When running rackup as a daemon, File.expand_path return / instead of the project folder

Question

I'm not sure if there's something I did wrong here in some config files. When I run rackup -D, doing this:

File.expand_path(__FILE__)

actually returns /file.rb. And adding File.dirname somehow returns /. So now all my file loading code didn't work as it tries to look in the / directory, rather than the project directory.

This does not happen if I remove the -D option. It returns the full path /home/blablabla/stuff/file.rb

Sample code:

test.rb:

require 'rubygems' if RUBY_VERSION <= '1.8.7'
require 'sinatra'

get '/expdir' do
  File.expand_path(File.dirname(__FILE__))
end

get '/exp' do
  File.expand_path(__FILE__)
end

get '/file' do
  __FILE__
end

get '/dirname' do
  File.dirname(__FILE__)
end

get '/dir' do
  Dir.entries(File.expand_path(File.dirname(__FILE__))).to_s
end

config.ru:

require 'test.rb'

run Sinatra::Application

Executed it with rackup -p 4567 and watched it return the correct values. Executed it with rackup -p 4567 -D and watched it return the wrong values.

Answer 1

Rack does indeed change the working directory to / when run as a daemon.

In Ruby 1.8.7, __FILE__ in a required file refers to the path used to load the file, which could be a relative path from the current working directory of the process. However this value is not updated if the working directory is later changed, e.g. with a call to Dir.chdir.

File.expand_path expands relative files paths relative to the working directory. So in this case File.expand_path(__FILE__) results in the paths relative to the root, but the value of __FILE__ is relative to the original working directory, giving the wrong result.

In Ruby 1.9.2 and 1.9.3, __FILE__ in a required file refers to the absolute path of the file, so this problem doesn’t arise.

One way to fix this in Ruby 1.8.7 is to use an absolute path when requiring your application file. Change the line require 'test.rb' in your config.ru to:

require File.expand_path('../test', __FILE__)

Now the references to __FILE__ will be absolute, so won’t be affected by the change in working directory when daemonising.

If your application is more complicated, with more files, it might be better to set up your load path instead. For example your could put all your .rb files into a lib/ directory, then in your config.ru add:

$LOAD_PATH.unshift(File.expand_path '../lib', __FILE__)

You can then just require your files without worrying about the relative paths.