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While browsing this site Text Files/Programming which contains historical data pertaining to programming and a lot of other stuff I came across this file Info sheet Linux

The file in question has a peculier paragraph with the following contents:

Although Linux is supplied with the complete source code, it is copyrighted software, not public domain. However, it is available for free under the GNU Public License. See the GPL for more information. The programs that run under Linux have each their own copyright, although much of it uses the GPL as well. All of the software on the FTP site is freely distributable (or else it shouldn't be there)

It says although Linux is available for free, but still its source code is copyrighted "not public domain"

What does it mean by saying that its copyrighted by still available for free, the file specifically says that the source is not under public domain, so is it against the law to modify linux kernel?

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  • Important distinction, copyright can give over 100 years of protection, whereas a patent generally 20. Even in the absence of GPL conditions you must attribute authorship. GPL conditions impose futther onerous conditions upon distributing the content, but you can modify it without passing it on. – mckenzm Sep 9 '16 at 2:56
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Copyrighted means there is a copyright and license protecting that. The license in the case of the Linux kernel is GPL (http://www.gnu.org/copyleft/gpl.html).

In a nutshell, you are allowed to modify the code in any way you wish. However, if you distribute your modified code, you have to license it GPL and keep the credit to the original authors. Also, if you distribute compiled versions of the modified source, you have to distribute that modified source code.

The kernel's license is a so called "copyleft", you do what you want but you have to let others do the same to your modifications.

PS: this is a very simple explanation, for more information and details see the above link.

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  • But then why does it say its not in "public domain" – Kartik Anand Jul 15 '12 at 14:04
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    @Kartik: public domain has a very specific (legal) meaning in some places, that is essentially "do whatever you want whichever way you want". GPL is more restrictive than that. – Mat Jul 15 '12 at 14:13
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    @Shawn J. Goff: I would appreciate if you edit my answer you do not add things I did not wrote. I understand and I agree with editors fixing issues with posts (like typos, wrong formatting, etc), but I consider it would be much better if you comment to add the extra information instead of putting in my answer as I wrote it. Thanks. – Patkos Csaba Jul 15 '12 at 15:11
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    @PatkosCsaba Editing is encouraged on this site. If you believe it is better without it, you are free to change it. It is best if the answer contains the important relevant information - not when the information is distributed in the comments, as those are less frequently read. – Shawn J. Goff Jul 15 '12 at 16:00
  • And additional link about Public Domain software: en.wikipedia.org/wiki/Public-domain_software (no OS inside) – Quora Feans Feb 5 at 17:45

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