Linux Operating System (4331602) - Winter 2024 Solution

Question 1(a) [3 marks]

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Explain Multiprogramming Operating System and give its advantages.

Answer:

Multiprogramming Operating System allows multiple programs to reside in memory simultaneously and execute concurrently by sharing CPU time efficiently.

Table: Multiprogramming System Features

• Increased CPU utilization: CPU remains busy switching between programs
• Better throughput: More programs completed per unit time
• Reduced response time: Programs execute faster due to parallel processing

Mnemonic: “MCP” - Memory sharing, CPU utilization, Parallel execution

Question 1(b) [4 marks]

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Explain Characteristics of Linux operating system.

Answer:

Table: Linux Operating System Characteristics

• Case sensitive: Distinguishes between uppercase and lowercase
• Command line interface: Powerful shell for system operations
• File system hierarchy: Organized directory structure starting from root (/)

Mnemonic: “LAMPS” - Linux is Accessible, Multi-user, Portable, Secure

Question 1(c) [7 marks]

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Explain FCFS scheduling algorithm with its advantages and disadvantages. Calculate Average waiting time and average turnaround time for FCFS algorithm with gantt chart for following data.

Answer:

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

Table: FCFS Algorithm Analysis

Advantages:

• Simple implementation: Easy to understand and code
• Fair scheduling: No starvation occurs

Disadvantages:

• Convoy effect: Short processes wait for long processes
• Poor average waiting time: Not optimal for system performance

Gantt Chart Calculation:

Table: Process Execution Analysis

Average Waiting Time = (0+2+3+4)/4 = 2.25 ms Average Turnaround Time = (5+5+5+11)/4 = 6.5 ms

Mnemonic: “FCFS-SiNo” - First Come First Serve is Simple but Not optimal

Question 1(c) OR [7 marks]

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Explain Round Robin algorithm with its advantages and disadvantages. Calculate Average waiting time and average turnaround time for Round Robin algorithm with gantt chart for following data. (Time Quantum = 2 ms)

Answer:

Round Robin is a preemptive scheduling algorithm where each process gets equal CPU time slice (quantum).

Table: Round Robin Features

Advantages:

• Fair allocation: Each process gets equal CPU time
• No starvation: All processes eventually get CPU

Disadvantages:

• Context switching overhead: Frequent process switching
• Performance depends on quantum: Too small or large affects efficiency

Gantt Chart (Quantum = 2ms):

Table: Round Robin Execution

Average Waiting Time = (10+10+7+3)/4 = 7.5 ms Average Turnaround Time = (14+15+10+4)/4 = 10.75 ms

Mnemonic: “RR-TEQ” - Round Robin uses Time Equal Quantum

Question 2(a) [3 marks]

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Explain Real Time Operation System.

Answer:

Real Time Operating System (RTOS) processes data and responds to events within strict time constraints.

Table: RTOS Types

• Deterministic behavior: Predictable response times
• Priority-based scheduling: Critical tasks get higher priority
• Minimal latency: Fast interrupt handling and context switching

Mnemonic: “RTD” - Real Time is Deterministic

Question 2(b) [4 marks]

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Explain Process Life Cycle with diagram.

Answer:

Process Life Cycle shows different states a process goes through during execution.

Diagram: Process State Transition

stateDiagram-v2
    [*] --> New : Create Process
    New --> Ready : Admitted
    Ready --> Running : Scheduler Dispatch
    Running --> Waiting : I/O Request
    Running --> Ready : Time Quantum Expired
    Running --> Terminated : Exit
    Waiting --> Ready : I/O Complete
    Terminated --> [*] : Process Cleanup

Table: Process States

Mnemonic: “NRRWT” - New Ready Running Waiting Terminated

Question 2(c) [7 marks]

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Explain Various file and directory related commands in Linux.

Answer:

Table: File Commands

Table: Directory Commands

• File permissions: Use chmod to modify access rights
• File ownership: Use chown to change file owner
• File information: Use stat for detailed file information

Mnemonic: “LCCMR-MRCP” - List, Cat, Copy, Move, Remove for files; Make, Remove, Change, Print for directories

Question 2(a) OR [3 marks]

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Describe operating system services in detail.

Answer:

Operating System Services provide interface between user applications and hardware resources.

Table: OS Services Categories

• Resource allocation: CPU, memory, and device management
• Accounting: Track resource usage and performance
• Protection and security: Access control and authentication

Mnemonic: “UPIFCE” - User interface, Program execution, I/O, File system, Communication, Error detection

Question 2(b) OR [4 marks]

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Explain Process Control Block.

Answer:

Process Control Block (PCB) is a data structure containing all information about a process.

Table: PCB Components

Diagram: PCB Structure

Mnemonic: “PPCMIA” - Process ID, Process state, Program Counter, CPU registers, Memory, I/O, Accounting

Question 2(c) OR [7 marks]

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Explain installation steps of Linux.

Answer:

Linux Installation involves preparing system and installing operating system from bootable media.

Table: Installation Steps

Partitioning Scheme:

• Root (/): 20GB minimum for system files
• Swap: 2x RAM size for virtual memory
• Home (/home): Remaining space for user data

Post-installation:

• Update system: sudo apt update && sudo apt upgrade
• Install drivers: Graphics, network, audio drivers
• Configure security: Firewall, user permissions

Mnemonic: “DCBSLNCIU” - Download, Create media, Boot, Select language, Layout disk, Network, Create user, Install bootloader, Update system

Question 3(a) [3 marks]

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Define: Process, Program, Swapping

Answer:

Table: Basic Definitions

• Process: Active entity with process ID, memory space, and execution state
• Program: Passive entity, executable file stored in secondary storage
• Swapping: Memory management technique to handle more processes than physical memory

Mnemonic: “PAP-MDS” - Process is Active Program; Program is instructions; Swapping is Memory-Disk transfer

Question 3(b) [4 marks]

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List out various file operations and describe each of them.

Answer:

Table: File Operations

• File attributes: Access permissions, timestamps, size information
• File locking: Prevent concurrent access conflicts
• Buffer management: Optimize I/O performance through caching

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

Question 3(c) [7 marks]

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Write a shell script to generate and print Fibonacci series.

Answer:

Fibonacci Series generates numbers where each number is sum of two preceding numbers.

Shell Script:

#!/bin/bash
# Fibonacci series generator

echo "Enter number of terms:"
read n

a=0
b=1

echo "Fibonacci Series:"
echo -n "$a $b "

for((i=2; i<n; i++))
do
    c=$((a + b))
    echo -n "$c "
    a=$b
    b=$c
done
echo

Table: Script Components

Output Example:

Enter number of terms: 8
Fibonacci Series: 0 1 1 2 3 5 8 13

Mnemonic: “FLAB” - Fibonacci uses Loop with Addition of Both previous numbers

Question 3(a) OR [3 marks]

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List out types of scheduler and explain any one of them.

Answer:

Table: Types of Schedulers

Short-term Scheduler (CPU Scheduler):

• Frequency: Executes very frequently (milliseconds)
• Function: Decides which process gets CPU next
• Algorithms: FCFS, SJF, Round Robin, Priority
• Goal: Maximize CPU utilization and throughput

Mnemonic: “LSM-JRC” - Long-term (Job), Short-term (Ready), Medium-term (swap Control)

Question 3(b) OR [4 marks]

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List out various file attributes and describe each of them.

Answer:

Table: File Attributes

Permission Structure:

• User (u): Owner permissions
• Group (g): Group member permissions
• Other (o): All other users permissions

Example: -rwxr-xr--

• File type: regular file (-)
• Owner: read, write, execute (rwx)
• Group: read, execute (r-x)
• Others: read only (r–)

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

Question 3(c) OR [7 marks]

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Write a shell script to sum of 1 to 10 using while loop.

Answer:

While Loop continues execution as long as specified condition remains true.

Shell Script:

#!/bin/bash
# Sum of numbers 1 to 10 using while loop

echo "Calculating sum of 1 to 10:"

i=1
sum=0

while [ $i -le 10 ]
do
    sum=$((sum + i))
    echo "Adding $i, current sum: $sum"
    i=$((i + 1))
done

echo "Final sum of 1 to 10 is: $sum"

Table: Script Logic

Output:

Calculating sum of 1 to 10:
Adding 1, current sum: 1
Adding 2, current sum: 3
...
Final sum of 1 to 10 is: 55

Mnemonic: “WICS” - While loop needs Initialize, Condition, Sum calculation

Question 4(a) [3 marks]

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List out and explain condition for Deadlock to occur.

Answer:

Deadlock occurs when processes wait indefinitely for resources held by each other.

Table: Deadlock Conditions (Coffman Conditions)

All four conditions must be true simultaneously for deadlock to occur.

Example Scenario:

• Process P1 holds Resource A, needs Resource B
• Process P2 holds Resource B, needs Resource A
• Both processes wait indefinitely

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

Question 4(b) [4 marks]

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List out File access methods. Explain any one.

Answer:

Table: File Access Methods

Sequential Access Method:

• Process: Read records one by one in order
• Advantages: Simple implementation, efficient for batch processing
• Disadvantages: Slow for specific record access
• Use cases: Log files, data backup, streaming

Operations:

read_next() - Read next record
write_next() - Write next record  
reset() - Return to beginning

Mnemonic: “SDI” - Sequential (start to end), Direct (jump anywhere), Index (combined approach)

Question 4(c) [7 marks]

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Describe Security measures in operating system.

Answer:

Operating System Security protects system resources from unauthorized access and threats.

Table: Security Mechanisms

Security Levels:

• Physical security: Protect hardware and facilities
• User authentication: Login credentials and biometrics
• File permissions: Read, write, execute controls
• Network security: Secure communication protocols

Threats Protection:

• Malware: Antivirus software and sandboxing
• Unauthorized access: Strong passwords and multi-factor authentication
• Data breaches: Encryption and backup strategies

Mnemonic: “AAAEAF” - Authentication, Authorization, Access control, Encryption, Audit, Firewall

Question 4(a) OR [3 marks]

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List out ways to deal with deadlock. Explain deadlock detection and recovery.

Answer:

Table: Deadlock Handling Methods

Deadlock Detection:

• Wait-for graph: Maintain graph of process dependencies
• Detection algorithm: Periodically check for cycles in graph
• Resource allocation graph: Track resource ownership and requests

Deadlock Recovery:

• Process termination: Kill one or more deadlocked processes
• Resource preemption: Take resources from processes
• Rollback: Return processes to safe state using checkpoints

Mnemonic: “PADI” - Prevention, Avoidance, Detection, Ignore

Question 4(b) OR [4 marks]

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List out File allocation methods. Explain any one.

Answer:

Table: File Allocation Methods

Contiguous Allocation:

• Structure: File occupies consecutive blocks on disk
• Advantages: Fast access, simple implementation, good for sequential access
• Disadvantages: External fragmentation, difficult to grow files
• Directory entry: Contains starting address and length

Example: File “test.txt” starts at block 100, length 5 blocks Occupies blocks: 100, 101, 102, 103, 104

Mnemonic: “CLI” - Contiguous (consecutive), Linked (pointers), Indexed (table)

Question 4(c) OR [7 marks]

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Describe program threats and system threats.

Answer:

Program Threats are malicious software that can harm system or data.

Table: Program Threats

System Threats target operating system and system resources.

Table: System Threats

Protection Strategies:

• Antivirus software: Detect and remove malicious programs
• Regular updates: Patch security vulnerabilities
• Access controls: Limit user privileges and resource access
• Network monitoring: Detect suspicious activities

Mnemonic: “VWTLB-BPDM” - Virus, Worm, Trojan, Logic bomb, Backdoor; Buffer overflow, Privilege escalation, DoS, Man-in-middle

Question 5(a) [3 marks]

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Explain Inter Process Communication.

Answer:

Inter Process Communication (IPC) enables processes to exchange data and synchronize activities.

Table: IPC Mechanisms

• Synchronous communication: Sender waits for receiver acknowledgment
• Asynchronous communication: Sender continues without waiting
• Buffering: Messages stored temporarily if receiver not ready

Mnemonic: “PMSSS” - Pipes, Message queues, Shared memory, Semaphores, Signals

Question 5(b) [4 marks]

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Explain File structure used by Linux.

Answer:

Linux File System follows hierarchical directory structure starting from root directory.

Diagram: Linux File System Hierarchy

Table: Important Directories

• Case sensitive: Distinguishes between File.txt and file.txt
• No drive letters: Everything under single root directory
• Mount points: External devices appear as subdirectories

Mnemonic: “BEHVUT” - Bin, Etc, Home, Var, Usr, Tmp

Question 5(c) [7 marks]

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Explain operating system security policies and procedures.

Answer:

Security Policies define rules and guidelines for protecting system resources and data.

Table: Security Policy Components

Security Procedures:

Authentication Procedures:

• Multi-factor authentication: Password + token/biometric
• Password complexity: Minimum length, special characters
• Account lockout: Temporary disable after failed attempts

Authorization Procedures:

• Principle of least privilege: Minimum necessary access
• Role-based access: Assign permissions based on job function
• Regular review: Periodic audit of user permissions

Monitoring Procedures:

• Log analysis: Review system and security logs
• Intrusion detection: Monitor for unauthorized access
• Vulnerability scanning: Identify security weaknesses

Mnemonic: “APABI” - Access control, Password, Audit, Backup, Incident response

Question 5(a) OR [3 marks]

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Explain Critical section.

Answer:

Critical Section is code segment where process accesses shared resources that must not be accessed concurrently.

Table: Critical Section Properties

Critical Section Structure:

do {
    entry_section();     // Request permission
    critical_section();  // Access shared resource
    exit_section();      // Release permission
    remainder_section(); // Other work
} while(true);

Solutions:

• Peterson’s algorithm: Software solution for two processes
• Semaphores: Hardware-supported synchronization
• Mutex locks: Binary semaphore for mutual exclusion

Mnemonic: “MPB” - Mutual exclusion, Progress, Bounded waiting

Question 5(b) OR [4 marks]

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Explain types of Linux file system.

Answer:

Linux File Systems organize and manage data storage on disk devices.

Table: Linux File System Types

ext4 Features:

• Journaling: Faster recovery after system crash
• Large file support: Files up to 16TB
• Backwards compatibility: Can mount ext2/ext3 partitions
• Extents: Improve performance for large files

File System Selection Factors:

• Performance requirements: Speed vs reliability
• File size limits: Maximum file and partition sizes
• Compatibility needs: Cross-platform support

Mnemonic: “EXBZNF” - Ext4, XFS, Btrfs, ZFS, NTFS, FAT32

Question 5(c) OR [7 marks]

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Explain need of protection mechanism and various protection domain.

Answer:

Protection Mechanism prevents processes from interfering with each other and system resources.

Need for Protection:

• Resource sharing: Multiple users/processes access same resources
• Error containment: Prevent bugs from affecting entire system
• Security enforcement: Implement access control policies
• System stability: Protect critical system components

Table: Protection Domains

Protection Mechanisms:

Hardware Protection:

• Memory protection: Base and limit registers
• CPU protection: Timer interrupts prevent infinite loops
• I/O protection: Privileged instructions for device access

Software Protection:

• Access control lists: Define resource permissions
• Capability lists: Token-based access control
• Domain switching: Change protection levels safely

Table: Access Rights

Mnemonic: “RECES-UKS” - Resource sharing, Error containment, Security; User domain, Kernel domain, System domain