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Phusion Passenger 4.0.1 final release

By Hongli Lai on May 6th, 2013

Phusion Passenger 4

Phusion Passenger is software that deploys Ruby and Python web apps, by integrating into Apache and Nginx and turning them into a fully-featured application server. It is very fast, stable and robust and thus used by the likes of New York Times, AirBnB, Symantec, Pixar, etc. It comes with many features that makes your life easier and your application perform better.

After a period of being in beta, we’re proud to announce the first stable release of the Phusion Passenger 4 series. The 4.x series is a huge improvement over the 3.x series: during the development of 4.0, we’ve introduced a myriad of changes which we’ve covered in past beta preview articles:

The beta period took a while because we wanted to ensure that the first stable release is indeed rock solid. People tend to say that one should skip “x.0.0” releases and wait until “x.0.1” for the first bug fixes. But we’re confident enough about the stability of the 4.x series that we gave this first release the version number 4.0.1.

Changes in 4.0.1

Compared to 4.0.0 RC 6, the following changes have been introduced:

  • Fixed a crasher bug in the Deployment Error Resistance feature.
  • Fixed a bug in PassengerDefaultUser and PassengerDefaultGroup.
  • Fixed a bug which could cause application processes to exit before they’ve finished their request.
  • Fixed some small file descriptor leaks.
  • Bumped the preferred Nginx version to 1.4.0.
  • Editing the Phusion Passenger Standalone Nginx config template is no longer discouraged.
  • Improved documentation.

Installing and testing 4.0.1

Quick install/upgrade

Phusion Passenger Enterprise users can download the Enterprise version of 4.0.1 from the Customer Area.

Open source users can install the open source version of 4.0.1 with the following commands:

gem install passenger

You can also download the tarball at Google Code. All our gems and tarballs can be cryptographically verified.

In-depth instructions

In-depth installation and upgrade instructions can be found in the Installation section of the documentation. The documentation has been updated to cover 4.0 changes, including Enterprise features. You can view them online here:


We would like to thank everybody who has helped with testing the betas and release candidates so far, and we would like to thank our Enterprise customers. We couldn’t have done it without you!

4.0.1 is just the beginning though. We have many excited changes on the pipeline. Want to stay up to date? Fill in your name and email address below and sign up for our newsletter. We won’t spam you, we promise.

  • thanks for your hard work. a cpanel integration plugin for passenger would disrupt the web industry like nothing else!

  • Awesome!!!!

    Keep rocking guys…

  • 大双 李


  • This is great news, the OOB GC is going to shave 20-30% off of all our actions.

    Question, though: since we’ve upgraded (we’re on Enterprise 4.0.1) the PassengerSpawnServer process from 3.x is no longer present, and the rack-preloader that now appears to start our Passenger processes is only loading 1-2 processes at a time, then it dies, starts again and has to reload the entire environment (~50s) just to generate 1 more Passenger process.

    Previously SpawnServer would stay in memory and spit out as many processes as necessary instantaneously. With this new method, it takes several minutes for our servers to start or restart.

    I have tried explicitly setting the spawn method to “smart” and still seeing this problem. Any ideas?

  • Rack-preloader fulfills the same tasks as the old spawn-server/ApplicationSpawner. Can you send more details to For example we would like to know what you mean by “then it dies, starts again”. Any error messages and stack traces would help.

  • Eason

    Awesome! Thank you so much for your team’s dedication!

  • dexter

    web hosting, dedicated servers, web development