In operating systems, which of the following lists common reasons for process termination by the system or by the process itself?

Introduction / Context:
Processes represent running programs in an operating system. A process does not run forever; eventually it terminates and its resources are released. Understanding the different reasons why a process may terminate helps in analyzing system behavior, designing robust applications, and answering exam questions on process management. Termination can be voluntary or forced, and can be triggered by the process itself, the operating system, or other processes.

Given Data / Assumptions:

• We are discussing a general purpose multitasking operating system.
• Processes can end normally or due to errors.
• The operating system enforces protection, resource limits, and parent child relationships.
• The question asks for a list of common reasons for process termination.

Concept / Approach:
Common reasons for process termination include normal completion when a program finishes its work and calls an exit routine. Processes may also terminate abnormally when they encounter unrecoverable errors such as invalid memory accesses, division by zero, or unhandled exceptions; the operating system often kills them in response. Resource or time limits, such as exceeding maximum CPU time or memory usage, can also cause termination. Additionally, one process, typically a parent or an administrator controlled process, can explicitly request the termination of another via system calls. These scenarios cover the main reasons studied in operating systems courses.

Step-by-Step Solution:
Step 1: Identify normal completion, where a process reaches the end of its main routine or calls an exit function to indicate successful termination.Step 2: Include abnormal or error exit, where the process encounters a condition it cannot handle and exits with an error status.Step 3: Recognize that protection violations or runtime errors such as illegal instructions or invalid memory accesses can cause the operating system to terminate the offending process.Step 4: Consider resource limit violations, such as exceeding allowed CPU time, memory quota, or other usage restrictions, which can trigger termination by the system.Step 5: Add termination by another process, such as a parent issuing a kill request or a system administrator stopping a runaway process, as another common reason.

Verification / Alternative check:
Operating systems documentation and textbooks often list these reasons explicitly. For example, Unix like systems document normal exit, signals that terminate processes due to errors or external requests, and resource limit enforcement. Windows and other systems have similar categories, such as normal termination, exceptions, and forced termination via system tools. In all cases, these reasons match the general categories of normal exit, abnormal error exit, protection or runtime errors, resource limits, and external kill requests.

Why Other Options Are Wrong:
Option B is incorrect because it claims that only normal completion is allowed and that processes are never terminated for errors or by other processes, which contradicts real operating system behavior. Option C is wrong because a context switch between user mode and kernel mode does not by itself terminate a process; it is part of routine system operation. Option D is incorrect because processes terminate many times for reasons unrelated to unmounting file systems or powering off; those events may affect processes but are not the only termination causes.

Common Pitfalls:
Students sometimes focus only on one category, such as normal exit, and forget that the operating system actively enforces protection and resource limits, which can lead to termination. Another pitfall is to conflate context switching or entering kernel mode with termination; these are distinct concepts. Remembering the range of reasons, from voluntary exit and errors to external termination requests, gives a complete picture of process life cycle events.

Final Answer:
Common reasons for process termination include normal completion, error or abnormal exit, fatal protection or runtime errors, exceeding resource or time limits, and termination requested by another process such as the parent or an administrator.