Restarting Postgres for Rails on MacOS

Last night I encountered this error message while building Ranting:

ActiveRecord::ConnectionNotEstablished (connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such file or directory
        Is the server running locally and accepting connections on that socket?
):

I vaguely remember encountering this error message a while back 🤔. I’m not certain what actually caused the error, however I figured restatrting Postgress would solve this. Here’s how to do it.

1. Look for Postgres Installation

My current setup has Postgres installed with Homebrew.

  $ brew list
  ==> Formulae
  ...
  cairo         liblqr          poppler
  coreutils     libnghttp2      postgresql@14
  docbook       libomp          protobuf
  ...

Seems that I have postgresql@14 installed.

2. Restart Postgres

Now, navigate to this folder:

  $ cd /usr/local/var

Look for the same Postgres installation folder as in Homebrew list above.

  $ ls
  cache		homebrew	mysql		run
  db		log		postgresql@14

cd into the Postgres folder and look for a file called postmaster.pid.

  $ cd postgresql@14

  $ ls
  PG_VERSION		pg_ident.conf		pg_snapshots		pg_wal
  base			pg_logical		pg_stat			pg_xact
  global                pg_multixact            pg_stat_tmp             postgresql.auto.conf
  pg_commit_ts		pg_notify		pg_subtrans		postgresql.conf
  pg_dynshmem		pg_replslot		pg_tblspc		postmaster.opts
  pg_hba.conf		pg_serial		pg_twophase		postmaster.pid

Found it! Next, backup the postmaster.pid file to another folder (eg. the Desktop folder) and restart Postgres.

  $ mv postmaster.pid ~/Desktop

  $ brew services restart postgresql@14
  Stopping `postgresql@14`... (might take a while)
  ==> Successfully stopped `postgresql@14` (label: homebrew.mxcl.postgresql@14)
  ==> Successfully started `postgresql@14` (label: homebrew.mxcl.postgresql@14)

3. Move On with Life

Run Rails server again and that should resolve the error.

It should be safe now to delete the postmaster.pid that was backed up earlier.