Unix Tutorial & overview

UNIX
AN INTRODUCTION
Compiled by :Compiled by :
Dinesh RAJUDinesh RAJU
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• What is an Operating System?
The 1960s definition of an operating system is “the
software that controls the hardware”. We see an
operating system as the programs that make the
hardware useable. In brief, an operating system is
the set of programs that controls a computer. Some
examples of operating systems are UNIX, Mach,
MS-DOS, MS-Windows, Windows/NT, Chicago,
OS/2, MacOS, VMS(Virtual Memory System),
MVS(Multiple Virtual Storage), and VM (Virtual
Machine). Controlling the computer involves
software at several levels.
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Operating Systems Structure:
• System Components:
• 1. Process Management
• Creation and deletion of user and system processes.
• Suspension and resumption of processes.
• A mechanism for process synchronization.
• A mechanism for process communication.
• A mechanism for deadlock handling.
• Main-Memory Management
• Keep track of which part of memory are currently being
used and by whom.
• Decide which process is loaded into memory when memory
space becomes available.
• Allocate and de-allocate memory space as needed.

• File Management:
• 1. The creation and deletion of files.
• 2. The creation and deletion of directions.
• 3. The support of primitives for manipulating files and
directions.
• 4. The mapping of files onto secondary storage.
• 5. The back up of files on stable storage media.
• Secondary-Storage Management
• 1. Managing the free space available on the secondary-
storage device.
• 2. Allocation of storage space when new files have to be
written.
• 3. Scheduling the requests for memory access.

• I/O System Management
• Networking
• Protection System
• Command Interpreter System
• Program Execution
• I/O Operations
• File System Manipulation
• Communications
• Error Detection

Introduction
UNIX is a CUI operating system. Operating
System is an interface between hardware
and applications software’s. It serves as
the operating system for all types of
computers, including single user personal
computers and engineering workstations,
multi-ser microcomputers mini computers,
mainframes and super computers as well
as special purpose devices.

History
UNIX operating system at AT & T Bell labs.
Software team lead by Ken Thomson, Dennis
Ritchie and Rudd Canday worked on MULTICS
project. MULTICS stands for Multi Information
Computing System. MULTICS was developed for
only two users. Based on the same concept in
1969, UNICS operating system was developed
for 100’s of users. UNICS stands for Uniplexed
Information Computing System. It was written in
assembly language in 1973 they re written in C
language named as UNIX.

Features of UNIX:
Multi-user: More than one user can use the machine at a time
supported via terminals (serial or network connection)
Multi-tasking: more than one program can be run at a time
hierarchical directory structure to support the organization and
maintenance of files.
Portability: only the kernel (<10%) written in assembler tools
for program development a wide range of support tools
(debuggers, compilers).
File Structure: Unix follows Hierarchical file system.

• Machine-independence: The System hides the
machine architecture from the user, making it easier
to write applications that can run on micros, mini
and mainframes
• Hierarchical File System: UNIX uses a hierarchal
file structure to store information. This structure has
the maximum flexibility in grouping information in
a way that reflects its natural state. It allows for easy
maintenance and efficient implementation.
• Multiprogramming -Support more than one
program, in memory, at a time. Amounts to multiple
user processes on the system.

Time Sharing
Modularity
Security
Strong networking support
Unix Shell
Pipes and Filters
Background processingQATRAININGHUB.COM Indisa's

Structure of UNIX Operating System

UNIX FILESYSTEMUNIX FILESYSTEM
The UNIX filesystem is hierarchical (resembling a
tree structure). The tree is anchored at a place called
the root, designated by a slash "/". Every item in the
UNIX filesystem tree is either a file, or a directory.
A directory is like a file folder. A directory can
contain files, and other directories. A directory
contained within another is called the child of the
other. A directory in the filesystem tree may have
many children, but it can only have one parent. A
file can hold information, but cannot contain other
files, or directories.

/ (Called root), this is equivalent to C: in the DOS/Windows world. You
cannot run a Linux system without the root partition. All other partitions are
a subset of the root partition.
/boot This contains the necessary stuff to start the machine, including the base
kernel. This partition is optional, but usually present. You will not need to
mess around in here if you have a running system.
/usr This is the directory where global executables are stored. It can be read-
only, if you want. Generally speaking, most software is installed here by
default.
/dev This is the directory where all of your devices are. There are a few useful
examples for you to know. /dev/hda is the first ide hard drive. /dev/hdb is
the second. /dev/sda would be the first SCSI drive, and /dev/sg0 is your
robotic arm.
/etc This is where most configuration files are stored. You will spend a lot of
time in here if you are an administrator. Most files require "root" access to
change.
/var Many of the system log files are here, as well as spools (mail, printer...)
/bin This directory is the home of binary executables. These include the
common commands we have already learned like ls, cat, gzip and tar.

Different Flavors of UNIX
BSD (Berkeley Software Distribution)
Sun Solaris (Sun Micro Systems)
Novell Netware (NOVELL)
IBM AIX (International Business Machines)
HP-UX (Hewllet Packard)
TRU 64 (Hewllet Packard)
LINUX

Unix File System Architecture
In UNIX Operating System, a hard disk partition is
considered as any array of disk block logically, where
as disk block can be a physical sector or multiples of
physical sectors on the disk. It contains four important
areas, they are
BOOT BLOCK
SUPER BLOCK
INODE BLOCK
DATA BLOCK QATRAININGHUB.COM Indisa's

Unix File System Organization

Boot Block: This stores bootable objects that are necessary
for booting the system. It has completely bootable
information.
Super Block: This Stores all the information about the
file system like
Size and status of the file system
Size of file system logical block
Date and time of the last update
Number blocks allocated
Number blocks un allocated
File System State QATRAININGHUB.COM Indisa's

Inode Block: An inode contains all the information
about a file except its name , which is kept in directory. It
contains the following
The type of the file and The mode of the file
The number of hard links to the file
Owner of the file and The number of bytes of the file
The data and time last accessed
The date and last modified and The date and time last created
Data Block: Data blocks are storage blocks contains the
rest of the space that is allocated to the file system.

MSDOS vs. UNIX vs. Linux vs. Windows?
MS-DOS
Single user operating system
Single tasking Operating System
It is Command User Interface
Less security when compare with UNIX

UNIX
Command User Interface (CUI)
Multi user OS
Multi tasking OS
Time Sharing OS
Provides Security in Networking
Unix is Open SystemQATRAININGHUB.COM Indisa's

LINUX
Linux is the kernel of an operating system
Linux was built on the Unix tradition
Linux was originally developed by LINUS
Torwalds of Finland, who currently owns the Linux
Trademark
Linux stands for Linus' Unix

WINDOWS
Windows provides a GUI and a command line
interface
Windows is more expensive
Less Secure compare with UNIX
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Unix Tutorial & overview

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