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                        LINUX--a free unix-386 kernel

                Linus Torvalds (torvalds@kruuna.helsinki.fi)

                              October 10, 1991

                             Introduction to LINUX

What is LINUX?

   LINUX is a free unix-like kernel for 386-AT computers, coming with full
   source code. It is meant for hackers/computer science students to use,
   learn and enjoy. It is written mostly in C, but parts of it are in
   gnu-format assembler, and the boot-sequence is in intel 086 assembly
   language. The C-code is relatively ANSI, with a few GNU enhancements
   (mostly __asm__ and inline).

   While there are a number of unices available for 386 computers, most of
   them cost a lot of money, and come with no source. Thus, they are ideal
   for actually using your computer, but if you want to learn how they
   work, you are f- -ked.

   There are also a few unices available with source. Minix, the learning
   tool written by Andrew S. Tanenbaum, has been used in universities as a
   teaching tool for years. The BSD-386 system comes with source, but has
   a restrictive copyright and costs a lot of money ($995 is the starting
   price, I think). The GNU kernel (Hurd) will be free, but is currently
   not ready, and will be too big to understand and learn.

   LINUX most closely resembles Minix, in that it is small and not very
   sophisticated, and thus easy (well...) to understand. LINUX was also
   written under Minix, so there are quite a bit of similarities, and any
   Minix hacker will feel relatively at home with LINUX. None of the Minix
   code was used in the project though, so the Minix copyright doesn't
   cover the new system. It also is completely free, and has a very loose
   copyright. Thus there is no need for megabytes of diffs like under
   Minix.

The LINUX copyright

   While being freely distributable, I do restrict the use of LINUX in a
   few ways:
     * You may freely copy and redistribute the source and binaries, as
       long as:
          + complete source is available. Thus binaries may not be
            distributed by themselves, even if you have made changes to
            them.
          + you do not profit from the distribution. In fact even
            ``handling costs'' are not acceptable.
          + you keep the appropriate copyrights intact.
     * You may change the source to your liking, but if you distribute
       parts of the new system (or just binaries), all the new code must
       be included.
     * You may make small excepts from the code without including
       copyrights. This is up to you, but a reference to me or the code
       would be appreciated.

   This should be loose enough not to cause any worry in anybody using or
   expanding the system. If you have a friend who really doesn't want the
   source, but just a working binary, you may of course give it to him
   without worrying whether I will sue you. Keep it between friends,
   though.

Hardware/software needed to get LINUX running

   LINUX was written on a 386-AT running Minix. As LINUX is a real
   operating system, and goes directly to the hardware to do things, you
   have to have a very similar system to get it going without problems:
     * 386-AT (PS/2's are different enough that things won't work)
     * VGA or EGA screen hardware.
     * Standard AT hard-disk interface, IDE disks work fine (in fact
       that's what I use).
     * Normal real-mode BIOS. Some machines seem to use virtual-86 mode to
       run the bootup program, and on such machines LINUX won't boot up
       and run correctly.

   While LINUX will be expanded to be a self-sufficient system, Minix-386
   is currently needed to get the ball rolling. You need Minix to make the
   initial root file system, and to compile the OS binary. After that
   LINUX is a self-sufficient system, but Minix is recommended in order to
   make file system checking (fsck) and to recompile the system after
   making changes.

Getting LINUX

   LINUX can currently be gotten by anonymous ftp from `nic.funet.fi' in
   the directory '/pub/OS/Linux'. This directory contains the full source
   to the operating system, as well as a couple of binaries so that you
   can actually use the system.

   NOTE! The binaries are mostly GNU software, and are under a stricter
   copyright (the GNU copyleft) than the LINUX sources. Thus you may not
   redistribute them without distributing their source, found in /pub/GNU.
   See any GNU software package for more information on the GNU copyleft.

   The various files found in this directory are:
     * linux-0.03.tar.Z--complete source to the operating system, in a
       16-bit compressed tar archive.
     * Linux.tex--L^ATEX source for this file.
     * bash.Z--bash binary to run under LINUX. This binary should be put
       under tha name /bin/sh in the file system reserved for LINUX (see
       installation).
     * update.Z--update binary, to be put in /bin/update.
     * gccbin.tar.Z--GNU cc binaries needed to get a working compiler.
       This tarred archive contains the compiler, loader, assembler and
       support programs (nm, strip etc). It also contains a small library
       sufficient for most programs.
     * include.tar.Z--include-files necessary to get gcc working.
     * unistd.tar.Z--source to the unistd library routines (ie system call
       interface). With this you can build a bigger library by using
       system-independent library sources.
     * utilbin.tar.Z--binaries to various GNU utilities, including GNU
       fileutils, make and tar. Also contains the emacs-clone uemacs.
     * README, RELNOTES-0.01, INSTALLATION--ascii files containing some
       (somewhat out-of-date) information about LINUX.

   The absolute minimum needed to get a system going is the OS source and
   the bash and update binaries. You won't be doing much with just these
   though.

                                  Installation

   After you have gotten the necessary LINUX files, you need to compile
   the system and make a root directory. The necessary binaries need to be
   put in the root file system. Do this:
    1. Back up your software. While LINUX never has destroyed any of my
       files, nothing is certain. Better safe than sorry.
    2. Choose/make a standard Minix HD-partition to be the new LINUX root
       file system.
    3. Make the necessary device nodes on the new root. LINUX uses the
       same type of nodes as Minix, so use the Minix mknod command to make
       the following devices:
          + /dev/tty
          + /dev/tty[0-2]
          + /dev/hd[0-9]
       Node numbers are the same as in Minix.
    4. Move the necessary files to the new root partition. The files
       should be in the following directories:
          + /bin:
               o sh, ie bash.Z.
               o update
          + /usr/bin:
               o Contents of utilbin.tar.Z
          + /usr/include:
               o Contents of include.tar.Z
          + /usr/local/lib:
               o Contents of gccbin.tar.Z, excepting gcc
          + /usr/local/bin:
               o gcc
               o links to files in /usr/local/lib of your choice. I link
                 ld, as, nm, strip and size to their counterparts in
                 /usr/local/lib/gcc-XXX.
          + Edit the linux/include/linux/config.h file for your system.
            This file contains the system-specific information: memory
            space, disk types, root partition number (again the numbering
            is the same as in Minix), keyboard type (currently just US and
            Finnish) etc.
          + Compile the LINUX sources. A simple make should do the trick,
            after you have edited the makefiles to suit your system (ie,
            removed the -mstring-insns flag and changed the paths to suit
            you.) Users of gcc versions earlier than 1.40 will probably
            have to add gnulib to the `LIBS ='-line in the makefile.
          + Copy the resultant Image-file to a floppy (ie, cp Image
            /dev/PS0 or similar.)
          + Reboot with the new floppy. The startup screen should tell you
            that the system is booting (Loading system ...), then some
            vital root file system information (xxx/XXX inodes/blocks
            free), followed by a Ok. and the bash prompt (initially bash#
            if you have no .bashrc file).
       Hopefully you now have a functioning unix, and you are logged in as
       root. LINUX currently has no 'init' process, and as soon as you log
       out, the system will sync and just wait. Use the
       three-finger-salute to reboot your machine.

                       Things missing/incomplete in LINUX

   While LINUX is meant to be a fully selfsufficient kernel, this is
   currently not the case. As already mentioned, you need Minix to set
   things up, and to check the file system once it's running. There are a
   number of other deficiencies:
     * Incomplete hardware-support. Some of the standard features of an AT
       are not currently supported. Most notably are floppy disk drives,
       making using LINUX for real work (backing up etc) currently not
       possible. Also some of the features of the serial lines aren't yet
       implemented (hard-wired to 2400bps, no hang-up notification etc).
     * Incomplete standard C library. The libc.a found in the gcc
       distribution package is not complete, and I'm very much interested
       in freely distributable library functions.
     * Some of the system calls are not fully implemented. This concerns
       mostly ``seldom-used'' features like debugging (yeah, who needs it
       anyway, don't all your programs work the first time :-) and some
       other features.
     * As mentioned, no login and init processes. Currently LINUX boots up
       in single-user mode, with the root as console-user. This is enough
       for some porting work, but not really practical.
     * 387-support is not yet implemented, although some skeleton routines
       are present. The gcc-binary found on `nic.funet.fi' will correctly
       use soft-float (ie emulation function calls) for the four basic
       math operations. 387-support will materialize as soon as a 387
       finds its way into my computer. Hopefully in a month or two.
     * None of the important system-administration commands has yet been
       written for LINUX. These include things like mkfs, format, fsck,
       mknod etc. Some of these need kernel features not yet implemented
       (format, mknod), some just need to be written. As with the library,
       I'd welcome any freely distributable files.

   As you can see, LINUX is as yet not a complete system. Your help is
   appreciated to make it better. I'm not interested in Minix-commands
   rewritten for LINUX, unless you have written them yourself from
   scratch. You are of course free (and encouraged) to use everything you
   have in your Minix-distribution for your own LINUX-system, but due to
   the Minix copyrights, they cannot be distributed to a wider audience.

   Some of the probelms mentioned here will be fixed by me (ie serial
   lines/387/floppy support) as soon as possible, but I'm hoping to get
   help with the libraries etc. Bug-reports/patches and wish-lists will be
   appreciated, and if you actually have the patch to the problem, I'll
   try to implement it right away. Small changes will be sent out as
   patches to the mailing list and be set up on `nic.funet.fi', but after
   heavy rewrites or bigger patches, the whole system will be updated at
   `nic.funet.fi'.

                           Porting software for LINUX

   LINUX was designed to make porting relatively easy. Thus the full
   termios-implementation, and the somewhat POSIX library. The (admittedly
   relativly few) programs I've ported posed no problems.

   Even though LINUX resembles Minix a great deal, Minix programs are not
   generally easier to port than programs designed for some other unix.
   Thus I wouldn't recommend starting from a Minix-version of a particular
   program, but instead trying to port the ``virgin'' program from
   scratch. Being closer to SYSV than BSD means that most programs port
   easily when given a -DUSG or -DSYSV flag.

   One of the more difficult problem in porting can be missing library
   functions. These must be written by you, or copied from some other
   source (Minix being one possibility for those that have it).
   Alternatively, some programs (notably GNU) have various flags making it
   possible to define which functions aren't available (the GNU fileutils
   will compile quite nicely, once a sufficient number of -DXXX_MISSING
   flags are added to the Makefile.)

Programs already ported

   These programs have already been ported to LINUX:
     * GNU cc (gcc, cc1, cpp)
     * GNU assembler (as386)
     * GNU binutils (ld, ar, nm, size, strip, ranlib)
     * GNU compress (16-bit)
     * GNU tar
     * GNU make
     * GNU bash (Bourne Again SHell)
     * GNU sed
     * GNU bison (yacc-lookalike)
     * GNU awk
     * GNU fileutils (ls, cp, rm, mkdir, rmdir, tail etc)
     * less
     * uemacs

   All of the above sources can be found on `nic.funet.fi' (mostly in
   `/pub/gnu'), and most of the LINUX-binaries can be found in the
   directory '/pub/OS/Linux'. All of these programs compiled without
   changes, even though gcc (cc1) has some enhancements of my own. Mail me
   for diffs/sources, but try first to compile them yourself.

   Additionally I have reports that GNU diff compiles cleanly and works.

                                 Technical help

   LINUX currently has a mailing-list, which you can subscribe to by
   mailing to the address: Linux-activists-request@niksula.hut.fi and
   asking to be included into the list. You can then ask questions by
   mailing them to Linux-activists@niksula.hut.fi, which will duplicate
   your question/answer/whatever and send them to all persons on the list.

   Note the difference between Linux-activists and Linux-activists-request
   -- the first sends mail to all persons on the list, the second is used
   only to subscribe and unsubscribe from the list.

   Naturally, you can also mail me directly at
   torvalds@kruuna.helsinki.fi. I'll try to answer all questions within a
   day or two.

   Although `nic.funet.fi' will probably be kept reasonably up-to-date,
   there are a few problems with it (ie, I cannot personally get to the
   files, but have to go through a couple of persons). Thus people on the
   mailing-list will get patches/binaries faster if they ask for them.

                                     Thanks

   I'd like to thank the academy ...

   Seriously, this system never would have seen the light of day or would
   have been much worse without the help of some others. Bruce Evans
   helped me find the places needed to be changed in order for gcc to
   correctly handle floating point, and came with a lot of useful
   ideas/suggestions (and his Minix-386 was used to build the system).
   Also, Earl Chew's estdio package was used for the standard IO-library.
   More freely distributable packages like this!

   Alain W Black and Richard Tobin made the gcc for Minix, without which I
   couldn't have compiled the thing. GNU made most of the programs I use
   under LINUX. Alfred Leung sent the US keyboard patches.

   PS. ``Thanks'' to wirzeniu@kruuna.helsinki.fi for his ``constructive''
   criticism and ``witty'' comments. He was also my first $\alpha$
   -tester, and should be given a medal for courage.

                            About this document ...

   LINUX--a free unix-386 kernel

   This document was generated using the LaTeX2HTML translator Version
   2002 (1.62)

   Copyright (c) 1993, 1994, 1995, 1996, Nikos Drakos, Computer Based
   Learning Unit, University of Leeds.
   Copyright (c) 1997, 1998, 1999, Ross Moore, Mathematics Department,
   Macquarie University, Sydney.

   The command line arguments were:
   latex2html -local_icons -address gohigh@sh163.net -split 1 Linux.tex

   The translation was initiated by root on 2004-05-08
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