Rails Tutorial 2.2: Puma Server - ruby-on-rails

Question

I'm trying to learn Rails from the Rails Tutorial book, got lubuntu so I could try to get the best experience possible. Now I'm stuck on something that should be easy and straight forward.
We're creating a little "toy app" a very basic twitter like thing, still at the very beginning, we used:
$ rails generate scaffold User name:string email:string
To generate a User Table if I'm not mistaken and then:
$ rails db:migrate
I guess to update a preexisting table structure (not sure, but it's said that later everything will be explained).
Finally we are supposed to run this:
$ rails server -b $IP -p $PORT
In a differente tab, I did and got this error:
~/workspace/toy_app$ rails server -b $IP -p $PORT
=> Booting Puma
=> Rails 5.0.0.1 application starting in development on http://-p:3000
=> Run `rails server -h` for more startup options
Puma starting in single mode...
* Version 3.4.0 (ruby 2.3.1-p112), codename: Owl Bowl Brawl
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://-p:3000
Exiting
/var/lib/gems/2.3.0/gems/puma-3.4.0/lib/puma/binder.rb:255:in `initialize': getaddrinfo: Name or service not known (SocketError)
from /var/lib/gems/2.3.0/gems/puma-3.4.0/lib/puma/binder.rb:255:in `new'
from /var/lib/gems/2.3.0/gems/puma-3.4.0/lib/puma/binder.rb:255:in `add_tcp_listener'
from /var/lib/gems/2.3.0/gems/puma-3.4.0/lib/puma/binder.rb:102:in `block in parse'
from /var/lib/gems/2.3.0/gems/puma-3.4.0/lib/puma/binder.rb:85:in `each'
from /var/lib/gems/2.3.0/gems/puma-3.4.0/lib/puma/binder.rb:85:in `parse'
from /var/lib/gems/2.3.0/gems/puma-3.4.0/lib/puma/runner.rb:129:in `load_and_bind'
from /var/lib/gems/2.3.0/gems/puma-3.4.0/lib/puma/single.rb:84:in `run'
from /var/lib/gems/2.3.0/gems/puma-3.4.0/lib/puma/launcher.rb:172:in `run'
from /var/lib/gems/2.3.0/gems/puma-3.4.0/lib/rack/handler/puma.rb:51:in `run'
from /var/lib/gems/2.3.0/gems/rack-2.0.1/lib/rack/server.rb:296:in `start'
from /var/lib/gems/2.3.0/gems/railties-5.0.0.1/lib/rails/commands/server.rb:79:in `start'
from /var/lib/gems/2.3.0/gems/railties-5.0.0.1/lib/rails/commands/commands_tasks.rb:90:in `block in server'
from /var/lib/gems/2.3.0/gems/railties-5.0.0.1/lib/rails/commands/commands_tasks.rb:85:in `tap'
from /var/lib/gems/2.3.0/gems/railties-5.0.0.1/lib/rails/commands/commands_tasks.rb:85:in `server'
from /var/lib/gems/2.3.0/gems/railties-5.0.0.1/lib/rails/commands/commands_tasks.rb:49:in `run_command!'
from /var/lib/gems/2.3.0/gems/railties-5.0.0.1/lib/rails/commands.rb:18:in `<top (required)>'
from /home/zero/workspace/toy_app/bin/rails:9:in `require'
from /home/zero/workspace/toy_app/bin/rails:9:in `<top (required)>'
from /var/lib/gems/2.3.0/gems/spring-1.7.2/lib/spring/client/rails.rb:28:in `load'
from /var/lib/gems/2.3.0/gems/spring-1.7.2/lib/spring/client/rails.rb:28:in `call'
from /var/lib/gems/2.3.0/gems/spring-1.7.2/lib/spring/client/command.rb:7:in `call'
from /var/lib/gems/2.3.0/gems/spring-1.7.2/lib/spring/client.rb:30:in `run'
from /var/lib/gems/2.3.0/gems/spring-1.7.2/bin/spring:49:in `<top (required)>'
from /var/lib/gems/2.3.0/gems/spring-1.7.2/lib/spring/binstub.rb:11:in `load'
from /var/lib/gems/2.3.0/gems/spring-1.7.2/lib/spring/binstub.rb:11:in `<top (required)>'
from /usr/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /home/zero/workspace/toy_app/bin/spring:13:in `<top (required)>'
from bin/rails:3:in `load'
from bin/rails:3:in `<main>'
Is anything corrupted? Did I do anything wrong? I went to check the files I remembered seeing puma (in the app folder) on and it's in the gem file:
gem 'puma', '3.4.0'
And the puma.rb file (took out the comments):
threads_count = ENV.fetch("RAILS_MAX_THREADS") { 5 }.to_i
threads threads_count, threads_count
port ENV.fetch("PORT") { 3000 }
environment ENV.fetch("RAILS_ENV") { "development" }
plugin :tmp_restart
I was going to put all the files mentioned but it's tons of code, if there's any that's useful I'll post it, I don't want to spam with possible useless code.

Answer 1

$IP is not defined in your environment, so rails server is trying to use -p as the IP address. Try this:
rails server -b ${IP:-127.0.0.1} -p ${PORT:-3000}
Alternatively, set these environment variables with export before running rails server -b $IP -p $PORT:
export IP=127.0.0.1
export PORT=3000
Or if you're fine with Rails' defaults, just forget all this and run rails server. :-)

Answer 2

If you are running locally you should be able to use rails server without arguments. If you are using the Hartl tutorial, it presumes you are using a web-based IDE that requires the extra arguments.

Answer 3

If you are using cloud based IDE, you need to listen at particular IP & PORT. For example, C9, you need to listen to 0.0.0.0 and 8080. So they have setup environment variables, $IP & $PORT.
If you execute,
echo $IP ###gives 0.0.0.0
echo $PORT ###gives 8080
rails s -b $IP -p $PORT ##Rails x.x.x application starting in development on http://0.0.0.0:8080
The -b option binds Rails to the specified IP, by default it is localhost.
If you are on your local machine, run
rails s ### Rails x.x.x application starting in development on http://localhost:3000