PG::ConnectionBad: could not connect to server: No such file or directory

I came across this error when attempting to start the server in my Rails API and JavaScript application.

Based on the initial Google search, I realized it was related to PostgreSQL (known as Postgres) and took the following steps to resolve the error.

Step 1: Confirm Postgres is installed locally

brew info postgresql

or

postgres -V

Step 2: Check for instances of Postgres

launchctl list | grep -i sql

Step 3: Stop any instances

brew services stop postgres

Step 4: Uninstall Postgres and remove related files

brew uninstall --force postgres
rm -rf /usr/local/var/postgres
rm -rf .psql_history .psqlrc .psql.local .pgpass .psqlrc.local

Step 5: Confirm Postgres has been removed

brew list | grep sql

This was the ah-ha moment for me! I realized I still had another version of Postgres (postgresql@12) installed. After discovering there was still another version installed, I decided to see if anything was running on port 5432, the default port for Postgres.

Step 6: Check port 5432

lsof -i :5432

Step 7: If there is anything running, kill the port

kill -9 PID (take PID from previous command)

In my case,

kill -1334

Step 8: Double check nothing is running (Postgres and PID should be gone)

lsof -i :5432

Step 9: Uninstall Postgresql@12 and related files

brew uninstall postgresql@12
rm -rf /usr/local/var/postgresql@12
rm -rf .psql_history .psqlrc .psql.local .pgpass .psqlrc.local

Step 10: Confirm the version is removed

brew list

If you don’t see Postgres in the list, it is successfully uninstalled. Run brew upgrade if instructed to do so by Homebrew.

Step 11: Reinstall Postgres

brew install postgresql

Step 12: Check it was successfully installed

brew list | grep sql

Step 13: Connect to Postgres server

brew services start postgresql

Step 14: Create a database to confirm it is working

createdb `whoami`
psql

If everything is working correctly, you should see something like this:

After successfully uninstalling and reinstalling Postgres (all versions) with Homebrew, I was able to create a database (rails db:create), migrate the schema (rails db:migrate), populate the table with my seed file (rails db:seed), and start up the server (rails s) with no issues. YAY!

This error could result from multiple causes — take time to investigate! I have listed additional solutions that worked for others below:

· https://stackoverflow.com/questions/13410686/postgres-could-not-connect-to-server

· https://techstacker.com/homebrew-uninstall-postgresql-mac/

· https://yuta-san.medium.com/pg-connectionbad-could-not-connect-to-server-no-such-file-or-directory-9a2eada16f9