How to redirect to a 404 in Rails?

I'd like to 'fake' a 404 page in Rails. In PHP, I would just send a header with the error code as such:

header("HTTP/1.0 404 Not Found");

How is that done with Rails?

Don't render 404 yourself, there's no reason to; Rails has this functionality built in already. If you want to show a 404 page, create a render_404 method (or not_found as I called it) in ApplicationController like this:

def not_found
  raise ActionController::RoutingError.new('Not Found')
end

Rails also handles AbstractController::ActionNotFound, and ActiveRecord::RecordNotFound the same way.

This does two things better:

1) It uses Rails' built in rescue_from handler to render the 404 page, and
2) it interrupts the execution of your code, letting you do nice things like:

user = User.find_by_email(params[:email]) or not_found
  user.do_something!

without having to write ugly conditional statements.

As a bonus, it's also super easy to handle in tests. For example, in an rspec integration test:

# RSpec 1

lambda {
  visit '/something/you/want/to/404'
}.should raise_error(ActionController::RoutingError)

# RSpec 2+

expect {
  get '/something/you/want/to/404'
}.to raise_error(ActionController::RoutingError)

And minitest:

assert_raises(ActionController::RoutingError) do 
  get '/something/you/want/to/404'
end

OR refer more info from Rails render 404 not found from a controller action

Stack Overflow Q#2385799, score: 1101