📘 PAPER 5 – OPERATING SYSTEM (UNIT 5 – SHELL PROGRAMMING & FILTER COMMANDS) university of allahabad

 

🔴 UNIT 5 – SHELL PROGRAMMING & FILTER COMMANDS

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🟢 1. Introduction to Shell

✅ What is a Shell?

A Shell is a command-line interpreter that:

• Accepts user commands

• Executes them

• Acts as an interface between user and OS

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🔹 Types of Shells in Linux

Shell	Description
sh	Bourne shell
bash	Bourne Again Shell (most used)
csh	C shell
ksh	Korn shell
zsh	Advanced shell

👉 Bash is most commonly used.

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🟢 2. Shell Programming

✅ Definition

Shell programming is writing a script to automate tasks using shell commands.

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🔹 Advantages

✔ Saves time
✔ Automates tasks
✔ Easy to write
✔ Used in system administration

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🟢 3. Structure of Shell Script

#!/bin/bash
echo "Hello World"

Explanation:

• #!/bin/bash → Shebang line

• echo → Print output

---

🔹 Running a Shell Script

chmod +x file.sh
./file.sh

---

🟢 4. Variables in Shell

User Defined Variable

name="Amit"
echo $name

---

System Variables

$HOME
$USER
$PATH

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🟢 5. Read Command

echo "Enter name:"
read name
echo "Hello $name"

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🟢 6. Conditional Statements

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🔹 if Statement

if [ $a -gt $b ]
then
  echo "A is greater"
fi

---

🔹 if-else

if [ $a -eq $b ]
then
  echo "Equal"
else
  echo "Not equal"
fi

---

🔹 Case Statement

case $choice in
1) echo "One";;
2) echo "Two";;
*) echo "Invalid";;
esac

---

🟢 7. Looping Statements

---

🔹 for Loop

for i in 1 2 3
do
  echo $i
done

---

🔹 while Loop

i=1
while [ $i -le 5 ]
do
  echo $i
  i=$((i+1))
done

---

🟢 8. Command Line Arguments

echo "File name: $0"
echo "First arg: $1"
echo "Second arg: $2"

---

🟢 9. Filter Commands

Filter commands process text input and give output.

---

🔹 1. grep

Search text in file

grep "hello" file.txt

---

🔹 2. sed

Stream editor (search & replace)

sed 's/old/new/' file.txt

---

🔹 3. awk

Used for report generation

awk '{print $1}' file.txt

---

🔹 4. cut

Extract columns

cut -d ":" -f1 file.txt

---

🔹 5. sort

Sort data

sort file.txt

---

🔹 6. uniq

Remove duplicate lines

uniq file.txt

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🟢 10. Pipes

Used to connect commands.

ls | grep ".txt"

---

🟢 11. Shell Keywords

Keyword	Use
if	Condition
then	Execution
fi	End if
for	Loop
do	Loop start
done	Loop end

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🟢 12. Shell Script Example

Program: Check Even or Odd

echo "Enter number:"
read n

if [ $((n % 2)) -eq 0 ]
then
  echo "Even"
else
  echo "Odd"
fi

---

📌 IMPORTANT EXAM QUESTIONS (UNIT 5)

✔ Explain shell scripting
✔ Write shell program for even/odd
✔ Explain grep, sed, awk
✔ Explain pipes & filters
✔ Write notes on shell variables
✔ Explain case statement

📘 PAPER 5 – OPERATING SYSTEM (UNIT 4 – UNIX & LINUX COMMANDS) university of allahabad

 

🔴 UNIT 4 – UNIX & LINUX COMMANDS

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1️⃣ Introduction to UNIX / Linux

✅ UNIX

UNIX is a multi-user, multitasking operating system developed at AT&T Bell Labs.

✅ Linux

Linux is an open-source UNIX-based operating system.

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🔹 Features of Linux

✔ Open source
✔ Secure
✔ Portable
✔ Multi-user
✔ Multitasking

---

2️⃣ Linux File System Structure

Directory	Purpose
/	Root directory
/bin	System commands
/etc	Configuration files
/home	User files
/usr	User programs
/var	Variable files
/tmp	Temporary files

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3️⃣ Basic Linux Commands

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📁 Directory Commands

Command	Description
pwd	Show current directory
ls	List files
cd	Change directory
mkdir	Create directory
rmdir	Remove empty directory

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📄 File Commands

Command	Description
touch	Create file
cat	View file
cp	Copy file
mv	Move/rename file
rm	Delete file
file	File type

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📘 Viewing Files

Command	Use
more	View page by page
less	Scrollable view
head	First 10 lines
tail	Last 10 lines

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4️⃣ File Permission Commands

Permission Types:

Symbol	Meaning
r	Read
w	Write
x	Execute

---

Example:

-rwxr-xr--

---

Change Permission:

chmod 755 file.txt

---

5️⃣ Disk Related Commands

Command	Description
df	Disk free space
du	Disk usage
mount	Mount disk
umount	Unmount disk

---

6️⃣ Process Management Commands

Command	Function
ps	Show running processes
top	Real-time process
kill	Kill process
nice	Set priority
sleep	Delay execution

---

7️⃣ Input / Output Redirection

Symbols:

Symbol	Use
>	Output redirect
>>	Append
<	Input redirect
`	`

---

Example:

ls > file.txt
cat file.txt | grep abc

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8️⃣ Background Processing

command &

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9️⃣ Process Scheduling Commands

Command	Purpose
at	Schedule job
cron	Repeated jobs
crontab	Cron table

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🔹 Example Cron Job:

* * * * * echo "Hello"

---

🔟 File Editing Commands

Editors:

✔ vi
✔ vim
✔ nano

---

vi Editor Modes:

1. Command mode

2. Insert mode

3. Exit mode

---

Important vi Commands:

Command	Function
i	Insert
:w	Save
:q	Quit
:wq	Save & quit
dd	Delete line

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📌 EXAM IMPORTANT QUESTIONS (UNIT 4)

✔ Explain Linux file system
✔ Explain Linux commands
✔ File permission in Linux
✔ Explain I/O redirection
✔ Explain process management commands
✔ Explain cron & at

📘 PAPER 5 – OPERATING SYSTEM (UNIT 3 – FILE SYSTEM & I/O MANAGEMENT) university of allahabad

 

🔴 UNIT 3 – FILE SYSTEM & I/O MANAGEMENT

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1️⃣ File System – Introduction

✅ What is a File?

A file is a collection of related information stored on secondary storage.

✅ File System

The file system is a method used by the OS to:

• Store files

• Retrieve files

• Organize data efficiently

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2️⃣ File Attributes

Each file has the following attributes:

Attribute	Description
Name	File name
Type	File extension
Size	File size
Location	Disk location
Protection	Access rights
Time & Date	Creation/modification time

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3️⃣ File Operations

Common file operations:

✔ Create
✔ Open
✔ Read
✔ Write
✔ Close
✔ Delete

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4️⃣ File Access Methods

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🔹 1. Sequential Access

• Data accessed sequentially

• Example: Text file

✔ Simple
❌ Slow for random access

---

🔹 2. Direct Access

• Access any record directly

• Example: Database files

✔ Fast
✔ Efficient

---

🔹 3. Indexed Access

• Uses index to locate data

• Combination of sequential & direct

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5️⃣ Directory Structure

Types of Directory Structures:

---

🔹 1. Single Level Directory

• All files in one directory
  ❌ Name conflict

---

🔹 2. Two-Level Directory

• Separate directories for each user

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🔹 3. Tree Structure Directory

• Hierarchical structure

• Most commonly used

---

🔹 4. Acyclic Graph Directory

• Shared files

• No cycles

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6️⃣ File Allocation Methods

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🔹 1. Contiguous Allocation

• Files stored in continuous memory

✔ Fast access
❌ External fragmentation

---

🔹 2. Linked Allocation

• File blocks linked using pointers

✔ No fragmentation
❌ Slow access

---

🔹 3. Indexed Allocation

• Index block stores pointers

✔ Fast access
✔ No fragmentation

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7️⃣ Free Space Management

Methods used to manage free disk space:

✔ Bit vector
✔ Linked list
✔ Grouping
✔ Counting

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8️⃣ Disk Scheduling

Purpose:

Reduce disk access time

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🔹 Disk Scheduling Algorithms

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1️⃣ FCFS (First Come First Serve)

✔ Simple
❌ High seek time

---

2️⃣ SSTF (Shortest Seek Time First)

✔ Better than FCFS
❌ Starvation possible

---

3️⃣ SCAN (Elevator Algorithm)

✔ Moves in one direction
✔ Reduces starvation

---

4️⃣ C-SCAN

✔ Uniform wait time
✔ Used in modern OS

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9️⃣ I/O Management

I/O System Responsibilities:

✔ Device communication
✔ Error handling
✔ Buffering
✔ Spooling

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🔹 I/O Techniques

1. Programmed I/O

CPU controls I/O
❌ Slow

---

2. Interrupt Driven I/O

CPU works during I/O
✔ Better performance

---

3. Direct Memory Access (DMA)

• Data transferred directly to memory

• CPU not involved

✔ Fastest
✔ Efficient

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🔟 Protection & Security

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🔹 Protection

Ensures controlled access to resources.

🔹 Security

Prevents unauthorized access.

---

Protection Mechanisms:

✔ Passwords
✔ Access control lists
✔ Encryption

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📌 EXAM IMPORTANT QUESTIONS (UNIT 3)

✔ Explain file allocation methods
✔ Disk scheduling algorithms
✔ Explain DMA
✔ File access methods
✔ Directory structure
✔ Difference between FCFS and SSTF

📘 PAPER 5 – OPERATING SYSTEM ( UNIT 2 – MEMORY MANAGEMENT) university of allahabad

 

🔴 UNIT 2 – MEMORY MANAGEMENT

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1️⃣ Memory Management – Introduction

✅ Definition

Memory management is the function of the OS that:

• Allocates memory to processes

• Deallocates memory after use

• Manages primary and secondary memory efficiently

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2️⃣ Memory Management Requirements

✔ Relocation
✔ Protection
✔ Sharing
✔ Logical organization
✔ Physical organization

---

3️⃣ Memory Management Techniques

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🔹 1. Multiprogramming with Fixed Partitions

Concept:

• Memory is divided into fixed-size partitions

• One process per partition

Advantages:

✔ Simple
✔ Easy implementation

Disadvantages:

❌ Internal fragmentation
❌ Wastage of memory

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🔹 2. Multiprogramming with Variable Partitions

Concept:

• Memory allocated as per process size

• No fixed partitions

Advantages:

✔ Less internal fragmentation

Disadvantages:

❌ External fragmentation

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4️⃣ Memory Allocation Strategies

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🔹 First Fit

Allocates first available memory block

✔ Fast
❌ Fragmentation

---

🔹 Best Fit

Allocates smallest possible block

✔ Less wastage
❌ Slow

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🔹 Worst Fit

Allocates largest block

❌ Poor utilization

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5️⃣ Swapping

Definition:

Process is temporarily moved from main memory to disk.

Purpose:

✔ Free memory
✔ Improve multiprogramming

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6️⃣ Virtual Memory

Definition:

Virtual memory allows execution of processes even if:

• Entire program is not in memory

Uses:
✔ Secondary memory
✔ Demand paging

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7️⃣ Paging

Concept:

• Memory divided into pages

• Physical memory divided into frames

Address Format:

Page number | Offset

---

Advantages:

✔ No external fragmentation
✔ Easy memory management

---

Disadvantages:

❌ Internal fragmentation

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8️⃣ Segmentation

Concept:

Memory divided based on logical units:

• Code

• Data

• Stack

Address Format:

Segment number | Offset

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Advantages:

✔ Logical view
✔ Better protection

Disadvantages:

❌ External fragmentation

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9️⃣ Paging vs Segmentation

Paging	Segmentation
Fixed size	Variable size
No external fragmentation	External fragmentation
Hardware based	Logical view
Fast	Flexible

---

🔟 Virtual Memory Techniques

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🔹 Demand Paging

Pages loaded only when needed.

---

🔹 Page Fault

Occurs when required page is not in memory.

---

🔹 Page Replacement Algorithms

1. FIFO

Oldest page removed

2. LRU

Least recently used page removed

3. Optimal

Replaces page not used for longest time (best but impractical)

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1️⃣1️⃣ Thrashing

Definition:

System spends more time paging than executing.

---

Causes:

• High degree of multiprogramming

• Insufficient memory

---

Prevention:

✔ Reduce multiprogramming
✔ Increase RAM
✔ Use good page replacement

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📌 EXAM IMPORTANT QUESTIONS (UNIT 2)

✔ Explain paging and segmentation
✔ Difference between paging & segmentation
✔ Explain virtual memory
✔ Explain page replacement algorithms
✔ What is thrashing?
✔ Explain memory allocation strategies

📘 PAPER 5 – OPERATING SYSTEM (UNIT 1 – INTRODUCTION & PROCESS MANAGEMENT) university of allahabad

 

📘 PAPER 5 – OPERATING SYSTEM

🔴 UNIT 1 – INTRODUCTION & PROCESS MANAGEMENT

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1️⃣ Introduction to Operating System

✅ What is an Operating System (OS)?

An Operating System is system software that:

• Acts as an interface between user and hardware

• Manages computer resources

• Controls execution of programs

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✅ Functions of Operating System

✔ Process management
✔ Memory management
✔ File management
✔ Device management
✔ Security & protection
✔ User interface

---

✅ Examples of Operating Systems

• Windows

• Linux

• macOS

• Android

• UNIX

---

2️⃣ Types of Operating Systems

🔹 1. Batch Operating System

• Jobs executed in batches

• No user interaction

🔹 2. Multiprogramming OS

• Multiple programs in memory

• CPU utilization increases

🔹 3. Time Sharing OS

• Multiple users at same time

• CPU shared among users

🔹 4. Real-Time OS

• Immediate response

• Used in medical & industrial systems

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3️⃣ Structure of Operating System

🔹 Layered Structure

• Hardware at bottom

• User interface at top

• Easy to debug and maintain

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4️⃣ Process Concept

✅ Process

A process is a program in execution.

---

Components of a Process

• Program counter

• Registers

• Stack

• Data section

---

5️⃣ Process States

🔹 Five States of Process

State	Description
New	Process created
Ready	Waiting for CPU
Running	Executing
Waiting	Waiting for I/O
Terminated	Finished

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6️⃣ Process Control Block (PCB)

Definition:

PCB stores all information about a process.

Contains:

• Process ID

• Process state

• CPU registers

• Memory info

• Scheduling info

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7️⃣ Process Scheduling

Types of Scheduling:

1. Long-term scheduler

2. Short-term scheduler

3. Medium-term scheduler

---

8️⃣ CPU Scheduling Algorithms

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🔹 1. FCFS (First Come First Serve)

✔ Simple
❌ High waiting time

---

🔹 2. SJF (Shortest Job First)

✔ Minimum waiting time
❌ Starvation problem

---

🔹 3. Priority Scheduling

• Process with highest priority executes first

---

🔹 4. Round Robin

• Time quantum based

• Fair scheduling

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9️⃣ Process Synchronization

Problem:

When multiple processes access shared data → inconsistency occurs.

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🔹 Critical Section Problem

Requirements:

✔ Mutual Exclusion
✔ Progress
✔ Bounded Waiting

---

🔟 Semaphores

Definition:

Semaphore is a synchronization tool.

Types:

1. Binary Semaphore

2. Counting Semaphore

---

Operations:

wait()
signal()

---

1️⃣1️⃣ Deadlock

Definition:

Deadlock occurs when:

• Each process waits for a resource held by others

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Conditions of Deadlock:

1. Mutual Exclusion

2. Hold and Wait

3. No Preemption

4. Circular Wait

---

Deadlock Handling:

✔ Prevention
✔ Avoidance
✔ Detection
✔ Recovery

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1️⃣2️⃣ Inter-Process Communication (IPC)

Methods:

• Pipes

• Message Queues

• Shared Memory

• Signals

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📌 EXAM IMPORTANT QUESTIONS (UNIT 1)

✔ Explain process states
✔ Explain CPU scheduling algorithms
✔ Explain semaphore
✔ What is deadlock? Explain conditions
✔ Explain PCB
✔ Difference between process and program