Top 50 Operating System Interview Questions (2026)

By : Nathaniel Brooks Nathaniel Brooks
Hours Updated

Preparing for an Operating System interview? It is time to explore what you might be asked. Operating System Interview Questions captures essential insights into how well candidates understand core computing principles.

Operating System concepts open diverse career opportunities across technical, mid-level, and senior roles. Professionals with strong technical experience, domain expertise, and analyzing skills can excel by mastering both basic and advanced questions and answers. These interviews help assess problem-solving skills, root-level experience, and practical understanding for freshers and experienced professionals alike.

Based on insights from over 80 technical leaders, 60 managers, and 100+ professionals, these Operating System Interview Questions reflect real hiring trends and practical expectations across multiple domains and experience levels.

Operating Systems Interview Questions

Top Operating Systems Interview Questions

1) What is an Operating System and what are its main functions?

An Operating System (OS) is system software that manages computer hardware and software resources and provides common services for computer programs. It acts as an intermediary between the user and the computer hardware, ensuring efficient execution of applications.

Core functions include:

  • Process management: Scheduling and execution of processes.
  • Memory management: Allocation and deallocation of memory.
  • File system management: Managing files, directories, and access permissions.
  • Device management: Handling I/O devices via drivers.
  • Security and access control: Ensuring data integrity and restricted access.

Example: Windows manages multiple user sessions through process isolation and memory protection mechanisms.

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2) Explain different types of Operating Systems with examples.

Operating Systems can be categorized based on their structure and task-handling capabilities:

Type Description Example
Batch OS Executes batches of jobs without user interaction. IBM Mainframe OS
Time-Sharing OS Multiple users share system resources simultaneously. UNIX
Distributed OS Manages group of connected computers as one system. Amoeba, LOCUS
Real-Time OS Provides immediate response to input. VxWorks, RTLinux
Network OS Manages data and applications in a networked environment. Novell NetWare

Each type is designed to handle specific operational requirements, from real-time control systems to multi-user environments.

3) What is the difference between Process and Thread?

A process is an independent program in execution with its own memory space, while a thread is the smallest unit of CPU utilization within a process that shares memory with other threads of the same process.

Feature Process Thread
Memory Space Independent Shared within the same process
Communication Inter-process Communication (IPC) Easier via shared memory
Overhead High Low
Example Running Chrome Tabs inside Chrome

Example: When using Chrome, each tab runs as a separate process, but the rendering threads within the same tab share resources.

4) What are system calls in an Operating System?

System calls act as an interface between user-level applications and kernel-level services. They allow user programs to request services from the OS kernel such as file manipulation, process control, or communication.

Types of system calls include:

  • Process control: fork(), exec(), exit()
  • File management: open(), read(), write(), close()
  • Device management: ioctl(), read(), write()
  • Information maintenance: getpid(), alarm(), sleep()

Example: In Linux, the fork() system call creates a new process by duplicating the parent.

5) How does process synchronization work in Operating Systems?

Process synchronization ensures orderly execution of processes when accessing shared resources, preventing race conditions. Synchronization can be achieved through mutex locks, semaphores, and monitors.

Example: If two processes try to update a shared counter simultaneously, synchronization mechanisms ensure one completes before the other begins.

Mechanism Description Example Use
Semaphore Integer variable controlling access. Producer-consumer problem
Mutex Binary lock for mutual exclusion. Thread synchronization
Monitor High-level construct for synchronization. Java synchronized methods

6) What is Deadlock? Explain its conditions.

A deadlock occurs when two or more processes are waiting indefinitely for resources held by each other, causing the system to halt further progress.

Four necessary conditions for deadlock (Coffman’s conditions):

  1. Mutual Exclusion – Only one process can access a resource at a time.
  2. Hold and Wait – A process holds one resource and waits for others.
  3. No Preemption – Resources cannot be forcibly taken away.
  4. Circular Wait – A closed chain of processes exists where each process waits for a resource held by the next.

Example: Two printers shared by multiple processes without proper resource allocation policies can cause deadlocks.

7) How can Deadlocks be prevented or avoided?

Deadlocks can be managed through prevention, avoidance, detection, and recovery.

Strategy Description Example
Prevention Eliminates one of the necessary conditions. Avoid hold and wait by requesting all resources at once.
Avoidance Dynamically checks resource allocation using Banker’s Algorithm. Used in real-time systems.
Detection Periodically checks for circular waits. Resource allocation graph analysis.
Recovery Terminates or rolls back processes. Restarting one process to release resources.

The Banker’s Algorithm ensures safe resource allocation by checking if granting a request keeps the system in a safe state.

8) What is the difference between Paging and Segmentation?

Both are memory management techniques, but they differ in how memory is divided and accessed.

Feature Paging Segmentation
Basis Fixed-size blocks (pages) Variable-size blocks (segments)
Size Equal Unequal
Logical Division Physical memory Logical program units
Example Virtual memory system Code, stack, data segment

Example: Paging is used in Linux for efficient memory allocation, while segmentation is used in Intel x86 architectures to manage logical address spaces.

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9) Explain Process Scheduling and its types.

Process scheduling determines the order in which processes are executed by the CPU. The scheduler selects processes from the ready queue and allocates CPU time.

Types of Scheduling:

  • Long-term (Job scheduling): Controls admission of processes.
  • Short-term (CPU scheduling): Decides which ready process gets CPU next.
  • Medium-term: Handles swapping between main memory and disk.

Example algorithms: FCFS, SJF, Round Robin, Priority Scheduling.

Each has trade-offs between throughput, turnaround time, and response time.

10) What are different types of CPU Scheduling Algorithms?

Algorithm Description Advantages Disadvantages
FCFS (First Come First Serve) Executes processes in arrival order. Simple Poor performance for long jobs
SJF (Shortest Job First) Executes smallest job first. Minimum waiting time Starvation possible
Round Robin Time-sharing algorithm with equal CPU quantum. Fair High context switching overhead
Priority Scheduling Based on priority values. Suitable for real-time Starvation of low-priority jobs

Example: Round Robin is ideal for time-sharing systems where fairness among users is required.

11) What is Virtual Memory and how does it work?

Virtual Memory is a memory management technique that allows the execution of processes that may not be completely in the main memory. It provides the illusion of a large contiguous memory space by combining physical RAM with disk space.

The OS uses paging to map virtual addresses to physical addresses. When a process needs data not in RAM, a page fault occurs, and the OS retrieves the data from the disk (swap space).

Advantages include:

  • Increased multitasking capabilities
  • Efficient use of physical memory
  • Isolation between processes

Example: Windows and Linux use virtual memory with a page replacement policy like Least Recently Used (LRU) to manage limited RAM efficiently.

12) What are Page Replacement Algorithms? Explain with examples.

When memory is full and a new page is needed, the OS decides which page to replace using page replacement algorithms.

Algorithm Description Example Behavior
FIFO Removes the oldest page in memory. Simple but can cause Belady’s anomaly.
LRU (Least Recently Used) Replaces page not used for longest time. Efficient for locality of reference.
Optimal Replaces page not used in the near future. Theoretical best, used for benchmarking.
Clock Circular queue with use bit. Approximation of LRU.

Example: In LRU, if pages A, B, and C are loaded and D arrives while A was least used, page A will be replaced.

13) What is Thrashing in an Operating System?

Thrashing occurs when the system spends more time swapping pages between RAM and disk than executing processes. It happens due to insufficient physical memory or excessive multiprogramming.

Symptoms include:

  • High CPU utilization with low throughput
  • Frequent page faults
  • Slow system response

Prevention Techniques:

  • Adjusting degree of multiprogramming
  • Using Working Set Model or Page Fault Frequency (PFF) methods
  • Increasing physical memory

Example: Running too many heavy applications simultaneously can cause thrashing, degrading performance drastically.

14) Explain the concept of File System and its functions.

A File System organizes and stores data on storage devices, providing a way to access, manage, and retrieve files.

Main Functions:

  • File creation, deletion, reading, and writing
  • Directory organization
  • Access control and permissions
  • Space allocation and management

Common File Systems:

File System Platform Key Feature
NTFS Windows Security, compression
EXT4 Linux Journaling, large file support
APFS macOS Snapshots, encryption

Example: In Linux, the ext4 file system supports journaling to prevent data corruption during crashes.

15) What are File Access Methods?

File access methods define how data in a file can be read or written. The three main methods are:

  1. Sequential Access:
    Data is accessed in a specific order, from beginning to end.
    Example: Log files or audio streams.
  2. Direct (Random) Access:
    Allows jumping directly to any record.
    Example: Databases or virtual memory systems.
  3. Indexed Access:
    Uses an index to access data quickly.
    Example: File systems like NTFS use indexing for fast lookups.

Comparison Table:

Method Speed Use Case Example
Sequential Slow Logs, streaming Tape drives
Direct Fast Databases Hard disks
Indexed Moderate File systems NTFS, FAT32

16) What is the difference between Internal and External Fragmentation?

Fragmentation refers to inefficient memory usage caused by allocation patterns.

Type Cause Description Example
Internal Fragmentation Fixed-size allocation Wasted space inside allocated memory blocks. Allocating 8 KB block for 6 KB data.
External Fragmentation Variable-size allocation Free spaces scattered across memory. Multiple small holes preventing large allocation.

Prevention:

  • Use paging to eliminate external fragmentation.
  • Use segmentation with paging for flexible management.

Example: Systems using fixed-size memory partitions often suffer from internal fragmentation.

17) What are the states of a Process in an Operating System?

A process moves through several states during its lifecycle.

State Description
New Process is being created.
Ready Waiting to be assigned to CPU.
Running Instructions are being executed.
Waiting/Blocked Waiting for I/O or event completion.
Terminated Execution completed or aborted.

Example: In UNIX, a process created by fork() starts in the ready state and moves to running when the scheduler selects it.

Lifecycle Example:

New → Ready → Running → Waiting → Ready → Terminated

18) What are Inter-Process Communication (IPC) mechanisms?

IPC allows processes to exchange data and synchronize their actions. It is vital in multi-process systems.

Common IPC methods:

  • Pipes: Unidirectional communication channel.
  • Message Queues: Exchange structured messages.
  • Shared Memory: Fastest method; processes share memory space.
  • Semaphores: Synchronization primitive to avoid race conditions.
  • Sockets: Network-based process communication.

Example: In Linux, parent and child processes use pipes (pipe()) to send data between them.

19) What is a Kernel, and what are its types?

A Kernel is the core component of an Operating System, managing hardware, processes, and system calls.

Type Description Example
Monolithic Kernel All OS services run in kernel mode. Linux, UNIX
Microkernel Minimal services in kernel mode; rest in user mode. QNX, Minix
Hybrid Kernel Combines monolithic and microkernel features. Windows NT, macOS
Exokernel Gives maximum control to applications. MIT Exokernel

Example: Linux’s monolithic kernel allows faster system calls, while microkernels offer better modularity and stability.

20) What are the differences between User Mode and Kernel Mode?

Feature User Mode Kernel Mode
Access Level Limited Full system access
Execution Applications OS and device drivers
Example Word Processor Memory Manager
System Calls Required for privileged operations Executes privileged instructions
Protection Prevents accidental system damage Can modify system configuration

Example: When a program requests file access via open(), the system switches from user mode to kernel mode to execute the system call safely.

21) What is Multithreading and what are its advantages?

Multithreading allows multiple threads of a single process to run concurrently, sharing the same memory space but executing independently. It improves application responsiveness and resource utilization.

Advantages include:

  • Improved performance: Utilizes CPU cores efficiently.
  • Better responsiveness: UI remains active during background tasks.
  • Resource sharing: Threads share code and data, reducing memory overhead.
  • Scalability: Suitable for multicore processors.

Example: A web browser uses multithreading — one thread handles user input, another downloads data, and another renders the UI.

Advantage Description
Responsiveness Keeps applications interactive
Resource Efficiency Threads share common memory
Faster Execution Parallel task handling
Scalability Supports multicore CPUs effectively

22) Explain the difference between Multithreading and Multiprocessing.

Aspect Multithreading Multiprocessing
Definition Multiple threads within one process. Multiple independent processes.
Memory Shared between threads. Separate for each process.
Overhead Low High due to separate memory.
Failure One thread crash can affect all. Independent processes; safer.
Example Java threads Multiple Python processes

Example: A modern web server uses multiprocessing to handle independent client requests, while each process may use multithreading for concurrent I/O.

Summary: Multithreading is lightweight and efficient for tasks sharing data, whereas multiprocessing offers fault isolation and better stability.

23) What are the different types of Scheduling Queues in an Operating System?

Scheduling queues organize processes based on their execution state.

Main Queues:

  1. Job Queue: Holds all system processes.
  2. Ready Queue: Contains processes ready for CPU allocation.
  3. Device Queue: Holds processes waiting for I/O operations.
  4. Wait Queue: Processes waiting for a specific event.

Example: In Linux, the ready queue is managed by the Completely Fair Scheduler (CFS) to ensure fair CPU distribution.

Queue Purpose Example
Job Queue Holds all system jobs Batch OS
Ready Queue Waiting for CPU Interactive programs
Device Queue Waiting for I/O Disk read/write
Wait Queue Waiting for events Signals or semaphores

24) What are System Programs in an Operating System?

System programs act as intermediaries between the user and system calls. They provide a convenient environment for program execution.

Categories include:

  • File Management: cp, mv, cat
  • Status Information: top, ps, df
  • Programming Support: Compilers, debuggers
  • Communication: Network utilities like ssh, ftp
  • Application Launching: Shells, window managers

Example: In Linux, the bash shell is a system program that interprets user commands and executes them through system calls.

25) Explain Critical Section and its problem.

A Critical Section is a code segment where shared resources are accessed. The Critical Section Problem arises when multiple processes execute this section simultaneously, causing race conditions.

To prevent conflicts, three conditions must be met:

  1. Mutual Exclusion: Only one process enters the section.
  2. Progress: A process should not block others unnecessarily.
  3. Bounded Waiting: Every process gets a chance eventually.

Example: In producer-consumer problems, updating the shared buffer must be in a critical section protected by semaphores.

26) What are different synchronization mechanisms used in OS?

Synchronization ensures consistency when multiple threads access shared resources.

Mechanism Description Example
Semaphore Integer used for signaling. Producer-consumer problem.
Mutex Lock for mutual exclusion. Thread-safe functions.
Spinlock Busy-wait lock for short waits. Kernel-level operations.
Monitor High-level synchronization construct. Java synchronized blocks.

Example: A semaphore is used in the dining philosophers problem to prevent deadlocks when philosophers compete for forks (resources).

27) What is a Context Switch and how does it occur?

A Context Switch occurs when the CPU switches from executing one process to another. It involves saving the current process state and loading the next process’s state.

Steps involved:

  1. Save CPU registers and process information.
  2. Update PCB (Process Control Block).
  3. Load the next process state.
  4. Resume execution.

Example: In Linux, a context switch happens during multitasking when CPU control shifts between threads or processes.

Metric Impact
Frequency High frequency reduces efficiency.
Time Cost Depends on hardware & OS.
Optimization Reduce unnecessary switches for performance.

28) Explain Demand Paging and its advantages.

Demand Paging is a lazy-loading technique where pages are loaded into memory only when required. This minimizes memory usage and startup time.

Advantages:

  • Efficient memory use
  • Faster program start
  • Supports large virtual memory
  • Reduces I/O overhead

Example: When opening a large program, only the required pages are loaded initially; others are fetched on demand during execution.

Parameter Demand Paging Pre-Paging
Loading On demand Pre-loaded
Efficiency High Moderate
Memory Use Minimal Higher

29) What are the different types of I/O Scheduling Algorithms?

I/O scheduling manages disk request order to minimize seek time.

Algorithm Description Advantage Disadvantage
FCFS Executes in arrival order. Fair and simple. High seek time.
SSTF Shortest seek time first. Reduces seek distance. Starvation possible.
SCAN (Elevator) Moves head back and forth across disk. Balanced performance. Slightly complex.
C-SCAN Circular version of SCAN. Uniform waiting time. More head movement.

Example: Modern Linux kernels use Completely Fair Queuing (CFQ) or Deadline Scheduler to balance latency and throughput.

30) Explain Spooling and its advantages.

Spooling (Simultaneous Peripheral Operation On-Line) is a process where data is temporarily stored in a buffer before being sent to an output device, like a printer.

Advantages:

  • Improves device utilization
  • Enables concurrent processing
  • Prevents device idle time
  • Increases overall system throughput

Example: Print jobs in a queue are spooled to disk before being printed sequentially.

Feature Description
Buffering Temporary storage before I/O operation
Parallelism Allows CPU and I/O overlap
Example Device Printers, Plotters

31) What are Daemons in Linux?

Daemons are background processes that run without user interaction and provide essential services in Unix/Linux systems. They typically start during boot and continue running to handle specific tasks.

Examples:

  • sshd → Manages remote SSH connections.
  • crond → Handles scheduled jobs.
  • httpd → Runs web servers like Apache.

Characteristics:

  • Run continuously in the background.
  • Initiated by the init or systemd process.
  • Typically have names ending with “d”.

Example: The systemd daemon manages system startup and service dependencies on most modern Linux distributions.

Daemon Function
sshd Secure remote access
crond Task scheduling
syslogd System logging
cupsd Printing service

32) What is the difference between a Shell and a Kernel?

Feature Shell Kernel
Function Interface between user and OS. Core part managing hardware and processes.
Interaction Accepts commands and executes them. Executes low-level operations.
Mode User mode Kernel mode
Example Bash, Zsh Linux kernel, Windows NT kernel

Explanation: The Shell acts as a command-line interpreter, translating user inputs into system calls executed by the Kernel.

For instance, typing ls in the shell makes a system call to the kernel to list directory contents.

33) Explain the Booting Process of a Linux System.

The booting process initializes the system from power-on to login.

Phases:

  1. BIOS/UEFI: Performs hardware checks (POST).
  2. Bootloader (GRUB/LILO): Loads kernel into memory.
  3. Kernel Initialization: Detects and configures hardware.
  4. init or systemd: Starts system and background services.
  5. Login Prompt: User authentication begins.

Example: Modern Linux uses systemd for parallel service startup, reducing boot time significantly compared to older SysVinit systems.

34) What is Swapping in an Operating System?

Swapping is the process of moving a process between main memory and secondary storage to manage memory efficiently.

Purpose:

  • To free memory for higher-priority processes.
  • To allow more processes to run concurrently.

Advantages:

  • Increases degree of multiprogramming.
  • Enables execution of large processes.

Disadvantages:

  • High disk I/O overhead.
  • Can lead to thrashing if used excessively.

Example: Linux uses a swap partition or swap file to extend virtual memory beyond physical RAM.

35) What is the difference between Hard Link and Soft Link in Linux?

Feature Hard Link Soft (Symbolic) Link
Points to Actual file data (inode) File path
File Deletion Original remains accessible Link becomes broken
Cross Filesystem Not allowed Allowed
Command ln file1 file2 ln -s file1 file2

Example: If you create a soft link to /home/user/data.txt and delete the original, the link becomes invalid. Hard links, however, remain until all references are removed.

36) Explain the concept of Zombie and Orphan Processes.

  • Zombie Process:

    A process that has finished execution but still has an entry in the process table waiting for the parent to read its exit status.

    Example: Occurs when a parent fails to call wait() after the child exits.

  • Orphan Process:

    A process whose parent has terminated before it. The init process adopts and cleans it up.

Process Type Description Resolution
Zombie Completed but not reaped Parent executes wait()
Orphan Parent terminated first Adopted by init/systemd

37) What is a Process Control Block (PCB)?

A Process Control Block (PCB) is a data structure maintained by the OS to store information about a process.

Contents of a PCB:

  • Process ID (PID)
  • Process state (ready, running, waiting)
  • CPU registers
  • Memory management info (page tables, segment tables)
  • Accounting information (CPU time, priority)
  • I/O status

Example: During a context switch, the OS saves the current process’s PCB and loads the next process’s PCB to resume execution.

38) What is the difference between Monolithic Kernel and Microkernel architecture?

Feature Monolithic Kernel Microkernel
Structure All OS services in kernel space Minimal services in kernel space
Performance Faster (less overhead) Slower (more user-kernel switches)
Stability Less modular Highly modular
Example Linux, UNIX MINIX, QNX

Explanation: In Monolithic Kernels, everything (drivers, file systems, etc.) runs in kernel space. Microkernels minimize kernel code, improving reliability but slightly reducing performance.

39) How does the OS handle security and protection?

Operating Systems use multiple layers of security mechanisms to protect data, memory, and user access.

Security Techniques:

  • Authentication: Validating user identity (e.g., via passwords, biometrics).
  • Authorization: Controlling access using permissions and ACLs.
  • Encryption: Protecting data confidentiality.
  • Isolation: Using process separation and virtual memory.
  • Auditing: Logging system events for monitoring.

Example: In Linux, chmod, chown, and sudo enforce file permissions and privilege escalation securely.

40) What are the advantages and disadvantages of Multitasking?

Multitasking allows multiple processes to execute concurrently by sharing CPU time.

Aspect Advantages Disadvantages
Performance Increases CPU utilization Overhead due to context switching
Responsiveness Improves user interaction Complex scheduling required
Resource Sharing Enables multiple app execution Potential for deadlocks
Efficiency Reduces idle CPU time Synchronization issues possible

Example: In Windows or Linux, multitasking allows the user to stream video, browse the internet, and download files simultaneously.

41) What is Virtualization in Operating Systems?

Virtualization is the technique of creating virtual instances of computing resources, such as servers, storage, or operating systems. It allows multiple OS environments to run on the same physical hardware, improving utilization and flexibility.

Key Components:

  • Hypervisor: Manages virtual machines (VMs).
  • Guest OS: OS running inside a VM.
  • Host OS: Base system controlling hardware.

Types of Virtualization:

Type Description Example
Hardware-level Emulates entire hardware stack. VMware ESXi
OS-level Containers share the host kernel. Docker
Application-level Virtualizes apps only. Wine, Sandboxie

Example: Running multiple Ubuntu servers on a single Windows host using VMware is hardware-level virtualization.

42) Explain the difference between a Hypervisor and a Container.

Feature Hypervisor Container
Definition Virtualizes hardware for multiple OSs. Virtualizes the OS kernel for isolated apps.
Resource Usage High (runs full OS). Lightweight (shares kernel).
Boot Time Slow Fast
Security Strong isolation Moderate isolation
Example VMware, Hyper-V Docker, Podman

Explanation: Hypervisors emulate hardware for guest OSs, while containers isolate applications in user space using the same kernel. Containers are faster and ideal for cloud-native deployments.

43) What is the difference between a Process and a Job in OS context?

A process is an executing instance of a program, while a job is a set of processes grouped for scheduling in batch systems.

Aspect Process Job
Definition Program in execution. Collection of processes.
System Type Modern OS Batch systems
Management Managed by scheduler. Managed by job control language (JCL).
Example Running Chrome Batch job for payroll processing

Example: In mainframe environments, job schedulers manage multiple batch processes as a single job.

44) Explain the concept of Load Balancing in Operating Systems.

Load balancing distributes workloads evenly across processors or systems to enhance performance, reliability, and throughput.

Techniques:

  • Static load balancing: Predefined task assignment (e.g., Round Robin).
  • Dynamic load balancing: Decisions made at runtime based on system state.

Example: In multicore processors, the Linux kernel scheduler distributes processes dynamically to prevent CPU overload.

Type Decision Time Example
Static Compile-time Round Robin
Dynamic Run-time Linux Scheduler

45) What are Real-Time Operating Systems (RTOS)?

An RTOS ensures deterministic responses to external events within strict timing constraints. It is used in embedded systems where timing is critical.

Types of RTOS:

Type Description Example
Hard RTOS Deadlines must always be met. VxWorks, QNX
Soft RTOS Occasional deadline misses allowed. RTLinux, Windows CE

Characteristics:

  • Predictable response time
  • Priority-based scheduling
  • Minimal latency

Example: In automotive systems, an RTOS ensures airbag deployment occurs within milliseconds after an impact is detected.

46) Explain Memory-Mapped I/O vs. Isolated I/O.

Feature Memory-Mapped I/O Isolated I/O
Address Space Shares memory address space Separate address space
Access Regular instructions Special I/O instructions
Speed Faster Slightly slower
Example ARM architecture x86 architecture

Explanation: In Memory-Mapped I/O, devices are accessed as if they were memory locations. Isolated I/O uses separate control signals, offering hardware-level separation.

47) What are System Performance Metrics in an OS?

System performance is measured using various metrics that evaluate CPU, memory, disk, and process efficiency.

Key Metrics:

  • CPU Utilization – % of CPU actively used.
  • Throughput – Number of processes completed per unit time.
  • Response Time – Delay from request to response.
  • Turnaround Time – Time from submission to completion.
  • Waiting Time – Time a process spends in the ready queue.

Example: In performance tuning, lowering context-switch frequency and optimizing disk I/O improves throughput and response time.

48) What are the advantages of using Linux for system-level programming?

Linux is widely used for OS-level and embedded development due to its flexibility and openness.

Advantages:

  • Open-source kernel for deep customization.
  • Strong support for multithreading and IPC.
  • Rich set of system calls for process and memory management.
  • High stability and community support.
  • Tools like strace, top, and perf aid debugging and profiling.

Example: Developers use Linux to build IoT systems, kernel modules, or cloud infrastructure services due to its lightweight modularity.

49) What is a System Call Interface (SCI)?

The System Call Interface acts as a gateway between user-mode applications and kernel-mode services.

Process Flow:

  1. User program invokes a system call (e.g., read()).
  2. Control transfers to the kernel using software interrupt (e.g., int 0x80 in x86).
  3. Kernel executes the requested service.
  4. Result returned to the user process.

Example: In Linux, every system call is assigned a unique number; the syscall table maps numbers to kernel functions.

Layer Example Function
User Space read(), write()
Kernel Space sys_read(), sys_write()

50) What are Containers and how do they differ from Virtual Machines?

Containers are lightweight OS-level virtualization units that run isolated applications sharing the host kernel.

Key Differences:

Feature Containers Virtual Machines
Virtualization Level OS-level Hardware-level
Boot Time Seconds Minutes
Resource Efficiency Very high Moderate
Isolation Process-level Full OS-level
Example Docker, Kubernetes Pods VMware, VirtualBox

Advantages of Containers:

  • Faster deployment
  • Efficient resource usage
  • Portability across environments

Example: Docker containers can run microservices across multiple cloud platforms without the overhead of full virtual machines.

🔍 Top Operating Systems Interview Questions with Real-World Scenarios & Strategic Responses

1) What are the key functions of an operating system?

Expected from candidate: The interviewer wants to assess your foundational understanding of OS components and their role in managing hardware and software resources.

Example answer: “The key functions of an operating system include process management, memory management, file system management, device management, and security. It acts as an interface between the user and the hardware, ensuring efficient resource allocation and system stability.”

2) Can you explain the concept of a process and a thread?

Expected from candidate: This question tests your understanding of multitasking and concurrency principles in operating systems.

Example answer: “A process is an independent program in execution that has its own memory space, while a thread is a lightweight sub-process that shares the same memory space with other threads of the same process. Threads enable parallel execution, improving system efficiency and responsiveness.”

3) Describe a situation where you had to troubleshoot a performance issue related to an operating system.

Expected from candidate: The interviewer wants to evaluate your problem-solving and diagnostic skills.

Example answer: “In my previous role, I identified a memory leak in a critical service that was degrading system performance. I used monitoring tools to analyze resource usage, isolated the process causing the leak, and worked with the development team to patch the application. This significantly improved system stability.”

4) How does virtual memory work, and why is it important?

Expected from candidate: The interviewer wants to see your understanding of memory management and system efficiency.

Example answer: “Virtual memory allows the operating system to use hard disk space as additional RAM, enabling larger applications to run simultaneously. It provides process isolation and prevents memory overflow by swapping data between physical memory and disk storage as needed.”

5) How do you handle file permissions and user access control in an operating system?

Expected from candidate: This question assesses your knowledge of security and administrative management.

Example answer: “File permissions define what actions users can perform on files or directories. For example, in Unix-like systems, I use read, write, and execute permissions assigned to the owner, group, and others. Proper permission management ensures system security and prevents unauthorized access.”

6) Describe a time when you managed a system crash or downtime incident.

Expected from candidate: The interviewer wants to evaluate your ability to stay calm under pressure and restore system functionality efficiently.

Example answer: “At a previous position, our main server crashed due to a kernel panic. I immediately initiated the incident response plan, booted into recovery mode, and analyzed system logs to identify the faulty driver. After replacing it, I restored services and implemented monitoring alerts to prevent recurrence.”

7) What are the differences between preemptive and non-preemptive scheduling?

Expected from candidate: This question examines your understanding of CPU scheduling techniques.

Example answer: “In preemptive scheduling, the CPU can be taken away from a running process to assign it to another, ensuring fair CPU utilization. Non-preemptive scheduling allows a process to complete before another starts. Preemptive scheduling is common in modern multitasking systems for better responsiveness.”

8) How do you ensure system security and protect against malware or unauthorized access?

Expected from candidate: The interviewer wants to assess your practical security awareness and proactive measures.

Example answer: “At my previous job, I implemented user privilege management, regularly updated security patches, and used access control lists. Additionally, I monitored system logs for unusual activities and enforced the principle of least privilege to minimize risks of unauthorized access.”

9) How would you prioritize processes in a high-load environment to maintain performance?

Expected from candidate: The interviewer wants to understand your decision-making under resource constraints.

Example answer: “In a high-load environment, I would use priority-based scheduling to ensure critical processes get sufficient CPU time. By adjusting process priorities and using tools like ‘nice’ and ‘renice’ in Linux, I can balance performance and responsiveness across essential tasks.”

10) What motivates you to work in the field of operating systems?

Expected from candidate: This question helps the interviewer understand your passion and long-term interest in systems engineering.

Example answer: “What motivates me is the complexity and importance of operating systems as the backbone of all computing. In my last role, I enjoyed optimizing system performance and learning how kernel-level changes affect the overall computing environment. It is both challenging and rewarding to work in this field.”

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