1. gemfile:

add gem "pg"

remove gem "sqlite"

2. console:

SCRIPT TO INSTALL LATEST VERSION OF POSTGRESQL

Install Postgresql and create a user:

sudo apt install postgresql libpq-dev
sudo su postgres
createuser --interactive
ubuntu
y 
exit

check version of postgresql

pg_config --version

To create another user with a password:

sudo su postgres
createuser --interactive --pwprompt
username
password
y
exit

Set default password for a postgresql user: in this case we set password myPassword for user postgres

sudo -u postgres psql
ALTER USER postgres PASSWORD 'myPassword';
\q

Now you can install the gem and run migrations:

bundle
rails db:create db:migrate
rails s

That’s it 🥳 !

Relevant links