Switch to postgres user on Mac

That looks consistent with the postgres user not having a login shell. Try sudo -u postgres bash

PostgreSQL is integrated in Server.app available through the App Store in Mountain Lion.

You would have this file:/Library/Server/PostgreSQL/Config/org.postgresql.postgres.plist

You can sudo:

sudo -u _postgres psql template1

Or connect:

psql -h localhost -U _postgres postgres

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