LIS508 lecture 8: looking at linux

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LIS508 lecture 8looking at linux

• Thomas Krichel
• 2002-11-11

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Structure

• History of unix and linux
• Using linux
• Free software

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Early Computing History

• In the 1940s and 1950s, all computers were
  personal computers in the sense that a user would
  sign up to use the machine and then take over the
  whole machine for that period.
• The early 1960s were dominated by batch systems
  in which a user would submit a job on punched
  cards and wait, usually hours, before any printed
  output appeared.

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Early Computing History

• To get around this unproductive environment, the
  concept of timesharing was invented by Dartmouth
  College and M.I.T.
• The M.I.T system CTSS (Compatible Time Sharing
  System) was an enormous success.
• M.I.T., Bell Labs, and General Electric created a
  second generation timesharing system named
  MULTICS (Multiplexed Information and Computing
  Service).

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Early UNIX History

• At Bell Labs, Ken Thompson decided to write a
  stripped down version of MULTICS for the very
  small PDP-7 minicomputer which he called UNICS.
• Dennis Ritchie, also at Bell Labs, joined
  Thompson in further developments of what was now
  called UNIX.
• Together they ported the system the the larger
  and very popular PDP-11/20 and PDP-11/45
  minicomputers.

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Early UNIX History

• Thompson also rewrote the operating system in
  high level language of his own design which he
  called B.
• The B language lacked many features and Ritchie
  decided to design a successor to B which he
  called C.
• They then rewrote UNIX in the C programming
  language to aid in portability.

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Early UNIX History

• In 1974, Ritchie and Thompson published a paper
  about UNIX and received the prestigious ACM
  Turing Award.
• This publication stimulated many universities to
  request a copies of UNIX.
• Since Bell Labs, part of ATT, was not allowed
  to be in the computer business, it licensed UNIX
  to universities.
• Also, at that time, the PDP-11 series was the
  workhorse of most computer science departments.
• Result UNIX was a hit on campus.

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Early UNIX History

• In Version 6, the source code of UNIX was 8200
  lines of C and 900 lines of assembler.
• The first portable version arrived with Version 7
  which had 18,800 lines of C and 2100 lines of
  assembler.
• By the 1980s the use of UNIX was widespread with
  many vendors selling their own versions based on
  Version 7.

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BSD UNIX

• One of the many universities that had received
  license for UNIX was the University of California
  at Berkeley.
• Aided by many government grants, Berkeley
  released an improved version named 1BSD (First
  Berkeley Software Distribution)
• In subsequent, versions Berkley added many new
  features including a new visual editor (vi) and
  a new shell (csh).

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Two UNIX Versions

• Because of these and other enhancements, many
  companies based their UNIX on Berkeleys version
  as opposed to ATTs so-called System V.
• By the late 1980s, two different and somewhat
  incompatible versions of UNIX were in widespread
  use 4.3 BSD and System V release 3.

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UNIX Standards

• In addition, every vendor added its own
  nonstandard enhancements.
• In an attempt to unify the troops, the IEEE
  Standards Board undertook the POSIX Project (POS
  for Portable Operating System) and IX to make it
  UNIX like.
• POSIX 1003.1 emerged as a common ground standard.
  
• 1003.1 is the intersection of System V and BSD.
  (a feature had to be on both to be included in
  the standard)

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UNIX Standards

• The POSIX standard defined a set of library
  procedures and systems calls that all compliant
  UNIX systems.
• It appeared that the split between System V and
  BSD had been somewhat dealt with.
• Unfortunately, a funny thing happened on the way
  back form the standards meeting.

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UNIX Standards

• A group of vendors led by IBM, DEC,
  Hewlett-Packard, and others formed the OSF (Open
  Software Foundation) to standardize an enhanced
  version of UNIX in an attempt to derail ATTs
  efforts to regain control of UNIX.
• ATT, Sun, UNISYS, Data General, and other
  companies countered and formed UI (UNIX
  International) based on System V.

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UNIX Like Systems

• In a new trend, UNIX like operating systems began
  to appear.
• MINIX, by Andrew Tanenbaum, used a microkernel
  design with only 1600 lines of C and 800 lines of
  assembler in its first version.
• In 1991, a Finnish student named Linus Torvalds
  released another UNIX clone named Linux version
  0.01.

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Linux

• Linux is a monolithic design rather than a
  microkernel design. (9,300 lines of C and 950 of
  assembler)
• Linux quickly grew in size and functionality.
• Version 1, shipped in 1994, contained about
  165,000 lines of code.
• Version 2 in 1996 contained about 470,00 lines of
  C and 8000 lines of assembler.
• Linux is released under the GNU public licence
  (we will cover this later).

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In the meantime, in the trenches

• In 1992, Berkeley decided to terminate BSD
  development with one final free release - 4.4BSD.
• ATT sued claiming the version contained ATT
  code.
• During the lawsuit, Berkeley was not allowed to
  distribute 4.4BSD thus giving time for Linux to
  become established.
• Had the lawsuit not occurred, there would have
  been serious competition between two freely
  available.

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ATTs Exit

• ATT eventually decided to focus on the long
  distance telephone business and sold its UNIX
  business to Novel in 1993.
• In turn, Novel sold it to Santa Cruz Operations
  in 1995.
• But who owned this version of UNIX was almost
  irrelevant since so many companies already had
  licenses.

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UNIX Consolidation

• Even though there have been many vendors and many
  version of UNIX over the last few decades, the
  market is now beginning to consolidate.
• IBM AIX
• Hewlett-Packard HP/UX
• Sun Solaris
• Macintosh OS X

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Linux Distributions

• Linux itself is free. It is packaged, provided
  with installation and management tools, and made
  available for a small fee by various vendors on
  CD.
• These packages are known as distributions.
• Some common distributions are
• Red Hat -- SuSE --Mandrake
• Debian -- Slackware
• Differences
• Locations of files (configuration, binaries,
  etc.)
• GUI
• Security, efficiency, etc.

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UNIX Philosophy

• Make each program do one thing well.
• These programs are sometimes called tools.
• Expect the output of every program to be the
  input to another yet unknown program.
• Simple tools can be connected to accomplish a
  complex task
• Do not hesitate to build new tools
• The UNIX tool library keeps growing

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UNIX Philosophy

• The UNIX philosophy has not proven to be the best
  for all applications.
• For example, there are lots of text manipulation
  tools that can be put together to accomplish a
  complex word processing task but the trend is
  definitely toward integrated word processing
  software.

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Layers in the UNIX System
User Interface
Users
Library Interface
Standard Utility Programs (shell, editors,
compilers, etc.)
System Interface calls
User Mode
Standard Library (open, close read, write, etc.)
UNIX Operating System (process management, memory
management, the file system, I/O, etc.)
Kernel Mode
Hardware (cpu, memory, disks, terminals, etc.)
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UNIX Structure

• The kernel is the core of the UNIX system,
  controlling the system hardware and performing
  various low-level functions. The other parts of
  the UNIX system, as well as user programs, call
  on the kernel to perform services for them.
• The shell is the command interpreter for the UNIX
  system. The shell accepts user commands and is
  responsible for seeing that they are carried out.

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Famous shells

• The Bourne shell /bin/sh (default)
• The Korn shell /bin/ksh
• The C shell /bin/csh
• The Bourne Again Shell /bin/bash
• The Z shell /bin/zsh
• In linux, /bin/sh is usually /bin/bash

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UNIX Structure

• Hundreds of applications are supplied with the
  UNIX system. They support a variety of tasks
• copying files
• editing text
• performing calculations
• developing software
• Serving web pages etc

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Using Linux/UNIX

• Depends on how it is set up. The following are
  true on wotan, on other machines it may be
  different.
• Wotan runs Debian GNU/Linux.
• / is the root directory
• /home/user (aka user) is the home directory of
  the user user.
• ls l lists files in long format.

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Permission model

• Permission of files are give to the owner, the
  group, and the rest of the world.
• A group is a grouping of users. Unix allows to
  define any number of groups and make users a
  member of it.
• The rest of the world are all other users who
  have access to the system, including public
  access on a web server, for example.

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First element in ls -l

• Type indicator
• d means directory
• l means link
• - means ordinary file
• 3 letters for permission of owner
• 3 letters for permission of group
• 3 letters for permission of rest of the world
• r means read, w means write, x means execute

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Change permission chmod

• A permission is a number
• 4 is read
• 2 is write
• 1 is execute
• Permissions are three numbers, for owner, group
  and rest of the world.
• Example chmod 764 file
• Directories need to be executable to get in them

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Bash features

• Bash is the default shell on wotan
• cd is a command to change directory
• File names and command names can be completed
  with TAB
• The command history can be activated with the
  arrow keys of the keyboard

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Copying and removing

• cp file copyfile
• scp user_at_machinefile user_at_machinefile
• User is a user
• Machine is a machine
• File is the path to a file
• Of course you will need permissions here!
• rm file there is no recycling bin!!
• -r flag copies and deletes recursively

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Directories and files

• mkdir file makes a directory
• rmdir file removes it
• touch file
• makes a new empty file
• sets the time on an existing file
• more file
• Pages contents of file, no way back
• less file
• Pages contents of file, u to go back, q to
  quit

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Editing files

• There are many file editors available.
• I use emacs, because I am a geek.
• My students use nano. Invoque it with
• nano filename
• If nano in not there, try pico.

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http//openlib.org/home/krichel

• Thank you for your attention!