Introduction to Unix Concets.pptx

Introduction to UNIX Concepts
Mrs.Harsha V Patil, MIT ACSC Alandi , Pune

Introduction to Unix Operating System:
 UNIX is a powerful Operating System initially developed by Ken
Thompson, Dennis Ritchie at AT&T Bell laboratories in 1970.
 It is prevalent among scientific, engineering, and academic institutions
due to its most appreciative features like multitasking, flexibility, and
many more.
 In UNIX, the file system is a hierarchical structure of files and
directories where users can store and retrieve information using the
files.

Features of Unix:

Multitasking: A UNIX operating system is a multitasking operating
system that allows you to initiate more than one task from the same
terminal so that one task is performed as a foreground and the other task
as a background process.
Multi-user: UNIX operating system supports more than one user to
access computer resources like main memory, hard disk, tape drives, etc.
Multiple users can log on to the system from different terminals and run
different jobs that share the resources of a command terminal.
Portability: This feature makes the UNIX work on different machines
and platforms with the easy transfer of code to any computer system.
Since a significant portion of UNIX is written in C language, and only a
tiny portion is coded in assembly language for specific hardware.
File Security and Protection: Being a multi-user system, UNIX makes
special consideration for file and system security.

 Command Structure: UNIX commands are easy to understand and
simple to use. Example: "cp", mv etc. While working in the UNIX
environment, the UNIX commands are case-sensitive and are entered
in lower case.
 Communication: In UNIX, communication is an excellent feature
that enables the user to communicate worldwide. It supports various
communication facilities provided using the write command, mail
command, talk command, etc.
 Open Source: UNIX operating system is open source it means it is
freely available to all and is a community-based development project.
 Accounting: UNIX keeps an account of jobs created by the user. This
feature enhances the system performance in terms of CPU monitoring
and disk space checking.

 UNIX Tools and Utilities: UNIX system provides various types of
tools and utilities facilities such as UNIX grep , sed and awk , etc. Some
of the general-purpose tools are compilers, interpreters, network
applications, etc.
Architecture of the Unix Operating System:
 A computer system contains hardware and software that controls and
manage computer hardware, software resources, and Operating system
required for the computer.
 The operating system acts as the intermediate between hardware and
the user-defined application software. Unix is a multitasking,
multiuser operating system.
 The software is of two types:
 System software
 Application software.

 The system software provides platform for other software on the
computer . Application Software is user-defined software that works on
the system software. An operating system is a system software.
The Unix system architecture is divided by into four layers.
 Kernel
 Shell
 Commands and Utilities
 User Applications

Unix Kernel
Kernel is the central core that interacts directly with the hardware of the
system.
The main functions of Kernel are:
 Computer hardware such as memory, disc, printers are controlled
by the kernel.
 The kernel schedules the processes, control and executes various
user-defined tasks.
 Manages the data storage
Unix Shell
 It is the interface between the user and the kernel. Users can interact
with the shell using shell commands.
 Users communicate directly with Shell. Translates user’s
commands into functions understandable by Kernel
 It interprets commands given by the users and executes them
using the kernel.

 Issues a shell prompt and waits for user response
 Provides programming ability to the users to write shell
commands
Commands and Utilities
Commands used by the Unix operating system are:
 ‘sh’ – shell commands providing a primary user interface,
 There are various commands and utilities which you can make
use of in your day to day activities. cp, mv, cat and grep
User Applications
 All the data/programs which the user writes.

UNIX FILE SYSTEM
Introduction
 A file is one in which data can be stored .
 It is a sequence of bits , bytes or lines and stored on a storage device like
a disk.
 In unix everything is stored in terms of files.
 It could be a program , an executable code, a file, a set of instructions, a
database , a directory or a subdirectory.
 A unix file is a tool or an application that defines the structure of the
file and its format.

Unix Filenames
 Unix is case sensitive! So a file named my data. Txt is different from
mydata.txt which is again different from mydata.txt.
 Unix filenames contain only letters, numbers and
the_(underscore)&.(dot)characters. All other characters should be
avoided. The /(slash) characters is especially important/since it is used
to designate subdirectories.
 It is also possible to have additional dots in the filename.
 The part of the name that follows the dot is often used to designate the
type of file.
 Files that end in.TXT are text files.
 Files that end in .C are source code in the ‘C’ language.
 Files that end in.HTML files for the web.

 But this is just a convention and not a rule enforced by the operating
system . This is a good and sensible convention which you should
follow.
 Most UNIX system allow a maximum of 14 characters as the length of a
filename. However it depends on the UNIX variant used.
FILE SYSTEM
The unix file system is organized as a hierarchical tree structure.
The structure of a simple unix file system divided into 4 parts.
1. The Boot block
2. The Super block
3. The Inode block
4. The Data blocks

1) The Boot Block
 The boot block is located at the beginning of the file system.
 It can be accessed with minimal code incorporated in the computer’s
ROM bios.
 It contains the initial bootstrap program used to load the os.
2) The Super Block
 It contains statistical information to keep track of the entire file
system. Whenever disk manipulation is required, the super block is
accessed.
The Super Block contains the following information:

1. Size of the file system: This is the storage size of the device.
2. List of storage blocks: The storage space is divided up into a series of
standard size blocks.
3. Number of free blocks on the file system.
4. A list of free blocks with their location.
5. Index to next free block on the list.
6. A list of free inodes.

3) The Inode Block
 Information about each file in the file system is a special kernel
structure called an inode.
 It contains a pointer to the disk blocks containing the data in the file,
information such as type of file, permission bits, the owner and group,
file size, file modification and so on.
 The name of each file is listed in the directory the file is associated
with. A directory is special type of containing a list of filenames and
associated inodes.
 When a user attempts to access a given file by name, the name is
looked up in the directory. Where the corresponding inode is found.

An inode for a file contains the following information.:
 File ownerid : It is the numeric id used in the password file to uniquely
identify a user on the system.
 Group id (GID) : This identifies a group that can be granted special
access by the owner.
 File type : It indicates whether inode represents a
file,adirectory,aFIFO,character device.

4) Data Block
 It contain the actual data contained in the files.
 These blocks follows the inode table and occupy most of the storage
device space.
 It allotted to one file cannot be allotted to another file, unless the two
files are linked.

File access permissions
 User access: Access by the person who owns the file.
 Group access: Access by the members of a specified group.
 Other access: The rest of the world, who are not the owner.
Types of Access
 Read access : To be able to read the data stored in file.
 Write access : To be able to modify the data stored in file.
 Execute access : To be able to request that the system attempt to
execute the file.

Introduction to File System and Process Environment.
Unix file system is a logical method of organizing and storing large
amounts of information in a way that makes it easy to manage.
A file is a smallest unit in which the information is stored. Unix file
system has several important features.
All data in Unix is organized into files.

Types of Files
The unix os is built around the concept of the a file system which is
which is used to store all of information. Including the operating sysem
kernel itself.
There are 4 types of files:
1. Ordinary or Regular files
2. Directory files
3. Device files or special files
4. Hidden files

1.Regular or ordinary files:
It can contain text, data, or program information, files cannot
contain other files or directories. Instead use the underscore(’_’)
symbol. it is ordinary file.
An ordinary file can be of 2 types.
i. Text file
ii. Binary
I. Text File: A text file contains only printable characters. It contains line
of character, each line terminated by a newline character .
Ex: text files include c and Java program ,shell and perl scripts.
II. Binary File: A binary file contains both printable and unprintable
character(0 to 255 ASCII code).
Ex: binary files include unix command ,object code of c programs
,pictures , sound , and video files. file

2. Directory files :
Directories are containers or folders that hold files, and other
directories . Directories can point to other directories which are known
as Sub directories.
The directories generally contains files and other sub directories along
with their link information . normally a directory contains 2 pieace of
information.
i. The file name
ii. A unique identification number.
When a user creates or remove a file ,the kernel updates the
corresponding directory by adding or removing the inode number and
files name associated with the file.

3. Device files :
To provide applications, with easy access to hardware devices. UNIX
allows them to be used in much the same way as ordinary files. The
video screen of your pc , RAM , disk , input ports and other such
devices are usually accessed through device file.
Two types of device files in unix:
 Block-oriented :Block-oriented devices which transfer data in blocks.
EX: Hard disk
 Character-oriented: Character oriented devices that transfer data on a
byte –by byte basis( eg. modems , printers and networks).
 Hidden files : The filename can begin with a dot character is called
hidden file.

Types of users
1. The owner of file(user)
2. The users who belong to the same group as the file(group)
3. Everyone else(other)
UNIX Directory Structure

 Directories are organised into a hierarchical structure that fan out like
an upside own tree.
 The top most directory is known as root and it is written as (/).
 The roots contains subdirectory and each of these can contains more
subdirectory and so on.

Directory Contents
/ The root directory
/bin Essential low-level system utilities
/usr/bin Higher-level system utilities and application programs
/sbin Super user system utilities (for performing system
administration tasks )
/lib Program libraries (collections of system calls that can be
included in programs by a compiler)for low level system utilities.
/usr/lib Program libraries for higher level user programs
/tmp Temporary file storage space (can be used by any user)

Directory Contents
/dev Holds the files /device drivers necessary to operate peripherals
such as terminals , keyboard, printer , hard disk etc
/var Contains files that vary in size , mail
Directories , printer , spool file , logs etc..
/usr/include Contains standard headed files used by c programs
/home User home directories containing personal file space for
each user. each directory is named after the login of the user.
/etc Unix system configuration and information files.

File access methods
Owner:
 It is the owner of the file . the owner’s permissions determine what
actions the owner of the File can perform on the file.
Group:
 It gives the name of the group . the groups permissions determine what
actions a user, who is a member of the group that a file belongs to , can
perform on the file.
Other:
 the rest of the world who are not the owner . the permissions for others
indicate what action all other users can perform on the file.

File and Directory related commands
1.Ls command : listing files
It is used to display all the files and sub directories in a current directory.
Syntax : ls options filename
Ls options :
-a : list all files including hidden files . Hidden file names start with a dot
character.
A single dot (.) refers to the current directory and a double dot (..) refer
to the parent Directory .
-x : list the content in a row – wise format.
-r : list contents , sorted in reverse alphabetical order.
*t : list all files ending with letter t .
t* : list all file names starting with letter t .
-u : list the contents based on the access time or using time .

2.Cat command : it is used to
i. Creating files :
cat command can be used to create small files
syntax :
cat options input file
Example : $cat > fruits
Apple
Banana
Orange
<ctrl d> or (ctrl + d)

ii. Displaying contents of a file :
cat display only the contents of the file
syntax :
$cat filename
Ex :
$cat > veg
Carrot
Beans
Tomato
< ctrl + d>
$cat fruits veg
Apple
Banana
orange
carrot
Beans
Tomato

iii. Concatenation of files :
 Cat command can concatenate the contents of two or more files and
start
 Store then in another file.
Syntax :
$cat test1 test2 > test3
Ex $cat fruits veg > food
$cat food
Apple
Banana
Orange
Carrot
Beans
Tomato

iv. Append files :
Cat command is to append or add data to the contents of the file
Syntax :
$cat >> filname1
Ex :
$cat fruit1
Grapes
(ctrl + d)
Options
-v : displays non-printable ASCII characters.
-n : numbers the lines in the file .
-s : silent (no error messages).

3.Cal command :
Cal command is used to print the calendar of a required month or year
Syntax :
cal { [month] year }
Ex :
$cal 2013 | more
Date and time command :
it displays the current date with time .
syntax :
date options arguments

options :
d : day of the month.
y : last two digits of the year .
H,M& S : hour ,minutes,seconds.
D : date in mm/dd/yy format .
T :time in hh : mm : ss format .
h :month name.
a :day of week.
Ex :
$date
Sat jan 05 15:35:30 1st 2016

4.Who Command:
 Who command provides the login details of all current users in 3
columns format.
Syntax :
 Who options am i
 First column shows login names , second column shows the devices
names of the terminals and third column shows the login date and
time .
Options :
-H :displays headers for the columns .
U :displays more details including idle time ,PID and comments .
PID is the process – ID , which is a unique number identifying a process .
Who am i gives the self login details of a week .

5.Printf : print formatted output command .
it is used to write formatted output .
syntax :
print f format arguments
TTY : terminal command
It is used to known the name of the device file .
Syntax :
tty
Ex :
$tty
/dev/pts /1

6.Uname : system name command
It is used to know the name and certain features of the system
Syntax :
Uname options
Options
-v :prints the versions of os .
-a :options displays all deatails of the system .
-m :machine details .

7.Passwd
It is used to change password in passwd .
Syntax :
$passwd
8.echo :
it is usually used in shell scripts to display messages on the terminal
Syntax :
echo options arguments
Ex :
$echo I am studying in 2 Bca
I am studying in 2 Bca
$echo “ I am studing in 2 Bca “
I am studing in 2 Bca

9.Bc : calculator command
there are two types of calculator .
1. Xcalc :it is a graphical object which
is used only on x- window system and is easy to use .
2. bc : it is a text – based command .
it behaves both as base calculator and a small language .
it can perform all arithmetic operations .
Syntax :
bc arguments
Ex :$bc $bc $bc
15+5 sqrt(49)10/3
20 7 3
21 22 23

10.Pwd : print working directory command
Pwd in a command that prints the absolute pathname of your current
working directory
Syntax :
Pwd
Ex :
$pwd
/home/rama

11.The home directory :
When you log into unix ,your current working directory is your user
home directory.
we can refer to home directory at any times as (tilde)” ~ ” .
so, ~std2/play is another way for user std 1 tp specify an absolute path
to the directory /home/std2/play ,user std2 may refer to the directory as
~ /play .
The home directory can be found using a shell variable called HOME
as shown :
$ echo $HOME
/home/rama

12.Pathnames :
It is the notation used to point to the particular file or directory
Pathnames is divided in to two
a) Absolute path
b) Relative path
a) Absolute path :
Absolute path all ways starts from root directory (/) .
Ex :
User /jen /person
b) Relative path :
It points to a file or directory relative to your current working directory .
Ex :
Person /art.html

13.Cd-changing the directory
It is used to move from one directory to another.it uses a pathname as its
arguments.
.(single dot)means current
directory.
..(double dot)means the parent
directory.
~(tilde)means your home directory.
A plain cd without pathname brings
you back to your home directory.
Syntax
Cd pathname

Ex :$pwd
/home/rama
$mkdir partha
$cd partha
$pwd
/home/rama/partha

14.mkdir:making directors
mkdir command is used to create new directories.
Syntax:
mkdir options dir-names
ex:$mkdirranjitha
$cd ranjitha
ranjitha $ pwd
/home/ranjitha
15.rmdir:
It removes one or more directories or subdirectories.
Syntax
rmdir dir-names
ex: $cd
$rmdir ranjitha

16. touch :
The ‘$ touch’ command creates a file(not directory) and you can simple
add an extension such as .txt after it to make it a Text File.
$ to
17. cp :
This ‘$ cp ‘ command stands for ‘copy’ and it simply copy/paste the file
wherever you want to.
$ cp
18. mv :
The ‘$ mv’ command stands for ‘move’ and it simply move a file from a
directory to another directory.
$ mv

19. rm : The ‘$ rm ‘ command for remove and the ‘-r’ simply recursively
deletes file. Try ‘$ rm filename.txt’ at your terminal
$ rm
20. chmod :
The ‘$ chmod’ command stands for change mode command.As there are
many modes in Unix that can be used to manipulate files in the Unix
environment. Basically there are 3 modes that we can use with the
‘chmod’ command
1. +w (stands for write and it changes file permissions to write)
2. +r (stands for read and it changes file permissions to read)
3. +x (generally it is used to m

21. file:
The ‘$ file’ command displays the type of file . As Linux treats everything
as a file so on executing the command file on a directory(Downloads) it
displays directory as the output
$ ls
22. sort :
As the name suggests the ‘$ sort’ sorts the contents of the file according to
the ASCII rules.
$ sort
23. grep :
grep is an acronym for ‘globally search a regular expression and print it’.
The ‘$ grep’ command searches the specified input fully(globally) for a
match with the supplied pattern and displays it.
$ grep

24.man :
The ‘$ man’ command stands for ‘manual’ and it can display the in-built
manual for most of the commands that we ever need.
$ man
25. lpr :
The ‘$ lpr’ command send a file to the printer for printing.
$ lpr

26. clear :
The ‘$ clear’ command is used to clean up the terminal so that you can
type with more accuracy
$ clear
27. history :
The ‘$ history’ command is used to get list of previous commands may be
obtained by executing the following command. you can also use
parameters like !n to re-execute the nth command, !! to executes the most
recent command, and !cp this will execute the most recent command that
starts with cp.
$ history

Thanks !!!

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