Section 2 of GPLv3 covers the fundamental permissions granted by the GPL to each recipient of the work. Here is the text of section 2 of GPLv3 in its entirety:
There is a lot going on here, and so we'll tackle each part in turn.
The GPL is irrevocable. This was understood to be true of GPLv2 and is now explicitly stated in GPLv3. If you license your work under the GPL and give someone a copy, you cannot later revoke the permissions the GPL grants them, as long as they remain in compliance. This is critical, and without this there would be a shadow cast over anyone using GPL'd software.
GPLv3 clearly states that running the unmodified software isn't
limited, restricted, or controlled by the GPL. If you are a
careful reader you may be thinking But what about running a modified version?
We'll come across the conditions for a modified version later
on.
The GPL licenses applied to the software doesn't affect the license of the output produced by the software unless there some other reason reason that would be the case. For example, playing music using a GPLv3-licensed music player doesn't affect the license of the music. Generally speaking: the license of what goes into a piece of software is the same as what comes out (there are exceptions, of course.) Parallel terms can be found in section 0 of GPLv2.
The GPL cannot and should not restrict the rights of copyright fair use.
This part clarifies that you may make in house
, or internal, copies of a work and run those copies
freely. However, the rights to internal propagation and
modifications are only in effect as long as your rights have not
been termination (see section 8). Your rights to modify the
program, even privately, can be curtailed if your rights under
the GPL have been terminated by a violation of the license.
GPL affrims your freedom to develop and run a work privately, and this extends this freedom to include working privately with contractors and their like. This means that you can hire a contractor to do private development work, under the terms of the GPL, just as long as you are the sole copyright holder of the work in question. Morevoer, it makes clear that those contractors can give copies to subcontractors, data-centers, etc. to do the work on your behalf under those terms.
GPLv3 now moves out of the realm of private running and modification and into the realm of distributing copies to the world at large.
The note about sublicensing may be obtuse to the casual reader and so warrants a bit more explanation: if you get some work with a non-GPL license which grants you rights A, B, and C, and you then further distribute that work but only grant the recipient rights A, and B, then you've sublicensed the work. The license you gave is lesser, sub (literally meaning beneath), than the one you received. But the GPL doesn't work like that. When you receive a work under GPLv3 then under section 10 you automatically receive all of the rights granted in the license. Similarly, when you further distribute that work, then once again under section 10 the recipient receives all of the rights you did. Every licensor gets the same rights; no sublicensing.