Linux Licenses

GNU General Public License

General “Four Freedoms”:
0. The freedom to run the program, for any purpose.

The freedom to study how the program works, and modify it so it does your computing as you wish.
The freedom to redistribute copies so you can help your others.
The freedom to distribute copies of your modified versions to others.

Condition

GNU is a recursive acronym: "GNU's Not Unix!"

GPL a copyleft license:
→ Changes have to be released under the same license
Programs linked with a library released under the GPL must also be released under the GPL

Linux Kernel sources are Free Software released under the GNU General Public License version 2 (GPLv2).

When you receive or buy a device with Linux on it, you must
→ receive the Linux sources, with the
→ right to study, modify and redistribute them.
When you produce Linux based devices, you must
→ release the sources to the recipient, with the same rights, with no restriction.

Providing source code?

If software isn't distributed -> no need to provide source code
=> Modification can be kept secret until delivery
If software is distributed -> following options:
- Release binary with
  a) copy of the source on a physical medium
  b) with the network address of a location pointing to source code
  c) with a written offer valid for 3 years that indicates how to fetch the source code

If you don’t want to provide Source Code, compile with LGPL (Lesser GPL)

LGPL also a copyleft license:
→ Changes have to be released under the same license

Programs linked against a library under the LGPL do not need to be released under the LGPL and can be kept proprietary.

User must keep the ability to update the library independently from the program.
→ Dynamic linking is the easiest solution.

MODULE_LICENSE: If this macro is not set to some sort of GPL license tag, then the kernel will become “tainted” when you load your module.

Tainted Status

G: All modules loaded were licensed under the GPL or a license compatible with the GPL.
P: The kernel has a proprietary license loaded. (Module or Kernel)

Decode tainted level on Bitlevel:

for i in $(seq 18); do echo $(($i-1)) $(($(cat /proc/sys/kernel/tainted)>>($i-1)&1));done

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MIT and BSD:
Common for both: “Permitted to do whatever the user wants without any legal obligation to the owner.”

In addition, the MIT license also explicitly allows:

Development of the Netscape Public License which was created with the publication of the Netscape source code in 1998.
Copyleft license: It grants liberal copyright and patent licenses allowing for free use, modification, distribution, and exploitation of the work
Modifications of MPL code must again be MPL