linux crash course chapter 01 3

Chapter 1:
Welcome to Linux
An intro to UNIX-related
operating systems


In this chapter …
• History of Unix
• GNU-Linux
• Why Linux?


Long ago, in a galaxy far away …
• Computing power was costly
– UNIVAC cost $1 million

• CPU time was a premium
– Most mainframes had less computing power than
a calculator on the shelf at Wal-Mart

• Jobs were submitted into a queue
– Only one process at a time – scheduling
nightmare


What was needed
• Allow multiple users to access the same data
and resources simultaneously
• Service many users more cheaply than
buying each their own machine
• The ability to run multiple processes at once

• And do so while maintaining user
segregation and data integrity


Enter Unix, pride of Bell Labs
• Originally written in PDP-7 assembly
language by Ken Thompson
• To make it work on multiple architectures
(portable), Thompson rewrote Unix in B
• Dennis Ritchie developed C, and with
Thompson, rewrote Unix in C


What was so great about it?
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Multiuser
Multiprocess
Non-proprietary
Economical for business
Initially given for free to colleges and
universities (great tactic!)


Descendents and bastards …
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Started at Bell Labs
Picked up and continued by AT&T (SVR4)
UC Berkeley derives BSD
Sun Solaris
IRIX
Minix, XINU
Linux


What happened?
• UNIX became commercialized
• Proprietary code, specialized distributions
• Costs started to become a hindrance
• So … let’s make our own Unix …


GNU
• Richard Stallman decides that there should
be a free version of Unix available
• Forms the GNU project – GNU’s Not Unix
• Writes all of the system programs and
utilities to mimic Unix variants
• Everything but a kernel (Hurd)

Final piece
• Universities trying to teach Unix and OS
design can’t afford Unix
• Andrew Tanenbaum writes Minix
• Linus Torvalds, dissatisfied with Minix, writes
his own – Linux


GNU-Linux
• Torvalds has a perfectly functioning kernel –
but no system programs
• Finds a perfect candidate in GNU
• Together, the operating system world was
changed dramatically


Free you say?
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GNU-Linux is free …
Free as in speech, not free as in beer
Free to view, copy, modify, and release
Profit still to be had from packaging, support,
and additional original code

Why Linux?
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Software
Hardware
Portability
Standards
$$$


Software
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An almost limitless library of programs
Applications, services, utilities
Many free, some commercial
Source code often available along with prebuilt binaries


Hardware
• Supports thousands of peripherals and
pieces of hardware

• Multi-platform: x86, PPC, Alpha, SPARC,
MIPS, 64-bit, SMP (multiproc systems)
• Emulation of hardware for testing and
development


Portability
• Entire operating system written in C
• Shared system libraries available for all
supported architectures
• Code written on one platform can be
compiled on any system with minimal, if any,
tweaks


Standards
• Much of GNU-Linux already meets POSIX
(Portable Operating System Interface for
Computer Environments) and Unix System V
Interface Definition (SVID)
• Standardized for commercial and
government use


And don’t forget …
• It’s free! (or at least really cheap!)
• That’s why Linux is often the operating
system of choice to teach OS design and
Unix courses
• We’ll be using RedHat Enterprise Linux 4 –

not free but a fraction of the cost of Unix


Features Overview
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Multiuser
Multiprocess / Multitasking
Hierarchical Filesystem
BASH Shell command line interface /
programming language
• Many useful utilities built-in
• Rich networking support