How to find out what the hostname is

Summary:I

I need to find out what the full hostname is (hostname.domain.tld)

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I am trying to install hestiacp using their instructions. I am running the installer sh and get errrors. Been able to solve some but now it says

Please use a valid hostname according to RFC1178 (ex. hostname.domain.tld).

Other services I have used just tell you the hostname, presumably because it is just a VPS in a datacenter somewhere without the infrastructure that Oracle uses. Using hostname I only get the one part of it that I created, i.e. satoshihost-oc1 but I cannot find the full hostname.