Towards a New Strategy of OS Design

collectives · gnu@gnu.org

The Unofficial (and no longer maintained) GNU Hurd FAQ, Version 0.13
+
+Contributions by:
+
+Michael I. Bushnell 
+Len Tower 
+Trent Fisher 
+jlr@usoft.spb.su
+Remy Card 
+Louis-Dominique Dubeau 
+
+Original Document by: Derek Upham 
+
+
+==============================
+
+Contents:
+
+Q0.  Where can I get the Unofficial GNU Hurd FAQ?
+Q1.  What is the Hurd?
+Q2.  Where can I get a copy?
+Q3.  Why bother writing a new OS when we have Linux and 386/BSD?
+Q4.  What's all this about Mach 3.0 (and Mach 4.0)?
+Q5.  Where can I find more information?
+Q6.  What's a proper machine?
+Q7.  What sort of machines will run Hurd in the future?
+Q8.  What is the current development status?
+Q9.  What sort of system would we have if the Hurd was bootable today?
+
+==============================
+
+Q0.  Where can I get the Unofficial GNU Hurd FAQ?
+
+The Unofficial Hurd FAQ (what you are reading now) is occasionally
+posted to the USENET newsgroup, gnu.misc.discuss.  It is also
+available from
+
+   http://www.enci.ucalgary.ca/~gord/hurd/hurd-faq.txt
+
+If you don't have WWW access, you may send mail to me, Gordon
+Matzigkeit  with a subject line that reads:
+
+   Subject: send hurd-faq
+
+You should receive a PGP-signed copy of the current version of this
+document in a matter of minutes.
+
+
+Q1.  What is the Hurd?
+
+The Hurd is the high-level operating system for GNU.  It is currently
+under development.  GNU was designed as a replacement for Unix, so the
+Hurd is multi-tasking and multi-user, POSIX-compliant, and will have
+networking and X-windows and all that good stuff.
+
+Hurd is an acronym for ``Hird of Unix-Replacing Daemons''.  Hird, in
+turn, is an acronym for ``Hurd of Interfaces Representing Depth''.
+
+
+Q2.  Where can I get a copy?
+
+To put it simply, you can't.  It is still under development (by
+Michael Bushnell, Roland McGrath and Miles Bader).  It is almost, but
+not quite, at the point where you can do real work on it.  Keep your
+fingers crossed.
+
+Some people have actually bootstrapped it, but the work is not easy,
+and the current snapshot won't work until a new multiserver boot
+mechanism is made.
+
+If you *really* want to try it, beware that it is still pre-alpha
+code, and that it will likely crash on you.  See Trent Fisher's Hurd
+pages (under question 5) for the latest information.
+
+
+Q3.  Why bother writing a new OS when we have Linux and 386/BSD?
+
+For one thing, Linux and BSD don't scale well.  Hardware designers are
+shifting more and more toward multiprocessor machines for performance,
+and standard Unix kernels do not provide much multiprocessor support.
+The Hurd, on the other hand, runs on top of the Mach 3.0 micro-kernel
+[[1]] from CMU.  Mach was designed precisely for multiprocessing
+machines, so its portability should carry over nicely to the Hurd.
+
+In addition, the Hurd will be considerably more flexible and robust
+than generic Unix.  Wherever possible, Unix kernel features have been
+moved into unprivileged space.  Once there, anyone who desires can
+develop custom replacements for them.  Users will be able to write and
+use their own file systems, their own `exec' servers, or their own
+network protocols if they like, all without disturbing other users.
+
+The Linux kernel has now been modified to allow user-level file
+systems, so there is proof that people will actually use features such
+as these.  It will be much easier to do under the Hurd, however,
+because the Hurd is almost entirely run in user space and because the
+various servers are designed for this sort of modification.
+
+
+Q4.  What's all this about Mach 3.0 (and Mach 4.0)?
+
+As mentioned above, Mach is a micro-kernel, written at Carnegie Mellon
+University.  A more descriptive term might be a greatest-common-factor
+kernel, since it provides facilities common to all ``real'' operating
+systems, such as memory management, interprocess communication,
+processes, and a bunch of other stuff.  Unfortunately, the system
+calls used to access these facilities are only vaguely related to the
+familiar and cherished Unix system calls.  There are no "fork",
+"wait", or "sleep" system-calls, no SIGHUPs, nothing like that.  All
+this makes it rather difficult to, say, port GNU Emacs to a Mach box.
+
+The trick is, of course, to write an emulation library.  Unix programs
+can then use (what they think are) POSIX system calls and facilities
+while they are really using Mach system calls and facilities.
+
+The simplest way of going about this is to take an ordinary Unix
+kernel, open it up, and rip out all the machine-specific guts; any
+time the Unix kernel talks to the machine, replace the code with calls
+to the Mach micro-kernel.  Run this fake kernel on a Mach machine and
+you end up with something that looks and acts just like Unix (even to
+GNU Emacs).  Note that the Unix kernel we have implemented is just one
+Really Big Mach program (called a single-server).
+
+The Hurd, on the other hand, breaks the giant Unix kernel down into
+various Mach programs running as daemons.  Working in concert with
+facilities placed in the C library, these daemons provide all of the
+POSIX system-calls and features; from the outside they look just like
+a standard Unix kernel.  This means that, for practical purposes,
+anything that you can port to Linux will also port to the Hurd.
+
+Of course, if a user wishes to run his own daemons, he can do that as
+well....
+
+Mach 4.0 is an enhanced version of Mach 3.0, put out by the people at
+the University of Utah.  They are working on another free operating
+system, and part of it includes an enhanced, more flexible version of
+Mach.  The Hurd has moved to Mach 4.0, which is good, because it is a
+lot easier to build than 3.0 was.
+
+You can find more information on Mach by browsing the Hurd pages given
+in the next answer, or by looking at the Project Mach and Flux
+homepages at:
+
+Carnegie Mellon University (for Mach versions before 4.0):
+
+   http://www.cs.cmu.edu/afs/cs.cmu.edu/project/mach/public/www/mach.html
+
+the University of Utah (for Mach 4.0):
+
+   http://www.cs.utah.edu/projects/flux/mach4/html/
+
+
+Q5.  Where can I find more information?
+
+The June 1995 GNU's Bulletin contains the following official
+information:
+
+   The GNU Hurd now runs programs native.  We have implemented both
+   shared libraries using ELF, & the popular `ext2' file system used
+   by Linux.  It can run GCC, `make', Emacs, & most other GNU
+   utilities.  Progress is being made so rapidly that by the time you
+   read this it probably does much more.  It is right on the verge of
+   being self-hosting (able to run on its own well enough to compile
+   its own source code, & be used for its own development).  We have
+   much better device supportm [sic] & some new utilities, including a
+   fancy `ps' & `settrans'.  For a complete system we still have much
+   more work to do, but we will make an alpha release as soon as the
+   network software is finished & shared libraries have been well
+   tested.  We have a mailing list to announce progress; to be added
+   to it, ask `hurd-announce-request@gnu.org'.
+
+The Portland State University CS department (via Trent Fisher)
+maintains a WWW server with various Hurd documents, including Michael
+Bushnell's Hurd paper, all the collected GNU's Bulletins, and various
+announcements posted to "gnu.misc.discuss".  The top-level GNU page is
+
+   http://www.cs.pdx.edu/~trent/gnu/gnu.html
+
+and the Hurd page is
+
+   http://www.cs.pdx.edu/~trent/gnu/hurd/hurd.html
+
+People in Europe might want to try the GNU WWW server for DESY
+Germany, first:
+
+   http://info.desy.de/gnu/www
+
+This site lacks culled, Hurd-specific information at the moment, but
+it does have the last two GNU's Bulletins plus lots of general
+information.
+
+There is a snapshot of the Hurd development tree on
+"alpha.gnu.ai.mit.edu" in the "/gnu" directory.  It is updated as
+significant changes are made, and not guaranteed to run.
+
+You can subscribe to the Hurd announcement list by sending a request
+to "hurd-announce-request@gnu.org".  This is a moderated list
+for distributing Hurd info to ``all and sundry'', and anyone can join.
+In addition, there is a private (invitation-only) list for developers
+to coordinate their efforts.  It's not even worth thinking about
+unless you (a) have a lot of free time on your hands, (b) know Unix
+internals and Mach very well, and (c) have a proper machine.
+
+
+Q6.  What's a proper machine?
+
+A ``proper machine'', at the moment, means an x86 box running Mach 3.0
+(or 4.0), with FreeBSD 2.x, NetBSD 1.x, or Linux.
+
+A single-server OS is no longer required for development because by
+the time the Hurd bootstrap mechanism is finished, the Hurd will
+probably be self-hosting.
+
+Linux, FreeBSD, or NetBSD will only be required to splat the Hurd
+binaries onto a partition of some sort, and to provide a way of
+transferring files to the Hurd until the networking code is ready.
+
+
+Q7.  What sort of machines will run Hurd in the future?
+
+The first thing a prospective Hurd machine needs is a Mach 3.0 port.
+According to the most recent "comp.os.mach" FAQ (which hasn't been
+updated since February 1994), the following chips have redistributable
+Mach micro-kernels and device drivers:
+
+    Intel 80x86         (ISA and PS/2 buses)
+    Motorola 68000      (Sun 3)
+    Motorola 88000      (Omron Luna)
+    DEC Vax
+    DEC Pmax            (DECstation 3100)
+    DEC Alpha
+    MIPS R4000          (DECstation 5000 et al.)
+    IBM RS/6000
+    Apple Macintosh
+
+IBM is planning to run WorkplaceOS (the OS/2 successor) over Mach 3.0
+on the PowerPC chip (closely related to the RS/6000), so the PowerPC
+will likely be added to this list soon.  The University of Utah has
+ported Mach 4.0 to the HP700, but it is not yet stable.
+
+Sun Sparc machines have a redistributable Mach microkernel, but the
+device drivers require a SunOS 4.1.1 source license.
+
+In addition, any prospective Hurd machine needs a port of the GNU C
+library.  Version 1.07.4 of the library can handle the following
+chips:
+
+    Intel 80x86         (BSD, Dynix, Hurd, SCO, SysV)
+    Motorola 68000      (HP BSD, NEWS, Sun 4)
+    MIPS R4000          (Ultrix)
+    Sun Sparc           (Solaris 2, Sun 4)
+    DEC Alpha           (OSF/1, mostly finished)
+
+So if the next Hurd snapshot is self-hosting, we will be able to run
+it (in theory) on Intel 80x86s, Motorola 68000s, MIPS R4000s and DEC
+Alphas.
+
+People who can port the Mach micro-kernel to new architectures are
+encouraged to do so.  People who can port the GNU C library to new
+chips (a much larger group) are also encouraged to do so.  You can
+help out here without knowing anything about Mach or having any
+special machine.  Note that once the GNU C library exists for a new
+chip, for _any_ OS, making a Hurd port later is simple (and making
+ports to other chips becomes easier as well---the effects are
+cumulative).
+
+By current indications, the other hardware requirements (RAM, disk
+space, and the like) will be about the same as those of BSD 4.4.
+
+
+Q8.  What is the current development status?
+
+Please see Trent Fisher's Hurd pages for details.
+
+
+Q9.  What sort of a system would we have if the Hurd was bootable
+today?
+
+Quite likely, if you already use an end-user system like Linux,
+FreeBSD, or NetBSD, you'll be disappointed with the Hurd.  It will
+take some time before the OS hackers really get to work on
+applications and major enhancements.
+
+But, rest assured, Hurd development should proceed very rapidly.
+
+Of course, if you think you can help, or you just enjoy neat stuff,
+then you'll probably like the Hurd.  When you actually understand a
+fraction of what's going on behind the scenes, it's very impressive.
+
+All I'm saying is that I'm not expecting all the Windows '95 users in
+the world to switch to the Hurd right away.  Wait a little while,
+maybe 5-6 years (ample time for GNUStep and Guile to be in use), and
+GNU users everywhere will be very happy that the FSF proceeded with
+the Hurd. :)
+
+
+==============================
+
+Footnotes:
+
+[[1]] Yes, I know that ``micro-kernel'' is about as apt a description
+as ``Reduced Instruction Set Chip'', but we're stuck with it.
+
+

The Hurd and Linux

GNU Hurd folks

What the name ``Hurd'' means

Towards a New Strategy of OS Design

Part 1: A More Usable Approach to OS Design

The Translator Mechanism

Generic Services

Clever Filesystem Pictures

What The User Can Do

Why This Is So Different

Part 2: A Look at Some of the Hurd's Beasts

The Authentication Server

The Process Server

Transparent FTP

Filesystems

Terminals

Executing Programs

New Processes

Asynchronous Messages

Making It Look Like Unix

Network Protocols

GNU Hurd information

Binary Distributions

General Information

Where to Get it

What if I'm having problems?

Current and Past Announcements

Other stuff and related projects

The Hurd and Linux

The Hurd and Linux

GNU Hurd information

Binary Distributions

General Information

Where to Get it

What if I'm having problems?

Current and Past Announcements

Other stuff and related projects

GNU Hurd information

Binary Distributions

General Information

Where to Get it

What if I'm having problems?

Current and Past Announcements

Other stuff and related projects

General Information

Acknowledgements

Current and Past Announcements

GNU Hurd information

GNU Hurd

What is the Hurd?

Binary Distributions

Advantages of the Hurd

General Information

Where to Get it

What the name ``Hurd'' means

What if I'm having problems?

Status of the project

Current and Past Announcements

Other stuff and related projects

GNU Hurd

What is the Hurd?

Advantages of the Hurd

What the name ``Hurd'' means

Status of the project

GNU Hurd

What is the Hurd?

Advantages of the Hurd

What the name ``Hurd'' means

Status of the project

The Hurd and Linux

NEWS

What is the Hurd?

Running a Subhurd

NEWS

What is the Hurd?

GNU Hurd

Translators

Mount Points

Device Files

Symbolic Links