Linux Operating System (4331602) - Summer 2025 Solution

Question 1(a) [3 marks]

#

Define Operating System and explain the need of OS.

Answer:

Operating System is a system software that acts as an intermediary between computer hardware and application software. It manages hardware resources and provides services to user programs.

Need of Operating System:

• Resource Management: Manages CPU, memory, storage, and I/O devices efficiently
• User Interface: Provides command-line and graphical interfaces for user interaction
• Program Execution: Loads and executes user programs safely

Mnemonic: “RUP - Resource, User, Program management”

Question 1(b) [4 marks]

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Write a short note on Process Control Block (PCB).

Answer:

Process Control Block (PCB) is a data structure maintained by the operating system for each running process.

Key Functions:

• Process Identification: Stores unique process ID and parent process ID
• State Information: Maintains current execution state and context
• Resource Allocation: Tracks allocated resources and memory usage

Mnemonic: “PIS - Process ID, Information, State tracking”

Question 1(c) [7 marks]

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List different types of Operating systems. Explain the working of batch operating systems with a suitable example.

Answer:

Types of Operating Systems:

Batch Operating System Working:

Example: Bank transaction processing where all day’s transactions are collected and processed together at night for efficiency.

Key Features:

• Job Grouping: Similar jobs executed together for efficiency
• No User Interaction: Jobs run without user intervention once submitted
• High Throughput: Maximizes system utilization

Mnemonic: “JNH - Jobs grouped, No interaction, High throughput”

Question 1(c) OR [7 marks]

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List different types of Operating systems. Explain the real time operating systems in detail.

Answer:

Types of Operating Systems: (Same table as above)

Real-Time Operating System (RTOS):

Real-time OS provides guaranteed response within specified time constraints for critical applications.

Types of RTOS:

Characteristics:

• Deterministic: Predictable response time for all operations
• Priority-based Scheduling: High-priority tasks get immediate attention
• Minimal Interrupt Latency: Fast context switching capabilities
• Memory Management: Real-time memory allocation without delays

Applications:

• Medical devices, automotive systems, industrial automation, aerospace control systems

Mnemonic: “DPMA - Deterministic, Priority-based, Minimal latency, Applications critical”

Question 2(a) [3 marks]

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Differentiate between program and process.

Answer:

Key Differences:

• Static vs Dynamic: Program is static file, process is dynamic execution
• Resource Usage: Process consumes system resources, program doesn’t
• Multiple Instances: One program can create multiple processes

Mnemonic: “SDR - Static vs Dynamic, Resource usage, Multiple instances”

Question 2(b) [4 marks]

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Explain the different states of a process with the help of a process state diagram.

Answer:

stateDiagram-v2
    direction LR
    [*] --> New: Program loaded
    New --> Ready: Admitted to ready queue
    Ready --> Running: CPU allocated
    Running --> Ready: Time quantum expires
    Running --> Waiting: I/O request
    Waiting --> Ready: I/O completed
    Running --> Terminated: Process completes
    Terminated --> [*]: Resources deallocated

Process States:

State Transitions:

• Ready to Running: Process scheduler assigns CPU
• Running to Ready: Time slice expires or higher priority process arrives
• Running to Waiting: Process requests I/O operation
• Waiting to Ready: I/O operation completes

Mnemonic: “NRWRT - New, Ready, Waiting, Running, Terminated states”

Question 2(c) [7 marks]

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Describe the Round Robin algorithm. Calculate the average waiting time & average turn-around time along with Gantt chart for the given data. Consider context switch = 01 ms and quantum time = 04 ms.

Answer:

Round Robin Algorithm: Round Robin is a preemptive scheduling algorithm where each process gets equal CPU time (quantum) in circular manner.

Given Data:

• Quantum Time = 4 ms
• Context Switch = 1 ms

Gantt Chart:

0   4  5   8  9  13 14  18 19  22 23  26 27  29
|P1 |CS|P3|CS|P1|CS|P2|CS|P3|CS|P4|CS|P3|CS|P4|

Calculations:

Average Waiting Time = (5 + 12 + 15 + 20) / 4 = 13 ms Average Turnaround Time = (13 + 15 + 25 + 25) / 4 = 19.5 ms

Key Features:

• Fair Scheduling: Each process gets equal CPU time
• Preemptive: Running process is interrupted after quantum expires
• Context Switching: Overhead included in calculations

Mnemonic: “FPC - Fair, Preemptive, Context switching overhead”

Question 2(a) OR [3 marks]

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Differentiate: CPU bound process v/s I/O bound process.

Answer:

Key Differences:

• Resource Consumption: CPU-bound uses more processor, I/O-bound uses more input/output
• Performance Impact: CPU-bound affected by processor speed, I/O-bound by storage speed
• Scheduling Priority: Different algorithms favor each type differently

Mnemonic: “CIR - CPU intensive, I/O intensive, Resource usage differs”

Question 2(b) OR [4 marks]

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What is a deadlock? Explain the necessary conditions for a deadlock to occur.

Answer:

Deadlock is a situation where two or more processes are permanently blocked, each waiting for resources held by others.

Necessary Conditions (Coffman Conditions):

Example Scenario:

Deadlock Prevention:

• Eliminate Mutual Exclusion: Make resources shareable when possible
• Prevent Hold and Wait: Require all resources at once
• Allow Preemption: Forcibly take resources when needed
• Prevent Circular Wait: Order resources and request in sequence

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

Question 2(c) OR [7 marks]

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Describe the FCFS algorithm. Calculate the average waiting time and average turn-around time along with Gantt chart for the given data.

Answer:

First Come First Serve (FCFS) Algorithm: FCFS is a non-preemptive scheduling algorithm where processes are executed in arrival order.

Given Data:

Gantt Chart:

0        7        13        22        26
|   P1   |   P2   |    P3   |   P4   |

Calculations:

Average Waiting Time = (0 + 4 + 8 + 16) / 4 = 7 ms Average Turnaround Time = (7 + 10 + 17 + 20) / 4 = 13.5 ms

Characteristics:

• Simple Implementation: Easy to understand and implement
• Non-preemptive: Once started, process runs to completion
• Convoy Effect: Short processes wait for long processes

Mnemonic: “SNC - Simple, Non-preemptive, Convoy effect possible”

Question 3(a) [3 marks]

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Explain single-level directory structure.

Answer:

Single-level directory structure is the simplest file organization where all files are stored in one directory.

Characteristics:

• Simple Structure: All files in one location
• Unique Names: Each file must have unique name
• No Organization: No grouping or categorization possible

Limitations:

• Name collision when multiple users create files with same names
• Difficult to organize large number of files
• No privacy or access control between users

Mnemonic: “SUN - Simple, Unique names, No organization”

Question 3(b) [4 marks]

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Explain the different file attributes.

Answer:

File attributes are metadata that provide information about files stored in the file system.

Common File Attributes:

• Identifier: Unique number for file system reference
• Type Information: MIME type or file extension
• Size and Allocation: Current size and allocated space
• Access Control: User permissions and group access rights

Storage Location: File attributes are typically stored in directory entries or file allocation tables.

Mnemonic: “NTSLPTO - Name, Type, Size, Location, Protection, Time, Owner”

Question 3(c) [7 marks]

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List the different file allocation methods and explain contiguous allocation with necessary diagram.

Answer:

File Allocation Methods:

Contiguous Allocation:

In contiguous allocation, each file occupies a set of contiguous blocks on the disk.

Advantages:

• Fast Access: Direct calculation of block addresses
• Minimal Seek Time: Consecutive blocks reduce head movement
• Simple Implementation: Easy to implement and manage

Disadvantages:

• External Fragmentation: Unused spaces between files
• File Size Limitation: Difficult to extend files
• Compaction Needed: Periodic reorganization required

Mnemonic: “FMS vs EFC - Fast access, Minimal seek, Simple vs External fragmentation, File size limits, Compaction needed”

Question 3(a) OR [3 marks]

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Explain the different types of Linux file systems in brief.

Answer:

Key Features:

• Journaling: ext3, ext4, XFS provide crash recovery
• Performance: ext4, XFS optimized for large files
• Advanced Features: Btrfs, ZFS offer snapshots and compression

Selection Criteria: Different filesystems suit different use cases based on performance, reliability, and feature requirements.

Mnemonic: “EEXBZ - ext2/3/4, XFS, Btrfs, ZFS options”

Question 3(b) OR [4 marks]

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Explain the different file operations.

Answer:

File Operation Sequence:

graph LR
    A[Create File] --> B[Open File]
    B --> C[Read/Write]
    C --> D[Seek if needed]
    D --> C
    C --> E[Close File]
    E --> F[Delete if needed]

Important Considerations:

• Error Handling: Each operation can fail and must be checked
• Permissions: User must have appropriate access rights
• Concurrent Access: Multiple processes may access same file

Mnemonic: “CORWSCD - Create, Open, Read, Write, Seek, Close, Delete”

Question 3(c) OR [7 marks]

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List the different file allocation methods and explain indexed allocation with necessary diagram.

Answer:

File Allocation Methods:

Indexed Allocation:

In indexed allocation, each file has an index block containing pointers to data blocks.

Types of Indexed Allocation:

• Single-level: One index block per file
• Multi-level: Index blocks point to other index blocks
• Combined: Mix of direct and indirect pointers

Advantages:

• No External Fragmentation: Blocks can be anywhere on disk
• Dynamic File Size: Easy to extend files
• Fast Random Access: Direct access to any block

Disadvantages:

• Index Block Overhead: Extra space for storing pointers
• Multiple Disk Access: Two accesses needed (index + data)
• Small File Inefficiency: Overhead high for small files

Mnemonic: “NDF vs IMI - No fragmentation, Dynamic size, Fast access vs Index overhead, Multiple access, Inefficient for small files”

Question 4(a) [3 marks]

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Define System threats and explain its types.

Answer:

System Threats are malicious attempts to disrupt or damage computer system operations, steal information, or gain unauthorized access.

Categories of System Threats:

• Network-based: Attacks through network connections and protocols
• Host-based: Attacks targeting specific computer systems
• Physical: Direct physical access to compromise systems

Impact: System threats can lead to data loss, system downtime, privacy breaches, and financial damage.

Mnemonic: “WVTDP - Worms, Viruses, Trojans, DoS, Port scanning”

Question 4(b) [4 marks]

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Differentiate: User Authentication v/s User Authorization.

Answer:

Authentication Methods:

• Something you know: Passwords, PINs
• Something you are: Fingerprints, retina scans
• Something you have: Smart cards, tokens

Authorization Models:

• Role-based Access Control (RBAC): Permissions based on user roles
• Discretionary Access Control (DAC): Owner controls access
• Mandatory Access Control (MAC): System-enforced security levels

Relationship: Authentication must occur before authorization. Both are essential for comprehensive security.

Mnemonic: “WHO vs WHAT - Authentication asks WHO, Authorization determines WHAT”

Question 4(c) [7 marks]

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Discuss various operating system security policies and procedures.

Answer:

Security Policies:

Security Procedures:

1. User Account Management:

• Regular review of user accounts and permissions
• Immediate revocation of access for terminated employees
• Principle of least privilege implementation

2. System Monitoring:

graph LR
    A[Log Collection] --> B[Analysis Engine]
    B --> C[Threat Detection]
    C --> D[Alert Generation]
    D --> E[Response Action]

3. Incident Response:

• Detection: Identify security incidents quickly
• Containment: Limit damage and prevent spread
• Recovery: Restore normal operations safely

4. Backup and Recovery:

• Regular data backups with tested restore procedures
• Disaster recovery planning and testing
• Business continuity measures

Implementation Framework:

• Risk Assessment: Identify vulnerabilities and threats
• Policy Development: Create comprehensive security guidelines
• Training: Educate users on security practices
• Compliance: Ensure adherence to regulations

Mnemonic: “AAPUD policies + UMSIR procedures - Access, Audit, Password, Update, Data classification + User management, Monitoring, System response, Incident handling, Recovery”

Question 4(a) OR [3 marks]

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Define Program threats and explain its types.

Answer:

Program Threats are malicious software designed to disrupt, damage, or gain unauthorized access to computer programs and data.

Program Threat Categories:

• Executable Threats: Standalone malicious programs
• Parasitic Threats: Attach to legitimate programs
• Network Threats: Spread through network connections

Common Attack Vectors:

• Email attachments and downloads
• Infected removable media
• Network vulnerabilities and exploits

Mnemonic: “MSARR - Malware, Spyware, Adware, Ransomware, Rootkits”

Question 4(b) OR [4 marks]

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Explain the protection domain with a suitable example.

Answer:

Protection Domain is a set of objects and access rights that define what resources a process can access and what operations it can perform.

Domain Structure:

Example - University System:

• Student Domain: Read access to course materials, write access to assignments
• Faculty Domain: Read/write access to grade databases, read access to student records
• Admin Domain: Full access to system configuration, user management

Domain Switching: Processes can switch between domains based on:

• User authentication and authorization
• Program execution context
• Security level requirements

Benefits:

• Isolation: Prevents unauthorized access between domains
• Flexibility: Allows controlled resource sharing
• Security: Implements principle of least privilege

Mnemonic: “OAS - Objects, Access rights, Subjects define domains”

Question 4(c) OR [7 marks]

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Explain Access Control List in detail.

Answer:

Access Control List (ACL) is a security mechanism that specifies which users or processes are granted access to objects and what operations are allowed.

ACL Structure:

ACL Implementation:

Types of ACL:

• Discretionary ACL (DACL): Owner controls access permissions
• System ACL (SACL): System controls auditing and logging
• Default ACL: Inherited permissions for new objects

ACL vs Capability Lists:

Advantages:

• Granular Control: Fine-grained permission management
• Centralized Management: Easy to modify object permissions
• Audit Trail: Clear record of who has access

Disadvantages:

• Performance Overhead: Must check ACL for each access
• Storage Requirements: Space needed for permission lists
• Complexity: Difficult to manage for many users/objects

Real-world Example: Linux file permissions use simplified ACL with owner, group, and others having read, write, execute rights.

Mnemonic: “SOA structure + GDSC advantages - Subject, Object, Access rights + Granular, Distributed, Centralized, Audit capabilities”

Question 5(a) [3 marks]

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Explain the following commands: (i) man (ii) cd (iii) ls

Answer:

Command Details:

1. man (manual) command:

• Function: Shows detailed documentation for Linux commands
• Example: man ls shows manual page for ls command
• Sections: Commands, system calls, library functions, etc.

2. cd (change directory) command:

• Function: Navigate between directories in filesystem
• Examples: cd /home, cd .. (parent), cd ~ (home)
• Special: cd without arguments goes to home directory

3. ls (list) command:

• Function: Display files and directories in current or specified location
• Options: -l (long format), -a (hidden files), -h (human readable)
• Example: ls -la shows detailed listing including hidden files

Mnemonic: “MCD - Manual pages, Change directory, Directory listing”

Question 5(b) [4 marks]

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Write a shell script to find maximum number among three numbers.

Answer:

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

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

# Find maximum using nested if-else
if [ $num1 -gt $num2 ]; then
    if [ $num1 -gt $num3 ]; then
        max=$num1
    else
        max=$num3
    fi
else
    if [ $num2 -gt $num3 ]; then
        max=$num2
    else
        max=$num3
    fi
fi

echo "Maximum number is: $max"

Key Features:

• Input Validation: Reads three numbers from user
• Comparison Logic: Uses nested if-else for finding maximum
• Output Display: Shows result with clear message

Alternative Approach:

max=$(echo "$num1 $num2 $num3" | tr ' ' '\n' | sort -nr | head -1)

Mnemonic: “ICD - Input, Compare, Display result”

Question 5(c) [7 marks]

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Write a shell script to find the sum of all the individual digits in a given 5-digit number.

Answer:

#!/bin/bash
# Script to find sum of digits in a 5-digit number

echo "Enter a 5-digit number:"
read number

# Validate input
if [ ${#number} -ne 5 ] || ! [[ $number =~ ^[0-9]+$ ]]; then
    echo "Error: Please enter exactly 5 digits"
    exit 1
fi

sum=0
temp=$number

# Extract and sum each digit
while [ $temp -gt 0 ]; do
    digit=$((temp % 10))    # Get last digit
    sum=$((sum + digit))    # Add to sum
    temp=$((temp / 10))     # Remove last digit
done

echo "Number: $number"
echo "Sum of digits: $sum"

# Display breakdown
echo "Breakdown:"

# Display individual digits
original=$number
echo -n "Digits: "
for ((i=0; i<5; i++)); do
    digit=$((original % 10))
    if [ $i -eq 4 ]; then
        echo -n "$digit"
    else
        echo -n "$digit + "
    fi
    original=$((original / 10))
done | tac
echo " = $sum"

Algorithm Steps:

• Input Validation: Check for exactly 5 digits
• Digit Extraction: Use modulo and division operations
• Sum Calculation: Add each extracted digit
• Display Results: Show breakdown and final sum

Example Output:

Enter a 5-digit number: 12345
Number: 12345
Sum of digits: 15
Breakdown: 1 + 2 + 3 + 4 + 5 = 15

Mnemonic: “VEDS - Validate, Extract, Display, Sum digits”

Question 5(a) OR [3 marks]

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Explain the following commands: (i) date (ii) top (iii) cmp

Answer:

Command Details:

1. date command:

• Function: Shows current system date and time
• Examples: date, date +%Y-%m-%d, date +%H:%M:%S
• Formatting: Custom output formats using + symbols

2. top command:

• Function: Real-time display of system processes and resource usage
• Interactive: Press ‘q’ to quit, ‘k’ to kill process
• Information: CPU usage, memory usage, process list

3. cmp command:

• Function: Compare two files and report differences
• Output: Shows first differing byte position
• Options: -s (silent), -l (verbose listing)

Mnemonic: “DTC - Date/time, Task monitor, Compare files”

Question 5(b) OR [4 marks]

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Explain the installation steps of Linux.

Answer:

Pre-installation Requirements:

• Hardware Compatibility: Check system requirements
• Backup Data: Secure important files before installation
• Internet Connection: For updates and additional packages

Installation Process Flow:

graph LR
    A[Download ISO] --> B[Create Bootable Media]
    B --> C[Boot from Media]
    C --> D[Language/Keyboard Setup]
    D --> E[Disk Partitioning]
    E --> F[User Account Setup]
    F --> G[Package Selection]
    G --> H[Install System]
    H --> I[Configure Bootloader]
    I --> J[Reboot to Linux]

Post-installation Tasks:

• System Updates: Install latest security patches
• Driver Installation: Configure hardware drivers
• Software Installation: Add required applications

Common Partition Scheme:

• / (root): 20GB minimum for system files
• /home: User data storage
• swap: 1-2x RAM size for virtual memory

Mnemonic: “DCBCPUPI - Download, Create media, Boot, Choose type, Partition, User setup, Package selection, Install”

Question 5(c) OR [7 marks]

#

Write a shell script to find sum and average of N numbers.

Answer:

#!/bin/bash
# Script to find sum and average of N numbers

echo "How many numbers do you want to enter?"
read n

# Validate input
if ! [[ $n =~ ^[0-9]+$ ]] || [ $n -le 0 ]; then
    echo "Error: Please enter a positive integer"
    exit 1
fi

sum=0
echo "Enter $n numbers:"

# Read N numbers and calculate sum
for ((i=1; i<=n; i++)); do
    echo -n "Enter number $i: "
    read number
    
    # Validate each number
    if ! [[ $number =~ ^-?[0-9]+([.][0-9]+)?$ ]]; then
        echo "Error: Invalid number format"
        exit 1
    fi
    
    sum=$(echo "$sum + $number" | bc -l)
done

# Calculate average
average=$(echo "scale=2; $sum / $n" | bc -l)

# Display results
echo ""
echo "Results:"
echo "========="
echo "Count of numbers: $n"
echo "Sum: $sum"
echo "Average: $average"

# Additional statistics
echo ""
echo "Summary:"
echo "Total numbers processed: $n"
echo "Sum of all numbers: $sum"
echo "Average value: $average"

Algorithm Features:

• Input Validation: Checks for positive count and valid numbers
• Flexible Input: Accepts integers and decimal numbers
• Precision Handling: Uses bc calculator for accurate arithmetic
• Error Handling: Validates each input and provides error messages

Example Execution:

How many numbers do you want to enter? 5
Enter number 1: 10
Enter number 2: 20
Enter number 3: 30
Enter number 4: 40
Enter number 5: 50

Results:
=========
Count of numbers: 5
Sum: 150
Average: 30.00

Alternative Simple Version:

#!/bin/bash
read -p "Enter count: " n
sum=0
for ((i=1; i<=n; i++)); do
    read -p "Number $i: " num
    sum=$((sum + num))
done
echo "Sum: $sum"
echo "Average: $((sum / n))"

Key Programming Concepts:

• Loop Control: For loop for iterating N times
• Arithmetic Operations: Addition and division
• Input/Output: Reading user input and displaying results
• Data Validation: Ensuring input correctness

Mnemonic: “VLAD - Validate input, Loop for numbers, Arithmetic calculation, Display results”