The Common UNIX Printing System™, ("CUPS™"), is provided under the GNU General Public License ("GPL ") and GNU Library General Public License ("LGPL "), Version 2, with exceptions for Apple operating systems and the OpenSSL toolkit. A copy of the exceptions and licenses follow this introduction.
The GNU LGPL applies to the CUPS API library, located in the "cups" subdirectory of the CUPS source distribution and in the "cups" include directory and library files in the binary distributions. The GNU GPL applies to the remainder of the CUPS distribution, including the "pdftops" filter which is based upon Xpdf and the CUPS imaging library.
For those not familiar with the GNU GPL, the license basically allows you to:
Use the CUPS software at no charge.
Distribute verbatim copies of the software in source or binary form.
Sell verbatim copies of the software for a media fee, or sell support for the software.
Distribute or sell printer drivers and filters that use CUPS so long as source code is made available under the GPL.
What this license *does not* allow you to do is make changes or add features to CUPS and then sell a binary distribution without source code. You must provide source for any new drivers, changes, or additions to the software, and all code must be provided under the GPL or LGPL as appropriate. The only exceptions to this are the portions of the CUPS software covered by the Apple operating system license exceptions outlined later in this license agreement.
The GNU LGPL relaxes the "link-to" restriction, allowing you to develop applications that use the CUPS API library under other licenses and/or conditions as appropriate for your application.