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You can read this in a nicely formatted README.pdf document.

1. Usage for the Impatient

  1. Add gem 'puma-daemon' to your Gemfile. If you prefer, you can add require: false (your Rails instances such as Sidekiq will have no use for this gem).

  2. You have two options to daemonize Puma using this gem:

    1. In your config/puma.rb file, add the following line: require 'puma/daemon' at the top, and at the bottom call daemonize.

    2. Wherever you use puma to start it (except using puma-ctl) replace puma with pumad and daemonization will be enabled automatically.

2. Introduction

Let’s start with the facts: Puma is the most popular server to run Ruby and Rails applications. It’s both multi-threaded and multi-process, making it one of the only servers that can truly saturate your web hardware. While 100% saturation is probably not what you want, the alternative is paying a fortune for under-utilized hardware. A good rule of thumb is to keep your web servers busy around 70-80% most of the time. Puma let’s you do that by configuring the number of workers and threads within each worker.

2.1. What is Daemonization?

Unix processes have the ability to daemonize and go into the background.

This is not a trivial task: to properly daemonize a process must detach the from controlling terminal and run in the background as a system daemon.

In Ruby this is accomplished with the Process.daemon method, which receives two boolean arguments:

  • Unless the first argument nochdir is true, it will change the current working directory to the root (“/”).

  • Unless the second argument noclose is true, daemon() will also redirect standard input, standard output and standard error to /dev/null.

  • Finally, it will return zero on success, or raise one of ` Errno::*` and pass the control to the subsequent Ruby code, which will now continue executing within a daemon.

2.2. Why was it removed from Puma v5?

For production deployments, tools like systemd offer much better alternative, including ability to cap overall memory and CPU consumed by the Puma and all of its workers using Linux cgroups.

The proliferation of Docker deployments meant that Puma is run on the foreground within a Docker container.

Finally, the code which previously daemonized Puma in version 4 was not really maintained, and for this reason was removed from Puma version 5.

2.3. What does puma-daemon do?

We thought that while the core Puma removing daemonization was the right move, it felt useful in some occastions and so we created this gem to restore the daemonization functionality to Puma v5+.

3. Compatibility

3.1. Ruby Versions

We did not restore the daemon functionality for JRuby; so at the moment this will work with the MRI distribution, and possibly others that support Process.daemon(true, true).

For supported MRI Ruby Versions see the Github Workflow file.

3.2. Puma Versions

Currently Puma versions 5 and 6 are supported.

3.3. Known Issues

Please see the list of open issues on the Issues Page. Any help is always welcomed.

3.4. How it works?

This gem’s goal was to surgically augment Puma’s source code to restore daemonization by merely requiring puma/daemon.

We accomplished this goal by adding the daemonization call to the routine output_header() which is invoked by both Puma::Single runner and the Puma::Cluster runner at the very beginning of the launch process. While relatively brittle, particularly if the future versions of Puma change this, this approach seems to work with the currently released version of Puma (5 and 6).

If you run into problems, please submit an issue.

4. Examples

Add this line to your application’s Gemfile:

gem 'puma-daemon', require: false
gem 'puma',  '~> 5' # or 6

In your config/puma.rb, eg.

require 'puma/daemon'
bind 'tcp://'
workers 2
threads 4

And then execute:

bundle install -j 12
bundle exec puma -C config/puma.rb []

Make sure you have Rackup file in the current folder. Checkout the shell script inside the example folder for more info.

Please see the example directory in the source of the gem. It contains and scripts that boot Puma via pumad binary.

4.1. Using Config File

If you want to specify daemonize in your config file, simply include require 'puma/daemon' at the top of your config file:

# file: config/puma.rb
require 'puma/daemon'

port 3001
workers 3
threads 2,3
# accepts true or false, and if false is passed will NOT daemonize

With this method you can continue using the standard puma executable to get it started, but (and this is important) — you must remove any -d or --daemonize from the command line, or Puma v5 and above will fail with an error.

Here is an example of daemonizing via the config file shown above, and using the regular puma binary:

❯ cd example
❯ bundle exec puma -I ../lib -C $(pwd)/puma.rb -w 4
[62235] Puma starting in cluster mode...
[62235] * Puma version: 6.1.1 (ruby 2.7.6-p219) ("The Way Up")
[62235] *  Min threads: 0
[62235] *  Max threads: 16
[62235] *  Environment: development
[62235] *   Master PID: 62235
[62235] *  Puma Daemon: Daemonizing...
[62235] *  Gem: puma-daemon v0.2.2
[62235] *  Gem: puma v6.1.1
[62258] *      Workers: 4
[62258] *     Restarts: (✔) hot (✔) phased
[62258] * Listening on unix:///tmp/puma.sock
[62258] * Listening on

Note that using this method you can decide whether to daemonize or not by passing true or false to the daemonize method.

4.2. Using Command Line

If you prefer to make a decision whether to daemonize or not on the command line, you only have to make one chance: replace puma with pumad.

We did not want to conflict with the puma gem by introducing another executable under the same name. The executable this gem provides is called pumad (where 'd' stands for daemon, and follows standard UNIX convention, as in eg sshd, ftpd, etc).

If you replace puma with pumad, you no longer need to pass any additional command line flag (-d and --daemonize) to daemonize. You can continue passing them or you can remove them (these flags are stripped out before ARGV is passed onto Puma’s CLI parser.)

❯ cd example
❯ ../exe/pumad -C $(pwd)/puma.rb -w 0

Puma starting in single mode...
* Puma version: 6.1.1 (ruby 2.7.6-p219) ("The Way Up")
*  Min threads: 0
*  Max threads: 16
*  Environment: development
*          PID: 63179
*  Puma Daemon: Daemonizing...
*  Gem: puma-daemon v0.2.2
*  Gem: puma v6.1.1
* Listening on unix:///tmp/puma.sock
* Listening on

As you can see, at the end it says "Daemonizing".

If you start puma this way, you can still specify daemonize(false) in the configuration file to turn it off, but the default is to daemonize. Also, if you start with pumad you do not need to include require 'puma/daemon' in your configuration file, as the pumad binary loads all dependencies prior to parsing the config.

5. Contributing

You do need a working make utility to use the below commands.
  • After checking out the repo, run make puma-v5 or make puma-v6 to configure your dependent vesion of Puma.

  • After that, run bin/setup to install dependencies.

  • Then, run rake spec to run the tests.

  • You can also run bin/console for an interactive prompt that will allow you to experiment.

  • To install this gem onto your local machine, run bundle exec rake install.

  • To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to

Bug reports and pull requests are welcome on GitHub at

6. License

The gem is available as open source under the terms of the MIT License.