Currently, the installer defaults to database host
127.0.0.1, which means a local TCPv4 database.
There are other local ways of connection, though: The server could be reachable via TCPv6 only, and, more importantly, via unix socket using the special value
localhost. Connecting via unix socket is the only way of connection where Unix Socket Authentication works. So to use that, the user currently has to change from
localhost - which seems very unintuitive.
Proposal: Have the installer try local database servers, first
127.0.0.1 and fill in the first thing that works as default for the database hostname field.