GNU General Public License
The GNU General Public License is a series of GNU licenses which fits the The Free Software Definition. There are three major versions of the GNU GPL.
The Linux kernel is mostly licensed under the GNU GPL v2.
The GNU licenses give end-users the freedom to use, study, modify and distribute software as they please as long as they keep the same GNU license. There are some restrictions on commercial use in the GNU General Public License. The GNU Lesser General Public License has less restrictions.
The GNU General Public License says that you must release the source code if you modify and distribute a GNU GPL licensed program. This does not apply if you do not distribute a modified GNU GPL program, you can make changes and run the software on your own machine with no obligation to share your modifications. You can not put a binary based on GNU GPL codoe inside a hardware device like a router and sell it and refuse to release the source.
The full text of the GNU GPL licenses can be found at gnu.org/licenses/licenses.html:
- GNU General Public License, version 1
- GNU General Public License Version 2
- GNU General Public License Version 3
- GNU Lesser General Public License
- GNU Affero General Public License v3.0
