When I try to access postgres via a webapp, or open the postgres shell with psql -d template1, I get an error.

psql: could not connect to server: No such file or directory Is the server running locally and accepting connections on Unix domain socket "/tmp/.s.PGSQL.5432"?

(*I've read a number of SO threads about this error, but recommended solutions did not fix this for me)

Start postgres as a service:

brew services restart postgresql

Stopping postgresql... (might take a while) ==> Successfully stopped postgresql (label: homebrew.mxcl.postgresql) ==> Successfully started postgresql (label: homebrew.mxcl.postgresql)

Manually run postgres in a terminal:

I can get everything to work by running below in a terminal window, but I would prefer to run it in the background.

postgres -D /usr/local/var/postgres9.6.3

Clusters:

I have 3 db clusters in /usr/local/var, but I would like to use postgres9.6.3/

postgres
postgres9.5/
postgres9.6.3/

Which:

which psql returns /usr/local/bin/psql

Path:

echo $PATH returns /usr/local/bin and /usr/local/var (added)

Other recommended solutions:

A lot of people where able to fix this by removing a /postgres/postmaster.pid, but this file doesn't exist for me.

UPDATE

Running ps -ef | grep postgres, outputs only,

501  2135  1530   0 12:08pm ttys002    0:00.00 grep postgres

After restarting postgres with brew servies, postgres.log in /usr/local/var/log contains,

FATAL:  database files are incompatible with server
DETAIL:  The data directory was initialized by PostgreSQL version 9.5, which is not compatible with this version 9.6.3.