Thomas Pircher <[email protected]> wrote: > On 2026-09-30 15:22, Chris Green wrote: > > Thomas Pircher <[email protected]> wrote: > >> What does not work exactly? > > chris$ ypdomainname > > chris$ domainname > > chris$ dnsdomainname > > ypdomainname and domainname relate to NIS, as Greg already pointed out. > This is not related to the DNS domain name. > The dnsdomainname and hostname --fqdn commands will give you a more > useful answer, given you r configuration. > > >> Is there a reason you use 127.0.1.1 instead of the more commonly used > >> value 127.0.0.1? > >> > > It's what a Debian 13 installation produces, I have 127.0.0.1 as > > localhost (see above). > > Yes, ignore what I wrote here. I was about 20 years out of date with my > comment. > > > However things like postfix and others use ypdomainname/domainname to > > get the domain. > > Postfix's documentation says it uses the fully-qualified domain name > from gethostname(2). This is slightly confusing, as I would expect that > to return just the hostname. If it wanted the DNS domain name, it would > have to resolve it using e.g. getaddrinfo(3). > > This all sounds very brittle to me. Please consider setting `mydomain` > or `myhostname` in the Postfix configuration explicitly. You want to be > in control of this information, if your mail server is public facing. > Yes, I've decided that's the way to go, set mydomain in the postfix configuration.
The only (very slight) downside is that I have one system with an otherwise identical main.cf which isn't on my LAN and thus needs a different mydomain value. Wherever possible I keep configurations the same for ease of maintenance. > Also see the discussion in "THE FQDN" in the man page of hostname(2): a > given machine can have zero, one or more domain names. > > Thomas -- Chris Green ยท
