Introduction to UNIX

Just Enough Unix, Chapter 1

What is UNIX?

• Operating system (OS), software

• Widely used in industry, government, academia

• Excellent OS for multiuser systems

Operating System Functions

• Management of computer resources, such as memory, CPU, and I/O devices

• Enables interaction with the user

• Management of other software, scheduling

UNIX History

• Began as a joint venture called Multics involving GE, MIT, and AT&T’s Bell Labs

• Multics was too ambitious and by 1969 failed.• Ken Thompson and Dennis Ritchie, who had

worked on Multics, wrote Unics (later called UNIX) for a minicomputer at Bell Labs.

• In 1971 they wrote a UNIX-based word- processing system for the Bell Labs patent department. It was very successful.

UNIX History

• Bell Labs could not, by law, compete in the computer industry so they gave UNIX away for free.

• Computer Scientist at Universities introduced improvements.– Berkeley produced its own version

• Many computer companies created their own versions.– CS computers use Sun’s Solaris

• In 1991 Linus Torvalds created Linux, an OS similar to UNIX, for personal computers.

Open vs. Proprietary

• Proprietary: Designed to work only on certain types of computer hardware.– MS-DOS (1980’s) ran only on machines with

Intel CPU’s (Central Processing Unit)– Original Macintosh OS ran only on machines

with Motorola CPU’s

• Open: No single company developed or owns UNIX– Unix is portable - runs on a variety of hardware

The Four Main Components of UNIX

• Kernel– Manages resources (memory, i/o devices, etc.)

• File System– Organization of data

• Shell– Interprets user commands and passes them to the

kernel

– Command-line interface

• Utilities– Commands

The UNIX “Onion”

Hardware

Kernel

Shell

Utilities

File system HardwareFile system

Kernel

Shell

Utilities

HardwareFile system

Kernel

Shell

Utilities

HardwareFile system

Hardware

• Hardware is what determines what version, or type, of UNIX is installed.

• Miller uses Solaris 8– Machine Hardware is i86pc– i386 Processor

• Grid uses Solaris 9– Machine Hardware is Sun4u – Sun Sparc Processor

Kernel

• The kernel is the master control of the computer.

• Controls resources and schedules users jobs

• Programs interact with the kernel through system calls.

Shell

• Is the user - interface

• Interpreter between the user and the kernel.

• Takes commands from the user, decides if it is a valid command, then sends it to the kernel for processing.

• Consistency across shells allows many version of UNIX to appear to be the same.

Utilities / Applications

• The utilities are also known as the commands– such as pwd, ls, cat

• Applications are software programs that allow users to solve specific problems.– Development tools

• g++ , gcc complilers• Debuggers and archivers

– Text Editors• Pico, Emacs, Vi

– Email tools• Pine, Elm, Mail

File System

• How all the data is organized on the system.

• The hierarchal file structure allows for organization of files into related groups

• The similar structure across many different UNIX systems makes each system feel familiar to the user.