busybox/docs/busybox.net/license.html

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<p>
<h3>BusyBox is licensed under the GNU General Public License, version 2</h3>

<p>BusyBox is licensed under <a href="http://www.gnu.org/licenses/gpl.html#SEC1">the
GNU General Public License</a> version 2, which is often abbreviated as GPLv2.
(This is the same license the Linux kernel is under, so you may be somewhat
familiar with it by now.)</p>

<p>A complete copy of the license text is included in the file LICENSE in
the BusyBox source code.</p>

<p><a href="/products.html">Anyone thinking of shipping BusyBox as part of a
product</a> should be familiar with the licensing terms under which they are
allowed to use and distribute BusyBox.  Read the full test of the GPL (either
through the above link, or in the file LICENSE in the busybox tarball), and
also read the <a href="http://www.gnu.org/licenses/gpl-faq.html">Frequently
Asked Questions about the GPL</a>.</p>

<p>Basically, if you distribute GPL software the license requires that you also
distribute the source code to that GPL-licensed software.  So if you distribute
BusyBox without making the source code to the version you distribute available,
you violate the license terms, and thus infringe on the copyrights of BusyBox.
(This requirement applies whether or not you modified BusyBox; either way the
license terms still apply to you.)  Read the license text for the details.</p>

<h3>A note on GPL versions</h3>

<p>Version 2 of the GPL is the only version of the GPL which current versions
of BusyBox may be distributed under.  New code added to the tree is licensed
GPL version 2, and the project's license is GPL version 2.</p>

<p>Older versions of BusyBox (versions 1.2.2 and earlier, up through about svn
16112) included variants of the recommended "GPL version 2 or (at your option)
later versions" boilerplate permission grant.  Ancient versions of BusyBox
(before svn 49) did not specify any version at all, and section 9 of GPLv2
(the most recent version at the time) says those old versions may be
redistributed under any version of GPL (including the obsolete V1).  This was
conceptually similar to a dual license, except that the different licenses were
different versions of the GPL.</p>

<p>However, BusyBox has apparently always contained chunks of code that were
licensed under GPL version 2 only.  Examples include applets written by Linus
Torvalds (util-linux/mkfs_minix.c and util_linux/mkswap.c) which stated they
"may be redistributed as per the Linux copyright" (which Linus clarified in the
2.4.0-pre8 release announcement in 2000 was GPLv2 only), and Linux kernel code
copied into libbb/loop.c (after Linus's announcement).  There are probably
more, because all we used to check was that the code was GPL, not which
version.  (Before the GPLv3 draft proceedings in 2006, it was a purely
theoretical issue that didn't come up much.)</p>

<p>To summarize: every version of BusyBox may be distributed under the terms of
GPL version 2.  New versions (after 1.2.2) may <b>only</b> be distributed under
GPLv2, not under other versions of the GPL.  Older versions of BusyBox might
(or might not) be distributable under other versions of the GPL.  If you
want to use a GPL version other than 2, you should start with one of the old
versions such as release 1.2.2 or SVN 16112, and do your own homework to
identify and remove any code that can't be licensed under the GPL version you
want to use.  New development is all GPLv2.</p>

<h3>License enforcement</h3>

<p>BusyBox's copyrights are enforced by the <a
href="http://www.softwarefreedom.org">Software Freedom Law Center</a>
(you can contact them at gpl@busybox.net), which
"accepts primary responsibility for enforcement of US copyrights on the
software... and coordinates international copyright enforcement efforts for
such works as necessary."  If you distribute BusyBox in a way that doesn't
comply with the terms of the license BusyBox is distributed under, expect to
hear from these guys.  Their entire reason for existing is to do pro-bono
legal work for free/open source software projects.  (We used to list people who
violate the BusyBox license in <a href="/shame.html">The Hall of Shame</a>,
but these days we find it much more effective to hand them over to the
lawyers.)</p>

<p>Our enforcement efforts are aimed at bringing people into compliance with
the BusyBox license.  Open source software is under a different license from
proprietary software, but if you violate that license you're still a software
pirate and the law gives the vendor (us) some big sticks to play with.  We
don't want monetary awards, injunctions, or to generate bad PR for a company,
unless that's the only way to get somebody that repeatedly ignores us to comply
with the license on our code.</p>

<h3>A Good Example</h3>

<p>These days, <a href="http://www.linksys.com/">Linksys</a> is
doing a good job at complying with the GPL, they get to be an
example of how to do things right.  Please take a moment and
check out what they do with
<a href="http://www.linksys.com/servlet/Satellite?c=L_Content_C1&childpagename=US%2FLayout&cid=1115416836002&pagename=Linksys%2FCommon%2FVisitorWrapper">
distributing the firmware for their WRT54G Router.</a>
Following their example would be a fine way to ensure that you
have also fulfilled your licensing obligations.</p>

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