Guide To UNIX Using Linux Fourth Edition

Chapter One

The Essence of UNIX and Linux

Guide To UNIX Using Linux Fourth Edition

Chapter 1 Unix (42 slides)

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• Explain operating systems, including PC, mainframe, and network operating systems

• Describe the UNIX and Linux operating systems• Explain the purpose of UNIX/Linux shells• Understand how to select user names and

passwords• Connect to UNIX/Linux using Telnet or SSH

Objectives


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• Use basic UNIX/Linux commands and command-line editing features

• Explain the role of a system administrator• Change your password for security• Use multiple commands to view the contents of

files• Redirect output to a file

Objectives (continued)


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• Operating System (OS)– The most fundamental computer

program– Enables you to store information, process

raw data, use application software, compile your own programs, and access attached hardware, such as a printer or keyboard

Understanding Operating Systems


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Understanding Operating Systems


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• A personal computer (PC) OS conducts all I/O, processing, and storage operations on a stand-alone computer

PC Operating Systems


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• A mainframe OS controls a large computer system with multiple processors for I/O, processing, and storage operations for many users

Mainframe Operating Systems


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• A network OS controls the operations of a server computer (host), which accepts requests from user programs running on other computers (clients)

Network Operating Systems


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• Server-based network– Centralized processing approach– Data and applications server resident– If server fails, entire network fails

• Peer-to-peer– Distributed processing approach– Data and applications workstation

resident– Each system is both a server and a client

Server-based vs. peer-to-peer networks


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UNIX/Linux can be used on systems functioning as: Dedicated servers or client workstations in a

server-based network Client/server workstations connected to a

peer-to-peer network Stand-alone workstations not connected to a

network

Introducing the UNIX and LinuxOperating Systems


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• UNIX/Linux is a multi-user system• UNIX/Linux is a multitasking system

– Can execute more than one program at a time

• UNIX/Linux is a portable operating system– Used in many computing environments

Introducing the UNIX and LinuxOperating Systems (continued)


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• Bell Labs originally developed UNIX in the late 1960s and early 1970s

• Distributed in source code form• Universities modified the code to work on different

machines

• Two standard versions of UNIX evolved– System V (Bell Labs)– Berkeley Software Distribution (BSD)

A Brief History of UNIX


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• Shell– The interface between user and OS

• Hierarchical Structure– Directory and subdirectory organization

• Layered components– Layers of software surround the computer’s

inner core

UNIX Concepts


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• Linux is UNIX-like– Not written from traditional UNIX code

• Linux is original code– Includes POSIX standards

• Other Linux information– Created by Linus Torvalds– Offers all the complexity of UNIX– Linux can coexist with other OSs

Linux and UNIX


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A shell is a UNIX/Linux program that interprets the commands you enter from the keyboard

Introducing UNIX/Linux Shells


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• Shells interpret commands and act as first-class programming languages

• A default shell is associated with your account when created; Bash is the default shell in Linux

• Some UNIX/Linux shells: Bourne, Korn, C shell, Bash• Can switch from shell to shell

Choosing Your Shell


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• To use UNIX/Linux, a user must log in by providing a unique user name and password

• UNIX/Linux system administrators create accounts by adding user names and passwords

• Users log in to UNIX or Linux systems as long as they have accounts on the workstation or host (server) computer

Choosing User Names and Passwords


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• Remotely through Telnet (Use SSH Mostly Now!)• Through network client software• As peer on peer-to-peer network• On a stand-alone PC• Through a dumb terminal

Connecting to UNIX/Linux Using Telnet or SSH


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• Telnet is terminal emulation software– Connects your PC to a server, or host

▫ PC could be running UNIX, Linux, Windows OS, or Macintosh OS

▫ Once connected to a UNIX/Linux host, work with UNIX/Linux may begin

– Uses IP addresses or domain names to access remote systems

Connecting to UNIX Using Telnet


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• Developed for UNIX/Linux systems to provide authentication security for TCP/IP applications, such as FTP and Telnet

• Can encrypt communications as they go across a network or the Internet

• openSSH includes protocols and software for free distribution on UNIX/Linux systems

Secure Shell (SSH)


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• Log in by entering username and password when UNIX/Linux system booted or connected to

• Enter at prompt (command-line mode) or into login box (GUI mode)

• Now commands can be issued at the command prompt

Logging In to UNIX/Linux


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With a standalone computer and an X Window desktop such as GNOME, you must open a terminal window to access the command prompt

Logging In to UNIX/Linux (continued)


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• To interact with UNIX/Linux, a command is entered at the command prompt

• UNIX/Linux is case-sensitive and most commands are typed in lower case

• Two categories of commands– User-level: perform tasks– System administration: system management

Using Commands


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• The date command– Displays the system date, which the system

administrator maintains• The cal command

– Shows the system calendar

Using Commands (continued)


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• The who Command– To get information about who is logged in– Useful for administrators and users

• The clear Command– Clears the screen

• The whatis command– Displays a brief description of a command for

help purposes



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The man program displays the UNIX/Linux online reference manual, called the man pages, for help purposes



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• Command-line editing– Certain keystrokes perform command-line

editing (shell dependent)• Multiple command entries

– More than one command on one line by separating with a semicolon(;)



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• Command-line history– Use up and down arrow keys to scroll through

command history• Logging out ends your current process and indicates

to UNIX that you are finished• Logging out is shell dependent

– Bourne, Korn, Bash – exit command– C shell – logout command



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• System administrator manages the UNIX/Linux system– Adds users and deletes old accounts– Also called the superuser– Unlimited permission to alter system– Unique user name: root– Prompt ends with # (pound) symbol

Understanding the Role of the UNIX/Linux System Administrator


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• The System Administrator’s Command Line– [root@hostname root]#

• The Ordinary User’s Command Line– [username@hostname username] $

Understanding the Role of the UNIX/Linux System Administrator (continued)


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• For security purposes, changing passwords is necessary– Use the passwd command– UNIX/Linux allows new password if:

▫ The new password differs by at least three characters

▫ It has six or more characters, including at least two letters and one number

▫ It is different from the user name

Changing Passwords


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• Use cat, more, and less to view an entire file contents– cat displays a whole file at one time– more displays a file one screen at a time,

allowing scroll down – less displays a file one screen at a time,

allowing scroll down and up

Viewing Files Using thecat, more, less, head, and tail Commands


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• Use head and tail to view the first few or last few lines of a file– head displays the first few lines (10 lines)– tail displays the last few lines (10 lines)

Viewing Files Using thecat, more, less, head, and tail Commands (continued)


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• The greater than sign (>) is called a redirection symbol

• Create a new file or overwrite an existing file by attaching (>) to a command that produces output

• To append to an existing file, use two redirection symbols (>>)

Redirecting Output


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• OS controls all computer resources and provides the base upon which application programs can be used or written

• A server-based network is centralized (handled by the system administrator)

• A peer-to-peer network is decentralized• UNIX/Linux are multi-user, multitasking

Chapter Summary


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• UNIX/Linux systems can be configured as servers, client workstations, client/server workstations, or stand-alone

• The concept of the layered components that make up an OS originated with UNIX

• Linux is a UNIX-like OS for a PC• You communicate with the OS programs through

an interpreter called the shell

Chapter Summary (continued)


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• The system administrator sets up accounts for users that supply a username and password

• You work with UNIX by typing commands that you can learn by referring to the online manual called man pages



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• Most shells provide basic command-line editing capabilities and keep a history of your most recently used commands

• You can view the contents of files with view commands such as cat, less, more, head, and tail



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• Work through Hands-on Projects at end of chapter 1

• Canvas: Review Questions 1- (Do not do questions 22,23,24

and 25 on All Unix Chapters!)

• Read chapter 2 before next class session

• Quiz 1 UNIX…

Chapter 1 Unix Exercises


42CTEC 110

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Guide To UNIX Using Linux Fourth Edition