DCA7105 UNIX & SHELL PROGRAMMING JULY SEPTEMBER 2025

Description

SESSION	SEPTEMBER 2025
PROGRAM	MASTER OF COMPUTER APPLICATIONS (MCA)
SEMESTER	III
COURSE CODE & NAME	DCA7105 UNIX & SHELL PROGRAMMING

 

 

Set-I

 

 

Q1. Discuss the major legal and licensing milestones in the evolution of UNIX. Explain AT&T’s licensing policies, the BSD lawsuit and its implications and how these events influenced the rise of open-source UNIX-like systems such as Linux and FreeBSD. 5+5

Ans 1.

Major Legal & Licensing Milestones in the Evolution of UNIX

The evolution of UNIX is deeply shaped not only by technological innovation but also by a series of legal, licensing, and commercial decisions that influenced its distribution, accessibility, and the eventual rise of open-source UNIX-like systems. UNIX began as a research project at AT&T’s Bell Labs, but its licensing and ownership journey ultimately defined the future of operating systems.

AT&T’s Early Licensing Policies

Initially, AT&T was restricted by federal regulations from entering the computer business.

 

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Q2. Explain the concepts of orphan and zombie processes in UNIX. How are they created, and what mechanisms does the operating system use to handle them? 5+5

Ans 2.

Orphan and Zombie Processes in UNIX

UNIX uses a hierarchical process model where every process has a parent, and the kernel manages creation, execution, and termination. Two special types of processes—orphans and zombies—emerge due to interruptions in this hierarchy. They are not errors but expected states arising from specific execution patterns.

Zombie Processes: Meaning and Creation

A zombie process is a process that has completed execution but still has an entry in the process

 

Q3. Explain the concept of a shell in UNIX and discuss its types. Differentiate between interactive and non-interactive shells and explain the role of the shebang (#!) in shell scripting. 5+5

Ans 3.

Concept of Shell and Its Types

In UNIX, the shell acts as a command interpreter that bridges the gap between the user and the operating system. It reads user input, interprets it, executes commands, and manages scripting features. The shell provides an interactive interface and a powerful scripting language for automation.

Types of UNIX Shells

UNIX offers multiple shells, each designed with unique scripting syntax and user features.

Bourne Shell (sh)

Developed by Stephen Bourne, it is the original UNIX shell. It forms the foundation for scripting

 

Set-II

 

Q4. Discuss the differences between system calls and library functions in C. Explain how they interact with the operating system and provide suitable examples.   5+5     

Ans 4.

System Calls vs Library Functions in C

In UNIX-based systems, both system calls and library functions form the foundation of program execution, interaction with the operating system, and access to system resources. Although they are often used together, they operate at different levels, serve different purposes, and play unique roles in how processes read data, write output, create files, manage memory, and interact with hardware. Understanding the distinctions between them is crucial for system programming,

 

 

Q5. Discuss in detail how UNIX manages user logins and organises processes into sessions. Explain the relationship between the user, shell, terminal, and processes after a successful login. 5+5       

Ans 5.

UNIX Login Mechanism and Process Sessions

In UNIX systems, logging in is a structured process involving authentication, environment setup, session creation, and shell initialization. This sequence establishes a secure environment where a user interacts with the system through commands, processes, and terminal interfaces. Understanding this mechanism reveals how UNIX manages security, multitasking, and process relationships in a unified manner.

User Login and Authentication

When a user attempts to log in, either through a physical terminal, remote SSH session, or

 

 

Q6. Describe the major types of errors encountered in system-level programming—syntax, runtime, logic, and system errors. For each, explain when it occurs and how it can be detected or handled, with relevant examples.  5+5     

Ans 6.

Types of Errors in System-Level Programming

System-level programming in C and UNIX involves interacting directly with memory, processes, files, and system calls. Because of this low-level control, different categories of errors frequently occur, each affecting program behavior in a unique way. Understanding syntax, runtime, logic, and system errors is essential for writing stable, reliable, and portable UNIX software.

Syntax Errors

Syntax errors occur when code violates the grammatical rules of the C programming language.