I encountered this problem with my Postfix install:
i.e. I was getting the error:
postfix/smtp: fatal: unknown service: smtp/tcp
and like at the url above, the solution was to manually copy
My impression is this "just started happening" and previously wasn't a problem, however I have only been making minor seemingly unrelated changes to postfix main.cf so I don't understand why.
The Postfix installation tutorials I was following don't mention anything about having to manually copy those files... this feels like something Postfix ought to do by itself and isn't for some reason.
Is there some underlying misconfiguration that would cause this?