network chapter 1

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____________________________________________________________________________________COS 231 Introduction to UNIX, AUB, V. Karagiozov [1]

COS 231 Introduction to UNIX

Lecture 1

Chapter 1: Overview of the UNIX System


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What is an Operating System?

Organized group of programsinterface

between machines and users.

provides a set of tools to make easier to

designing, programming, debugging, testing

and maintaining programs

manage resources distribution to ensureeffectiveness of work of the computer


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OS Functions

To manage computer resources:

CPU, basic storage, disc storage,

I/O devices, buses, channels, controllers,

Process management, etc.

To manage jobs execution

To provide tools for software engineering

To provide tools for data security, priorities,authorized access

Networking


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Types of Operating Systems

Batch OS - Sequential execution of the jobs. User are not allowed anyinterface during the program execution. The program used all computer'sresources during execution

Time sharing OS - Simultaneously stored several jobs in basicmemory. Provides for each of the jobs a "unit" of CPU's time (CPU time isshared among jobs) and distributed other computing resources. Allow user tointeract with his/her program during the execution.

Real time OS -Execute job immediately (in real time) when request

for execution occur.Multitasking/Time sharing - Simultaneous execution of several

jobs (tasks). To reach this effect some techniques are available:timesharing, swapping, paging, multiprocessors.


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Network operating system capabilities

All versions of UNIX and most other modern

network operating systems (NOS) support

advanced features:

Multiuser capability

Multitasking

Distributed processing

High level of security


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Network Operating Systems


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Types of users

1. End-users - are not involved in programming, only using.

2. Applied software engineers - involved in applied

programs developing.

3. System software engineers - involved in system programsdeveloping, setting up OS for certain system hardware, organizing

the upper level of computing environment.

4. System engineers - developing hardware, firmware,organizing the low-level computing environment.


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History of developing UNIX OS

The original Bell Labs UNIX: 1969/70 Ken Thompson - UNiplexed Information and

Computing Service(the spelling of UNICS was later changed

to UNIX)

1973 Ken Thompson and Dennis Ritchie (the author of C

language) rewrote the system in C

The Berkeley Standard Distribution (late 70s):

communication and networking functions, usingcommunication protocol TCP/IP

one of the first full-screen editors - Vi (visual editors)

CShell command interpreter


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Overview of the UNIX System

Well-thought-out family of utility programs Can support many users (multiuser OS)

Can support many tasks (multitask OS)

UNIX system kernel

File structure

Security

The Shell

Device-Independent Input and Output Interprocess Communications

Networking utilities


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Major features of UNIX

Multiuser: UNIX is written in such a way that it is able torecognize and handle many requests for services at the same time.

Under UNIX every user is identified and has his own private part of

the resources.

Multitasking: the logical extension of multiuser behavior. Notonly several users can be on the system at once, but also they may be

running different programs at the same time.

Shared Peripherals: UNIX has abilities to place various jobrequests in a temporary storage area (queue) and deliver them in an

orderly fashion to limited hardware devices.


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Major features of UNIX

Hierarchical File & Directory structure:The storage of data on the hard disk in an organized and

hierarchical fashion. This logical structure of data storageallows endless potential for categorization and ongoing

manipulation of files and directories.

Open communication: UNIX allows wide variety

of communication: Email, communication betweenterminals, access to the worldwide network.


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Major features of UNIX Shell environment: user interaction with the UNIX OS is

accomplished through a program known as the shell. The shell servesas a command interpreter and translate commands (human languagecode) to machine language code. The shell also provides a rich and

powerful environment for programming known as shell script. Theshell provides opportunity to run program in the background (notvisible on the terminal) and to combine several commands to performone more complex task.

Security, accounting, auditing: because of sharing thesame disk among the users, the authorized access to directories andfiles in the UNIX was build up a comprehensive system for accountingand data security and also for auditing any actions performed on the

system.

UNIX utilities: there are more than 400 utilities or commandsavailable to the UNIX user.

Networking.


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The UNIX Kernel

Process management: control the execution of the requests from programs that require responses

from system hardware - ability to cover multiuser and multitasking

requests; making decisions about scheduling of the processing competing for the

CPU's and other peripheral devices time - time sharing. Rotate all waitingprocesses one by one.

File management: manage the efficient storage and retrieval of all files.

It is responsible for establishing the organization structure known as filesystem.

multiplelogin


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The UNIX Kernel

Control the allocation of space in mainmemory (RAM)

Swapping Paging

Security, accounting, auditing (C2 security

level) Security is established for files, devices,

memory and processes.


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Device independence

Communications with the core of UNIX (the kernel) is

accomplished through a standardized set of system calls.

All device drivers (device managing programs) use this

scheme of system calls. It is always possible to enter adevice driver for new device into kernel.

Devices (printer, terminal, etc.) and disk files all appear as

files to UNIX programs.

Input and output are device-independentcan beredirected to or from any appropriate device (redirection).


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Interprocess Communications

(InterProcess Communication) - The exchange of

data between one program and another either within

the same computer or over a network. It implies a

protocol that guarantees a response to a request.

Unix uses pipes and filters

A pipe sends the output of one program to another

program as input

A filter is a program designed to to process a stream

of input data and yield a stream of output data.


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Networking

Network communication support was introducedin Berkeley Unix 4.2

TCP/IP is the predominant network protocol usedin Unix

Networking utilities:

check the status of remote computers and their users

log-in on remote systems run commands on remote systems

copy files from one system to another

interact with users on remote systems


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Additional Features of the UNIX System

Job controlto run several jobs at once in background and

foreground

Screen-oriented editorvi

Shell functionsUNIX shell can be used as a

programming languageallow defining new commands

GUIX Window system created in 1984 at the MIT:

portable and flexible

Operates in a networked environmentuser can run a program on

a remote system and can send the results on a local display


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The OS Shell


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Different shells available within a UNIX

environment:

The Bourne shell (/bin/sh) was the original shell program forUNIX.

The Korn shell (/bin/ksh) is a superset of the Bourne shell and

was developed by David Korn at Bell Labs. It has many of theBourne shell features, plus added features such as aliasing and

history.

The C shell (/bin/csh) is based on the C programming language.

The Bourne-Again Shell (bash) has the feel of the Bourne and

Korn shells and incorporates features from the C and Kornshells. Bash is the most popular shell with Linux and is the

default for most distributions.


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Text reading:

Chapter 1- Overview of the UNIX System

After reading it try to answer to all questions

from Review Exercises section


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Self-test:

Put the OS components in correct

place


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Before you start

How can I connect to Linux-system from my networked PC?Terminal emulator.

Start-Run

telnet linux.stud.aubg.bg

telnet linux

telnet 172.17.48.11 What is my login name? ( Your e-mail)

What is my password? (You should received your password fromOCC by e-mail)

CHANGE YOUR PASSWORD!!!$ passwd

Changing password for xxxxxx

Old password:

New password:

Re-enter new password:

Obsolete !

Use F-secure client or

PuTTy


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How to pick a password?

At least six char long At least two letters and one number (special

symbols, upper-, lower-case)

DO NOT use easily guessed passwords: your

login name, your names, your spouses name,mother, father, sister, pet, etc. names, your ID#,

birthday, word from a dictionary, words in reverseorder

New password must differ from the previous oneat least by 3 characters

Keep password in mind


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More rules for choosing a good password

DO NOT:

use a word (or words) in any language use a proper name

use information that can be found in your wallet

use information commonly known about you (car license, pet name, etc)

use control characters. Some systems can't handle them

write your password anywhere

ever give your password to *anybody*

DO

use a mixture of character types (alphabetic, numeric, special)

use a mixture of upper case and lower case

choose a password you can remember

change your password often

make sure nobody is looking over your shoulder when you are enteringyour password


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COS 231 Introduction to UNIX AUB V Karagiozov [30]

Logging Out

After changing the password log out and try

logging back in using your new password

When finish you work log out: Ctrl+D, or

logout, or

exit

Always log out using one of these commands. Do

not leave your terminal window opened!

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network chapter 1