Modifying DNS Data Files

Whenever you modify one of the DNS data files in the master DNS server, you must also do the following.

• Change the serial number in the SOA resource record so the slave servers modify their data accordingly see How to Change the SOA Serial Number.

• Inform in.named on the master server that the daemon should reread the data files and update its internal database. See How to Force in.named to Reload DNS Data.

How to Change the SOA Serial Number

Every DNS database file begins with a Start of Authority (SOA) resource record. Whenever you alter any data in a DNS database file, you must increment the SOA serial number by one integer.

For example, if the current SOA Serial Number in a data file is 101, and you make a change to the file's data, you must change 101 to 102. If you don't change the SOA serial number, the domain's slave servers do not update their copy of the database files with the new information. The master and slave servers would then be out of sync.

A typical SOA record of a sample hosts file looks like the following.

; sample  hosts  file
@	IN       SOA 	nismaster.doc.com. root.nismaster.doc.com. (
			109 ; Serial
			10800 ; Refresh
 	                1800 ; Retry
			3600000 ; Expire
			86400 ) ; Minimum

Therefore, if you made a change to this hosts file, you would change 109 to 110. The next time that you change the file, you would change 110 to 111.

How to Force in.named to Reload DNS Data

When in.named successfully starts, the daemon writes its process ID to the file /etc/named.pid. To have in.named reread named.conf and reload the database do the following.

1. Become superuser.

2. # kill -HUP `cat /etc/named.pid`

The above procedure eliminates all of the existing cache. The caching process then restarts.

Do not attempt to run in.named from inetd. Doing so continuously restarts the name server, which defeats the purpose of having a cache.