LIS508 lecture 6: looking at linux

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LIS508 lecture 6looking at linux

• Thomas Krichel
• 2003-11-11

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Structure

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

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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. (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 license,
  which, very basically means that anyone can copy
  and change it.

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Linux Distributions

• Linux itself is free. It is aggregated with
  installation and management tools, and many other
  software packages, and made available for a small
  fee by various vendors on CD.
• These aggregates 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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GNU

• GNU is a project started by Richard M. Stallman
  (RMS) to write a completely free implementation
  of Unix available.
• GNU stands for GNU is not Unix
• Most of Unix has been rewritten by him and his
  friends.
• Many other software packages have been released
  for free.
• My favorite linux distribution has over 13,000
  packages.

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This is Richard Stallman.
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free software according to RMS

• Free software comes with four freedoms
• The freedom to run the software, for any purpose
• The freedom to study how the program works, and
  adapt it to your needs
• The freedom to redistribute copies so you can
  help your neighbor
• The freedom to improve the program, and release
  your improvements to the public, so that the
  whole community benefits

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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.

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directories

• / is the root directory
• /home/user (aka user) is the home directory of
  the user user.
• ls l lists files in long format
• The command to change directory is cd.
• The directory above the current one is ..
• just like it was in old DOS.

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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!