PostgreSQL not running on Mac

The problem can also be attributed to a crashed process that left postmaster.pid file behind.

$ brew services stop postgresql
$ rm /usr/local/var/postgres/postmaster.pid # adjust path accordingly to your install
$ brew services start postgresql

I was getting the same

Is the server running locally and accepting connections on Unix domain 
socket "/tmp/.s.PGSQL.5432"?

loop of Homebrew install / start / stop / restart to no avail...

Finally, brew postgresql-upgrade-database worked.

Seems I was on 9.6 instead of 10.4, and something my latest App Store restart restarted all my database servers...

The answer is here.

Run this command to manually start the server:

pg_ctl -D /usr/local/var/postgres -l /usr/local/var/postgres/server.log start