I’m currently following along with Lynda’s “Learning Flask,” which requires one to use some Postgres.

“Cool,” I thought, “I installed that a while back.”

No, not cool. Things weren’t working. Or I just didn’t remember how to use it. Or both.

I kepth getting error messages, like

• no database directory specified and environment variable PGDATA unset
• no operation specified
• could not connect to server: No such file or directory

At one point it just seemed easier to uninstall everything postgres-related, then reinstall and start over clean.

Only this didn’t work…

Thankfully other people already had this problem!

Basically, in short, I had to do this:

brew uninstall postgres
rm -rf /usr/local/var/postgres/
brew install postgres

You will see a new a directory at /usr/local/var/postgres/.

Start the database service

If you try to run psql at this point, you will receive a message:

psql: could not connect to server: No such file or directory Is the server running locally and accepting connections on Unix domain socket “/tmp/.s.PGSQL.5432”?

This is because you need to launch a PostgreSQL server.

# Option A: Have launchd start postgresql now and restart at login
brew services start postgresql
# Option B: If you don't want/need a background service
pg_ctl -D /usr/local/var/postgres start

Create the username database

Still, if you try to run psql, you will receive another message:

FATAL: database “<yourUserName>” does not exist

Time to make it exist!

createdb `whoami`

Now you should be able to interactively work with Postgres.

psql

To exit psql:

\q

Stop the PostgreSQL Server

Depends on how you started it…

# Scenario A: Brew Services
brew services stop postgresql
# Scenario B: pg_ctl
pg_ctl -D /usr/local/var/postgres stop