UNIX Linux Basics Final

7/30/2019 UNIX Linux Basics Final

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UNIX/Linux Overview


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Object ives What is Unix?

Why do I need to know Unix?

Unix history.

Architecture of Unix/Linux.

Important files and commands.

How is Unix/Linux booted?


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What is Unix?

What is an operating system?

The low-level (first layer loaded) softwarewhich handles the interface to system hardware(input/output devices, memory, file system, etc),

schedules tasks, and provides common coreservices such as a basic user interface.

Colloquially, all of the software that comeswith a system before applications are installed.


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What is Unix?A por tab le, mu lt i-task ing and

mult i -user operat ing system

Portable: runs on many different hardwarearchitectures (Intel x86 and IA-64, Alpha,

MIPS, HP PA-RISC, PowerPC, IBM S/390,SPARC, Motorola 680x0, etc.).

Preemptive multi-tasking: several programs

can run at the same time (time slices,interrupts, and task switching).

Multi-user: many users can share thecomputer system at the same time.


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What is Unix?Other Featu res

Uses a simple, uniform file model which includesdevices and access to other services in aflexible, hierarchical file system.

Written in a high-level language (C) making iteasy to read, understand, change and port.

The command prompt is a simple user process,the Unix shell, which is also a convenient jobprogramming language.

Includes support forregular expressions whichare convenient for complex searching.


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Is L INUX really UNIX?

Well , yes and no :

Yes, because it has essent ial ly the same look and

feel l ike any UNIX operating Sys tem.

Yes, because it offers the abi l i ty to run nearly any

prog ram that runs on UNIX systems (through API

convention s such as POSIX, etc..).

No because the heart of the system (kernel) has a

lot of new features that go beyond the classical

design phi losop hy of UNIX kernels.


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Unix Histo ry

1964 joint project between AT&T Bell Labs,GE, and MIT to develop a new OS.

Goal : develop an OS that could providecomputational power, data storage and theability to share data among multiple users.

Result: Multiplexed Information & ComputerService - MULTICS.


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Unix Histo ry

1969 Bell Labs withdraws from group.

Two Bell Lab scientists, Ken Thompson and

Dennis Ritchie, continue research. Theywere still left without a Convenientinteractive computing service*.

* Ritchie, D.M. The Evolution of the Unix Time-sharing System, AT&T Bell Laboratories

Technical Journal, Oct. 1984, Vol 63, No.8, Part 2, pp. 1577-1594.


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Unix Histo ry

At the same time KenThompson wrote a gamespace travel in Fortran torun on GECOS OS

(Honeywell 635).

The spaceship was hardto control and it was

expensive to run. He wastold to get the game off hiswork computer.


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Unix Histo ry

Thompson ported the game to a littleused PDP-7 computer.

Unics (later Unix) was born as a punon Multics.


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Unix Histo ryPDP-7


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Unix Histo ry

Dennis Ritchiedeveloped B . Thenwrote C a compiled

language.

In 1973 entire OSported to C.


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Linus Torvalds

1991 Linux 0.02 is first released to the public.

1994 Linux 1.0 is released.


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Three Defini t ions o f Linux

Linux Kernel:The very low-level software that managesyour computer hardware and provides a library (POSIX)

interface for user-level software. The Linux kernel runs on

many platforms (Intel x86 and IA-64, Alpha, MIPS, HP PA-

RISC, PowerPC, IBM S/390, SPARC, Motorola 680x0, etc.).

GNU/Linux OS:The Linux kernel plus utility software to

provide a useful working environment.

Linux Distributions:The packaging of the Linux Kernel,

the GNU/Linux OS and lots of other software to make Linux

easy to install, configure, and use (at least for the target

audience).


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Tux , the Linux Masco t


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e ree o ware ovemen The GNU Pro jec t:www.gnu.org

The Four Freedoms The freedom to run the program, for any purpose.

The freedom to study how the program works,

and adapt it to your needs. The freedom to redistribute copies so you can

help your neighbor.

The freedom to improve the program, and

release your improvements to the public, so thatthe whole community benefits.

G ?


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What is GNU?

GNU stands for GNU's Not Unix. The three letter

abbreviation is not a joke. It emphasizes a major proje

of the Free Software Foundation (FSF) that really

created the LINUX operating system with many of its

popular tools.

Richard Stallman created FSF, in order to encourage

the development and use of freely redistributable code

Freely means the freedom of redistributing your code

under certain conditions. It does NOT mean zero

financial cost!

The Gnu Public License (GPL) defines the terms and

conditions of redistributing the LINUX kernel and other

tools that make it usable, forming a LINUX distribution.


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Arch i tectu re of Unix

Kernel: Schedules programs,Manages data/file access and storage,

Enforces security,

Performs all hardware access.

Init: First program run by kernel on booting.

Shell: Presents each user a prompt,Interprets commands typed by user,

Executes users commands,

Provides user/programming environment.


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Arch i tectu re of Unix


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Arch i tectu re of UnixUnix f i le system

root (/)

bin

devetc

tmpvar

home

spool

mail

(users mail)

log

usr

X11R6

bin

(users accounts)


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Typ ical Direc to r ies

/ : Root of the tree. Where it starts.

bin, sbin, usr/bin: software for the shells and

most common Unix commands.

dev: short for devices, holds the files necessaryto operate peripherals such as printers and

terminals.

home: contains the home directories of users(/export/home on sun computers).


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Typ ical Direc to r ies

tmp: holds temporary files.

var: contains files that vary in size;

(Mail directories, printer spool files, logs,etc.)

etc: administrative files such as lists ofuser names and passwords.


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File and Direc to ry Name Rules

Valid names can be made up of:

Uppercase letters (A to Z).

Lower case letters (a to z). Case sensitive!!!

Numbers (0 to 9). Period (.), underscore (_), commas (,).

Should not contain spaces or the following:

& * \ | [ ] { } $ < > ( ) # ? ; ^ ! ~ %. Never /. You should avoid naming files or directories with

Unix commands.


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Fi le Sys tem Structu re

Unix stores a file's administrativeinformation (its physical location ondisk, permissions including ownershipand modification times) in aninode(i-

node or Index Node).

The file name (link) is stored in thecontents of a directory entry. Deleting

a file consists of removing a link to theinode (the inode itself is not deleted).


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Fi le System Structu re

Data Recovery: When a file is deleted the number oflinks to the inode is reduced by one.

Note: an inode may have more thanone link (or name) --- see ln(1).

If the number of links becomes zero,the kernel may reuse the disk space

making recovery difficult. MagneticForce Microscopy (MFM) can recovermost data unless wipe(1) is used.


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The K Desk top Env ironm ent (KDE)


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GNOME


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OpenLook Windows Manager (o lwm )


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Common Desktop Env i ronment (CDE)


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How Do You Boo t Unix?Mult i -boot Prog rams

Windows NT OS loader- select the OS ofchoice

Linux LILO (Linux loader)-the tab key will

show

Selections. Type the name of the OS to load

GrubNewer versions of Linux (i.e., 9.0) use this loaderto choose the OS

Other methods to boot- Norton systemcommander, boot disc, Boot Magic


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Shell

Program that interacts with kernel Bridge between kernel and the user Command interpreter

User can type command and thecommand is conveyed to the kernel and itwill be executed


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Types o f Shel l

Sh simple shell

BASH Bourne Again Shell

KSH Korne Shell

CSH C Shell

SSH Secure Shell To use a particular shell type the shell name at the command

prompt.

Eg $csh will switch the current shell to c shell

To view the available shells in the system, type cat /etc/shells atthe command prompt

To view the current shell that is being used, type echo $SHELL at

the command prompt


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UNIX COMMANDS

UNIX Commands


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UNIX Commands

A command is a program which interacts with the kernel

to provide the environment and perform the functionscalled for by the user.

A command can be: a built-in shell command; anexecutable shell file, known as a shell script; or a source

compiled, object code file.

The shell is a command line interpreter. The userinteracts with the kernel through the shell. You can writeASCII (text) scripts to be acted upon by a shell.


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L inux Command Bas ics

To execute a command, type its nameand arguments at the command line

ls -l /etc

Command nameOptions(flags)

Arguments


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Standard Files

UNIX concept of standard files standard input (where a command gets its

input) - default is the terminal

standard output (where a command writes it

output) - default is the terminal

standard error (where a command writes

error messages) - default is the terminal


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Redirect ing Outpu t

The output of a command may be sent(piped) to a file:

ls -l >output> is used to specify

the output file
http://linux.com.hk/man/showman.cgi?manpath=/man/man1/ls.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/ls.1.inc


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Redirect ing Input

The input of a command may come (bepiped) from a file:

wc


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Common Commands

pwd - print (display) the working directory cd- change the current working

directory to dir ls - list the files in the current working directory ls -l - list the files in the current working

directory in long format
http://linux.com.hk/man/showman.cgi?manpath=/man/man1/pwd.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/cd.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/ls.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/ls.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/ls.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/ls.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/cd.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/pwd.1.inc


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Fi le Commands

cp Copy from the to the

mv Move/rename the to the

rm Remove the file named

mkdir Make a new directory called

rmdir

Remove an (empty) directory
http://linux.com.hk/man/showman.cgi?manpath=/man/man1/cp.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/mv.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/rm.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/mkdir.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/mkdir.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/mkdir.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/mkdir.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/rm.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/mv.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/cp.1.inc


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More Commands

who List who is currently logged on to the system

whoami Report what user you are logged on as

ps List yourprocesses on the system

ps aux List all the processes on the system

echoA string to be echoed Echo a string (or list of arguments) to the terminal
http://linux.com.hk/man/showman.cgi?manpath=/man/man1/who.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/whoami.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/ps.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/ps.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/echo.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/echo.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/ps.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/ps.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/whoami.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/who.1.inc


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More Commands

alias - used to tailor commands: alias erase=rm

alias grep=grep -i

ar- Maintain archive libraries: acollection of files (usually object fileswhich may be linked to a program, like aCMS TXTLIB)

M C d
http://linux.com.hk/man/showman.cgi?manpath=/man/man1/alias.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/ar.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/ar.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/alias.1.inc


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More Commands

awk -a file processing language that iswell suited to data manipulation andretrieval of information from text files

chown -sets the user ID (UID) to ownerfor the files and directories named bypathname arguments. This command is

useful when from test to production

M C d
http://linux.com.hk/man/showman.cgi?manpath=/man/man1/awk.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/chown.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/chown.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/awk.1.inc


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More Commands

diff- attempts to determine theminimal set of changes needed toconvert a file specified by the firstargument into the file specified by thesecond argument

find -Searches a given file hierarchyspecified by path, finding files that match

the criteria given by expression

M C d
http://linux.com.hk/man/showman.cgi?manpath=/man/man1/diff.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/find.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/find.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/diff.1.inc


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More Commands

grep -Searches files for one or morepattern arguments. It does plain string,basic regular expression, and extendedregular expression searching
http://linux.com.hk/man/showman.cgi?manpath=/man/man1/grep.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/grep.1.inc


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More Commands

kill - sends a signal to a process orprocess group

You can only kill your own processes

unless you are root

UID PID PPID C STIME TTY TIME CMD

root 6715 6692 2 14:34 ttyp0 00:00:00 sleep 10h

root 6716 6692 0 14:34 ttyp0 00:00:00 ps -ef

[root@penguinvm log]# kill 6715

[1]+ Terminated sleep 10h

M C d
http://linux.com.hk/man/showman.cgi?manpath=/man/man1/kill.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/kill.1.inc


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More Commands

make - helps you manage projectscontaining a set of interdependent files(e.g. a program with many source and

object files; a document built from sourcefiles; macro files) make keeps all such files up to date with

one another: If one file changes, make

updates all the other files that depend onthe changed file Roughly the equivalent of VMFBLD

M C d
http://linux.com.hk/man/showman.cgi?manpath=/man/man1/make.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/make.1.inc


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More Commands

sed -applies a set of editingsubcommands contained in a script to eachargument input file

find ./ -name "*.c,v" | seds/,v//g | xargsgrep "PATH"

This finds all files in the current and subsequent directories with an extension of c,v. sed then

strips the ,v off the results of the find command. xargs then uses the results ofsed and builds agrep command which searches for occurrences of the word PATH in the C source files.

Pi
http://linux.com.hk/man/showman.cgi?manpath=/man/man1/sed.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/find.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/sed.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/xargs.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/grep.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/grep.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/xargs.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/sed.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/find.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/find.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/sed.1.inc


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Pipes

An important early development in Unix was theinvention of "pipes," a way to pass the output ofone tool to the input of another.

eg. $ who | wc l

By combining these two tools, giving the wccommand the output of who, you can build a newcommand to list the number of users currently onthe system

Basic Unix commands (vs. DOS)


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cat file Concatenate or type out a file,

cat file1 file2... Type out a number of files

cd directory1 Change current directory to directory1cd /usr/bin Change current directory to /usr/bin

cd Change back to your home directory

clear Clear the current screen

cp file1 file2 Copy file1 to file2

cp file1 file2... dirCopy a number of files to a directory

ls List the files in the current directory

ls /usr/bin List the files in the /usr/bin directory

lpr file1 Print file1 out , lprfile1 file2 .. Print a number of files out

more file Look at the content of a file with paging, use q to get out


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mkdir directory Create a directory

mvfile1 file2 Movefile1 tofile2, like rename.

mvfile1 file2 ... dirMove a number of files into a directory

mv dir1 dir2 Move or rename a directory

rm file Remove a file

rm file1 file2... Remove a number of files

rm -r directory Remove a directory include the sub-directory

rmdirdirectory Remove a directory


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DOS Command Unix

CommandDescriptions

CDCHKDSK

CLS

COPY

DEL

DIRMD

MOREPRINT

RDRENAME

TYPE

cdduclear

cp

rm

lsmkdirmorelprrmdirmv

cat

Change directoryDisk usageClear the current screen

Copying filesRemoving files or directoriFile listing of directories

Create a directory

Type out a file with pagingPrint out a fileRemove a directory

Moving fi les around

Type out files


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Who, When, Why , What and Where?

man cp Display on-line manual for the cp command

man -kkeyword Display manual help file related to the keyword

passwd Change your login password

pwd Display the path name of where you are

uptime Tell you how long the machine has been up and running

users Tell you who is logging in

who Tell you who is logging-in in detail

w Tell you who is logging in and doing what!

whoami Show you the owner of this account

fingeruser Find out the personal information of a user

fingername Try to find the persons info. by his/her name

fingeremail-address Try to find the persons info across the network

write user Write a message on somebodys screen

talkuser Talk to the person logging in the same system with you

talkemail-address Talk to somebody logging in the network

date Display todays time and date

calyear Display the calendar of the specified year (e.g. 1997)

Sh l l S i t i


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Shel l Scr ipt ing

Shell scripting is the most useful andpowerful feature in Linux

Minimizes typing of repetitive command

Can schedule jobs to run in the system Can initiate back up activities for system

administration

Similar to batch files in DOS, but more

powerful than Batch files

W ki i th h l l i t


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Working w i th shel l sc r ip t

Open a file with extension .sh using vieditor

We can type any number of commandsthat we use to type at command prompt

Save the file Execute the file

sh file.sh

./file.sh (if the file has execution permission)

VI Edito r


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Popular text editor Just type vi at the prompt

and hit the enter key.

A new file will be opened Type the contents needed and save To save, press the Esc Key and then

press : (colon) w q and then enter

To quit with out saving Esc + : + q andthen enter

Vi d it


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Vi ed ito r

Navigation Left - h Down - j Up - k Right - l Top of the screen H (shift + h) //caps lock will not work Middle of the screen M (shift + m) Bottom of the screen L (shift + l) $ - End Key, 0 Home Key

Edit Commands Cut X, x

Copy yy, yw Paste P, p

Vi ed ito r


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Xcuts the letter after cursor positionxcuts the letter before cursor position

yyCopies a line at which cursor is currently positioned

ywCopies a word at which cursor is currently positioned

PPastes the copied content after cursor position

pPastes the copied content before cursor position

ddDeletes a line

Vi ed ito r

Shel l Scrip ts


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Shel l Scrip ts

To Print a line echo Hello World (Prints Hello World in the screen)

To read a line read n (Stores the content entered by user in variable

n

To Comment a line # This is a comment Only single line comment is available. For multi line

comment, we need to use # symbol in lines which wewant to comment.

Condi t ions


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Condi t ions We can have if, if else, if elif else and case statements (Nested if

statements are also possible

1. if [ condn ]then

fi

2. if [ condn ]then

elsefi

3. if [ condn ]then

elif [ condn ]then

elsefi

Condit ions (Case)


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Condit ions (Case)

case expr in

Option1) stmt ;;Option2) stmt ;;*) stmt ;;esac

Every option should be terminated with adouble semicolon.

Denotes default case

Case should be termniated with esac

Loops


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Loops

For loopfor i in 1 2 3 4 5 //Loops 5 times

do

Body of the loopdone

for (( i=0; i


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Whi le Loop

while [ condn ]do

body of the loop

done

We need to ensure that the while loopcondition is terminated in a finite way

Compar ison


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Compar ison

For integer comparison we have the

following-eq : equal to

-ne : not equal to

-lt : less than

-gt : greater than

-le : less than or equal to

-ge : greater than or equal to

Compar ison


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Compar ison

For string comparison we have- = : equal to

- ~= : not equal to

For logical operators-a : AND

-o : OR

Arrays


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Arrays

Initialising an array A[0] = 10 A[1] = Hi

Using an array ${A[0]} : retrieves 10

Here arrays can contain data belonging todifferent data types

Uninitialised index in arrays will have null valueby default

Funct ions


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Funct ions

Local Function Written at the command prompt Lasts for the current session alone Global Function

Written in .bashrc file Available as long as the definition is there in

.bashrc file Function in shell script

Available with in the file alone

Parameters


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Parameters

Sample functionFunctionname()

{echo $1

}

Calling function:Functionname Ram

Result:Ram


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We can pass any number of parameters like this

$0File name

$1,$2 - first, second parameters and so on

$?stores the status (success or failure status of the last command that was

executed)

$# - stores the number of parameters passed through the command line

#pwd

/home

#echo $?

0 // As the last command is success

#abcError:command not found

#echo $?

127 // as the last command didnt execute successfully

C Prog ram in Linux


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C Prog ram in Linux

Open a file with extension .c from the command prompt using vi

editor

vi hello.c

Type the contents and save (Esc : wq!)

Compile the file

gcc hello.c Run the executable

./a.out

Compile file with output option

gcco hello hello.c

Run the executable

./hello


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UNIX Linux Basics Final

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