How to log DNS server activity?
Ans : Sometimes you require to log DNS server activity to a file for future reference for analyse the activity on DNS server and whether DNS server is properly resolving accurately or not. rndc(remote name daemon control) is the command to use for DNS server activity logging. Let’s have a look how to log DNS server activity. In order to log DNS server entries just execute below command (you have to do this one as root user)

#rndc querylog

Note : When you execute the above command DNS server activity is logged on to server /var/log/messages file.
Example output of the clipped log file

bash-2.05b# /usr/sbin/rndc querylog
bash-2.05b# tail -f /var/log/messages

Nov 18 18:00:16 ns1.abc.in named[29413]: query logging is now on
Nov 18 18:00:18 ns1.abc.in named[29413]: client 194.158.122.34#43071: query: abc.co.in IN MX
Nov 18 18:00:18 ns1.abc.in named[29413]: client 194.158.122.6#43587: query: smtp.abc.co.in IN A
Nov 18 18:00:19 ns1.abc.in named[29413]: client 82.8.211.193#19305: query: MX2.abc.co.in IN A
Nov 18 18:00:20 ns1.abc.in named[29413]: client 200.49.130.26#4111: query: abc.co.in IN MX
Nov 18 18:00:21 ns1.abc.in named[29413]: client 212.24.128.8#46547: query: abc.co.in IN MX
Nov 18 18:00:22 ns1.abc.in named[29413]: client 200.75.51.132#26540: query: MX2.abc.co.in IN A
In order to stop DNS logging activity please execute below command

#rndc querylog

Note : If you observe this command it is same as for starting the log activity, it is similar to how a walky-talky works.. You have to press same button for both on/off operations.
Example output of how it is stopped

bash-2.05b# /usr/sbin/rndc querylog
bash-2.05b# tail -f messages

Nov 18 18:08:53 ns1.abc.com named[29413]: client 200.12.232.4#60450: query: abc.co.in IN MX
Nov 18 18:08:59 ns1.abc.com named[29413]: client 212.54.35.233#39027: query: ns1.abc.co.in IN A
Nov 18 18:08:59 ns1.abc.com named[29413]: client 212.54.35.233#10163: query: ns1.abc.co.in IN A
Nov 18 18:09:00 ns1.abc.com named[29413]: client 88.156.63.9#3661: query: abc.co.in IN MX
Nov 18 18:09:00 ns1.abc.com named[29413]: client 89.2.2.146#44622: query: abc.co.in IN MX
Nov 18 18:09:05 ns1.abc.com named[29413]: client 203.199.147.5#14678: query: cmex01.clairmail.local.intranet.abc.co.in IN A
Nov 18 18:09:06 ns1.abc.com named[29413]: client 117.98.17.34#1766: query: abc.co.in IN MX
Nov 18 18:09:06 ns1.abc.com named[29413]: client 203.119.8.106#28142: query: abc.co.in IN MX
Nov 18 18:09:11 ns1.abc.com named[29413]: client 217.171.113.9#4861: query: MX2.abc.co.in IN A
Nov 18 18:09:11 ns1.abc.com named[29413]: query logging is now off

Some FAQ’s:

1.Is it advaisable to restart a production DNS server?
Ans : No, Never try to restart a production DNS server without prior notice from your higher officials.

2.Then how can I update any changes I made to DNS server?
Ans : You can use rndc command to update the changes to dns server.

3.I want to update DNS server zone file entries to DNS server without restarting the named/bind server?
Ans : We can do it by using rndc command

#rndc reload

4.I want to reload named.conf file without restarting DNS server?

#rndc refresh

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Surendra Anne

Mr Surendra Anne is from Vijayawada, Andhra Pradesh, India. He is a Linux/Open source supporter who believes in Hard work, A down to earth person, Likes to share knowledge with others, Loves dogs, Likes photography. He works as Devops Engineer with Taggle systems, an IOT automatic water metering company, Sydney . You can contact him at surendra (@) linuxnix dot com.