Linux Operating System (4331602) - Summer 2024 Solution

Question 1(a) [3 marks]

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Define Operating System and give its goal.

Answer:

Operating System Definition: A program that acts as an interface between computer hardware and users, managing system resources and controlling program execution.

Goals of Operating System:

Mnemonic: “RUS” - Resource management, User convenience, System protection

Question 1(b) [4 marks]

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Give name Components of Computer System & Explain need of Operating system.

Answer:

Computer System Components:

graph TD
    A[Computer System] --> B[Hardware]
    A --> C[Operating System]
    A --> D[Application Programs]
    A --> E[Users]
    
    B --> F[CPU]
    B --> G[Memory]
    B --> H[I/O Devices]

Need of Operating System:

• Resource Manager: Controls hardware allocation
• Interface Provider: Easy communication between user and hardware
• Security: Protects system from threats
• Error Handling: Manages system errors efficiently

Mnemonic: “RISE” - Resource management, Interface, Security, Error handling

Question 1(c) [7 marks]

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Explain below types of Operating system.

Answer:

I. Batch Operating System

II. Multiprogramming Operating System

III. Time Sharing Operating System

Mnemonic: “BMT” - Batch (no interaction), Multiprogramming (many programs), Time-sharing (time slices)

Question 1(c) OR [7 marks]

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Explain Linux Architecture & characteristics with its components.

Answer:

Linux Architecture:

graph TD
    A[User Applications] --> B[System Libraries]
    B --> C[System Call Interface]
    C --> D[Linux Kernel]
    D --> E[Hardware]
    
    D --> F[Process Management]
    D --> G[Memory Management]
    D --> H[File System]
    D --> I[Device Drivers]

Linux Characteristics:

Components:

• Kernel: Core of operating system
• Shell: Command interpreter
• File System: Organizes data storage

Mnemonic: “COMP” - Core (kernel), Open source, Multiuser, Portable

Question 2(a) [3 marks]

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Describe Process Control Block. And define (1) PID (2) stack pointer (3) program counter

Answer:

Process Control Block (PCB): Data structure containing process information for OS management.

Definitions:

Mnemonic: “PSP” - PID (identifier), Stack pointer (top), Program counter (next)

Question 2(b) [4 marks]

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Describe the Process Model and Process states

Answer:

Process Model: Conceptual representation of how processes are managed by OS.

Process States:

stateDiagram-v2
    [*] --> New
    New --> Ready
    Ready --> Running
    Running --> Waiting
    Running --> Ready
    Waiting --> Ready
    Running --> Terminated
    Terminated --> [*]

Mnemonic: “NRRWT” - New, Ready, Running, Waiting, Terminated

Question 2(c) [7 marks]

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Demonstrate Scheduling Algorithm:(I) First Come First Serve, (II) Shortest Job First

Answer:

I. First Come First Serve (FCFS)

Average Turnaround Time = (4+6+7)/3 = 5.67

II. Shortest Job First (SJF)

Average Turnaround Time = (2+6+11)/3 = 6.33

Mnemonic: “FS” - FCFS (First order), SJF (Shortest first)

Question 2(a) OR [3 marks]

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Define Race condition, Mutual Exclusion

Answer:

Example: Two processes updating same bank account balance.

Mnemonic: “RM” - Race (simultaneous access), Mutual (one at a time)

Question 2(b) OR [4 marks]

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Define all Throughput, Turnaround Time, Waiting Time, Response Time

Answer:

Formula Table:

Mnemonic: “TTWR” - Throughput, Turnaround, Waiting, Response

Question 2(c) OR [7 marks]

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Explain Round Robin Algorithm with example.

Answer:

Round Robin: Each process gets equal CPU time slice (quantum).

Example (Time Quantum = 2):

Execution Timeline:

Average Turnaround Time = (12+6+10)/3 = 9.33

Advantages:

• Fair: Equal time to all processes
• Responsive: Good for interactive systems

Mnemonic: “RR-FE” - Round Robin gives Fair and Equal time

Question 3(a) [3 marks]

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Give File Access Methods type

Answer:

Mnemonic: “SDI” - Sequential (order), Direct (any), Indexed (index)

Question 3(b) [4 marks]

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Give Deadlock characteristics and Describe: Deadlock Prevention, Deadlock Avoidance

Answer:

Deadlock Characteristics:

Deadlock Prevention: Remove any one of four conditions.

Deadlock Avoidance: Use algorithms like Banker’s algorithm to avoid unsafe states.

Mnemonic: “MHNC” - Mutual exclusion, Hold and wait, No preemption, Circular wait

Question 3(c) [7 marks]

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Explain the File Allocation Methods Contiguous, linked, indexed

Answer:

File Allocation Methods:

Contiguous Allocation:

Linked Allocation:

Indexed Allocation:

Mnemonic: “CLI” - Contiguous (together), Linked (pointers), Indexed (index block)

Question 3(a) OR [3 marks]

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Give knowledge Linux File System Structure

Answer:

Linux File System Hierarchy:

Mnemonic: “BEH” - Bin (binaries), Etc (config), Home (users)

Question 3(b) OR [4 marks]

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Explain Critical Section and Semaphore with example.

Answer:

Critical Section: Code segment accessing shared resources.

Semaphore: Synchronization tool using counter variable.

Example:

# Binary Semaphore
wait(S):
  while S <= 0 do nothing
  S = S - 1

signal(S):
  S = S + 1

Critical Section Structure:

Mnemonic: “ECER” - Entry, Critical, Exit, Remainder

Question 3(c) OR [7 marks]

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Define and explain Deadlock Avoidance, Deadlock Detection and Recovery

Answer:

Deadlock Avoidance:

• Use Banker’s Algorithm
• Check if resource allocation leads to safe state

Deadlock Detection:

• Periodically check for deadlock using Wait-for Graph

Deadlock Recovery Methods:

Banker’s Algorithm Steps:

1. Check if request ≤ available resources
2. Simulate allocation
3. Check if safe state exists

Wait-for Graph:

graph LR
    P1 --> P2
    P2 --> P3
    P3 --> P1

Mnemonic: “ADR-BWT” - Avoidance (Banker’s), Detection (Wait-for), Recovery (Terminate)

Question 4(a) [3 marks]

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Why Need of file Protection explain?

Answer:

Need for File Protection:

Protection Mechanisms:

• Access Control Lists (ACL)
• File Permissions (Read, Write, Execute)
• User Authentication

Mnemonic: “PSI” - Privacy, Security, Integrity

Question 4(b) [4 marks]

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Illustrate Program threats, System threats

Answer:

Program Threats:

System Threats:

Protection Methods:

• Antivirus Software
• Firewalls
• Regular Updates

Mnemonic: “VWT-DPM” - Virus, Worm, Trojan; DoS, Port scan, Man-in-middle

Question 4(c) [7 marks]

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Briefly detailing Operating System security policies and procedures

Answer:

Security Policies:

Security Procedures:

flowchart TD
    A[User Login] --> B[Authentication]
    B --> C[Authorization Check]
    C --> D[Resource Access]
    D --> E[Activity Logging]
    E --> F[Audit Review]

Implementation Steps:

1. User Registration and credential setup
2. Multi-factor Authentication
3. Role-based Access Control
4. Regular Security Audits

Common Security Measures:

• Password Policies
• Encryption
• Backup Procedures
• Incident Response Plans

Mnemonic: “AAAA” - Access control, Authentication, Authorization, Audit

Question 4(a) OR [3 marks]

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Give idea Authentication and Authorization.

Answer:

Authentication Methods:

• Password-based
• Biometric
• Token-based

Mnemonic: “AA” - Authentication (who you are), Authorization (what you can do)

Question 4(b) OR [4 marks]

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Explain Operating System security policies and procedures

Answer:

Security Policies Framework:

Implementation Procedures:

1. Risk Assessment
2. Policy Development
3. Training Programs
4. Regular Reviews

Mnemonic: “UDNS” - User management, Data protection, Network security, System monitoring

Question 4(c) OR [7 marks]

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Detailing the Security measures in Operating System

Answer:

Comprehensive Security Measures:

Access Control Matrix:

Security Implementation Timeline:

gantt
    title Security Implementation
    dateFormat  YYYY-MM-DD
    section Phase 1
    Risk Assessment    :2024-01-01, 30d
    Policy Development :2024-01-15, 45d
    section Phase 2
    System Hardening   :2024-02-01, 60d
    Training Program   :2024-02-15, 30d

Monitoring Tools:

• Log Analysis
• Intrusion Detection Systems
• Vulnerability Scanners

Mnemonic: “PNSAD” - Physical, Network, System, Application, Data security

Question 5(a) [3 marks]

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Give five Basic commands: calendar, date

Answer:

Basic Linux Commands:

Command Examples:

# Display calendar for specific month
cal 6 2024

# Format date output
date "+%A, %B %d, %Y"

Mnemonic: “CDWPC” - Cal, Date, Who, Pwd, Clear

Question 5(b) [4 marks]

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Explain Linux File and Directory Commands: ls, cat, mkdir, rmdir, pwd.

Answer:

File and Directory Commands:

Usage Examples:

# List files with details
ls -l /home/user

# Create multiple directories
mkdir -p dir1/dir2/dir3

# Display file with line numbers
cat -n document.txt

Common Options:

• ls -l: Long format
• ls -a: Show hidden files
• mkdir -p: Create parent directories

Mnemonic: “LCMRP” - List, Cat, Mkdir, Rmdir, Pwd

Question 5(c) [7 marks]

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Understand and apply control statements Write a shell script to perform given operations: Write a shell script to find maximum number among three numbers.

Answer:

Shell Script for Maximum of Three Numbers:

#!/bin/bash
# Script to find maximum of three numbers

echo "Enter three numbers:"
read -p "First number: " num1
read -p "Second number: " num2
read -p "Third number: " num3

# Method 1: Using if-elif-else
if [ $num1 -ge $num2 ] && [ $num1 -ge $num3 ]; then
    max=$num1
elif [ $num2 -ge $num1 ] && [ $num2 -ge $num3 ]; then
    max=$num2
else
    max=$num3
fi

echo "Maximum number is: $max"

# Method 2: Using nested if
if [ $num1 -gt $num2 ]; then
    if [ $num1 -gt $num3 ]; then
        echo "Maximum: $num1"
    else
        echo "Maximum: $num3"
    fi
else
    if [ $num2 -gt $num3 ]; then
        echo "Maximum: $num2"
    else
        echo "Maximum: $num3"
    fi
fi

Control Statements Used:

Comparison Operators:

• -eq: Equal to
• -ne: Not equal to
• -gt: Greater than
• -ge: Greater than or equal to
• -lt: Less than
• -le: Less than or equal to

Mnemonic: “IER” - If (condition), Echo (output), Read (input)

Question 5(a) OR [3 marks]

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What is Linux Process commands: top, ps, kill

Answer:

Linux Process Commands:

Command Details:

top command:

• Shows real-time process information
• CPU and memory usage
• Load average

ps command options:

• ps aux: All processes with details
• ps -ef: Full format listing

kill command:

• kill -9 PID: Force kill process
• killall process_name: Kill by name

Mnemonic: “TPK” - Top (real-time), Ps (status), Kill (terminate)

Question 5(b) OR [4 marks]

#

Linux File and Directory Commands: rm, mv,split,diff, grep

Answer:

Advanced File Commands:

Usage Examples:

# Remove directory recursively
rm -rf /tmp/oldfiles

# Move and rename
mv /home/user/doc.txt /backup/document.txt

# Split file into 50-line chunks
split -l 50 largefile.txt chunk_

# Find differences between files
diff -u original.txt modified.txt

# Search for pattern in multiple files
grep -r "TODO" /project/src/

Common Options:

• rm -i: Interactive mode
• mv -i: Prompt before overwrite
• grep -i: Case insensitive search

Mnemonic: “RMSDG” - Remove, Move, Split, Diff, Grep

Question 5(c) OR [7 marks]

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Write a shell script to read five numbers from user and find average of five numbers.

Answer:

Shell Script for Average of Five Numbers:

#!/bin/bash
# Script to calculate average of five numbers

echo "=== Average Calculator ==="
echo "Enter five numbers:"

# Read five numbers
read -p "Enter number 1: " num1
read -p "Enter number 2: " num2
read -p "Enter number 3: " num3
read -p "Enter number 4: " num4
read -p "Enter number 5: " num5

# Calculate sum
sum=$((num1 + num2 + num3 + num4 + num5))

# Calculate average
average=$((sum / 5))

# Display results
echo "================================"
echo "Numbers entered: $num1, $num2, $num3, $num4, $num5"
echo "Sum: $sum"
echo "Average: $average"
echo "================================"

# Enhanced version with decimal precision
sum_float=$(echo "$num1 + $num2 + $num3 + $num4 + $num5" | bc)
avg_float=$(echo "scale=2; $sum_float / 5" | bc)
echo "Precise Average: $avg_float"

Alternative Method using Arrays:

#!/bin/bash
# Using array approach

declare -a numbers
sum=0

echo "Enter 5 numbers:"
for i in {0..4}; do
    read -p "Number $((i+1)): " numbers[i]
    sum=$((sum + numbers[i]))
done

average=$((sum / 5))

echo "Numbers: ${numbers[@]}"
echo "Sum: $sum"
echo "Average: $average"

Script Features:

Mathematical Operations in Bash:

• $((expression)): Integer arithmetic
• bc: Calculator for floating point
• expr: Expression evaluation

Mnemonic: “RSAR” - Read (input), Sum (add), Average (divide), Result (output)