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Table of Contents

Introduction to the Hurd

The GNU Hurd is the GNU project's replacement for the Unix kernel. The Hurd is a collection of servers that run on the Mach microkernel to implement file systems, network protocols, file access control, and other features that are implemented by the Unix kernel or similar kernels (such as Linux).

Currently, the Hurd runs on IA32 machines. The Hurd should, and probably will, be ported to other hardware architectures or other microkernels in the future.

Advantages of the Hurd

The Hurd is not the most advanced kernel known to the planet (yet), but it does have a number of enticing features:
it's free software
Anybody can use, modify, and redistribute it under the terms of the GNU General Public License (GPL).
it's compatible
The Hurd provides a familiar programming and user environment. For all intents and purposes, the Hurd is a modern Unix-like kernel. The Hurd uses the GNU C Library, whose development closely tracks standards such as ANSI/ISO, BSD, POSIX, Single Unix, SVID, and X/Open.
it's built to survive
Unlike other popular kernel software, the Hurd has an object-oriented structure that allows it to evolve without compromising its design. This structure will help the Hurd undergo major redesign and modifications without having to be entirely rewritten.
it's scalable
The Hurd implementation is aggressively multithreaded so that it runs efficiently on both single processors and symmetric multiprocessors. The Hurd interfaces are designed to allow transparent network clusters (collectives), although this feature has not yet been implemented.
it's extensible
The Hurd is an attractive platform for learning how to become a kernel hacker or for implementing new ideas in kernel technology. Every part of the system is designed to be modified and extended.
it's stable
It is possible to develop and test new Hurd kernel components without rebooting the machine (not even accidentally). Running your own kernel components doesn't interfere with other users, and so no special system privileges are required. The mechanism for kernel extensions is secure by design: it is impossible to impose your changes upon other users unless they authorize them or you are the system administrator.
it exists
The Hurd is real software that works Right Now. It is not a research project or a proposal. You don't have to wait at all before you can start using and developing it.

What the Hurd means

According to Thomas Bushnell, BSG, the primary architect of the Hurd:
`Hurd' stands for `Hird of Unix-Replacing Daemons'. And, then, `Hird' stands for `Hurd of Interfaces Representing Depth'. We have here, to my knowledge, the first software to be named by a pair of mutually recursive acronyms.

Status of the project

The Hurd, together with the GNU Mach microkernel, the GNU C Library and the other GNU and non-GNU programs in the GNU system, provide a rather complete and usable operating system today. It is not ready for production use, as there are still many bugs and missing features. However, it should be a good base for further development and non-critical application usage.

The GNU system (also called GNU/Hurd) is completely self-contained (you can compile all parts of it using GNU itself). You can run several instances of the Hurd in parallel, and debug even critical servers in one Hurd instance with gdb running on another Hurd instance. You can run the X window system, applications that use it, and advanced server applications like the Apache webserver.

On the negative side, the support for character devices (like sound cards) and other hardware is mostly missing. Although the POSIX interface is provided, some additional interfaces like POSIX shared memory or semaphores are still under development.

All this applies to the current development version, and not to the last release (0.2). We encourage everybody who is interested to try out the latest development version, and send feedback to the Hurd developers.

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Updated: $Date: 2005/10/02 11:27:11 $ $Author: ams $