Puma is a Ruby web server built for speed and parallelism. It is designed for running Rack apps only. It is licensed under the BSD 3-Clause license. This guide explains how to install Puma and run a minimal, custom Ruby application.


For this guide you should be familiar with the basic concepts of


We’re using Ruby in the stable version 2.5:

[isabell@stardust ~]$ uberspace tools version show ruby
Using 'Ruby' version: '2.5'
[isabell@stardust ~]$

If you want to use Puma with your own domain you need to setup your domain first:

[isabell@stardust ~]$ uberspace web domain list
[isabell@stardust ~]$


Use gem to install the latest version of Puma:

[isabell@stardust ~]$ gem install puma
Fetching: puma-3.12.0.gem (100%)
Building native extensions. This could take a while...
Successfully installed puma-3.12.0
1 gem installed
[isabell@stardust ~]$

Create a directory, and inside the directory a file rubyapp.ru for the application:

[isabell@stardust ~]$ mkdir ~/puma
[isabell@stardust ~]$ touch ~/puma/rubyapp.ru
[isabell@stardust ~]$

This file is the Rackup file for the application. Add the following content to ~/puma/rubyapp.ru, a simple Hello World application:

class HelloWorld
  def call(env)
    [200, {"Content-Type" => "text/plain"}, ["Hello World"]]

run HelloWorld.new

Create the folder for logs:

[isabell@stardust ~]$ mkdir ~/logs/puma
[isabell@stardust ~]$


Puma configuration file

Next, create a Puma configuration file:

[isabell@stardust ~]$ touch ~/puma/config.rb
[isabell@stardust ~]$

… and add the following content. Adapt the highlighted lines to your setup.

#!/usr/bin/env puma

# The directory to operate out of.
directory '/home/isabell/puma'

# The path to the rackup file
rackup '/home/isabell/puma/rubyapp.ru'

# Bind Puma to the port
bind 'tcp://'

# Enable logging
stdout_redirect '/home/isabell/logs/puma/out.log', '/home/isabell/logs/puma/err.log', true

Setup supervisord

Create ~/etc/services.d/puma.ini with the following content. Adapt the highlighted lines to your setup.

command=/opt/uberspace/etc/isabell/binpaths/ruby/puma --config %(ENV_HOME)s/puma/config.rb

The --config parameter provides the path to the configuration file.

Tell supervisord to refresh its configuration and start the service:

[isabell@stardust ~]$ supervisorctl reread
puma: available
[isabell@stardust ~]$ supervisorctl update
puma: added process group
[isabell@stardust ~]$

Configure web server


puma is running on port 9000.

To make the application accessible from the outside, configure a web backend:

[isabell@stardust ~]$ uberspace web backend set / --http --port <port>
Set backend for / to port <port>; please make sure something is listening!
You can always check the status of your backend using "uberspace web backend list".
[isabell@stardust ~]$


To validate the installation, open a browser and visit isabell.uber.space. If everything is set up correctly, you will see “Hello World”.



Check the update feed regularly to stay informed about the newest version.

Use gem to update Puma:

[isabell@stardust ~]$ gem update puma
[isabell@stardust ~]$

Further Reading

Tested with Puma 3.12, Uberspace 7.1.17

Written by: Theodor Müller <info@trilliarden.net>