Linux Operating System (4331602) - Winter 2023 Solution

Question 1(a) [3 marks]

#

Draw the architecture of Linux and explain various layers in brief.

Answer:

Diagram:

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

• User Space: Contains user applications and system utilities
• System Call Interface: Provides interface between user programs and kernel
• Kernel Space: Core operating system with process, memory, file management

Mnemonic: “Users System Kernel Drives Hardware”

Question 1(b) [4 marks]

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What is a race condition? Explain with a suitable example.

Answer:

Example Process:

• Process A: Reads balance = 1000, adds 100
• Process B: Reads balance = 1000, subtracts 50
• Result: Final balance could be 1050, 950, or 1100 instead of correct 1050

Mnemonic: “Race Results Random Resources”

Question 1(c) [7 marks]

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

Answer:

Table: Types of Operating Systems

Multiprogramming Working:

• Memory Management: Multiple programs loaded simultaneously
• CPU Scheduling: Switches between programs when I/O occurs
• Resource Sharing: Efficient utilization of CPU and memory
• Example: Word processor, music player, and browser running together

Mnemonic: “Multiple Programs Maximize Performance”

Question 1(c OR) [7 marks]

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

Answer:

Types of Operating Systems: Same table as above.

Batch Operating System Details:

• Job Collection: Jobs collected offline and grouped into batches
• Sequential Processing: Jobs executed one after another without user interaction
• No Direct Interaction: User submits job and collects output later
• Efficiency: High throughput for similar type jobs
• Disadvantages: No real-time processing, long turnaround time

Mnemonic: “Batch Brings Better Business”

Question 2(a) [3 marks]

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Draw and explain the Process life cycle.

Answer:

Diagram:

stateDiagram-v2
    [*] --> New
    New --> Ready : Admitted
    Ready --> Running : Scheduler_dispatch
    Running --> Ready : Interrupt
    Running --> Waiting : I/O_request
    Waiting --> Ready : I/O_completion
    Running --> Terminated : Exit
    Terminated --> [*]

• New: Process being created
• Ready: Process waiting for CPU assignment
• Running: Process currently executing
• Waiting: Process waiting for I/O operation
• Terminated: Process has finished execution

Mnemonic: “New Ready Running Waiting Terminated”

Question 2(b) [4 marks]

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Define deadlock and discuss necessary conditions for a deadlock to occur.

Answer:

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

Table: Deadlock Conditions

Mnemonic: “My Hold Never Circles”

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 = 05 ms.

Answer:

Round Robin Algorithm:

• Time Quantum: Fixed time slice for each process
• Preemptive: Process preempted after quantum expires
• Fair Scheduling: Equal CPU time distribution

Given Data:

• Context Switch = 1 ms, Quantum = 5 ms

Gantt Chart:

|P1|CS|P2|CS|P3|CS|P4|CS|P1|CS|P3|CS|P1|CS|P3|CS|
0  5  6 10 11 16 17 22 23 28 29 34 35 40 41 46 47

Calculations Table:

• Average Waiting Time: (28+3+29+12)/4 = 18 ms
• Average Turnaround Time: (40+7+44+17)/4 = 27 ms

Mnemonic: “Round Robin Rotates Regularly”

Question 2(a OR) [3 marks]

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

Answer:

Table: CPU vs I/O Bound Processes

Mnemonic: “CPU Computes, I/O Interacts”

Question 2(b OR) [4 marks]

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Define Critical Section and discuss the general structure of a critical section solution.

Answer:

Definition: Critical section is code segment where shared resources are accessed and must be executed atomically.

Table: Critical Section Structure

Solution Requirements:

• Mutual Exclusion: Only one process in critical section
• Progress: Selection of next process cannot be postponed indefinitely
• Bounded Waiting: Limit on waiting time

Mnemonic: “Enter Critical Exit Remainder”

Question 2(c OR) [7 marks]

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

Answer:

SJF Algorithm:

• Shortest Job First: Process with smallest burst time scheduled first
• Non-preemptive: Process runs to completion
• Optimal: Minimizes average waiting time

Execution Order: P2(4), P4(5), P1(8), P3(9)

Gantt Chart:

|  P1  |  P2  |  P4  |     P3     |
0      8     12     17          26

Calculations Table:

• Average Waiting Time: (0+5+12+6)/4 = 5.75 ms
• Average Turnaround Time: (8+9+21+11)/4 = 12.25 ms

Mnemonic: “Shortest Jobs Start Soon”

Question 3(a) [3 marks]

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Explain two-level directory structure.

Answer:

Diagram:

• Master File Directory: Contains entries for each user
• User File Directory: Separate directory for each user’s files
• Path Structure: /user/filename
• Advantages: Solves naming conflicts, provides user isolation

Mnemonic: “Two Tiers Tackle Troubles”

Question 3(b) [4 marks]

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Explain the different file operations.

Answer:

Table: File Operations

Mnemonic: “Create Open Read Write Close Delete”

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
• Linked Allocation
• Indexed Allocation

Contiguous Allocation:

Diagram:

Table: Contiguous Allocation

Directory Entry: (Start block, Length)

Mnemonic: “Contiguous Creates Continuous Clusters”

Question 3(a OR) [3 marks]

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Describe the types of file structures.

Answer:

Table: File Structure Types

Mnemonic: “Sequential Direct Indexed Hierarchical”

Question 3(b OR) [4 marks]

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Explain the different file attributes.

Answer:

Table: File Attributes

Mnemonic: “Name Type Size Location Permissions Time”

Question 3(c OR) [7 marks]

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

Answer:

File Allocation Methods: Same as previous answer.

Linked Allocation:

Diagram:

Table: Linked Allocation

Directory Entry: (Start block pointer)

Mnemonic: “Links Lead Logical Locations”

Question 4(a) [3 marks]

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Define Program threats and explain its types.

Answer:

Definition: Program threats are malicious programs that compromise system security and integrity.

Table: Program Threat Types

Mnemonic: “Trojans Viruses Worms Logic-bombs”

Question 4(b) [4 marks]

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Explain System Authentication.

Answer:

Definition: Process of verifying user identity before granting system access.

Table: Authentication Methods

Authentication Process:

• Identification: User claims identity
• Verification: System validates claim
• Authorization: Access rights granted

Mnemonic: “Passwords Biometrics Tokens Multi-factor”

Question 4(c) [7 marks]

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Explain Access Control List in detail.

Answer:

Definition: ACL specifies permissions for each user/group on system resources.

Table: ACL Components

ACL Structure:

User: john    File: /etc/passwd    Permission: read    Action: allow
Group: users  File: /tmp/*        Permission: write   Action: allow
User: guest   File: /etc/*        Permission: write   Action: deny

Advantages:

• Granular Control: Fine-grained permissions
• Flexibility: Per-resource access control
• Scalability: Handles complex organizations

Mnemonic: “Access Controls Limit Users”

Question 4(a OR) [3 marks]

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Define System threats and explain its types.

Answer:

Definition: System threats target operating system components and system integrity.

Table: System Threat Types

Mnemonic: “Denial Privilege Buffer Rootkit”

Question 4(b OR) [4 marks]

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Discuss the needs and goals of protection in OS.

Answer:

Table: Protection Needs and Goals

Protection Mechanisms:

• Access Control: Limit resource access
• Capability Lists: Define user permissions
• Security Domains: Isolate processes

Mnemonic: “Confidentiality Integrity Availability Authentication”

Question 4(c OR) [7 marks]

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Discuss various operating system security policies and procedures.

Answer:

Table: Security Policies and Procedures

Security Procedures:

• Regular Updates: Patch management
• Monitoring: Log analysis, intrusion detection
• Training: User security awareness
• Audit: Compliance checking

Mnemonic: “Access Password Backup Incident”

Question 5(a) [3 marks]

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Explain the following commands: (i) pwd (ii) cd (iii) comm

Answer:

Table: Linux Commands

• pwd: Shows current directory path
• cd: Navigate between directories
• comm: Displays common and unique lines between files

Mnemonic: “Print Working Directory, Change Directory, Compare Common”

Question 5(b) [4 marks]

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Write a shell script to concatenate the contents of two files in a third file.

Answer:

Shell Script:

#!/bin/bash
# Script to concatenate two files into third file

echo "Enter first file name:"
read file1
echo "Enter second file name:" 
read file2
echo "Enter output file name:"
read file3

# Check if input files exist
if [ -f "$file1" ] && [ -f "$file2" ]; then
    cat "$file1" "$file2" > "$file3"
    echo "Files concatenated successfully into $file3"
else
    echo "Error: Input files not found"
fi

Mnemonic: “Cat Combines Content Correctly”

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:

Shell Script:

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

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

# Validate input
if [ ${#number} -ne 5 ]; then
    echo "Error: Please enter exactly 5 digits"
    exit 1
fi

sum=0
temp=$number

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

echo "Sum of digits in $number is: $sum"

Algorithm:

• Input Validation: Check for 5-digit number
• Digit Extraction: Use modulo operation
• Sum Calculation: Add each digit
• Display Result: Show final sum

Mnemonic: “Sum Separates Single Symbols”

Question 5(a OR) [3 marks]

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Explain the following commands: (i) man (ii) mkdir (iii) grep

Answer:

Table: Linux Commands

• man: Provides documentation for commands
• mkdir: Creates new directories with specified names
• grep: Searches for patterns in files using regular expressions

Mnemonic: “Manual Make Directories, Grep Examines Patterns”

Question 5(b OR) [4 marks]

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Write a shell script to generate and display Fibonacci series.

Answer:

Shell Script:

#!/bin/bash
# Script to generate Fibonacci series

echo "Enter number of terms:"
read n

# Validate input
if [ $n -le 0 ]; then
    echo "Error: Please enter positive number"
    exit 1
fi

# Initialize first two terms
a=0
b=1

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

if [ $n -gt 1 ]; then
    echo -n "$b "
fi

# Generate remaining terms
for ((i=3; i<=n; i++)); do
    c=$(($a + $b))
    echo -n "$c "
    a=$b
    b=$c
done
echo

Mnemonic: “Fibonacci Follows Forward Formula”

Question 5(c OR) [7 marks]

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Write a shell script to determine whether a given string is palindrome.

Answer:

Shell Script:

#!/bin/bash
# Script to check if string is palindrome

echo "Enter a string:"
read string

# Convert to lowercase and remove spaces
clean_string=$(echo "$string" | tr '[:upper:]' '[:lower:]' | tr -d ' ')

# Get string length
length=${#clean_string}

# Initialize flag
is_palindrome=true

# Check palindrome
for ((i=0; i<length/2; i++)); do
    if [ "${clean_string:$i:1}" != "${clean_string:$((length-1-i)):1}" ]; then
        is_palindrome=false
        break
    fi
done

# Display result
if [ "$is_palindrome" = true ]; then
    echo "'$string' is a palindrome"
else
    echo "'$string' is not a palindrome"
fi

Algorithm:

• String Cleaning: Convert to lowercase, remove spaces
• Character Comparison: Compare characters from both ends
• Palindrome Check: Verify if all comparisons match

Mnemonic: “Palindromes Proceed Perfectly Parallel”