how to setup domain name permentaly?

[bbaa aaa]

We have Redhat AS 2.1 and 3.0 on DELL servers.  Due to some applications 
need domain name setup.  I put  following on /etc/hosts first line:

192.9.202.5          server1.aaa.com

after reboot, domain name still empty.


I can use "domainname  aaa.com" temporary setup domain name.

Does there has way permentally setup domain name?

Thanks.

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