During OpenBSD installation, what is "DNS domain name" for?

Question

During the installation of OpenBSD 6.1, right after setting up network interfaces, the installer prompts me: DNS domain name? (e.g. 'bar.com') [my.domain]

I am not sure what this setting is for, I left it at default my.domain and besides showing up on my prompt, I did not notice anything not working as intended.

Is this option just for proper labeling of the system environment, if not, what is it for? Should it just be set to the future domain address? What if the system holds multiple domains?

Answer 1

It wants to know the domain name of the system, so that it can pair that with the hostname to come up with the system's full-qualified domain name (FQDN). See here.

I'm guessing this is an installation for your home, where you don't have a default DNS domain, per se. As such, this should probably be asked on Super User rather than Server Fault.

The impact this will have is that software that looks for the FQDN will find it, e.g., mail server software.. It will also impact the domain that gets appended to a lookup. For example, if you type "ping systemxyz" it will actually try ping systemxyz.my.domain based on what you entered. Running man resolv.conf will also help you understand some of the DNS resolution things that go on behind the scenes of your operating system.