# About Cygwin

What is it?

Cygwin is a distribution of popular GNU and other Open Source tools running on Microsoft Windows. The core part is the Cygwin library which provides the POSIX system calls and environment these programs expect.

The Cygwin distribution contains thousands of packages from the Open Source world including most GNU tools, many BSD tools, an X server and a full set of X applications. If you're a developer you will find tools, headers and libraries allowing to write Windows console or GUI applications that make use of significant parts of the POSIX API. Cygwin allows easy porting of many Unix programs without the need for extensive changes to the source code. This includes configuring and building most of the available GNU or BSD software, including the packages included with the Cygwin distribution themselves. They can be used from one of the provided Unix shells like bash, tcsh or zsh.

What versions of Windows are supported?

Cygwin can be expected to run on all modern, released versions of Windows. State January 2015 this includes Windows XP SP3, Windows Server 2003/2003R2 and all later versions of Windows up to Windows 8.1 and Windows Server 2012R2. The 32 bit version of Cygwin also runs in the WOW64 32 bit environment on released 64 bit versions of Windows (XP SP3 up to 8.1/2012R2), the 64 bit version of course only on 64 bit Windows.

Keep in mind that Cygwin can only do as much as the underlying OS supports. Because of this, Cygwin will behave differently, and exhibit different limitations, on the various versions of Windows.

Where can I get it?

The home page for the Cygwin project is . There you should find everything you need for Cygwin, including links for download and setup, a current list of mirror sites, a User's Guide, an API Reference, mailing lists and archives.

You can find documentation for the individual GNU tools typically as man pages or info pages as part of the Cygwin net distribution. Additionally you can get the latest docs at . (You should read GNU manuals from a local mirror. Check for a list of them.)

Is it free software?

Yes. Parts are GNU software (gcc, gas, ld, etc...), parts are covered by the standard X11 license, some of it is public domain, some of it was written by Red Hat (or the former Cygnus Solutions) and placed under the GPL. None of it is shareware. You don't have to pay anyone to use it but you should be sure to read the copyright section of the FAQ for more information on how the GNU General Public License may affect your use of these tools.

In particular, if you intend to port a proprietary (non-GPL'd) application using Cygwin, you will need the proprietary-use license for the Cygwin library. This is available for purchase from Red Hat; please visit for more information. All other questions should be sent to the public project mailing list cygwin@cygwin.com.

Note that when we say "free" we mean freedom, not price. The goal of such freedom is that the people who use a given piece of software should be able to change it to fit their needs, learn from it, share it with their friends, etc. The Cygwin license allows you those freedoms, so it is free software.

What version of Cygwin is this, anyway?

To find the version of the Cygwin DLL installed, you can use `uname` as on Linux or `cygcheck`. Refer to each command's `--help` output and the Cygwin User's Guide for more information.

If you are looking for the version number for the whole Cygwin release, there is none. Each package in the Cygwin release has its own version. The packages in Cygwin are continually improving, thanks to the efforts of net volunteers who maintain the Cygwin binary ports. Each package has its own version numbers and its own release process.

So, how do you get the most up-to-date version of Cygwin? Easy. Just download the Cygwin Setup program by following the instructions here. The setup program will handle the task of updating the packages on your system to the latest version. For more information about using Cygwin's `setup.exe`, see Setting Up Cygwin in the Cygwin User's Guide.

Who's behind the project?

(Please note that if you have cygwin-specific questions, all of these people will appreciate it if you use the cygwin mailing lists rather than sending personal email.)

Corinna Vinschen is the current project lead. Corinna is a senior Red Hat engineer. Corinna is responsible for the Cygwin library and maintains a couple of packages, for instance OpenSSH, OpenSSL, and a lot more.

Yaakov Selkowitz is another Red Hat engineer working on the Cygwin project. He's the guy behind the current build and packaging system and maintains by far the most packages in the Cygwin distribution.

Jon Turney is developer and maintainer of the Cygwin X server and a couple of related packages.

The packages in the Net release are maintained by a large group of people; a complete list can be found here.

Please note that all of us working on Cygwin try to be as responsive as possible and deal with patches and questions as we get them, but realistically we don't have time to answer all of the email that is sent to the main mailing list. Making Net releases of the Win32 tools and helping people on the Net out is not our primary job function, so some email will have to go unanswered.

Many thanks to everyone using the tools for their many contributions in the form of advice, bug reports, and code fixes. Keep them coming!