The Unix System

1
The Unix System

• Unix is a Multi-user and Multi-tasking operating
  system
• History
• MULTICS (MULTIplexed Information and Computing
  Service) (1965)
• Ken Thompson (Bell Laboratories -1969)
• Space Wars, PDP-7, written in ASSEMBLER
• UNICS (UNiplexed Information and Computing
  Service)
• Ken Thompson, Dennis Ritchie (1970-1974)
• UNIX, PDP-11
• Ritchie develops C language (starting from B
  language)
• The third version of UNIX is written in C
• A paper on UNIX is published in 1974 (ACM Turing
  Award 1984)

2
The Unix System

• History, Bell Labs and ATT UNIX
• PDP-11 is the computer of many departments of
  computer science and so UNIX becomes the OS of
  the Universities
• Bell Labs and ATT UNIX development groups
  develop several version of UNIX
• first edition (1969), ,seventh edition (1978,on
  PDP-11/70)
• a version for Interdata 8/2 and VAX
• UNIX for a network of computers
• System III (1982 - first commercial version)
• System V based on System III(1983)
• System V release 2, 3, 4 (1984 - 1989)
• SVR4 (System V release 4 1989 ATT and Sun
  Micro systems)
• 1993 ATT becomes a phone company and sells UNIX
  to Novell

3
The Unix System

• History University of California at Berkeley
• The most influential of the non-Bell Labs and
  non-ATT UNIX development groups.
• Thompson and some students develop 1BSD
  (Berkeley Software Distributions) starting from
  sixth edition (the first one out of Bell Labs)
  (1978).
• 3BSD - 4BSD UNIX resulted from DARPA funding to
  develop a standard UNIX system for government
  use.
• This series contains 4.1BSD, 4.2BSD, 4.3BSD and
  4.4BSD (1980-93) and has some important new
  tools virtual memory, paging, multiuser, network
  connection by means of TCP/IP.
• 4.2BSD contains the text editor vi, the shell
  csh, Pascal and Lisp compilers,
• Sun Microsystem, DEC and some other companies
  decides to develop their UNIX version starting
  from BSD versions instead of System V.

4
History of UNIX Versions
5
The Standardization Projects

• History
• Several standardization projects seek to
  consolidate the variant flavors of UNIX leading
  to one programming interface to UNIX. The most
  important are
• POSIX (Portable Operating System) merge of
  System V and BSD (1984)
• IBM, DEC, Hewlett-Packard create OSF (Open
  Software Foundation) and their UNIX system is
  OSF/1 (1988)
• X/OPEN defines the Single UNIX specification
  (1993) and the systems satisfying this
  specification have the trademark UNIX 95
• Open group (merge of Open Software Foundation and
  X/OPEN http//www.opengroup.com 1996)
• Definition of the second version of the Single
  UNIX specification (1997) with the trademark UNIX
  98

6
A variant of the UNIX System

• Although there are many version of UNIX, the most
  important companies provide version based on UNIX
  System V Release 4 (SVR4) and the last the Single
  UNIX specification
• ex. Solaris 2.x is the most widely used and most
  successful commercial UNIX implementation.
• These systems are very big and very complicated
  (the contrary of the Thompsons basic idea) and
  in same case expensive.
• So, Tanenbaum develops MINIX (1987) a small free
  UNIX system (11800 rows of C code and 800 rows of
  Assembler code) satisfying POSIX.
• MINIX is a free educational system based on
  micro-kernel model (www.cs.vu.nl/ast/minix.html)

7
Common System Components of an OS

• Process Management
• Main Memory Management
• File Management
• Secondary Memory Management
• I/O System Management
• Networking
• Protection System
• Command-Interpreter System (Shell)

8
System Structure

• System structure defines the connections and
  manages the System Components
• Some system structures
• Monolithic
• Client-Server model (micro-kernel)

9
Monolithic Operating System Structure

• A monolithic system has not a well defined
  structure. It includes virtually all of the
  operating-system functionality in one large block
  of code that runs as a single process with a
  single address space. All the functional
  components of the kernel have access to all of
  its internal data structures and routines.

10
The Client-Server Model

• Moves as much from the kernel into user space.
  In this way it remains only a micro-kernel.
• Communication takes place between user modules
  using message passing.

11
The Client-Server Model

• Advantages
• easier to extend a micro-kernel
• easier to port the operating system to new
  architectures
• more reliable (less code is running in kernel
  mode)
• more secure
• Disadvantages
• Deterioration of the performances
• MINIX has the I/O drivers into the kernel (this
  is for technical reasons connected to 8088
  architecture), while the Main Memory Management,
  and the File Management are two different user
  processes.

12
The Linux System

• There is not a free BSD system at the end of the
  eighties, and so many members of MINIX newsgroup
  ask to Tanenbaum to introduce many modifications
  for improving the performances of MINIX. Some of
  these modifications could change the original
  educational project of Tanenbaum, and so often he
  said NO to these requests.
• So, Linus Torvalds using a pc 386 with MINIX
  develops a small but self-contained kernel in
  1991 (Linux 0.01), with the major design goal of
  UNIX compatibility (i.e., satisfying POSIX).

13
Linux 0.01

• The first version of Linux (Linux 0.01) has some
  of features of MINIX (ex. File system), but the
  main differences between Linux and MINIX are
• The Linux kernel uses a monolithic model, and it
  has many more functions than the micro-kernel of
  MINIX.
• From a theoretical point of view MINIX is better
  than Linux, but from a practical point of view
  the performances of Linux are better than that
  one of MINIX.
• However, for a description of the point of view
  of Torvalds on the advantages-disadvantages of
  Linux-MINIX see the flame war between Torvalds
  and Tanenbaum in
• Rivoluzionario per caso come ho creato Linux
  (solo per divertirmi), Linus Torvalds, Garzanti

14
The Linux Kernel

• Linux 0.01 (May 1991) had no networking, ran only
  on 80386-compatible Intel processors and on PC
  hardware, had extremely limited device-drive
  support, and supported only the Minix file
  system.
• Linux 1.0 (March 1994) included these new
  features
• Support for UNIXs standard TCP/IP networking
  protocols
• BSD-compatible socket interface for networking
  programming
• Device-driver support for running IP over an
  Ethernet
• Enhanced file system
• Support for a range of SCSI controllers for
  high-performance disk access
• Extra hardware support
• This version is sufficient compatible with UNIX
  and many people are interested in developing
  Linux under Torvald supervision.
• Linux 1.2 (March 1995) was the final PC-only
  Linux kernel.

15
Linux 2.0

• Released in June 1996, 2.0 added two major new
  capabilities
• Support for multiple architectures
• Support for multiprocessor architectures
• Other new features included
• Improved memory-management code
• Improved TCP/IP performance
• Support for internal kernel threads, for handling
  dependencies between loadable modules, and for
  automatic loading of modules on demand.
• Standardized configuration interface
• Available for Motorola 68000-series processors,
  Sun Sparc systems, and for PC and PowerMac
  systems.
• Linux 2.2 January 1999 improves some aspects of
  Linux 2.0
• The last release is Linux 2.4.20 (production)
  Linux 2.5.64 (development)

16
The Moral of the Story

• Linux is a modern, free operating system based on
  UNIX standards.
• First developed as a small but self-contained
  kernel in 1991 by Linus Torvalds, with the major
  design goal of UNIX compatibility.
• Its history has been one of collaboration by many
  users from all around the world, corresponding
  almost exclusively over the Internet (software
  open source).
• It has been designed to run efficiently and
  reliably on common PC hardware, but also runs on
  a variety of other platforms.
• The core Linux operating system kernel is
  entirely original, but it can run much existing
  free UNIX software, resulting in an entire
  UNIX-compatible operating system free from
  proprietary code.

17
The Linux System

• Linux uses many tools developed as part of
  Berkeleys BSD operating system, System V, MITs
  X Window System, and the Free Software
  Foundation's GNU project.
• The main system libraries were started by the GNU
  (GNUs Not Unix) project (ex. gcc (GNU C
  compiler)), with improvements provided by the
  Linux community.
• Linux networking-administration tools were
  derived from 4.3 BSD code recent BSD derivatives
  such as FreeBSD have borrowed code from Linux in
  return.
• The Linux system is maintained by a network of
  developers collaborating on Internet (see
  /usr/src/linux/CREDITS), with a small number of
  public ftp sites acting as de facto standard
  repositories.

18
Linux Distributions

• Standard, precompiled sets of packages, or
  distributions, include the basic Linux system,
  system installation and management utilities, and
  ready-to-install packages of common UNIX tools.
• The first distributions managed these packages by
  simply providing a means of unpacking all the
  files into the appropriate places modern
  distributions include advanced package
  management.
• Red Hat, Debian, SuSE, Mandrake are popular
  distributions from commercial and noncommercial
  sources, respectively (see www.linux.org).
• The RPM Package file format permits compatibility
  among the various Linux distributions (see
  www.linuxbase.org).

19
Which distribution to use ?

• RedHat (www.redhat.com)
• Big, professional, very widely used
• Debian (www.debian.org/)
• Open development model, excellent packaging
  system
• Mandrake (www.mandrakesoft.com)
• Aims to be very easy to install and use
• SuSE (www.suse.com/)
• Compromise between Red Hat and Mandrake
• Slackware (www.slackware.com/)
• Most traditional little extra help

20
Mandrake Distribution

• Mandrake provides a simple and friendly
  distribution. Maybe, it is the best distribution
  for the desktop (www.mandrakesoft.com).
• The last release of Mandrake distribution is
  Mandrake 9.0 Dolphin and it is contained in
  three CDs. It contains the Linux kernel 2.4.19.
• The minimum installation requires only the
  first CD and takes only 60MB. The other two CD
  contain many packages.
• There are two different GUI (Graphical User
  Interface)
• KDE (release 3.0.3) and GNOME (2.0.1)

21
Mandrake Installation

• The installation of Mandrake 9.0 Dolphin is
  very easy.
• You can select Italian language
• The first time you should choose the installation
  for principiante
• The more difficult step is the partition of the
  hard disk. A partition correspond to a logic
  disk. If you want to install some operating
  systems on your hard disk, you have to define a
  partition for each OS. A disk has at most 4
  primary partitions. You can make these partitions
  by means of the command fdisk.The Mandrake
  installation provides a simple graphical tool for
  making the Linux partitions.
• We wish to point out that from DOS/Windows you
  cannot see the other partitions. On the contrary,
  Linux see DOS/Windows partition (/mnt/windows).
• However, all the steps of the installation will
  be illustrated during the lecture.

22
The Moral of the Installation

• Varies from distribution to distribution
• Most modern distributions make it easy
• Buy CD / download and burn CD image
• Boot
• Follow instructions
• Need to think about partitioning.
• Install a boot loader (probably LILO (LInux
  LOader), maybe something else). This needs to be
  configured to boot whatever other operating
  systems you have installed.

23
Users

• Linux is an intrinsically multi-user system
• Every user on the system has its own username and
  password
• The root user has ultimate power to run the
  system. You should not log in as root unless you
  really need to.
• During installation, you should have been
  prompted for a root password and also a username
  and password for an ordinary user account.
• The command passwd allows to change the password.
• Careful you have to perform the program shutdown
  h now before to switch off the PC

24
Linux Licensing

• The Linux kernel is distributed under the GNU
  General Public License (GPL), the terms of which
  are set out by the Free Software Foundation.
• See /usr/src/linux/COPYING
• The main consequence of GPL is that anyone using
  Linux, or creating their own derivative of Linux,
  may not make the derived product proprietary
  software released under the GPL may not be
  redistributed as a binary-only product.
• For a deeper examination of this subject see
  www.gnu.org/home.it.html