How do I fix stale postmaster.pid file on Postgres?

The problem is that the postmaster.pid file needs to be removed manually and then regenerated by Postgres. These are the steps to do remove it. (for MacOs, linux also probably pretty close to this)

Keep in mind the version might changed, (var-12, could be var-13,var-14,var-15 etc). But the general theory remains the same for now. Just swap the 12 for your version. We will use 12 as the example as that was i was working with at the time.

1. Open your terminal, and cd into the postgres directory: cd /Users/$USER/Library/Application\ Support/Postgres
2. Make sure you're in the right place, run ls, you should see a directory like var-12
3. Verify the PID file is inside that "var-12" directory using ls: e.g. ls var-12/

Library/Application Support/Postgres
➜ ls var-12
PG_VERSION           pg_hba.conf          
pg_replslot          pg_subtrans
postgresql.auto.conf base
pg_ident.conf        pg_serial
pg_tblspc            postgresql.conf
global               pg_logical
pg_snapshots         pg_twophase
postgresql.log       pg_commit_ts
pg_multixact         pg_stat
pg_wal               postmaster.opts
pg_dynshmem          pg_notify
pg_stat_tmp          pg_xact
postmaster.pid  <--- (This is what you're looking for!)

1. Before you remove the file, verify the Postgres server is not running by viewing desktop app or CLI. Terminate Postgres server if needed
2. Then remove postmaster.pid, e.g. rm var-12/postmaster.pid
3. Go back to your console, start your Postgres server, and it should regenerate the PID, and it should start successfully and you will have full access to your schemas.