Installing and configuring postgress in ubuntu

sudo apt-get update
sudo apt-get install postgresql postgresql-contrib

sudo -i -u postgres

You can get a Postgres prompt immediately by typing:

psql

Exit out of the PostgreSQL prompt by typing:

\q

We can create a new role (user_test) by typing: createuser --interactive

You can create the appropriate database by simply calling this command as the postgres user:

createdb db_test
sudo -i -u user_test

create role myapp with createdb login password 'password';

you can login as postgres user, which is generally a super user, and he can be logged in if you are sudoer or root user.

sudo -u postgres psql

Changing a password via postgres user

ALTER USER postgres PASSWORD 'newPassword';