Linux: Free Unix Information Sheet
0.1 Introduction to Linux
Linux is a completely free clone of the unix operating system
which is available in both source code and binary form. It is
copyrighted by Linus B. Torvalds (email@example.com),
and is freely redistributable under the terms of the Gnu Public
License. Linux runs only on 386/486 machines with an ISA or EISA
bus. MCA (IBM's proprietary bus) is not currently supported
because there is little available documentation. However,
support for MCA is being added at this time. Porting to other
architectures is likely to be difficult, as the kernel makes
extensive use of 386 memory management and task primitives.
However, despite these difficulties, there are people
successfully working on a port to the Amiga.
Linux is still considered to be in beta testing. There are still
bugs in the system, and since Linux develops rapidly (new
versions come out about once every two weeks), new bugs creep
up. However, these bugs are fixed quickly as well. Most versions
are quite stable, and you can keep using those if they do what
you need and you don't want to be on the bleeding edge. One site
has had a computer running version 0.97 patchlevel 1 (dating
from last summer) for over 136 days without an error or crash.
(It would have been longer if the backhoe operator hadn't
mistaken a main power transformer for a dumpster...)
One thing to be aware of is that Linux is developed using an
open and distributed model, instead of a closed and centralized
model like much other software. This means that the current
development version is always public (with up to a week or two's
delay) so that anybody can use it. The result is that whenever a
version with new functionality is released, it almost always
contains bugs, but it also results in a very rapid development
so that the bugs are found and corrected quickly, often in
hours, as many people work to fix them. Furthermore, the bugs
are generally discovered within hours of a kernel release,
especially those which might endanger a user's data, so it is
easy for an end-user to avoid these bugs.
In contrast, the closed and centralized model means that there
is only one person or team working on the project, and they only
release software that they think is working well. Often this
leads to long intervals between releases, long waiting for bug
fixes, and slower development. Of course, the latest release of
such software to the public is often of higher quality, but the
development speed is generally much slower.
As of March 17, 1993, the current version of Linux is 0.99
0.2 Linux Features
* multitasking: several programs running at once.
* multiuser: several users on the same machine at once (and NO
* runs in 386 protected mode.
* has memory protection between processes, so that one program
can't bring the whole system down.
* demand loads executables: Linux only reads from disk those
parts of a program that are actually used.
* shared copy-on-write pages among executables.
* virtual memory using paging (not swapping whole processes) to
disk: to a separate partition or a file in the filesystem, or
both, with the possibility of adding more swapping areas
during runtime (yes, they're still called swapping areas). A
total of 16 of these 16 MB swapping areas can be used at
once, for a total 256 MB of useable swap space.
* a unified memory pool for user programs and disk cache (so
that all free memory can be used for caching, and the cache
can be reduced when running large programs).
* dynamically linked shared libraries (DLL's)(static libraries
too, of course).
* does core dumps for post-mortem analysis (using a debugger on
a program after it has crashed).
* mostly compatible with POSIX, System V, and BSD at the source
* all source code is available, including the whole kernel and
all drivers, the development tools and all user programs;
also, all of it is freely distributable.
* POSIX job control.
* pseudoterminals (pty's).
* 387-emulation in the kernel so that programs don't need to do
their own math emulation. Every computer running Linux
appears to have a math coprocessor.
* support for many national or customized keyboards, and it is
fairly easy to add new ones.
* multiple virtual consoles: several independent login sessions
through the console, you switch by pressing a hot-key
combination (not dependent on video hardware).
* Supports several common filesystems, including minix-1 and
Xenix, and has an advanced filesystem of its own, which
offers filesystems of up to 4 TB, and names up to 255
* transparent access to MS-DOS partitions (or OS/2 FAT
partitions) via a special filesystem: you don't need any
special commands to use the MS-DOS partition, it looks just
like a normal Unix filesystem (except for funny restrictions
on filenames, permissions, and so on).
* CD-ROM filesystem which reads all standard formats of
* TCP/IP networking, including ftp, telnet, NFS, etc.
0.3 Hardware Issues
0.3.1 Minimal configuration
The following is probably the smallest possible configuration
that Linux will work on: 386SX/16, 2 MB RAM, 1.44 MB or 1.2 MB
floppy, any supported video card (+ keyboards, monitors, and so
on of course). This should allow you to boot and test whether it
works at all on the machine, but you won't be able to do
In order to do something, you will want some hard disk space as
well, 5 to 10 MB should suffice for a very minimal setup (with
only the most important commands and perhaps one or two small
applications installed, like, say, a terminal program). This is
still very, very limited, and very uncomfortable, as it doesn't
leave enough room to do just about anything, unless your
applications are quite limited. It's generally not recommended
for anything but testing if things work, and of course to be
able to brag about small resource requirements.
0.3.2 Usable configuration
If you are going to run computationally intensive programs, such
as gcc, X, and TeX, you will probably want a faster processor
than a 386SX/16, but even that should suffice if you are
In practice, you need at least 4 MB of RAM if you don't use X,
and 8 MB if you do. Also, if you want to have several users at a
time, or run several large programs (compilations for example)
at a time, you may want more than 4 MB of memory. It will still
work with a smaller amount of memory (should work even with 2
MB), but it will use virtual memory (using the hard drive as
slow memory) and that will be so slow as to be unusable.
The amount of hard disk you need depends on what software you
want to install. The normal basic set of Unix utilities, shells,
and administrative programs should be comfortable in less than
10 MB, with a bit of room to spare for user files. For a more
complete system, SLS reports that a full base system without X
fits into 45 MB, with X into 70 MB (this is only binaries), and
a complete distribution with everything takes 90 MB. Add the
whatever space you want to reserve for user files to these
Add more memory, more hard disk, a faster processor and other
stuff depending on your needs, wishes and budget to go beyond
the merely usable. In general, one big difference from DOS is
that with Linux, adding memory makes a large difference, whereas
with dos, extra memory doesn't make that much difference. This
of course has something to do with DOS's 640KB limit.
0.3.3 Supported hardware
CPU: Anything that runs 386 protected mode programs (all models
of 386s and 486s should work; 286s don't work, and never will).
Architecture: ISA or EISA bus (you still need an ISA-bus hard
disk controller, though). MCA (aka PS/2) does not work. Local
RAM: Theoretically up to 1 GB, but using more than 16 MB
requires that the kernel be recompiled.
Data storage: Generic AT drives (IDE, 16 bit HD controllers with
MFM or RLL) are supported, as are SCSI hard disks and CD-ROMs,
with a supported SCSI adaptor. Generic XT controllers (8 bit
controllers with MFM or RLL) need a special driver which is not
currently part of the standard kernel. Supported SCSI adaptors:
Adaptec 1542 (but not 1522), 1740 in extended (not 1542
compatible) mode, Seagate ST-01 and ST-02, Future Domain TMC-88x
series (or any board based on the TMC950 chip) and TMC1660/1680,
Ultrastor 14F, and Western Digital wd7000. SCSI and QIC-02 tapes
are also supported.
Video: VGA, EGA, CGA, or Hercules (and compatibles) work in text
mode. For graphics and X, there is support for (at least) EGA,
normal VGA, some super-VGA cards (most of the cards based on
ET3000, ET4000, Paradise, and some Trident chipsets), some S3
cards (not Diamond Stealth, because the manufacturer won't tell
how to program it), 8514/A, and hercules. (Linux uses the
Xfree86 X server, so that determines what cards are supported.)
Other hardware: SoundBlaster, AST Fourport cards (with 4 serial
boards), several flavours of bus mice (Microsoft, Logitech,
0.4 An Incomplete List of Ported Programs and Other Software
Most of the common Unix tools and programs have been ported to
Linux, including almost all of the GNU stuff and many X clients
from various sources. Actually, ported is often too strong a
word, since many programs compile out of the box without
modifications, or only small modifications, because Linux tracks
POSIX quite closely. Unfortunately, there are not very many
end-user applications at this time. Nevertheless, here is an
incomplete list of software that is known to work under Linux.
Basic Unix commands: ls, tr, sed, awk and so on (you name it,
we've probably got it).
Development tools: gcc, gdb, make, bison, flex, perl, rcs, cvs,
Graphical environments: X11R5 (Xfree86), MGR.
Editors: GNU Emacs, Lucid Emacs, MicroEmacs, jove, epoch, elvis,
Shells: Bash, zsh (include ksh compatiblity mode), tcsh, csh,
Telecommunication: Taylor (BNU-compatible) UUCP, kermit, szrz,
minicom, pcomm, xcomm, term/slap (runs multiple shells over one
modem line), and Seyon.
News and mail: C-news, trn, nn, tin, smail, elm, mh.
Textprocessing: TeX, groff, doc.
Games: Nethack, several Muds and X games.
All of these programs (and this isn't even a hundredth of what
is available) are freely available.
0.5 Getting Linux
0.5.4 Anonymous FTP
At least the following anonymous ftp sites carry Linux. This
list is taken from the Meta-FAQ list, which is posted every week
to the comp.os.linux newsgroup (the Meta-FAQ is updated more
often than this information sheet, so the list below may not be
the most current one).
Textual name Numeric address Linux directory
============================= =============== ===============
tsx-11.mit.edu 184.108.40.206 /pub/linux
sunsite.unc.edu 220.127.116.11 /pub/Linux
nic.funet.fi 18.104.22.168 /pub/OS/Linux
ftp.mcc.ac.uk 22.214.171.124 /pub/linux
fgb1.fgb.mw.tu-muenchen.de 126.96.36.199 /pub/linux
ftp.informatik.tu-muenchen.de 188.8.131.52 /pub/Linux
ftp.dfv.rwth-aachen.de 184.108.40.206 /pub/linux
ftp.informatik.rwth-aachen.de 220.127.116.11 /pub/Linux
ftp.ibp.fr 18.104.22.168 /pub/linux
kirk.bu.oz.au 22.214.171.124 /pub/OS/Linux
ftp.uu.net 126.96.36.199 /systems/unix/linux
wuarchive.wustl.edu 188.8.131.52 mirrors/linux
ftp.win.tue.nl 184.108.40.206 /pub/linux
ftp.stack.urc.tue.nl 220.127.116.11 /pub/linux
ftp.ibr.cs.tu-bs.de 18.104.22.168 /pub/os/linux
ftp.denet.dk 22.214.171.124 /pub/OS/linux
tsx-11.mit.edu and fgb1.fgb.mw.tu-muenchen.de are the official
sites for Linux' GCC. Some sites mirror other sites. Please use
the site closest (network-wise) to you whenever possible.
0.5.5 Other methods of obtaining Linux
There are many BBS's that have Linux files. A list of them is
maintained by Zane Healy; he posts it to the comp.os.linux
newsgroup around the beginning and middle of the month, please
see that post for more information. comp.os.linux is echoed on
the LINUX echoid on fidonet. This list is available as
tsx-11.mit.edu:/pub/docs/bbs.list, and is mirrored on fine
There is also at least one organization that distributes Linux
on floppies, for a fee. Contact
910 Lodge Ave.
Victoria, B.C., Canada
+1 604 360 0188
FAX: 604 385 1292
for information on purchasing. There is also an organization
which sells Linux on CD-ROM --- contact
Yggdrasil Computing, Incorporated
PO Box 8418
for information on purchasing the CD-ROM. Also, don't forget
about friends and user's groups, who are usually glad to let you
make a copy.
0.5.6 Getting started
As mentioned at the beginning, Linux is not centrally
administered. Because of this, there is no ``official'' release
that one could point at, and say ``That's Linux.'' Instead,
there are various ``distributions,'' which are more or less
complete collections of software configured and packaged so that
they can be used to install a Linux system. The most important
one is currently the SLS release.
SLS is put together by Peter MacDonald, and is the more
full-featured one. It contains much of the available software,
and includes X. I really recommend SLS to anyone who's serious
about getting started with Linux.
The first thing you should do is to get and read the list of
Frequently Asked Questions (FAQ) from one of the FTP sites, or
by using the normal Usenet FAQ archives (e.g.
pit-manager.mit.edu). This document has plenty of instructions
on what to do to get started, what files you need, and how to
solve most of the common problems (during installation or
0.6 Legal Status of Linux
Although Linux is supplied with the complete source code, it is
copyrighted software, not public domain. However, it is
available for free under the GNU Public License. See the GPL for
more information. The programs that run under Linux have each
their own copyright, although much of it uses the GPL as well.
All of the software on the FTP site is freely distributable (or
else it shouldn't be there).
0.7 News About Linux
There is a Usenet newsgroup, comp.os.linux, for Linux
discussion, and also several mailing lists. See the Linux FAQ
for more information about the mailing lists (you should be able
to find the FAQ either in the newsgroup or on the FTP sites).
The newsgroup comp.os.linux.announce is a moderated newsgroup
for announcements about Linux (new programs, bug fixes, etc).
For the current status of the Linux kernel and a summary of the
most recent versions, finger firstname.lastname@example.org
There is also a more or less weekly ``newsletter,'' Linux News,
which summarizes the most important announcements and uploads,
and has occasional other articles as well. Look in
comp.os.linux.announce for a sample issue.
0.8 Future Plans
Work is underway on Linux version 1.0, which will close some of
the gaps in the present implementation. The major functionality
shortcomings are advanced interprocess communication
(semaphores, shared memory), closer compatibility with POSIX,
and a lot of tweaking. Documentation is also sorely missing, but
is being worked on by those on the ``Linux Documentation
Project'' (the DOC channel of the email@example.com
mailing list). By April 1993 there should be a complete
installation and getting started manual for Linux.
0.9 This document
This document is maintained by Michael K. Johnson,
firstname.lastname@example.org. Please mail me with any comments, no matter
how small. I can't do a good job of maintaining this document
without your help. A current copy of this document can always be
found as tsx-11.mit.edu:/pub/linux/docs/INFO-SHEET, and a .dvi
version can be found as INFO-SHEET.dvi, in the same directory.
Trademarks are owned by their owners. There is no warranty about
the information in this document. Use and distribute at your own
risk. The content of this document is in the public domain, but
please be polite and attribute any quotes.