Fix: The data directory contains an old postmaster.pid

This error occurs when PostgreSQL didn’t shut down cleanly and left a stale postmaster.pid file behind. The fix is simply to delete that file.

The error

Solution

Step 1: Delete the stale PID file

rm ~/Library/Application\ Support/Postgres/var-12/postmaster.pid

Replace var-12 with your actual PostgreSQL version directory if different (e.g., var-14, var-15).

Step 2: Start PostgreSQL again

Open the Postgres.app and click Start, or run:

pg_ctl -D /Users/$(whoami)/Library/Application\ Support/Postgres/var-12 start

PostgreSQL should start normally now.