Running into FATAL: Peer authentication failed for user "postgres" with ruby on rails

Question

I am running into this problem with rails 5.2.3 when trying to make it work with postgresql 11.

FATAL: Peer authentication failed for user "postgres"

I have been checking 1 and 2

They talk about pg_hba.conf and how the methods should be changed to md5 or trust. In my hard disk, there is no such file. These archives are found within /var/lib/postgresql/11/ :

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

If I try to locate the file it will appear here:

$locate pg_hba.conf
/home/linuxbrew/.linuxbrew/var/postgres/pg_hba.conf

If I go inside, the method trust is already used.

I have already uninstalled postgresql and install it again.

This is my database.yml file:

# PostgreSQL. Versions 9.1 and up are supported.
#
# Install the pg driver:
#   gem install pg
# On OS X with Homebrew:
#   gem install pg -- --with-pg-config=/usr/local/bin/pg_config
# On OS X with MacPorts:
#   gem install pg -- --with-pg-config=/opt/local/lib/postgresql84/bin/pg_config
# On Windows:
#   gem install pg
#       Choose the win32 build.
#       Install PostgreSQL and put its /bin directory on your path.
#
# Configure Using Gemfile
# gem 'pg'
#
default: &default
  adapter: postgresql
  encoding: unicode
  # For details on connection pooling, see Rails configuration guide
  # http://guides.rubyonrails.org/configuring.html#database-pooling
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>

development:
  <<: *default
  database: postgres
  username: postgres
  #host: localhost
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  # The specified database role being used to connect to postgres.
  # To create additional roles in postgres see `$ createuser --help`.
  # When left blank, postgres will use the default role. This is
  # the same name as the operating system user that initialized the database.

  # The password associated with the postgres role (username).

  # Connect on a TCP socket. Omitted by default since the client uses a
  # domain socket that doesn't need configuration. Windows does not have
  # domain sockets, so uncomment these lines.
  #host: localhost

  # The TCP port the server listens on. Defaults to 5432.
  # If your server runs on a different port number, change accordingly.
   # port: 5432

  # Schema search path. The server defaults to $user,public
  #schema_search_path: myapp,sharedapp,public

  # Minimum log levels, in increasing order:
  #   debug5, debug4, debug3, debug2, debug1,
  #   log, notice, warning, error, fatal, and panic
  # Defaults to warning.
  #min_messages: notice

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test:
  <<: *default
  database: postgres
  username: postgres
  host: localhost
  pool: 5




# As with config/secrets.yml, you never want to store sensitive information,
# like your database password, in your source code. If your source code is
# ever seen by anyone, they now have access to your database.
#
# Instead, provide the password as a unix environment variable when you boot
# the app. Read http://guides.rubyonrails.org/configuring.html#configuring-a-database
# for a full rundown on how to provide these environment variables in a
# production deployment.
#
# On Heroku and other platform providers, you may have a full connection URL
# available as an environment variable. For example:
#
#   DATABASE_URL="postgres://myuser:mypass@localhost/somedatabase"
#
# You can use this database configuration with:
#
#   production:
#     url: <%= ENV['DATABASE_URL'] %>
#
production:
  <<: *default
  database: postgres
  username: postgres

If I remove the line

  username: postgres

I get

FATAL: role "root" does not exist

Answer 1

Did you create a user with the name postgres? If so you would've set a password for it. So you should include password attribute that in your config/database.yml file: (Also it's best practice to name your test, development and production databases name as different):

default: &default
  adapter: postgresql
  encoding: unicode
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>

development:
  <<: *default
  database: yourappname_dev
  username: postgres
  password: 1234
  host: localhost

test:
  <<: *default
  database: yourappname_test
  username: postgres
  password: 1234
  host: localhost

production:
  <<: *default
  host: localhost
  database: yourappname_prod
  password: 1234
  username: postgres

If you don't remember the password for postgres, create a new user and set password for it from the below commands and then update the above code with your new username and password:

$ sudo -u postgres createuser yournamehere -s
$ sudo -u postgres psql

postgres=# \password yournamehere
# enter your password

# now quit
\q

Answer 2

I had faced this issue yesterday. Try this ... This should do

default: &default
  adapter: postgresql
  pool: 5
  host: localhost

development:
  <<: *default
  database: prj_development
  username: pg_username
  password: pg_password

The only difference I noticed while making it work was the host key

host: localhost

To make sure I just commented the key host and reproduced the following error

PG::ConnectionBad: FATAL: Peer authentication failed for user "postgres"