01 unix overview

8/14/2019 01 Unix Overview

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1

Date

PresenterThe only thing more powerful than a great

idea,is a great idea powerfully executed.

- William Blake

Copyright 2002 Wipro Technologies


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For WASE & Team Rainbow

1 Day Session

Unix Overview

Copyright 2002 Wipro Technologies


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3Wipro Confidential

Operating Systems

What is an Operating System? By operating system, we mean the suite of programs which

make the computer work. These are the set of programs whichare loaded during the startup of a computer and runs until thesystem is switched off.

It is the operating system, which loads and runs otherapplications like MS-office suite or other such userapplications.

Examples of popular operating systems

Windows

Novell Netware

Unix

Single-user operating systems, like DOS, or the MacintoshSystem


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Operating Systems

Single User Operating Systems

Such operating systems allows only one user to use thecomputer at a time. MS-DOS, Windows-95 etc are suchoperating systems.

Such OS are primarily used in personnel computers.

Multi-User / Multi-Tasking Operating Systems Such operating systems allows multiple users to use the

computer at the same time.

Each user can run multiple programs at the same time.

Such Operating Systems has various level of user accessprivileges. Certain users (super users) will have completecontrol over the system, where as other users will have onlylimited access rights.

Such restrictions are essential to control the system and toensure availability to the system users.

Examples of such OS are: Unix, DB2, Windows-NT etc..


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Unix Operating System

UNIX was created in the late 1960s, in an effort to provide a multi-user, multitasking system for use by programmers. The philosophybehind the design of UNIX was to provide simple, yet powerfulutilities that could be pieced together in a flexible manner toperform a wide variety of tasks.

The UNIX operating system comprises of three parts:

The kernel

The standard utility programs

The system configuration files

Unix is mainly written in C and Assembly-Language.

There are various flavors available in the market.


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Unix flavors

Every Unix-box hardware vendor come out with their version of Unix. These versions has all Unix System V features tuned to work

with their hardware architecture.

Available Unix Flavors

Sequent Dynix/Ptx

Sun Solaris

HP-UX

Sco Unix

Digital Unix

IBM AIX Linux


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Unix Architecture overview



Unix Architecture overview

Typical computer system consists of: Hardware

Operating system

Applications and utilities

Operating system controls the computer hardware and interfaceuser with the hardware

Typical OS includes a user interface orcommand interpreter.

Unix is somewhat unique in that the command interpreter is notintegrated with the OS but is a separate program. This enablevendors / developers to develop custom / better commandinterpreters for Unix.



Files and processes

Everything in UNIX is either a file or a process.

A process is an instance of executing program . Each process is identified by a unique PID (process

identifier).

Processes can spawn other processes.

A file is a collection of data. They are created by users usingtext editors, running compilers etc. Examples of files:

A document (report, essay etc.)

The text of a program written in some high-levelprogramming language

Instructions comprehensible directly to the machine andincomprehensible to a casual user, for example, a collectionof binary digits (an executable or binary file);

A directory, containing information about its contents,which may be a mixture of other directories (subdirectories)and ordinary files.



The Directory Structure

All the stored information on a UNIX computer is kept in a

filesystem. Any time you interact with the UNIX shell, the shellconsiders you to be located somewhere within a filesystem.Although it may seem strange to be "located" somewhere in acomputer's filesystem, the concept is not so different from real life.After all, you can't just be, you have to be somewhere. The place inthe filesystem tree where you are located is called the current

working directory.

CONCEPT: The UNIX filesystem is hierarchical (resembling a treestructure). The tree is anchored at a place called the root,designated by a slash "/". Every item in the UNIX filesystem tree iseither a file, or a directory. A directory is like a file folder. Adirectory can contain files, and other directories. A directorycontained within another is called the childof the other. A directoryin the filesystem tree may have many children, but it can have onlyone parent. A file can hold information, but cannot contain otherfiles, or directories.



The Directory Structure

/File 1

File 5

Sub-dir 1

Sub-dir 2

File 3

File 4

Sub-dir 3

File 6

File 7

File 8

File 8

Sub-dir 3

File 9

File 10

Working Directory

Current directory where user is placed

Root Directory

Unix directory structure starting point

Home Directory

Default directory for the user

Changing current working directories

cd Set current directory to home directory

cd / - Set current directory to root

cd .. Set current directory one level up

cd ../.. Set current directory two levels up

cd ../ - Set current directory to sub directory a level up

pwd Shows the current directory



Accessing a UNIX System

The main mode of access to a UNIX machine is through a terminal,which usually includes a keyboard, and a video monitor. For eachterminal connected to the UNIX system, the kernel runs a processcalled a ttythat accepts input from the terminal, and sends output tothe terminal. tty processes are general programs, and must be toldthe capabilities of the terminal in order to correctly read from, and

write to, the terminal.

Initially Unix supported only character terminals. However, later x-Windows got evolved to provide a graphical user interface.

There are terminal programs available in Windows, which mimic acharacter terminal, and through such terminal programs, a Unixsystem can be accessed from Windows.



Logging In and Logging Out

To access a Unix system, one has to start a user session from aterminal.

A user session is started by providing a valid Unix user id andpassword.

Upon providing the right user id and password, Unix starts a usersession and a command interpreter is spawned.

Command interpreter waits for the user to enter a command in itsprompt. Execute the command and waits for the next command.

To end the session, a command exit is entered in the commandinterpreters prompt. This will make the Unix to clean-up the usersession, end all user processes and remove the user session fromthe system.



Space Management / mount points

A file system is created on a hard disk and same can be mounted on theUnix system.

File System creation is the process of readying a portion of hard disk for Unix tokeep its files.

Mounting is a process by which the file system is made available to the users.

Once mounted, the file system is available under the directory structure as adirectory.

There are commands to describe the mounted files systems / mount points.df is such a command available in Unix.

Filesystem kbytes used avail capacity Mounted on/dev/md/dsk/d10 6050182 5701570 288111 96% /

/dev/dsk/c0t0d0s5 3009327 2852761 96380 97% /u01



Backup & Recovery

Backup

Backup is the process in which data stored in a computer is copied toan alternative storage medium (e.g Tapes, CDs etc..)

Hot & Cold Backup Backups taken during the normal system operations are called hot backups.

Here the files could be get modified while backing them up.

Cold backups are taken while system is not performing any file operations.All cold backups will be stable and are independent backups.

Recovery Process by which systems data is restored from backup device after a

system/media crash.

There are vendors who offer backup & recovery mechanism(software & hardware).



UNIX Shell

A Unix shell is the command interpreter, the primary user interface to UNIX which

interpret and execute commands

There are number of shells available. /bin/sh - Bourne shell /bin/csh - C shell /bin/ksh K shell /bin/bash - Bourne again shell

/bin/tcsh - modified, updated C shell

A Shell can be tuned for each user by keeping the initialization commands, scriptsin the shell startup file.

Shell scripting allows users to write procedural programs using shell scriptinglanguage. These scripts can be executed within the shell.

Each Unix command consists of a command name, followed by commandoptions (if any are desired) and command arguments (if any are desired). Thecommand name, options, and arguments, are separated by blank space.e.g: cd /



Main memory / Shared memory

Kinds of Memory:

Main - The physical Random Access Memory located on the CPUmotherboard that most people think of when they talk about RAM. Alsocalled Real Memory. This does not include processor caches, videomemory, or other peripheral memory.

File System - Disk memory accessible via pathnames. This does notinclude raw devices, tape drives, swap space, or other storage notaddressable via normal pathnames. It does include all network filesystems.

Swap Space - Disk memory used to hold data that is not in Real or FileSystem memory. Swap space is most efficient when it is on a separatedisk or partition, but sometimes it is just a large file in the File System

Shared Memory Part of Main memory which is shared between processes across unix

users. Typically each process get part of main memory as a privatearea, where only that process operates. Shared memory is the placewhere multiple processes has access to.



Unix Processes

Foreground / Interactive Processes

Processes that are spawned from shell command prompt. Shell waits forthe process to complete before returning the command prompt.Command / Process output will be written to users terminal.

Background processes Processes that are run non-interactively. Such processes are not

associated with any terminal. Kernel processes are examples ofbackground processes. A user can submit such processes fromcommand prompt by appending the command with & sign.

Input / Output Each process has the following devices attached to it.

Standard input Device to get the input data. Normally the keyboard. Standard output Device to output data from the process. Normally the

terminal.

Standard error Device to output error messages. Normally the terminal.



User Management

User

Unix users created to access the system. A password is alwaysattached to each user id. The right combination of user id andpassword allows one to access the Unix system and create a Unixsession.

Various level of privileges can be set at the user level.

Groups Unix administrator can create Groups where one or more Unix users

can made members.

Various level of privileges can be set to group, which will be applicableto all group members.

One unix user can be made members of multiple groups.


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File / Directory Permissions

Each file / directory in Unix has access permissions associated to

it. Read Whether the file/directory can be read?

Write Whether the file/directory can be modified? In case ofdirectories, this means whether files can be created/modified under thisdirectory.

Execute Whether the file can be executed. Applicable for shell scripts

and other executable programs.

Read / Write / Execute permissions are denoted by rwx flags.

For each file/directory, r,w,x permissions are attached to User, Groupand Others level.

User Owner or an Administror Group Unix group(s) where the user is a member of

Others Users who are not members of group(s) where the User ismember of.


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Popular Unix Commands

Help on Unix commands are available by typing the following

command at the command prompt man

User Commands man(1)

NAME

man - find and display reference manual pages

SYNOPSIS

man [ - ] [ -adFlrt ] [ -M path ] [ -T macro-package ]

[-s section ] name ...

man [ -M path ] -k keyword ...

man [ -M path ] -f file ...

DESCRIPTION

The man command displays information from the reference

manuals. It displays complete manual pages that you selectby name, or one-line summaries selected either by keyword

(-k), or by the name of an associated file (-f). If no

manual page is located, man prints an error message.

Source Format

Reference Manual pages are marked up with either nroff(1) or

sgml(5) (Standard Generalized Markup Language) tags. The

man command recognizes the type of markup and processes the


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Popular Unix Commands - Navigation

cd Change working directories

ls List directory contents pwd Show current working directory

$

$ pwd

/u14/home/gie

$

$ cd ../..

$ pwd/u14

$ ls

GIE_DATA_CORR.fmb home patchsso visappl

TT_DB lost+found testdata viscomn

$ ls -l

total 992

-rw-r--r-- 1 gie users 483328 Jan 7 17:20 GIE_DATA_CORR.fmb

drwxr-xr-x 2 root root 512 Jan 23 20:10 TT_DB

drwxrwxrwx 10 root other 512 Dec 1 14:57 home

drwx------ 2 root root 8192 Apr 16 2002 lost+founddrwxr-xr-x 6 app1159 dba 512 Oct 15 13:43 patchsso

drwxr-xr-x 2 ora1159 dba 512 Oct 7 18:45 testdata

drwxr-xr-x 204 app1159 dba 3072 Jan 19 10:08 visappl

drwxr-xr-x 9 app1159 dba 512 Sep 3 23:29 viscomn

$

$ ls -CF

GIE_DATA_CORR.fmb home/ patchsso/ visappl/

TT_DB/ lost+found/ testdata/ viscomn/

$


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Popular Unix Commands File Operations

cp Copy files mv Move / Rename files rm Remove files touch Create file with zero bytes or mark files modified chmod Change file permissions chown Set the owner for the file chgrp Set the group for the file

$ touch TeamRainbow

$ ls -l TeamRainbow

-rw-r--r-- 1 gie users 0 Jan 26 14:45 TeamRainbow

$ mv TeamRainbow Batch100

$ ls -l Batch100-rw-r--r-- 1 gie users 0 Jan 26 14:45 Batch100

$ chmod g+w Batch100

$ ls -l Batch100

-rw-rw-r-- 1 gie users 0 Jan 26 14:45 Batch100

$

$ su

Password:

# chgrp other Batch100

# ls -l Batch100

-rw-rw-r-- 1 gie other 0 Jan 26 14:45 Batch100

#

# chown root Batch100

# ls -l Batch100

-rw-rw-r-- 1 root other 0 Jan 26 14:45 Batch100

#

# rm Batch100

#

# ls -l Batch100

Batch100: No such file or directory

#


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Popular Unix Commands File Operations

mkdir Create Directory rmdir Remove directories

cat Output file contents pg / more Output file contents page by page

$ ls -l

total 0

-rw-r--r-- 1 rainbow rainbow 0 Jan 26 14:52 test

$ mkdir Mydir

$ ls -ltotal 2

drwxr-xr-x 2 rainbow rainbow 512 Jan 26 15:03 Mydir-rw-r--r-- 1 rainbow rainbow 0 Jan 26 14:52 test

$ cd Mydir

$ ls -l

total 0

$ cd ..

$ pwd

/u02/home/rainbow

$ rmdir Mydir

$ ls -l

total 0


$

$ cat test

This is line 1

This is line 2

This is line 3

This is line 4

This is line 5

$


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clear Clear screen date Displays system date echo Prints the argument values to screen file Shows the type of file passwd Command to change the user password uid Shows the current user & group details ps Shows the current processes running

$ dateMon Jan 26 15:14:18 IST 2004

$

$ echo This is a testThis is a test

$ echo $LOGNAMErainbow

$ file *

test: English text$ file /bin/at

/bin/at: ELF 32-bit MSB executable SPARC Version 1, dynamically linked, stripped

$ iduid=1099(rainbow) gid=1005(rainbow)

$

$ passwd rainbowEnter login password:

New password:

Re-enter new password:passwd (SYSTEM): passwd successfully changed for rainbow

$ ps

PID TTY TIME CMD11363 pts/7 0:00 ksh

10540 pts/7 0:00 sh

$ ps -fu gieUID PID PPID C STIME TTY TIME CMD

gie 9235 9233 0 14:30:08 pts/7 0:00 -ksh$ ps -l

F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD

8 S 1099 11363 10540 0 51 20 627e21f8 207 627e2268 pts/7 0:00 ksh8 S 1099 10540 9235 0 51 20 6344b668 121 6344b6d8 pts/7 0:00 sh

$


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cal Calendar program cut Shows file contents after vertical filtration grep Shows file contents after horizontal (lines) filtration

$ cal

January 2004S M Tu W Th F S

1 2 3

4 5 6 7 8 9 1011 12 13 14 15 16 17

18 19 20 21 22 23 24

25 26 27 28 29 30 31

$

$ cat test

This is line 1This is line 2


This is line 5$

$ cut -c1-10 test

This is liThis is li

This is li

This is liThis is li

$$ cut -d' ' -f3 testline

line

lineline

Line

$$ grep [35] test

This is line 3

This is line 5$


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head Shows the initial part of the files tail Shows the trailing part of the file sort Shows the file contents after sorting

$ cat testThis is line 1This is line 2


This is line 5

$$ head -2 test

This is line 1

This is line 2$

$ head -4 test


This is line 3

This is line 4$

$ tail -3 test


This is line 5

$$ cat test


This is line 3


$

$ sort -r testThis is line 5

This is line 4


This is line 1

$


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diff Shows the difference in file contents

find Command to search for file(s) in a directory structure

$ cat test

This is line 1

This is line 2

This is line 3

This is line 4

This is line 5

$

$ cat test1This is line 1

This is line 2

This is line 3

$

$ diff test test1

4,5d3

< This is line 4

< This is line 5

$

$ cd ..

$ pwd/u02/home

$

$ find . -name 'test' -print

./rainbow/test

./abshah/test

find: cannot read dir ./easdba/bin: Permission denied

$


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Pipe - Feature

Unix provides a powerful feature in which output from a command can be directed as input for anothercommand. This way, commands can be joined to process data in a very efficient manner.

Example: cat | sort

Here, output of the cat command (file contents) are fed to command sort. The final output of thiscommand will be sorted file contents

$ cat test

John received 30 marksPeter received 25 marks

Abraham received 15 marks

$$ cat test | cut -d' ' -f1,3 | sort

Abraham 15John 30

Peter 25

$

$ cat test | cut -d' ' -f1,3 | sort +1

Abraham 15

Peter 25

John 30

$


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vi Unix Text Editor

vi is the most popular text editor available in Unix. It operates in two modes,command & input mode.

In the command mode, vi accepts commands.

In the input mode, whatever user types are taken as file contents.

While in input mode, pressing Esc will change the mode into command mode.

Popular vi commands i Goes into the input mode. Start insertion from the current cursor position.

a Goes into the input mode. Start insertion from the current cursor position + 1 (append)

A Start insertion from end of line

c Change mode. Start replacing from the current cursor position.

dd Deletes the current line

:w Perform a save operations

:wq Save and Exit

:q! Discard the changes and exit.

:w Save into a different file name.

dw Delete word

d$ Delete till end of line

/ Search for

n Search for the next occurrence (find next)

N Search backwards (find previous)

:e Edit the file name

dG Deletes till end of file

u Undo the last command


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Shell Variables

Unix allows you to define variables within a Shell. Unlike other programming languages, Shell variablesdo not have any types. All values are stored as character strings.

There are many variables defined in a users environment.

$ env

_=/usr/bin/env

HZ=100

PATH=/usr/bin::/usr/local/bin::/usr/opt/SUNWmd/sbin

LOGNAME=rainbow

SHELL=/bin/sh

HOME=/u02/home/rainbow

TERM=ansi

PWD=/u02/home/rainbowTZ=IST

$

$ TESTVAR="Hello World"

$

$ echo $TESTVAR

Hello World

$

$ ksh

$

$ echo $TESTVAR

$ exit

$ export TESTVAR

$

$ ksh

$ echo $TESTVAR

Hello World

$ exit$


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Introduction to Shell Scripting

Shell script is a script file which contains commands and other controlstatements. A shell script can be executed within a Unix shell. Unix shell will

execute each line in the shell script like any other interpreter.

$ vi myshell.ksh

ls -l

date

echo "Log Name is : " $LOGNAME

~

~

~~

~

~

~

~

~

"myshell.ksh" [New file] 4 lines, 43 characters

$ ls -l myshell*

-rw-r--r-- 1 rainbow rainbow 43 Jan 26 16:31 myshell.ksh

$ chmod +x myshell*$ ls -l myshell.ksh

-rwxr-xr-x 1 rainbow rainbow 43 Jan 26 16:31 myshell.ksh

$ myshell.ksh

total 6

-rwxr-xr-x 1 rainbow rainbow 43 Jan 26 16:31 myshell.ksh


-rw-r--r-- 1 rainbow rainbow 45 Jan 26 15:40 test1

Mon Jan 26 16:31:42 IST 2004

Log Name is : rainbow

$


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Introduction to Shell Scripting

Shell also provides control/procedural statements for ShellScripting.

for identifier [ in word ... ] ; do list ; done select identifier [ in word ... ] ; do list ; done

case word in [ pattern [ | pattern ] ) list ;; ] ... Esac

if list ; then list ;

[ elif list ; then list ; ... ] [ else list ; ] fi

while list ; do list ; done

until list ; do list ; done

Do a man ksh at the command prompt and go through the kshuser manual to understand the full capabilities of ksh and also shellscripting features.


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Class room Assignment

Go through the man pages of the commands listed in the

previous slides. Practice them with different command options.

Write a shell script to satisfy the following requirement. File mydata.txt has the following content (create this file using vi):

Bill 10

Joe 243

Kirthi 54

Write a Shell script to get an output as follows (lines sorted on marks):

Bill Received 10 marks.

Kirthi Received 54 marks.

Joe Received 243 marks.


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01 unix overview

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