How To Determine the DNS Domain Name

If the file /etc/resolv.conf is used to specify the domain for the current machine, that value is the DNS domain name. For example, the domain name is superhero.com in this /etc/resolv.conf file:

------------/etc/resolv.conf------------
domain			superhero.com
nameserver			111.22.33.444
------end of /etc/resolv.conf------

If there is no domain name specified in /etc/resolv.conf, the /usr/ucb/hostname command can be used to determine the DNS domain name. If the hostname command returns a value which contains a period (.), the value returned will be used as the DNS domain name. For example, the value mighty_mouse.superhero.com is returned by this /usr/ucb/hostname command:

% /usr/ucb/hostname
mighty_mouse.superhero.com

If the domain name listed in the /etc/resolv.conf file differs from the one returned by the /usr/ucb/hostname command, the value in the /etc/resolv.conf file takes precedence and should be registered as your required domain.