Modifying DNS Data Files

Whenever you add or delete a host or make some other change in one of the DNS data files in the master DNS server or otherwise modify DNS data files, 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 it should reread the data files and update its internal database. See Forcing 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 fail to change the SOA serial number, the domain's slave servers will not update their copy of the database files with the new information and the master and slave servers will become 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

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

Forcing 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.

How to force in.named to reload DNS data.

1. Become superuser.

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

This will eliminate all previously cache, and the caching process will start over again.

Do not attempt to run in.named from inetd. This will continuously restart the name server and defeat the purpose of having a cache.