If you’re trying to follow along the Elixir Phoenix Up and Running guide you may run straight into this error if you’re using homebrew’s Postgres install when you run mix ecto.create

$ mix ecto.create
18:54:52.762 [error] GenServer #PID<0.292.0> terminating
** (Postgrex.Error) FATAL 28000 (invalid_authorization_specification) role "postgres" does not exist
    (db_connection 2.4.0) lib/db_connection/connection.ex:100: DBConnection.Connection.connect/2
    (connection 1.1.0) lib/connection.ex:622: Connection.enter_connect/5
    (stdlib 3.15.2) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
Last message: nil
State: Postgrex.Protocol

18:54:52.773 [error] GenServer #PID<0.299.0> terminating
** (Postgrex.Error) FATAL 28000 (invalid_authorization_specification) role "postgres" does not exist
    (db_connection 2.4.0) lib/db_connection/connection.ex:100: DBConnection.Connection.connect/2
    (connection 1.1.0) lib/connection.ex:622: Connection.enter_connect/5
    (stdlib 3.15.2) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
Last message: nil
State: Postgrex.Protocol
** (Mix) The database for Hello.Repo couldn't be created: killed

That’s not ideal! The core issue in that stack trace error is role "postgres" does not exist

There’s a couple of ways to fix the problem.

One: Fix the Phoenix config to match up with homebrew

Open config/dev.exs and change the config to have your username and a blank password.

By default Phoenix assumes “postgres” for the username and password.

config :hello, Hello.Repo,
  username: "sdball",
  password: "",
  database: "hello_dev",
  hostname: "localhost",
  show_sensitive_data_on_connection_error: true,
  pool_size: 10

Two: Fix the postgres config to match up with Phoenix

1. Connect to postgres

$ psql -d postgres

2. Create the “postgres” user

CREATE ROLE postgres LOGIN CREATEDB;

3. (ctrl-d) to close the connection to postgres

Things should be working!

After either fix you should be able to create the postgres database!

$ mix ecto.create

The database for Hello.Repo has been created