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= unicorn: Rack HTTP server for fast clients and Unix
unicorn is an HTTP server for Rack applications designed to only serve
fast clients on low-latency, high-bandwidth connections and take
advantage of features in Unix/Unix-like kernels. Slow clients should
only be served by placing a reverse proxy capable of fully buffering
both the the request and response in between unicorn and slow clients.
== Features
* Designed for Rack, Unix, fast clients, and ease-of-debugging. We
cut out everything that is better supported by the operating system,
{nginx}[] or {Rack}[].
* Compatible with Ruby 1.9.3 and later.
unicorn 4.x remains supported for Ruby 1.8 users.
* Process management: unicorn will reap and restart workers that
die from broken apps. There is no need to manage multiple processes
or ports yourself. unicorn can spawn and manage any number of
worker processes you choose to scale to your backend.
* Load balancing is done entirely by the operating system kernel.
Requests never pile up behind a busy worker process.
* Does not care if your application is thread-safe or not, workers
all run within their own isolated address space and only serve one
client at a time for maximum robustness.
* Builtin reopening of all log files in your application via
USR1 signal. This allows logrotate to rotate files atomically and
quickly via rename instead of the racy and slow copytruncate method.
unicorn also takes steps to ensure multi-line log entries from one
request all stay within the same file.
* nginx-style binary upgrades without losing connections.
You can upgrade unicorn, your entire application, libraries
and even your Ruby interpreter without dropping clients.
* before_fork and after_fork hooks in case your application
has special needs when dealing with forked processes. These
should not be needed when the "preload_app" directive is
false (the default).
* Can be used with copy-on-write-friendly memory management
to save memory (by setting "preload_app" to true).
* Able to listen on multiple interfaces including UNIX sockets,
each worker process can also bind to a private port via the
after_fork hook for easy debugging.
* Simple and easy Ruby DSL for configuration.
* Decodes chunked requests on-the-fly.
== License
unicorn is copyright 2009-2016 by all contributors (see logs in git).
It is based on Mongrel 1.1.5.
Mongrel is copyright 2007 Zed A. Shaw and contributors.
unicorn is licensed under (your choice) of the GPLv2 or later
(GPLv3+ preferred), or Ruby (1.8)-specific terms.
See the included LICENSE file for details.
unicorn is 100% Free Software (including all development tools used).
== Install
The library consists of a C extension so you'll need a C compiler
and Ruby development libraries/headers.
You may install it via RubyGems on
gem install unicorn
You can get the latest source via git from the following locations
(these versions may not be stable):
git:// (mirror)
You may browse the code from the web:
* (gitweb)
See the HACKING guide on how to contribute and build prerelease gems
from git.
== Usage
=== Rack (including Rails 3+) applications
In APP_ROOT, run:
unicorn will bind to all interfaces on TCP port 8080 by default.
You may use the +--listen/-l+ switch to bind to a different
address:port or a UNIX socket.
=== Configuration File(s)
unicorn will look for the file used by rackup in APP_ROOT.
For deployments, it can use a config file for unicorn-specific options
specified by the +--config-file/-c+ command-line switch. See
Unicorn::Configurator for the syntax of the unicorn-specific options.
The default settings are designed for maximum out-of-the-box
compatibility with existing applications.
Most command-line options for other Rack applications (above) are also
supported. Run `unicorn -h` to see command-line options.
== Disclaimer
There is NO WARRANTY whatsoever if anything goes wrong, but
{let us know}[link:ISSUES.html] and we'll try our best to fix it.
unicorn is designed to only serve fast clients either on the local host
or a fast LAN. See the PHILOSOPHY and DESIGN documents for more details
regarding this.
== Contact
All feedback (bug reports, user/development dicussion, patches, pull
requests) go to the mailing list/newsgroup. See the ISSUES document for
information on the {mailing list}[].
The mailing list is archived at
Read-only NNTP access is available at:
nntp:// and
For the latest on unicorn releases, you may also finger us at or check our NEWS page (and subscribe to our Atom