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Phusion Passenger is an Apache module, which makes deploying Ruby and Ruby on Rails applications on Apache a breeze. It follows the usual Ruby on Rails conventions, such as "Don't-Repeat-Yourself" and ease of setup, while at the same time providing enough flexibility.

This users guide will teach you:

  • How to install Phusion Passenger.

  • How to configure Phusion Passenger.

  • How to deploy a Ruby on Rails application.

  • How to deploy a Rack-based Ruby application.

  • How to solve common problems.

This guide assumes that the reader is somewhat familiar with Apache and with using the commandline.

1. Supported operating systems

Phusion Passenger works on any POSIX-compliant operating system. In other words: practically any operating system on earth, except Microsoft Windows.

Phusion Passenger has been tested on:

Other operating systems have not been tested, but Phusion Passenger will probably work fine on them. Please report a bug or join our discussion list if it doesn't.

2. Installing Phusion Passenger

2.1. Generic installation instructions

2.1.1. Overview of download and installation methods

There are two ways to install Phusion Passenger:

  1. By installing the Phusion Passenger gem, as instructed on the “Install” page on the Phusion Passenger website.

  2. By downloading a native Linux package (e.g. Debian package) from the Phusion Passenger website.

  3. By downloading the source tarball from the Phusion Passenger website (passenger-x.x.x.tar.gz).

In our opinion, installing the gem or the native package is easiest.

Phusion Passenger provides an easy-to-use installer for installing the Phusion Passenger Apache module (mod_passenger).

Tip You might have to run the installation commands in the following sections as root. If the installer fails because of permission errors, it will tell you.

2.1.2. Specifying the correct Apache installation

Note You can skip this section if you've installed Phusion Passenger via a native Linux package, because no compilation is necessary.

If your system has multiple Apache installations (this is likely the case on MacOS X), then you will need to tell the Phusion Passenger installer which one to use. If you only have one Apache installation (the case on most Linux systems), then you can skip this section because Phusion Passenger will automatically detect it.

Every Apache installation has its own apxs program. You will need to tell Phusion Passenger the location of this program, by specifying the APXS2 environment variable. Suppose that you want to use the Apache installation in /opt/apache2. Then, assuming that the corresponding apxs program is located /opt/apache2/bin/apxs, type:

export APXS2=/opt/apache2/bin/apxs
Note On some systems, the apxs program might be called apxs2, and it might be located in the sbin folder instead of the bin folder.

2.1.3. Specifying the correct Ruby installation

Note You can skip this section if you've installed Phusion Passenger via a native Linux package, because no compilation is necessary.

If your system has multiple Ruby installations (this is likely the case on MacOS X), then you will need to tell the Phusion Passenger installer which one to use. If you only have one Ruby installation (the case on most Linux systems), then you can skip this section because Phusion Passenger will automatically detect it.

To specify the Ruby installation, prepend your Ruby installation's bin directory to the PATH environment variable. For example, if you have the following Ruby installations:

and you want to use the latter, then type:

export PATH=/opt/myruby/bin:$PATH

2.1.4. Installing via the gem

Please install the gem and then run the Phusion Passenger installer, by typing the following commands:

gem install passenger-x.x.x.gem
passenger-install-apache2-module

Please follow the instructions given by the installer.

2.1.5. Installing via a native Linux package

Please install the native Linux package, e.g.:

gdebi passenger_x.x.x-i386.deb

Next, you'll need to configure Apache. Run the "installer", as it will tell you the correct configuration options for Apache:

passenger-install-apache2-module
Note The installer doesn't actually install anything because it will automatically detect that Phusion Passenger has already been installed. The only thing the installer will do in this case, is showing the correct Apache configurations.

2.1.6. Installing via the source tarball

Extract the tarball to whatever location you prefer. The Phusion Passenger files are to reside in that location permanently. For example, if you would like Phusion Passenger to reside in /opt/passenger-x.x.x:

cd /opt
tar xzvf ~/YourDownloadsFolder/passenger-x.x.x.tar.gz

Next, run the included installer:

/opt/passenger-x.x.x/bin/passenger-install-apache2-module

Please follow the instructions given by the installer.

Important Please do not remove the passenger-x.x.x folder after installation. Furthermore, the passenger-x.x.x folder must be accessible by Apache.

2.2. Operating system-specific instructions and information

2.2.1. MacOS X

Ben Ruebenstein has written an excellent tutorial on installing Phusion Passenger on OS X.

2.2.2. Ubuntu Linux

Ben Hughes has written an article on installing Phusion Passenger on Ubuntu.

3. Deploying a Ruby on Rails application

Suppose you have a Ruby on Rails application in /webapps/mycook, and you own the domain www.mycook.com. You can either deploy your application to the virtual host's root (i.e. the application will be accessible from the root URL, http://www.mycook.com/), or in a sub URI (i.e. the application will be accessible from a sub URL, such as http://www.mycook.com/railsapplication).

Note The default RAILS_ENV environment in which deployed Rails applications are run, is “production”. You can change this by changing the RailsEnv configuration option.

3.1. Deploying to a virtual host's root

Add a virtual host entry to your Apache configuration file. The virtual host's document root must point to your Ruby on Rails application's public folder. For example:

<VirtualHost *:80>
    ServerName www.mycook.com
    DocumentRoot /webapps/mycook/public
</VirtualHost>

Then restart Apache. The application has now been deployed.

3.2. Deploying to a sub URI

Suppose that you already have a virtual host:

<VirtualHost *:80>
    ServerName www.phusion.nl
    DocumentRoot /websites/phusion
</VirtualHost>

And you want your Ruby on Rails application to be accessible from the URL http://www.phusion.nl/rails.

To do this, make a symlink from your Ruby on Rails application's public folder to a directory in the document root. For example:

ln -s /webapps/mycook/public /websites/phusion/rails

Next, add a RailsBaseURI option to the virtual host configuration:

<VirtualHost *:80>
    ServerName www.phusion.nl
    DocumentRoot /websites/phusion
    RailsBaseURI /rails                # This line has been added.
</VirtualHost>

Then restart Apache. The application has now been deployed.

Tip

You can deploy multiple Rails applications under a virtual host, by specifying RailsBaseURI multiple times. For example:

<VirtualHost *:80>
    ....
    RailsBaseURI /app1
    RailsBaseURI /app2
    RailsBaseURI /app3
</VirtualHost>

3.3. Redeploying (restarting the Ruby on Rails application)

Deploying a new version of a Ruby on Rails application is as simple as re-uploading the application files, and restarting the application.

There are two ways to restart the application:

  1. By restarting Apache.

  2. By creating or modifying the file tmp/restart.txt in the Rails application's root folder. Phusion Passenger will automatically restart the application.

For example, to restart our example MyCook application, we type this in the command line:

touch /webapps/mycook/tmp/restart.txt

3.4. Migrations

Phusion Passenger is not related to Ruby on Rails migrations in any way. To run migrations on your deployment server, please login to your deployment server (e.g. with ssh) and type rake db:migrate RAILS_ENV=production in a shell console, just like one would normally run migrations.

3.5. Capistrano integration

See Capistrano recipe.

4. Deploying a Rack-based Ruby application

Phusion Passenger supports arbitrary Ruby web applications that follow the Rack interface.

Phusion Passenger assumes that Rack application directories have a certain layout. Suppose that you have a Rack application in /webapps/rackapp. Then that folder must contain at least two entries:

So /webapps/rackapp must, at minimum, look like this:

/webapps/rackapp
  |
  +-- config.ru
  |
  +-- public/
  |
  +-- tmp/

Suppose you own the domain www.rackapp.com. You can either deploy your application to the virtual host's root (i.e. the application will be accessible from the root URL, http://www.rackapp.com/), or in a sub URI (i.e. the application will be accessible from a sub URL, such as http://www.rackapp.com/rackapp).

Note The default RACK_ENV environment in which deployed Rack applications are run, is “production”. You can change this by changing the RackEnv configuration option.

4.1. Tutorial/example: writing and deploying a Hello World Rack application

First we create a Phusion Passenger-compliant Rack directory structure:

$ mkdir /webapps/rack_example
$ mkdir /webapps/rack_example/public
$ mkdir /webapps/rack_example/tmp

Next, we write a minimal "hello world" Rack application:

$ cd /webapps/rack_example
$ some_awesome_editor config.ru
...type in some source code...
$ cat config.ru
app = proc do |env|
    return [200, { "Content-Type" => "text/html" }, "hello <b>world</b>"]
end
run app

Finally, we deploy it by adding the following configuration options to the Apache configuration file:

<VirtualHost *:80>
    ServerName www.rackexample.com
    DocumentRoot /webapps/rack_example/public
</VirtualHost>

And we're done! After an Apache restart, the above Rack application will be available under the URL http://www.rackexample.com/.

4.2. Deploying to a virtual host's root

Add a virtual host entry to your Apache configuration file. The virtual host's document root must point to your Rack application's public folder. For example:

<VirtualHost *:80>
    ServerName www.rackapp.com
    DocumentRoot /webapps/rackapp/public
</VirtualHost>

Then restart Apache. The application has now been deployed.

4.3. Deploying to a sub URI

Suppose that you already have a virtual host:

<VirtualHost *:80>
    ServerName www.phusion.nl
    DocumentRoot /websites/phusion
</VirtualHost>

And you want your Rack application to be accessible from the URL http://www.phusion.nl/rack.

To do this, make a symlink from your Rack application's public folder to a directory in the document root. For example:

ln -s /webapps/rackapp/public /websites/phusion/rack

Next, add a RackBaseURI option to the virtual host configuration:

<VirtualHost *:80>
    ServerName www.phusion.nl
    DocumentRoot /websites/phusion
    RackBaseURI /rack                # This line has been added.
</VirtualHost>

Then restart Apache. The application has now been deployed.

Tip

You can deploy multiple Rack applications under a virtual host, by specifying RackBaseURI multiple times. For example:

<VirtualHost *:80>
    ....
    RacksBaseURI /app1
    RacksBaseURI /app2
    RacksBaseURI /app3
</VirtualHost>

4.4. Redeploying (restarting the Rack application)

Deploying a new version of a Rack application is as simple as re-uploading the application files, and restarting the application.

There are two ways to restart the application:

  1. By restarting Apache.

  2. By creating or modifying the file tmp/restart.txt in the Rack application's root folder. Phusion Passenger will automatically restart the application.

For example, to restart our example application, we type this in the command line:

touch /webapps/rackapp/tmp/restart.txt

4.5. Rackup specifications for various web frameworks

This subsection shows example config.ru files for various web frameworks.

4.5.1. Camping

require 'rubygems'
require 'rack'
require 'camping'

##### Begin Camping application
Camping.goes :Blog

...your application code here...
##### End Camping application

run Rack::Adapter::Camping.new(Blog)

For Camping versions 2.0 and up, using run Blog as the final line will do.

4.5.2. Halcyon

require 'rubygems'
require 'halcyon'
$LOAD_PATH.unshift(Halcyon.root / 'lib')
Halcyon::Runner.load_config Halcyon.root/'config'/'config.yml'
run Halcyon::Runner.new

4.5.3. Mack

ENV["MACK_ENV"] = ENV["RACK_ENV"]
load("Rakefile")
require 'rubygems'
require 'mack'
run Mack::Utils::Server.build_app

4.5.4. Merb

require 'rubygems'
require 'merb-core'

Merb::Config.setup(:merb_root   => ".",
                   :environment => ENV['RACK_ENV'])
Merb.environment = Merb::Config[:environment]
Merb.root = Merb::Config[:merb_root]
Merb::BootLoader.run

run Merb::Rack::Application.new

4.5.5. Ramaze

require "start"
Ramaze.trait[:essentials].delete Ramaze::Adapter
Ramaze.start :force => true
run Ramaze::Adapter::Base

4.5.6. Sinatra

require 'rubygems'
require 'sinatra'
Sinatra::Application.default_options.merge!(
  :run => false,
  :env => ENV['RACK_ENV']
)

### ...your Sinatra application code here... ###

run Sinatra.application

5. Configuring Phusion Passenger

After installation, Phusion Passenger does not need any further configurations. Nevertheless, the system administrator may be interested in changing Phusion Passenger's behavior. Phusion Passenger's Apache module supports the following configuration options:

5.1. PassengerRoot <directory>

The location to the Phusion Passenger root directory. This configuration option is essential to Phusion Passenger. The correct value is given by the installer, and should usually not be changed manually.

This required option may only occur once, in the global server configuration.

5.2. PassengerLogLevel <integer>

This option allows one to specify how much information Phusion Passenger should write to the Apache error log file. A higher log level value means that more information will be logged.

Possible values are:

This option may only occur once, in the global server configuration. The default is 0.

5.3. PassengerRuby <filename>

This option allows one to specify the Ruby interpreter to use.

This option may only occur once, in the global server configuration. The default is ruby.

5.4. PassengerUserSwitching <on|off>

Whether to enable user switching support.

This option may only occur once, in the global server configuration. The default value is on.

5.5. PassengerDefaultUser <username>

Passenger enables user switching support by default. This configuration option allows one to specify which user Rails/Rack applications must run as, if user switching fails or is disabled.

This option may only occur once, in the global server configuration. The default value is nobody.

5.6. Resource control and optimization options

5.6.1. PassengerMaxPoolSize <integer>

The maximum number of Ruby on Rails or Rack application instances that may be simultaneously active. A larger number results in higher memory usage, but improved ability to handle concurrent HTTP clients.

The optimal value depends on your system's hardware and the server's average load. You should experiment with different values. But generally speaking, the value should be at least equal to the number of CPUs (or CPU cores) that you have. If your system has 2 GB of RAM, then we recommend a value of 30. If your system is a Virtual Private Server (VPS) and has about 256 MB RAM, and is also running other services such as MySQL, then we recommend a value of 2.

If you find that your server is unable to handle the load on your Rails/Rack websites (i.e. running out of memory) then you should lower this value. (Though if your sites are really that popular, then you should strongly consider upgrading your hardware or getting more servers.)

This option may only occur once, in the global server configuration. The default value is 6.

Tip We strongly recommend you to use Ruby Enterprise Edition. This allows you to reduce the memory usage of your Ruby on Rails applications by about 33%. And it's not hard to install.

5.6.2. PassengerMaxInstancesPerApp <integer>

The maximum number of application instances that may be simultaneously active for a single application. This helps to make sure that a single application will not occupy all available slots in the application pool.

This value must be less than PassengerMaxPoolSize. A value of 0 means that there is no limit placed on the number of instances a single application may use, i.e. only the global limit of PassengerMaxPoolSize will be enforced.

This option may only occur once, in the global server configuration. The default value is 0.

5.6.3. PassengerPoolIdleTime <integer>

The maximum number of seconds that a Ruby on Rails or Rack application instance may be idle. That is, if an application instance hasn't done anything after the given number of seconds, then it will be shutdown in order to conserve memory.

Decreasing this value means that applications will have to be spawned more often. Since spawning is a relatively slow operation, some visitors may notice a small delay when they visit your Rails/Rack website. However, it will also free up resources used by applications more quickly.

The optimal value depends on the average time that a visitor spends on a single Rails/Rack web page. We recommend a value of 2 * x, where x is the average number of seconds that a visitor spends on a single Rails/Rack web page. But your mileage may vary.

This option may only occur once, in the global server configuration. The default value is 300.

5.7. Ruby on Rails-specific options

5.7.1. RailsAutoDetect <on|off>

Whether Phusion Passenger should automatically detect whether a virtual host's document root is a Ruby on Rails application. The default is on.

This option may occur in the global server configuration or in a virtual host configuration block.

For example, consider the following configuration:

RailsAutoDetect off
<VirtualHost *:80>
    ServerName www.mycook.com
    DocumentRoot /webapps/mycook/public
</VirtualHost>

If one goes to http://www.mycook.com/, the visitor will see the contents of the /webapps/mycook/public folder, instead of the output of the Ruby on Rails application.

It is possible to explicitly specify that the host is a Ruby on Rails application by using the RailsBaseURI configuration option:

RailsAutoDetect off
<VirtualHost *:80>
    ServerName www.mycook.com
    DocumentRoot /webapps/mycook/public
    RailsBaseURI /           # This line has been added.
</VirtualHost>

5.7.2. RailsBaseURI <uri>

Used to specify that the given URI is a Rails application. See Deploying Rails to a sub URI for an example.

This option may occur multiple times, in the global server configuration or in a virtual host configuration block.

5.7.3. RailsAllowModRewrite <on|off>

If enabled, Phusion Passenger will not override mod_rewrite rules. Please read Conflicting Apache modules for details.

This option may occur once, in the global server configuration or in a virtual host configuration block. The default value is off.

5.7.4. RailsEnv <string>

This option allows one to specify the default RAILS_ENV value.

This option may occur once, in the global server configuration or in a virtual host configuration block. The default value is production.

5.7.5. RailsSpawnMethod <string>

Tip
"What spawn method should I use?"

This subsection attempts to describe spawn methods, but it's okay if you don't (want to) understand it, as it's mostly a technical detail. You can basically follow this rule of thumb:

If your application works on Mongrel, but not on Phusion Passenger, then set RailsSpawnMethod to conservative. Otherwise, leave it at smart (the default).

However, we do recommend you to try to understand it. The smart spawn method brings many benefits.

Internally, Phusion Passenger spawns multiple Ruby on Rails processes in order to handle requests. But there are multiple ways with which processes can be spawned, each having its own set of pros and cons. Supported spawn methods are:

smart

When this spawn method is used, Phusion Passenger will attempt to cache Ruby on Rails framework code and application code for a limited period of time.

Pros: This can significantly decrease spawn time (by as much as 90%). And, when Ruby Enterprise Edition is used, memory usage can be reduced by 33% on average.

Cons: Some Ruby on Rails applications and libraries are not compatible with smart spawning. If that's the case for your application, then you should use conservative as spawning method.

conservative

This spawning method is similar to the one used in Mongrel Cluster. It does not perform any code caching at all.

Pros: Conservative spawning is guaranteed to be compatible with all applications and libraries.

Cons: Much slower than smart spawning. Every spawn action will be equally slow, though no slower than the startup time of a single server in Mongrel Cluster. Conservative spawning will also render Ruby Enterprise Edition's memory reduction technology useless.

This option may occur once, in the global server configuration or in a virtual host configuration block. The default value is smart.

5.8. Rack-specific options

5.8.1. RackAutoDetect <on|off>

Whether Phusion Passenger should automatically detect whether a virtual host's document root is a Rack application. The default is on.

This option may occur in the global server configuration or in a virtual host configuration block.

For example, consider the following configuration:

RackAutoDetect off
<VirtualHost *:80>
    ServerName www.rackapp.com
    DocumentRoot /webapps/my_rack_app/public
</VirtualHost>

If one goes to http://www.rackapp.com/, the visitor will see the contents of the /webapps/my_rack_app/public folder, instead of the output of the Rack application.

It is possible to explicitly specify that the host is a Rack application by using the RackBaseURI configuration option:

RackAutoDetect off
<VirtualHost *:80>
    ServerName www.rackapp.com
    DocumentRoot /webapps/my_rack_app/public
    RackBaseURI /       # This line was added
</VirtualHost>

5.8.2. RackBaseURI <uri>

Used to specify that the given URI is a Rack application. See Deploying Rack to a sub URI for an example.

5.8.3. RackEnv <string>

The given value will be accessible in Rack applications in the RACK_ENV environment variable. This allows one to define the environment in which Rack applications are run, very similar to RAILS_ENV.

This option may occur once, in the global server configuration or in a virtual host configuration block. The default value is production.

5.9. Deprecated options

The following options have been deprecated, but are still supported for backwards compatibility reasons.

5.9.1. RailsRuby

Deprecated in favor of PassengerRuby.

5.9.2. RailsUserSwitching

Deprecated in favor of PassengerUserSwitching.

5.9.3. RailsDefaultUser

Deprecated in favor of PassengerDefaultUser.

6. Troubleshooting

6.1. Operating system-specific problems

6.1.1. MacOS X: The installer cannot locate MAMP's Apache

Symptoms

The installer finds Apache 2 development headers at /Applications/MAMP/Library/bin/apxs. However, Apache cannot be found. The installer also outputs the following error:

cannot open /Applications/MAMP/Library/build/config_vars.mk:
No such file or directory at /Applications/MAMP/Library/bin/apxs line 218.

Your MAMP installation seems to be broken. In particular, config_vars.mk is missing. Please read this forum topic to learn how to fix this problem.

See also this bug report.

6.2. Problems during installation

6.2.1. Ruby development headers aren't installed

Symptoms

Installing Phusion Passenger fails because of one of the following errors:

  • The Phusion Passenger installer tells you that the Ruby development headers aren't installed.

  • The error message “no such file to load — mkmf” occurs.

  • The error message “ruby.h: No such file or directory” occurs.

Phusion Passenger makes use of a native extension, so the Ruby development headers must be installed. On most Linux systems, Ruby and the Ruby development headers are contained in separate packages, so having Ruby installed does not automatically imply having the development headers installed.

Here's how you can install the development headers:

Ubuntu/Debian

Please type: 

sudo apt-get install ruby1.8-dev
Fedora/CentOS/RHEL

Please type: 

su -c 'yum install ruby-devel'
FreeBSD

Please install Ruby from ports or with pkg_add. If that fails, please install Ruby from source.

MacOS X

Please install Ruby from source.

Other operating systems

Please consult your operating system's native package database. There should be a package containing the Ruby development headers. If that fails, please install Ruby from source.

Note If you've installed a new Ruby version (i.e. your system now contains multiple Ruby installations), then you will need to tell Phusion Passenger which Ruby installation you want to use. Please read Specifying the correct Ruby installation.

6.2.2. Apache development headers aren't installed

Symptoms

Installing Phusion Passenger fails because of one of the following errors:

  • The installer says that the Apache development headers aren't installed.

  • The error message “httpd.h: No such file or directory” occurs.

    (Instead of httpd.h, the message might also be http_config.h or something else similar to http_*.h.)

Ubuntu

Please type: 

sudo apt-get install apache2-prefork-dev
Debian

Please type: 

sudo apt-get install apache2-dev
Fedora/CentOS/RHEL

Please type: 

su -c 'yum install httpd-devel'
FreeBSD

Please install Apache from ports or with pkg_add. If that fails, please install Apache from source.

MacOS X

Please install Apache from source.

Other operating systems

Please consult your operating system's native package database. There should be a package containing the Apache development headers. If that fails, please install Apache from source.

6.2.3. APR development headers aren't installed

Symptoms

Installing Phusion Passenger fails because one of the following errors:

  • The installer tells you that APR development headers aren't installed.

  • The error message “apr_pools.h: No such file or directory” occurs.

  • The error message “apr_strings.h: No such file or directory” occurs.

Ubuntu

Please type: 

sudo apt-get install libapr1-dev
Debian

Please type: 

sudo apt-get install libapr1-dev
Fedora/CentOS/RHEL

Please type: 

su -c 'yum install apr-devel'
Other Linux distributions

Please consult your distribution's package database. There should be a package which provides APR development headers.

Other operating systems

The APR development are bundled with Apache. If the APR headers aren't, then it probably means that they have been removed after Apache's been installed. Please reinstall Apache to get back the APR headers.

6.2.4. Phusion Passenger is using the wrong Apache during installation

Please Specifying the correct Apache installation, and re-run the Phusion Passenger installer.

6.2.5. Phusion Passenger is using the wrong Ruby during installation

Please Specifying the correct Ruby installation, and re-run the Phusion Passenger installer.

6.3. Problems after installation

Tip
The golden tip: read your Apache error logs!

mod_passenger will write all errors to the Apache error log. So if you're experiencing post-installation problems, please look inside the Apache error logs. It will tell you what exactly went wrong.

6.3.1. My Rails application works on Mongrel, but not on Phusion Passenger

Please try setting RailsSpawnMethod to conservative.

6.3.2. Phusion Passenger has been compiled against the wrong Apache installation

Symptoms

Apache crashes during startup (after being daemonized). The Apache error log says “seg fault or similar nasty error detected in the parent process”.

This problem is most likely to occur on MacOS X. Most OS X users have multiple Apache installations on their system.

To solve this problem, please specify the correct Apache installation, and reinstall Phusion Passenger.

6.3.3. I get a "304 Forbidden" error

See next subsection.

6.3.4. Static assets such as images and stylesheets aren't being displayed

Static assets are accelerated, i.e. they are served directly by Apache and do not go through the Rails stack. There are two reasons why Apache doesn't serve static assets correctly:

  1. Your Apache configuration is too strict, and does not allow HTTP clients to access static assets. This can be achieved with an Allow from all directive in the correct place. For example: 

    <Directory "/webapps/mycook/public">
   Options FollowSymLinks
   AllowOverride None
   Order allow,deny
   Allow from all
</Directory>

    See also this discussion.

  2. The Apache process doesn't have permission to access your Rails application's folder. Please make sure that the Rails application's folder, as well as all of its parent folders, have the correct permissions and/or ownerships.

6.3.5. The Apache error log says that the spawn manager script does not exist, or that it does not have permission to execute it

If you are sure that the PassengerRoot configuration option is set correctly, then this problem is most likely caused by the fact that you're running Apache with SELinux. On Fedora, CentOS and RedHat Enterprise Linux, Apache is locked down by SELinux policies.

To solve this problem, you must set some permissions on the Phusion Passenger files and folders, so that Apache can access them.

Once the permissions are fixed, restart Apache.

6.3.6. The Rails application reports that it's unable to start because of a permission error

Please check whether your Rails application's folder has the correct permissions. By default, Rails applications are started as the owner of the file config/environment.rb, except if the file is owned by root. If the file is owned by root, then the Rails application will be started as nobody (or as the user specify by RailsDefaultUser, if that's specified).

Please read User switching (security) for details.

6.3.7. My Rails application's log file is not being written to

There are a couple things that you should be aware of:

If you're using a RedHat-derived Linux distribution (such as Fedora or CentOS) then it is possible that SELinux is interfering. RedHat's SELinux policy only allows Apache to read/write directories that have the httpd_sys_content_t security context. Please run the following command to give your Rails application folder that context:

chcon -R -h -t httpd_sys_content_t /path/to/your/rails/app

6.4. Conflicting Apache modules

6.4.1. mod_rewrite and mod_alias

Phusion Passenger conflicts with mod_rewrite and mod_alias. Those modules may be installed and loaded together with mod_passenger, and they will work fine outside virtual hosts that contain a Rails application, but we recommend you not to use their features inside virtual hosts that contain a Rails application.

By default, Phusion Passenger will override mod_rewrite rules on Rails hosts. This is because the default .htaccess, as provided by Ruby on Rails, redirects all requests to `dispatch.cgi' using mod_rewrite. This is a CGI application which loads the entire Ruby on Rails framework for every request, and thus is very slow. If we do not override mod_rewrite, then Ruby on Rails apps will be slow on Phusion Passenger by default — but we want a good out-of-the-box experience.

Furthermore, the primary reason why people use mod_rewrite with Rails applications, is to accelerate page caching. Phusion Passenger supports page caching out-of-the-box, without mod_rewrite.

It is not fully understood how mod_alias conflicts with Phusion Passenger, but we recommend you not to use it on Rails virtual hosts. mod_alias rules can result in surprising problems.

If you really want to use mod_rewrite on Rails virtual hosts, then please set the RailsAllowModRewrite configuration option. But please note that you will have to delete Rails applications' default .htaccess file, or add rewrite rules to negate its effects.

6.4.2. mod_userdir

mod_userdir is not compatible with Phusion Passenger at the moment.

6.4.3. VirtualDocumentRoot

VirtualDocumentRoot is not compatible with Phusion Passenger at the moment.

7. Analysis and system maintenance tools

Phusion Passenger provides a set of tools, which are useful for system analysis, maintenance and troubleshooting.

7.1. Inspecting memory usage

Process inspection tools such as ps and top are useful, but they rarely show the correct memory usage. The real memory usage is usually lower than what ps and top report.

There are many technical reasons why this is so, but an explanation is beyond the scope of this Users Guide. We kindly refer the interested reader to operating systems literature about virtual memory and copy-on-write.

The tool passenger-memory-stats allows one to easily analyze Phusion Passenger's and Apache's real memory usage. For example:

[bash@localhost root]# passenger-memory-stats
------------- Apache processes --------------.
PID    PPID  Threads  VMSize   Private  Name
---------------------------------------------.
5947   1     9        90.6 MB  0.5 MB   /usr/sbin/apache2 -k start
5948   5947  1        18.9 MB  0.7 MB   /usr/sbin/fcgi-pm -k start
6029   5947  1        42.7 MB  0.5 MB   /usr/sbin/apache2 -k start
6030   5947  1        42.7 MB  0.5 MB   /usr/sbin/apache2 -k start
6031   5947  1        42.5 MB  0.3 MB   /usr/sbin/apache2 -k start
6033   5947  1        42.5 MB  0.4 MB   /usr/sbin/apache2 -k start
6034   5947  1        50.5 MB  0.4 MB   /usr/sbin/apache2 -k start
23482  5947  1        82.6 MB  0.4 MB   /usr/sbin/apache2 -k start
### Processes: 8
### Total private dirty RSS: 3.50 MB

--------- Passenger processes ---------.
PID    Threads  VMSize   Private  Name
---------------------------------------.
6026   1        10.9 MB  4.7 MB   Passenger spawn server
23481  1        26.7 MB  3.0 MB   Passenger FrameworkSpawner: 2.0.2
23791  1        26.8 MB  2.9 MB   Passenger ApplicationSpawner: /var/www/projects/app1-foobar
23793  1        26.9 MB  17.1 MB  Rails: /var/www/projects/app1-foobar
### Processes: 4
### Total private dirty RSS: 27.76 M

The Private or private dirty RSS field shows the real memory usage of processes. Here, we see that all the Apache worker processes only take less than 1 MB memory each. This is a lot less than the 50 MB-ish memory usage as shown in the VMSize column (which is what a lot of people think is the real memory usage, but is actually not).

Note This tool only works on Linux. Unfortunately other operating systems don't provide facilities for determining processes' private dirty RSS.

7.2. Inspecting Phusion Passenger's internal status

One can inspect Phusion Passenger's internal status with the tool passenger-status. This tool must typically be run as root. For example:

[bash@localhost root]# passenger-status
----------- General information -----------
max      = 6
count    = 1
active   = 0
inactive = 1

----------- Applications -----------
/var/www/projects/app1-foobar:
  PID: 9617      Sessions: 0

The general information section shows the following information:

max The maximum number of application instances that Phusion Passenger will spawn. This equals the value given for PassengerMaxPoolSize.
count The number of application instances that are currently alive. This value is always less than or equal to max.
active The number of application instances that are currently processing requests. This value is always less than or equal to count.
inactive The number of application instances that are currently not processing requests, i.e. are idle. Idle application instances will be shutdown after a while, as can be specified with PassengerPoolIdleTime. The value of inactive equals count - active.

The applications section shows each application instance, which directory it belongs to. The sessions field shows how many HTTP client are currently being processed by that application instance.

Since Phusion Passenger uses fair load balancing by default, the number of sessions for the application instances should be fairly close to each other. For example, this is fairly normal:

  PID: 4281      Sessions: 2
  PID: 4268      Sessions: 0
  PID: 4265      Sessions: 1
  PID: 4275      Sessions: 1

But if you see a "spike", i.e. an application instance has an unusually high number of sessions compared to the others, then there might be a problem:

  PID: 4281      Sessions: 2
  PID: 17468     Sessions: 8     <---- "spike"
  PID: 4265      Sessions: 1
  PID: 4275      Sessions: 1

Possible reasons why spikes can occur:

  1. Your application is busy processing a request that takes a very long time.

  2. Your application is frozen, i.e. has stopped responding. See Debugging frozen applications for tips.

7.3. Debugging frozen applications

If one of your application instances is frozen (stopped responding), then you can figure out where it is frozen by killing it with SIGABRT. This will cause the application to raise an exception, with a backtrace.

The exception (with full backtrace information) is normally logged into the Apache error log. But if your application or if its web framework has its own exception logging routines, then exceptions might be logged into the application's log files instead. This is the case with Ruby on Rails. So if you kill a Ruby on Rails application with SIGABRT, please check the application's production.log first (assuming that you're running it in a production environment). If you don't see a backtrace there, check the Apache error log.

Note It is safe to kill application instances, even in live environments. Phusion Passenger will restart killed application instances, as if nothing bad happened.

8. Tips

8.1. User switching (security)

There is a problem that plagues most PHP web host, namely the fact that all PHP applications are run in the same user context as the web server. So for example, Joe's PHP application will be able to read Jane's PHP application's passwords. This is obviously undesirable on many servers.

Phusion Passenger solves this problem by implementing user switching. A Rails application is started as the owner of the file config/environment.rb, and a Rack application is started as the owner of the file config.ru. So if /home/webapps/foo/config/environment.rb is owned by joe, then Phusion Passenger will launch the corresponding Rails application as joe as well.

This behavior is the default, and you don't need to configure anything. But there are things that you should keep in mind:

User switching can be disabled with the PassengerUserSwitching option.

8.2. Reducing memory consumption of Ruby on Rails applications by 33%

Is it possible to reduce memory consumption of your Rails applications by 33% on average, by using Ruby Enterprise Edition. Please visit the website for details.

Note that this feature does not apply to Rack applications.

8.3. Capistrano recipe

Phusion Passenger can be combined with Capistrano. The following Capistrano recipe demonstrates Phusion Passenger support. It assumes that you're using Git as version control system.

set :application, "myapp"
set :domain,      "example.com"
set :repository,  "ssh://#{domain}/path-to-your-git-repo/#{application}.git"
set :use_sudo,    false
set :deploy_to,   "/path-to-your-web-app-directory/#{application}"
set :scm,         "git"

role :app, domain
role :web, domain
role :db,  domain, :primary => true

namespace :deploy do
  desc "Restart Application"
  task :restart, :roles => :app do
    run "touch #{current_path}/tmp/restart.txt"
  end
end
Note

You may notice that for each deploy, a new spawner server is created (it'll show up in passenger-memory-stats). Indeed, Capistrano will deploy to a path ending with /current (ie : /var/www/yourapp/current), so that you don't have to care about revisions in your virtual host configuration. This /current directory is a symlink to the current revision deployed (/path_to_app/releases/date_of_the_release). Therefore, when deploying a new version, the symlink will change, and Phusion Passenger will think it's a new application, thereby creating a new spawner server:

1001   30291   [...]   Passenger ApplicationSpawner: /var/www/my_app/releases/20080509104413
1001   31371   [...]   Passenger ApplicationSpawner: /var/www/my_app/releases/20080509104632

Don't worry about this. The (old) spawner server will terminate itself after its default timeout (10 minutes), so you will not run out of memory.

If you really want to release the spawner server's memory immediately, then you can add a command to your Capistrano script to terminate the Passenger spawn server after each deploy. That command is as follows:

kill $( passenger-memory-stats | grep 'Passenger spawn server' | awk '{ print $1 }' )

Killing the spawn server is completely safe, because Phusion Passenger will restart the spawn server if it has been terminated.

8.4. Moving Phusion Passenger to a different directory

It is possible to relocate the Phusion Passenger files to a different directory. It involves two steps:

  1. Moving the directory.

  2. Updating the “PassengerRoot” configuration option in Apache.

For example, if Phusion Passenger is located in /opt/passenger/, and you'd like to move it to /usr/local/passenger/, then do this:

  1. Run the following command: 

    mv /opt/passenger /usr/local/passenger

  2. Edit your Apache configuration file, and set: 

    PassengerRoot /usr/local/passenger

8.5. Installing multiple Ruby on Rails versions

Each Ruby on Rails applications that are going to be deployed may require a specific Ruby on Rails version. You can install a specific version with this command:

gem install rails -v X.X.X

where X.X.X is the version number of Ruby on Rails.

All of these versions will exist in parallel, and will not conflict with each other. Phusion Passenger will automatically make use of the correct version.

8.6. X-Sendfile support

Phusion Passenger does not provide X-Sendfile support by itself. Please install mod_xsendfile for X-Sendfile support.

9. Appendix A: About this document

The text of this document is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported License.

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Phusion Passenger is brought to you by Phusion.

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Phusion Passenger is a trademark of Hongli Lai & Ninh Bui.