This document provides an introduction to the Unix operating system, including its history, components, features, and file system organization. It discusses the kernel and shell components, types of shells like Bourn shell and C shell, and features such as multi-user capability, multitasking, security, and portability. It also describes the Unix file system structure, types of files, directories, and permission blocks.

1. Unix & Shell Programming
Introduction to Unix

2. Unix and Shell Programming
• Introduction to Unix Operating System.
• Features of Unix Operating System.
• Multiuser Capability.
• Types of Terminals
• Dumb Terminal
• Terminal Emulation
• Dial in Terminal
• Multitasking Capability
• Communication
• Security
• Portability

3. Unix and Shell Programming
• Unix System Organization.
• Unix System Kernel and Utilities.
• Kernel
• Shell
• Bourn Shell
• C Shell
• Korn Shell
• Unix File System.
• Files
• Ordinary Files
• Special Files
• Directory Files
• Features of Unix File System
• Directories

4. Unix and Shell Programming
• Blocks of the Unix File System.
• The Boot Block
• The Super Block
• Inode Table
• Data Block
• File Permission.

5. Introduction to Unix Operating System
In 1969 a time sharing computing system known as Multics was popular. It is written
in assembly language.
UNIX known as UNICS (Uniplexed Information and Computing System)is an operating
system which was first developed in the 1960s, But originally developed in 1969 by
Dennis Ritchie, Douglas McIroy and Joe Ossanna at AT&T Bell Labs.
It is multiuser, multitasking system for servers, desktop and laptops.
It is completely written in C language by Dennis Ritchie.
Types of UNIX
The most common UNIX’s varieties are Sun Solaris, GNU/Linux (UBNTU) and MaxOS X.
Mostly in School and Colleges use Solaris on their servers and Fedora Linux on the
desktop PCs.

6. Introduction to Unix Operating System
Hardware Requirement for Unix-
The hardware which are required by the Unix Operating system are
80 MB Hard Disk
4 MB Ram
16 bit Microprocessor
Out of 80 MB space actual 40 MB is used by actual OS. 10-20 Mb used as swap
space.
1 MB for each terminal.

7. Introduction to Unix Operating System
The UNIX OS is made up of three parts
1. Kernel
2. Shell
3. Programs/ Application

8. Unix Architecture

9. Introduction to Unix Operating System
1. Kernel
It manages files carries out all the data transfer b/w the file system and
the hardware and also manage memory.
It also hanfle any interrupt issue as it is the entity that has direct dealing with
hardware.
Kernel program is usually stored in a file, called unix.
“The kernel of UNIX is the hub of the operating system: it allocates time and
memory to programs and handles the filestore and communications in response to
system calls.”

10. Introduction to Unix Operating System
2. Shell
It is the mediator b/w the user and kernel. It is known as command line
interpreter (CLI).
The shell keeps a list of the commands you have typed in. If you need to repeat a
command, use the cursor keys to scroll up and down the list or type history for a list of
previous commands.
Types of Shells
1. Broun Shell
2. C Shell
3. Korn Shell

11. Introduction to Unix Operating System
1. Bourn Shell
It is the Steve Bourn Creation. It is bundled with every Unix System and this
shell is use by many Unix user.
2. C shell
This shell was created by Bill Joy when perusing his graduation at the
university of California.
It has the two advantages over the bourn shell.
a. It uses the alias name. You can simply enter short name of a long command.
b. You can recall previously typed command. It keeps the track all the command
issued at command line.

12. Introduction to Unix Operating System
3. Korn Shell
Korn shell is the superset of Bourn shell. It offers a lot of more capacity
and is decide more efficient than the other.. It is designed by David Korn at AT&T
Bell Lab.

13. Features of UNIX
The UNIX operating system offers several features. The important of which are as
follows-
1. Multiuser Capability
2. Multitasking Capability
3. Communication
4. Security

14. Features of UNIX
1. Multiuser Capability
UNIX is a multiuser operating system. In multiuser system. The same
computer resources such as Hard-Disk, Memory Processor are accessible to many
users.
Here we use terminal, different users have different terminal to operate from. A
terminal is a keyboard and monitor which are the input and output devices for
that user.
All terminals are connected to main computer or server (Host Machine)
Every user can use another peripheral such as printer.

15. Features of UNIX
Types of Terminals
1. Dumb Terminal
2. Terminal Emulation
3. Dial in Terminal

16. Features of UNIX
1. Dumb Terminal
These terminals consist of a keyboard and a display unit with no memory
or disk of its own.
This can never act as independent machine.
If they are to be used they have to be
connected to the host machine.

18. Features of UNIX
2. Terminal Emulation
PC has its own microprocessor, memory and disk drivers by attracting this
PC to the host through a cable and running a software this PC emulate it work as a
dumb terminal
Like a dumb terminal it transmits its processing jobs to the host machine. The
software that makes the PC work like a dump terminal is called terminal
emulation software.
VTERM and XTALK

20. Features of UNIX
3. Dial in Terminal
These terminal use the telephone lines to connect with the host machine
to communicate every telephone lines. It is necessary to attach a unit called
modem to the terminal as well as to the host.

21. Telephone Cable

22. Features of UNIX
2. Multitasking
It is capable of carrying out more than one job at the same time.
MSDOS also provide multitasking capability known as Serial Multitasking.
But Unix OS use fast switching by which we see that microprocessor run all the
programme simultaneously.
3. Communication
Communication may be within the network of a single main computer or
b/w two or more such computer. The user can easily exchange data program
through such program.

23. Features of UNIX
4. Security
Unix has three inherent provisions for protection.
a. The first is provided by assigning passwords and login names to individual user.
b. At the file level such as read, write and execute permission to each files.
c. File encrypting .
5. Portability
It can be ported to almost any computer system.

24. Unix File System
UNIX treats everything as a file even a directory also.
Unix file system represented by a tree like structure which start with root node
presented by /root.

25. Unix File System
1. bin
It contain executable files.
2. lib
It contains all the library function.
3. dev
It contains the files that control various input, output device like terminal, printer, disk drive etc.
4. usr
Each user’s files. Created by system administrator at time of account creations for users.
5. temp
It contain temporary files.

26. Unix File System
Types of files in Unix file system
• Ordinary Files − An ordinary file is a file on the system that contains data, text,
or program instructions.
• Directories − Directories store both special and ordinary files. For users
familiar with Windows or Mac OS, Unix directories are equivalent to folders.
• Special Files − Some special files provide access to hardware such as hard
drives, CD-ROM drives, modems, and Ethernet adapters. Other special files are
similar to aliases or shortcuts and enable you to access a single file using
different names.

27. Unix File System
Features of Unix file system
1. It has a hierarchical file structure.
2. Files can grow dynamically.
3. Files have access permissions.
4. All the devices are implemented as files.

28. Unix File System
Directories
A directory is a file the solo job of which is to store the file names and the related
information. All the files, whether ordinary, special, or directory, are contained in
directories.

29. Blocks of the Unix file system
A Unix file system is made up of blocks each blocks are 512 bytes. Some file system
have 1024 or 2048 bytes. It depends on how the file system have been implemented on
a particular installation.
We can use cmchk command to show block size .
1. The Boot Block
This represent beginning of the file system. It contains a program called boot
strap loader. This program is execute when we boot the host machine. Although only
one boot block is needed to start-up the system.
2. The Super Block
The super block describe the state of file system that is how large it is how many
maximum can it accommodate, how many more files can created etc.

30. Blocks of the Unix file system
3. Inode Table
We know that all the entities in Unix are treated as files. The information related to all
these files (not the content) is stored in an Inode table on the disk. For each file these is an
node entry in the table.
a. Who is the owner of the file
b. Group to which owner belongs
c. Type of file
d. File access permissions
e. Date and time of last access
f. Date and time of last access
g. Date and time of last modification
h. No of links to the file
i. Address of blocks where the file is physically present.

31. Blocks of the Unix file system
4. Data Block
These contains the actual file’s contents and allocated block can belong to
only one file in the file system. This block cannot be used for storing any other files
content unless the file to which originally belong is deleted.

32. File Permissions
There are three types of permission here
1. Owner Permissions
2. Group Permissions
3. Other (world) Permissions
There are three file access modes
1. Read
2. Write
3. Execute

33. File Permissions
Here is the code for understanding the file permissions
We use the chmod command to assign or modify the permission.

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Class 1 82 95
Class 2 76 88
Class 3 84 90

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