
yahoo.com.              741     IN      MX      1 mta5.am0.yahoodns.net.
yahoo.com.              741     IN      MX      1 mta6.am0.yahoodns.net.
[root@k8smaster ~]#

Reverse lookup

To perform a reverse lookup on 81.171.33.201 you would type:

[root@k8smaster ~]# dig -x 81.171.33.201 +noall +answer

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-9.P2.el7 <<>> -x 81.171.33.201 +noall +answer
;; global options: +cmd
201.33.171.81.in-addr.arpa. 86400 IN    PTR     ip-81.171.33.201.centos.org.
[root@k8smaster ~]#