Pow — A Great Server for your Mac Bat Cave

Somehow I stumbled across this great little tool  — oh yeah, John Nunemaker mentioned “powder,” which was “Syntactic sugar for http://pow.cx/

Huh? Syntactic what? For “pow” what? John hasn’t steered me wrong yet, so I decided I needed to look at what Pow was. In 37Signals own words:

Pow: Zero-configuration Rack Server for Mac OS X

In other words:

You can run a bunch of your rails apps all at once, with ease.

This is worth the effort to try and get running to see if it will help ease how you work with multiple Rails apps.

Since my experience was a bit off from the awesome-looking Screencast teaser, I figured I would share it in case others might benefit from the troubleshooting.

Once I solved the Pow-not-working-like-magic-from-the-start problems, it worked right out of the box with a Rails3 App. Not so much with my Rails2 apps. So, you can either try to do it the Rails3 way from the start (see below for instructions), or barge ahead and see how far you get (knowing now what I do for Rails2, barging is probably a pretty safe bet).

Yes, I am repeating what is in the main website… but then aggregating common troubleshooting experiences ad fixes below, to save you (and my colleagues) time.

Install Pow:

$ curl get.pow.cx | sh

Be certain you see “*** Installed” or it is not! (See Troubleshooting section below if need be.)

jonsmac2-2:.pow jon$ curl get.pow.cx | sh
% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
Dload  Upload   Total   Spent    Left  Speed
100  2722  100  2722    0     0  17322      0 --:--:-- --:--:-- --:--:-- 34455
*** Installing Pow 0.2.2...
*** Installing local configuration files...
*** Starting the Pow server...
*** Installed

If you get upset, just uninstall:

$ curl get.pow.cx/uninstall.sh | sh
Symbolic Link to Rails3 App
Symbolic Link to Rails3 App


$ cd ~/.pow
$ ln -s /path/to/myapp

To the right is an example. Name the link if you do not want to use the default folder name. For example:

ln -s ~/railsprojects/first_app jkfirstapp

This allows you to then enter the following into the browser, using the symbolic link name (or the default folder name):


If that didn’t work, continue onward, your journey will be short (I hope).


I was disappointed when the magic didn’t happen right away. Boy does the Ruby community spoil us! So a hunting I will go…

Create a Rails3 App

If you are only doing Rails2, see below for the config.ru fix. Otherwise, creating a vanilla Rails3 app is a good way to test that Pow is properly configured. Here is a simple Rails3 app (from Michael Hartl’s Ruby on Rails3 Tutorial):

mkdir ~/railsprojects
rails new first_app

edit the Gemfile:

gem 'rails', '3.0.1'
gem 'sqlite3-ruby', '1.2.5', :require => 'sqlite3'

Then execute:

bundle install
rails server

It should be running with the default server page.

I got Nothing!

If pow did not install, or you get seemingly NOTHING when going to the browser webpage, look no further than here. The following worked for me (and others). Seems that the permissions are not quite right sometimes:


-rw-rw-r--   1 jon  staff   518B Apr 18 13:42 cx.pow.powd.plist

So I ran this:

jonsmac2-2:.pow jon$ launchctl load -Fw ~/Library/LaunchAgents/cx.pow.powd.plist
jonsmac2-2:.pow jon$ chmod 644 ~/Library/LaunchAgents/cx.pow.powd.plist
jonsmac2-2:.pow jon$ curl get.pow.cx | sh

And, after the re-install, the perms ended up as you might expect:

-rw-r--r--   1 jon  staff   518B Apr 18 13:42 cx.pow.powd.plist

Checking It’s Running

This is admittedly odd output for a “working” install, but it gives you at least one data point to compare what you get versus this. Do the following:

cd ~/Library/Application Support/Pow/Current/bin
jonsmac2-2:bin jon$ ./pow

On my Mac it results in:

    throw e; // process.nextTick error, or 'error' event on first tick
Error: EADDRINUSE, Address already in use
at HttpServer._doListen (net.js:1089:5)
at net.js:1060:14
at Object.lookup (dns.js:159:5)
at HttpServer.listen (net.js:1054:20)
at Array.<anonymous> (/Users/jon/Library/Application Support/Pow/Versions/0.2.2/lib/daemon.js:34:27)
at EventEmitter._tickCallback (node.js:126:26)

Domain Isn’t Setup

If you see this:

No such app
No such application can be found!

Then you know you have screwed up the symbolic link.

Try again, and be careful and exact.

Trouble Accessing Dev domains

Some folks needed this simple fix:

touch /etc/resolver/dev

Rails2: Cannot GET /? –> config.ru is Missing!

That’s right, you see: Cannot GET / in the browser. Bet you never saw that before!

This means that you are missing the Rackup config.ru file in your application’s root. Try adding this file (you can see it in the folder screenshot above):

# This file is used by Rack-based servers to start the application.
require "./config/environment"
use Rails::Rack::LogTailer
use Rails::Rack::Static
run ActionController::Dispatcher.new

Pow Can’t Start Your App

This is most likely, genuinely, truly your error… Sorry to say!

The error below is because the config.ru was completely wrong (I was trying the Rails3 project file (duh — it invokes a class in a module named after the app itself)):

Pow can’t start your application.

/Users/jon/railsprojects/track_my_league/tml raised an exception during boot.
NameError: uninitialized constant FirstApp
/Users/jon/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:443:in `load_missing_constant'
/Users/jon/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:80:in `const_missing'
/Users/jon/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:92:in `const_missing'
/Users/jon/Library/Application Support/Pow/Versions/0.2.2/node_modules/nack/lib/nack/builder.rb:4:in `instance_eval'
/Users/jon/Library/Application Support/Pow/Versions/0.2.2/node_modules/nack/lib/nack/builder.rb:4:in `initialize'
/Users/jon/railsprojects/track_my_league/tml/config.ru:1:in `new'

Here the error is that I do not have the gem environment set up properly with RVM (using .rvmrc). Easily diagnosed because I can’t even start the app manually!

SystemExit: exit
./config/boot.rb:66:in `exit'
./config/boot.rb:66:in `load_rails_gem'
./config/boot.rb:54:in `load_initializer'
./config/boot.rb:38:in `run'
./config/boot.rb:11:in `boot!'
./config/environment.rb:7:in `require'
/Users/jon/railsprojects/tml/TML/config.ru:3:in `require'
/Users/jon/Library/Application Support/Pow/Versions/0.2.2/node_modules/nack/lib/nack/builder.rb:4:in `instance_eval'
/Users/jon/Library/Application Support/Pow/Versions/0.2.2/node_modules/nack/lib/nack/builder.rb:4:in `initialize'
/Users/jon/railsprojects/tml/TML/config.ru:1:in `new'

Hope this helps!

4 thoughts on “Pow — A Great Server for your Mac Bat Cave”

  1. Great post, there should be more like this when something new comes out…

    Is the config.ru code you have at “Rails2: Cannot GET /? –> config.ru is Missing!” kind of the most general version of config.ru and should it work with all Rails 2 apps?

  2. I’ve also found if you’re running RBM but havent set up a specific version(just using the default) for an an app… you need to add an .rvmrc (hidden) file to your app to make it boot properly..

    Im not sure this is documented anywhere… (or if *I* in fact am making the error by not setting a version in rvm….) but I’ve been stuck on this a few times…

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