@dircategory Kernel * Hurd: (hurd). Using and programming the Hurd kernel servers.
Copyright (C) 1994--1998 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.
Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.
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The GNU Hurd(1) 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 normally implemented by the Unix kernel or similar kernels (such as Linux).
This manual is designed to be useful to everybody who is interested in using, administering, or programming the Hurd.
If you are an end-user and you are looking for help on running the Hurd, the first few chapters of this manual describe the essential parts of installing, starting up, and shutting down a Hurd workstation. If you need help with a specific program, the best way to use this manual is to find the program's name in the index and go directly to the appropriate section. You may also wish to try running program --help, which will display a brief usage message for program (see section Foundations).
The rest of this manual is a technical discussion of the Hurd servers and their implementation, and would not be helpful until you want to learn how to modify the Hurd.
This manual is organized according to the subsystems of the Hurd, and each chapter begins with descriptions of utilities and servers that are related to that subsystem. If you are a system administrator, and you want to learn more about, say, the Hurd networking subsystem, you can skip to the networking chapter (see section Networking), and read about the related utilities and servers.
Programmers who are interested in learning how to modify Hurd servers, or write new ones, should begin by learning about a microkernel to which the Hurd has been ported (currently only GNU Mach) and reading section Foundations. You should then familiarize yourself with a subsystem that interests you by reading about existing servers and the libraries they use. At that point, you should be able to study the source code of existing Hurd servers and understand how they use the Hurd libraries.
The final level of mastery is learning the RPC(2) interfaces which the Hurd libraries implement. The last section of each chapter describes any Hurd interfaces used in that subsystem. Those sections assume that you are perusing the referenced interface definitions as you read. After you have understood a given interface, you will be in a good position to improve the Hurd libraries, design your own interfaces, and implement new subsystems.
The Hurd is not the most advanced operating system known to the planet (yet), but it does have a number of enticing features:
FIXME: overview of basic Hurd architecture, FAQish in nature
Richard Stallman (RMS) started GNU in 1983, as a project to create a complete free operating system. In the text of the GNU Manifesto, he mentioned that there is a primitive kernel. In the first GNUsletter, Feb. 1986, he says that GNU's kernel is TRIX, which was developed at the Massachusetts Institute of Technology.
By December of 1986, the Free Software Foundation (FSF) had "started working on the changes needed to TRIX" [Gnusletter, Jan. 1987]. Shortly thereafter, the FSF began "negotiating with Professor Rashid of Carnegie-Mellon University about working with them on the development of the Mach kernel" [Gnusletter, June, 1987]. The text implies that the FSF wanted to use someone else's work, rather than have to fix TRIX.
In [Gnusletter, Feb. 1988], RMS was talking about taking Mach and putting the Berkeley Sprite filesystem on top of it, "after the parts of Berkeley Unix... have been replaced."
Six months later, the FSF is saying that "if we can't get Mach, we'll use TRIX or Berkeley's Sprite." Here, they present Sprite as a full-kernel option, rather than just a filesystem.
In January, 1990, they say "we aren't doing any kernel work. It does not make sense for us to start a kernel project now, when we still hope to use Mach" [Gnusletter, Jan. 1990]. Nothing significant occurs until 1991, when a more detailed plan is announced:
``We are still interested in a multi-process kernel running on top of Mach. The CMU lawyers are currently deciding if they can release Mach with distribution conditions that will enable us to distribute it. If they decide to do so, then we will probably start work. CMU has available under the same terms as Mach a single-server partial Unix emulator named Poe; it is rather slow and provides minimal functionality. We would probably begin by extending Poe to provide full functionality. Later we hope to have a modular emulator divided into multiple processes.'' [Gnusletter, Jan. 1991].
RMS explains the relationship between the Hurd and Linux in http://www.gnu.org/software/hurd/hurd-and-linux.html, where he mentions that the FSF started developing the Hurd in 1990. As of [Gnusletter, Nov. 1991], the Hurd (running on Mach) is GNU's official kernel.
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