Inatall Ruby on Rails in ubuntu

sudo apt install curl
curl -sL https://deb.nodesource.com/setup_12.x | sudo -E bash -
curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list

sudo apt-get update
sudo apt-get install git-core zlib1g-dev build-essential libssl-dev libreadline-dev libyaml-dev libsqlite3-dev sqlite3 libxml2-dev libxslt1-dev libcurl4-openssl-dev software-properties-common libffi-dev nodejs yarn

cd
git clone https://github.com/rbenv/rbenv.git ~/.rbenv
echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc
echo 'eval "$(rbenv init -)"' >> ~/.bashrc
exec $SHELL

git clone https://github.com/rbenv/ruby-build.git ~/.rbenv/plugins/ruby-build
echo 'export PATH="$HOME/.rbenv/plugins/ruby-build/bin:$PATH"' >> ~/.bashrc
exec $SHELL

rbenv install 2.7.1
rbenv global 2.7.1
ruby -v

git config --global color.ui true
git config --global user.name "YOUR NAME"
git config --global user.email "YOUR@EMAIL.com"
ssh-keygen -t rsa -b 4096 -C "YOUR@EMAIL.com"

cat ~/.ssh/id_rsa.pub

ssh -T git@github.com

gem install rails -v 6.0.2.2

rbenv rehash

rails -v

sudo apt-get install mysql-server mysql-client libmysqlclient-dev

Setting Up PostgreSQL
For PostgreSQL, we're going to add a new repository to easily install a recent version of Postgres.

sudo apt install postgresql-11 libpq-dev
The postgres installation doesn't setup a user for you, so you'll need to follow these steps to create a user with permission to create databases. Feel free to replace chris with your username.

sudo -u postgres createuser chris -s

# If you would like to set a password for the user, you can do the following
sudo -u postgres psql
postgres=# \password chris
Final Steps
And now for the moment of truth. Let's create your first Rails application:

#### If you want to use SQLite (not recommended)
rails new myapp

#### If you want to use MySQL
rails new myapp -d mysql

#### If you want to use Postgres
# Note that this will expect a postgres user with the same username
# as your app, you may need to edit config/database.yml to match the
# user you created earlier
rails new myapp -d postgresql

# Move into the application directory
cd myapp

# If you setup MySQL or Postgres with a username/password, modify the
# config/database.yml file to contain the username/password that you specified

# Create the database
rake db:create

rails server