What does the GNU general public license require software developers to do when modifying Linux versions?

Answer 1

GNU doesn't regulate anything.

The GPL, on the other hand, requires that if you redistribute Linux with your modifications, that you make the source code of your modifications available as well.

Keep in mind this only applied to DISTRIBUTION. In-house/personal-use stuff you are literally unrestricted and can even keep modifications to yourself.

To make this a little less confusing, consider this:

1. Distributor X makes Y modification to Linux.

2. X sends out Linux with Y modification and has to make Y available openly without restriction.

3. End user Z gets Linux with Y.

4. Z modifies Linux with Y with further modification W.

5. Because Z is not sharing Linux with modifications Y and W, he doesn't have to share W at all.

A more real world example:

1. nVidia makes an excellent proprietary driver for their video cards on Linux.

2. Because the driver is proprietary, this driver cannot be included with the kernel tree itself.

3. Instead, the end user typically has Linux installed with a kernel and has to download and install the driver themselves, typically over their distribution's repositories.

There used to be a debate about whether this driver violates the GPL anyway over "derived works" clauses, though even the FSF (Responsible for the GPL and its terms.) has pretty much held there is no such violation.

Further, the GPL, being a license and not a law, cannot take away the rights of the OWNER of the copyright. If I am the sole owner of code I have licensed under the GPL, the GPL can't stop me at all from relicensing the whole shebang under a proprietary commercial license. Some companies, such as Canonical, even have "copyright reassignment" agreements with contributors that legally transfers copyright from the modder to Canonical and it won't violate the GPL, however a lot of people find this shady and against the spirit of free software.

Still, because of this, if you're sole copyright holder and want to include proprietary code with your work, you won't be able to use the GPL without violating it, though technically a copyright holder cannot violate their own copyright. I am unsure if the GPL can stop a copyright holder from including proprietary software of their own creation directly into GPL code of their own creation, but it would definitely stop anyone else from redistributing the whole package themselves unless they remove the proprietary parts.