The following bug has been logged on the website:
Bug reference: 15429
Logged by: Ryan Murphy
Email address: murphy6239@gmail.com
PostgreSQL version: 10.5
Operating system: Ubuntu 14.04.5 LTS
Description:
We've encountered an issue where psql requires "-h localhost" to run any
commands on PostgreSQL 10.5 machine.
$ psql --version
Error: Invalid data directory for cluster 10 main
$ psql -h localhost --version
psql (PostgreSQL) 10.5 (Ubuntu 10.5-1.pgdg14.04+1)
The issue is resolved by adding world-read access to postgresql.conf to
allow psql to read "data_directory", but this is something we've never had
to do with previous postgres versions.