Free Penguin Download - Linux Kernel
Kernel Linux 3.0.4
Stable Version:
3.0.4 - Source
2.6.39.4 - Source
2.6.38.8 - Source
Long term: 2.6.35.14 - Source
The Linux kernel is a Unix-like operating system kernel.
It is the namesake of the Linux family of operating systems.
Released under the GNU General Public License version and developed by contributors worldwide,
Linux is one of the most prominent examples of free software. The Linux Kernel was initially conceived and assembled
by Linus Torvalds in 1991. Early on, the Minix community contributed code and ideas to the Linux kernel.
At the time, the GNU Project had created many of the components required for a free software operating system, but its own kernel,
GNU Hurd was incomplete and unavailable.
The BSD operating system had not yet freed itself from legal encumbrances.
This meant that despite the limited functionality of the early versions, Linux rapidly accumulated developers and users who adopted code from those projects for use with the new operating system.
Today the Linux kernel has received contributions
from thousands of programmers. It is debated whether Loadable Kernel Modules (LKMs) should be considered derivative works under copyright law, and thereby fall
under the terms of the GPL.
Torvalds has stated his belief that LKMs using only a limited, "public" subset of the kernel interfaces can sometimes be non-derived works, thus allowing some binary-only drivers and other LKMs that are not licensed under the GPL.Not all Linux contributors agree with this interpretation, however, and even Torvalds agrees that many LKMs are clearly derived works, and indeed he writes that "kernel modules ARE derivative 'by default'".
On the other hand Torvalds has also said that "one gray area in particular is something like a driver that was originally written for another operating system (ie. clearly not a derived work of Linux in origin).
That is a gray area, and _that_ is the area where I personally believe that some modules may be considered to not be derived works simply because they weren't designed for Linux and don't depend on any special Linux behaviour."
Especially proprietary graphics drivers are heavily discussed.
Ultimately, such questions can most likely only be resolved by a court. One point of licensing controversy is Linux's use of firmware "binary blobs" to support some hardware devices.
Richard Stallman claims that these blobs make Linux partially non-free software, and that distributing Linux may even be violating the GPL (which requires "complete corresponding source code" to be available). Linux supports true preemptive multitasking (both in user mode and kernel mode), virtual memory, shared libraries, demand loading, shared copy-on-write executables, memory management, the Internet protocol suite, and threading. Linux is a monolithic kernel.
Device drivers and kernel extensions run in kernel space (ring 0), with full access to the hardware, although some exceptions run in user space.
Unlike Microsoft Windows, the graphics system most people
use with Linux doesn't run in the kernel. Kernel mode preemption allows device drivers to be preempted under certain conditions.
This feature was added to handle hardware interrupts correctly and improve support for symmetric multiprocessing (SMP).
Preemption also improves latency, increasing responsiveness and making Linux more suitable for real-time applications. The fact that Linux is a monolithic kernel rather than a microkernel was the topic of the Tanenbaum-Torvalds debate
between Andrew S. Tanenbaum and Linus Torvalds.
The debate started in 1992 about Linux and kernel architecture in general on the Usenet discussion group comp.os.minix.
Tanenbaum argued that microkernels are superior to monolithic kernels and that therefore Linux is obsolete. Unlike traditional monolithic kernels, device drivers are easily configured as Loadable Kernel Modules, and loaded or unloaded while running the system.
This subject was revisited on 9 May 2006, and on 12 May 2006
Tanenbaum authored a position statement.