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?• Multiuser

• Multiprocess

• Non-proprietary

• Economical for business

• Initially given for free to colleges and universities (great tactic!)

Descendents and bastards …• 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?• 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?• Software

• Hardware

• Portability

• Standards

• $$$

Software• An almost limitless library of programs

• Applications, services, utilities

• Many free, some commercial

• Source code often available along with pre-built 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• Multiuser

• Multiprocess / Multitasking

• Hierarchical Filesystem

• BASH Shell command line interface / programming language

• Many useful utilities built-in

• Rich networking support