Looking to learn more about "EXCEPTIONS" -- gnu style

Tom Hull thull at sco.com
Wed Mar 8 17:22:25 UTC 2000

David Johnson wrote:
> I still wonder why the Linux kernel is GPL+exception, instead of being LGPL.
> Can anyone shed light on this? Was the LGPL available when Linux was put under
> the GPL?

Since GPL extends coverage to whole works, Linux uses the GPL to
ensure that all kernel drivers/modules are GPL-clean. It is a big
advantage for Linux to have all of the drivers and modules in
source form. Had LGPL been used, it would be possible for someone
to build a new non-free kernel using some/all of the Linux kernel
as subroutines.

Note that the exception does not extend to kernel modules, even
though they could be considered "normal use", given that they work
through defined interfaces. The exact wording is "user programs
that use kernel services by normal system calls".

> According to Linus from an interview, the exception is there so
> that programs can make kernel calls without falling under the GPL. Without it,
> one could argue that *every* program running under Linux would be a derivative
> of the kernel and thus have to be GPLd. This would have killed Linux before it
> got a foot off of the ground.

If every user level program had to be GPL in order to run on Linux,
that would either preclude use of or require relicensing of all
sorts of important pieces, including glibc and xfree86. Glibc is
especially interesting, in that almost all user programs access
the kernel through it.

 * Tom Hull -- thull at sco.com * http://www.ocston.org/~thull

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