Operating Systems Lab Assignments (4th Semester)

This repository contains the solutions for the Operating Systems Laboratory assignments. The code demonstrates proficiency in Linux shell scripting, system calls, process management, and file handling in a UNIX environment.

| Abhinav Mishra | 24AI004 |

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🛠️ Environment & Tools

• OS: Ubuntu Linux (22.04 LTS / 24.04 LTS)
• Shell: Bash (Bourne Again SHell)
• Compiler: GCC (GNU Compiler Collection)
• Debuggers/Tools: strace, gdb, top, bc

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📂 Assignment 1: Basic Linux Commands & File Management

Objective: To understand basic Linux commands for file handling (touch, cat, cp, mv) and hierarchical directory management.

• File: assignment1.sh
• Description: An automated shell script that:
  1. Creates a directory structure (ProjectWorkspace/Docs, Code, etc.).
  2. Performs file creation and redirection (echo, >).
  3. Analyzes file statistics (wc).
  4. Demonstrates pattern matching by moving files based on wildcards.
• Execution:

  chmod +x assignment1.sh
  ./assignment1.sh

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📂 Assignment 2: Advanced Shell Scripting

Objective: To implement logic using control structures (loops, conditions) and design menu-driven programs.

1. Factorial Calculator

• File: factorial.sh
• Logic: Calculates $n!$ using a for loop. Handles negative number validation.

2. Address Book (CRUD)

• File: addressbook.sh
• Logic: A menu-driven program to Create, Read, Update, and Delete contacts in a persistent text file (contacts.txt). Uses grep and sed for data manipulation.

3. Bulk Image Renamer

• File: rename_jpg.sh
• Logic: Automatically renames all .jpg files in the directory by prefixing the current date (YYYY-MM-DD).

4. Geometry Calculator

• File: geometry.sh
• Logic: Calculates Area and Circumference for various shapes. Uses bc (Basic Calculator) for high-precision floating-point arithmetic.

📂 Assignment 3: System Calls & Process Interactions

Objective: To understand the boundary between user-space and kernel-space by implementing standard Linux system calls in C and analyzing them with system monitoring tools.

1. System Call Implementation

• File: syscall_demo.c
• Description: A C program that bypasses standard library functions (fopen, fprintf) to interact directly with the kernel.
• Key Concepts Implemented:
  • File I/O: Used open() (with flags O_CREAT|O_WRONLY), write(), and close() for direct file manipulation.
  • Process Creation: Used fork() to create a child process.
  • Process Identification: Used getpid() to retrieve Process IDs for both parent and child.
  • Synchronization: Implemented wait() to ensure the parent process waits for the child to terminate, preventing "zombie" processes.

2. System Analysis & Debugging

Objective: Apply debugging techniques to observe system-level behavior.

• Tool: strace (System Call Tracer)

  • Used to intercept and record the system calls invoked by the process.
  • Observation: Verified that printf internally calls write and fork internally calls clone.
  • Command: strace ./syscall_demo

• Tool: gdb (GNU Debugger)

  • Used for step-by-step execution and inspecting file descriptors.
  • Observation: Inspected the file descriptor integer values (typically returning 3 for the first open file).
  • Command: gdb ./syscall_demo

• Tool: top (Process Monitor)

  • Used to observe the process status and CPU consumption during the execution loop.

Compilation & Execution

# Compile with debugging information included
gcc -g syscall_demo.c -o syscall_demo

# Execute the program
./syscall_demo

# Verify the output file created by system calls
cat syscall_output.txt