Rails / Postgres connection issue (psql and pg working fine)

Question

My rails app connects to the database on my development machine, and in production just fine. I've cloned the project to a coworker's machine, and recreated the database locally from a pgdump. The same process works fine on my machine. But on his,

psql at the command line is having no trouble:

$ psql ROL2
psql (9.5.2)
Type "help" for help.

ROL2=#

And to test the pg gem (pg-0.18.4), I've written a simple ruby script to output our users' names:

#!/usr/bin/env ruby

require 'pg'
conn = PG.connect( dbname: 'ROL2' )
conn.exec( "SELECT * FROM users" ) do |result|
  result.each do |row|
    puts "#{row['first_name']} #{row['last_name']}"
  end
end

No problem; works fine. But when I try connecting via the rails console or a task in the app:

$ rails db 
  psql: server closed the connection unexpectedly
    This probably means the server terminated abnormally
    before or while processing the request.

Here's the database.yml:

# LOCAL POSTGRES
development:
  adapter:  postgresql
  encoding: utf8
  host:     localhost
  port:     5432
  database: ROL2
  pool:     5

Ditto when I try to connect with a client (Postico). I've tried with both the postgres user and his username / password.

ROL2=# \du
                                    List of roles
  Role name  |                         Attributes                         | Member of
-------------+------------------------------------------------------------+-----------
 joeschmo    | Superuser, Create role, Create DB                          | {}
 postgres    | Superuser, Create role, Create DB, Replication, Bypass RLS | {}

Why might Rails have trouble connecting to the database, even though psql and the pg gem are working fine?

Added: the error as it appears in the Rails development logs:

PG::ConnectionBad (server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.
):
activerecord (4.2.4) lib/active_record/connection_adapters/postgresql_adapter.rb:655:in `initialize'
activerecord (4.2.4) lib/active_record/connection_adapters/postgresql_adapter.rb:655:in `new'
activerecord (4.2.4) lib/active_record/connection_adapters/postgresql_adapter.rb:655:in `connect'
activerecord (4.2.4) lib/active_record/connection_adapters/postgresql_adapter.rb:242:in `initialize'
activerecord (4.2.4) lib/active_record/connection_adapters/postgresql_adapter.rb:44:in `new'
activerecord (4.2.4) lib/active_record/connection_adapters/postgresql_adapter.rb:44:in `postgresql_connection'
activerecord (4.2.4) lib/active_record/connection_adapters/abstract/connection_pool.rb:438:in `new_connection'
activerecord (4.2.4) lib/active_record/connection_adapters/abstract/connection_pool.rb:448:in `checkout_new_connection'
activerecord (4.2.4) lib/active_record/connection_adapters/abstract/connection_pool.rb:422:in `acquire_connection'
activerecord (4.2.4) lib/active_record/connection_adapters/abstract/connection_pool.rb:349:in `block in checkout'
/Users/mac_osx_username/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/monitor.rb:211:in `mon_synchronize'
activerecord (4.2.4) lib/active_record/connection_adapters/postgresql_adapter.rb:655:in `new'
activerecord (4.2.4) lib/active_record/connection_adapters/postgresql_adapter.rb:655:in `connect'
activerecord (4.2.4) lib/active_record/connection_adapters/postgresql_adapter.rb:242:in `initialize'
activerecord (4.2.4) lib/active_record/connection_adapters/postgresql_adapter.rb:44:in `new'
activerecord (4.2.4) lib/active_record/connection_adapters/postgresql_adapter.rb:44:in `postgresql_connection'
activerecord (4.2.4) lib/active_record/connection_adapters/abstract/connection_pool.rb:438:in `new_connection'
activerecord (4.2.4) lib/active_record/connection_adapters/abstract/connection_pool.rb:448:in `checkout_new_connection'
activerecord (4.2.4) lib/active_record/connection_adapters/abstract/connection_pool.rb:422:in `acquire_connection'
activerecord (4.2.4) lib/active_record/connection_adapters/abstract/connection_pool.rb:349:in `block in checkout'
/Users/mac_osx_username/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/monitor.rb:211:in `mon_synchronize'
activerecord (4.2.4) lib/active_record/connection_adapters/abstract/connection_pool.rb:348:in `checkout'
activerecord (4.2.4) lib/active_record/connection_adapters/abstract/connection_pool.rb:263:in `block in connection'
/Users/mac_osx_username/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/monitor.rb:211:in `mon_synchronize'
activerecord (4.2.4) lib/active_record/connection_adapters/abstract/connection_pool.rb:262:in `connection'
activerecord (4.2.4) lib/active_record/connection_adapters/abstract/connection_pool.rb:571:in `retrieve_connection'
activerecord (4.2.4) lib/active_record/connection_handling.rb:113:in `retrieve_connection'
activerecord (4.2.4) lib/active_record/connection_handling.rb:87:in `connection'
activerecord (4.2.4) lib/active_record/migration.rb:383:in `connection'
activerecord (4.2.4) lib/active_record/migration.rb:370:in `call'
actionpack (4.2.4) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.2.4) lib/active_support/callbacks.rb:88:in `__run_callbacks__'
activesupport (4.2.4) lib/active_support/callbacks.rb:778:in `_run_call_callbacks'
activesupport (4.2.4) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (4.2.4) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.2.4) lib/action_dispatch/middleware/reloader.rb:73:in `call'
actionpack (4.2.4) lib/action_dispatch/middleware/remote_ip.rb:78:in `call'
actionpack (4.2.4) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
web-console (2.2.1) lib/web_console/middleware.rb:39:in `call'
actionpack (4.2.4) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.2.4) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.2.4) lib/rails/rack/logger.rb:20:in `block in call'
activesupport (4.2.4) lib/active_support/tagged_logging.rb:68:in `block in tagged'
activesupport (4.2.4) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (4.2.4) lib/active_support/tagged_logging.rb:68:in `tagged'
railties (4.2.4) lib/rails/rack/logger.rb:20:in `call'
quiet_assets (1.1.0) lib/quiet_assets.rb:27:in `call_with_quiet_assets'
actionpack (4.2.4) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.6.4) lib/rack/methodoverride.rb:22:in `call'
rack (1.6.4) lib/rack/runtime.rb:18:in `call'
activesupport (4.2.4) lib/active_support/cache/strategy/local_cache_middleware.rb:28:in `call'
rack (1.6.4) lib/rack/lock.rb:17:in `call'
actionpack (4.2.4) lib/action_dispatch/middleware/static.rb:116:in `call'
rack (1.6.4) lib/rack/sendfile.rb:113:in `call'
railties (4.2.4) lib/rails/engine.rb:518:in `call'
railties (4.2.4) lib/rails/application.rb:165:in `call'
rack (1.6.4) lib/rack/lock.rb:17:in `call'
rack (1.6.4) lib/rack/content_length.rb:15:in `call'
rack (1.6.4) lib/rack/handler/webrick.rb:88:in `service'

Answer 1

Since the database.yml includes host and port, Rails is probably trying to connect to the TCP socket, whereas your connections via psql and pg (since they don't specify host or port) are using the UNIX socket. PostgreSQL comes configured out of the box to not listen to the TCP socket, so look at the postgresql.conf and ensure it has listen_addresses uncommented. If it doesn't, you can try either taking host and port out of the database.yml or modifying the config to enable TCP connections and restarting PostgreSQL.