Day 82: Linux Interview Questions

Introduction:

Linux, an open-source operating system, has become a cornerstone in the world of computing, powering servers, embedded systems, and even personal devices. As the demand for Linux-savvy professionals continues to rise, interviews often delve into a spectrum of topics, assessing a candidate's depth of knowledge. In this collection of Linux interview questions, we explore fundamental concepts, history, commands, and system administration skills essential for anyone navigating the Linux landscape. Whether you're a seasoned administrator or a budding enthusiast, these questions provide a holistic overview of what it takes to master Linux in a professional setting.

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Sure, here are the answers to each of the questions:

1. What is Linux?

   • Answer: Linux is an open-source, Unix-like operating system kernel that serves as the core of various Linux distributions. It provides a foundation for the development of a complete operating system.

2. Who invented Linux? Explain the history of Linux.

   • Answer: Linux was created by Linus Torvalds in 1991. It originated as a personal project, with Torvalds developing the kernel and inviting others to contribute. Over time, a community of developers grew, leading to the collaborative development of the Linux operating system.

3. What is the difference between Linux and Unix?

   • Answer: Linux and Unix are similar in many aspects, but Linux is open-source, while Unix refers to a family of operating systems. Linux is based on Unix principles but has its own kernel.

4. What is Linux Kernel? Is it legal to edit Linux Kernel?

   • Answer: The Linux Kernel is the core component of the Linux operating system. Editing the Linux Kernel is legal and encouraged, as it follows the principles of open-source software. Users can modify the kernel to suit their needs, but it is essential to adhere to the licensing terms.

5. What is BASH?

   • Answer: BASH (Bourne Again SHell) is a command processor that typically runs in a text window. It is the default shell for most Linux distributions and provides a command-line interface for interacting with the operating system.

6. What are two types of Linux User Mode?

   • Answer: The two types of Linux User Modes are User Mode and Kernel Mode. User Mode allows user-level applications to run, while Kernel Mode is a more privileged mode where the operating system's kernel has direct access to hardware resources.

7. What is LILO?

   • Answer: LILO (LInux LOader) is a bootloader used in some Linux distributions. It is responsible for loading the Linux operating system into memory during the boot process.

8. What are the basic components of Linux?

   • Answer: The basic components of Linux include the Kernel, Shell, System Libraries, System Utilities, and Application Programs.

9. What is the Linux Shell? What types of Shells are there in Linux?

   • Answer: The Linux Shell is a command-line interpreter that translates user commands into actions. Common types of Shells include BASH, C Shell (csh), Korn Shell (ksh), and Z Shell (zsh).

10. Which are the Shells used in Linux?

    • Answer: Some commonly used Shells in Linux are BASH, csh, ksh, and zsh.

11. What is Swap Space?

    • Answer: Swap space is a designated area on a hard disk that the operating system uses as virtual memory when the physical RAM is fully utilized. It helps prevent system slowdowns or crashes due to insufficient memory.

12. What is the difference between BASH and DOS?

    • Answer: BASH is a Unix-like shell used in Linux, while DOS (Disk Operating System) is a command-line-based operating system used primarily in older versions of Microsoft Windows. They have different command syntax, functionalities, and design philosophies.

13. What command would you use to check how much memory is being used by Linux?

    • Answer: The free command is used to check the amount of free and used memory in a Linux system.

14. What is a maximum length for a filename under Linux?

    • Answer: The maximum length for a filename under Linux is typically 255 characters.

15. Explain file permission in Linux.

    • Answer: File permissions in Linux determine who can access a file and what actions they can perform. Permissions are categorized into read, write, and execute for the owner, group, and others.

16. What are inode and process id?

    • Answer: An inode is a data structure on a filesystem that stores information about a file. Process ID (PID) is a unique identifier assigned to each process running in the operating system.

17. What is LVM? Is it a requirement in Linux?

    • Answer: LVM (Logical Volume Manager) is a system for managing disk drives and volumes. It is not a strict requirement but is often used to provide flexibility in managing storage.

18. Which are the Linux Directory Commands?

    • Answer: Linux directory commands include ls (list), cd (change directory), mkdir (make directory), rmdir (remove directory), and pwd (print working directory).

19. What is Virtual Desktop?

    • Answer: A Virtual Desktop in Linux refers to a desktop environment that allows users to have multiple desktops or workspaces, each with its set of applications and windows.

20. Which are the different modes of the vi editor?

    • Answer: The different modes of the vi editor are Normal mode, Insert mode, and Command-Line mode.

21. What are daemons?

    • Answer: Daemons are background processes that run without direct user interaction. They perform various system tasks and are often initiated during the system boot.

22. What are the process states in Linux?

    • Answer: The process states in Linux include Running, Sleeping, Stopped, and Zombie.

23. Explain grep command.

    • Answer: The grep command is used to search for a specific pattern or expression in a file or a stream of text. It displays lines that match the specified pattern.

24. Explain Process Management System Calls in Linux

    • Answer: Process Management System Calls in Linux include fork() (creates a new process), exec() (replaces the current process with a new one), wait() (waits for a child process to finish), and exit() (terminates the current process).

25. Explain the ‘ls’ command in Linux

    • Answer: The ls command in Linux is used to list the files and directories in a directory. It provides information such as file permissions, ownership, size, and modification time.

26. Explain the redirection operator.

    • Answer: The redirection operator (> or <) is used to redirect input or output from or to a file in Linux. For example, `command

      file.txt` redirects the command's output to a file.

27. Why is the tar command used?

    • Answer: The tar command is used to create, compress, or extract archive files. It bundles multiple files and directories into a single file, making it easier to manage and transfer.

28. What is a Latch?

    • Answer: A Latch is a synchronization mechanism used in computer systems to control access to shared resources. It is a primitive form of a semaphore.

29. What is a Microprocessor?

    • Answer: A microprocessor is an integrated circuit that contains the functions of a central processing unit (CPU). It is the brain of a computer and executes instructions stored in memory.

30. Explain Regular Expressions and Grep

    • Answer: Regular expressions are patterns used for matching character combinations. Grep is a command-line tool that searches for patterns in files using regular expressions.

31. What is the minimum number of disk partitions required to install Linux?

    • Answer: The minimum number of disk partitions required to install Linux is two: one for the root file system ("/") and one for the swap space.

32. What is a “/proc” file system?

    • Answer: The "/proc" file system in Linux is a virtual file system that provides information about processes and system configuration. It exposes kernel data structures as files.

33. Daemon that controls the print spooling process.

    • Answer: The daemon that controls the print spooling process is typically the Common Unix Printing System (CUPS) daemon.

34. Name the Linux that is specially designed by Sun Microsystems.

    • Answer: The Linux distribution specially designed by Sun Microsystems is called "Oracle Linux."

35. Under the Linux system, what is the typical size for swap partitions?

    • Answer: The typical size for swap partitions under the Linux system is recommended to be at least the size of the physical RAM, but it can vary based on system requirements.

36. What is a Zombie Process?

    • Answer: A Zombie Process in Linux is a terminated process that has completed its execution but still has an entry in the process table. It exists in a "zombie" state until its parent process acknowledges its termination.

37. What is the difference between cron and anacron?

    • Answer: Cron and Anacron are both used for job scheduling in Linux. The main difference is that Cron is used for regular periodic tasks, while Anacron is designed for systems that may not run continuously, ensuring tasks are performed even if the system is not always on.

38. What is load average in Linux?

    • Answer: Load average in Linux indicates the average system load over a specific period. It represents the average number of processes waiting for CPU time. The load average values typically include one, five, and fifteen-minute averages.

39. What do you mean by Shell Script?

    • Answer: A Shell Script is a series of commands written in a scripting language (e.g., Bash) that can be executed in a Unix or Linux shell. It automates repetitive tasks and provides a way to sequence multiple commands.

40. What is CLI and GUI?

    • Answer: CLI (Command Line Interface) and GUI (Graphical User Interface) are two types of interfaces for interacting with a computer. CLI involves commands entered in a text-based terminal, while GUI provides a visual interface with icons, windows, and menus.

41. Why /etc/resolv.conf and /etc/hosts files are used?

    • Answer: The "/etc/resolv.conf" file contains information about the domain name system (DNS) servers, while the "/etc/hosts" file associates IP addresses with hostnames. Both files are used to resolve domain names to IP addresses.

42. What are the advantages of using NIC teaming?

    • Answer: NIC teaming, or network bonding, provides fault tolerance and load balancing by combining multiple network interfaces into a single logical interface. It improves network reliability and performance.

43. What do you mean by Network bonding?

    • Answer: Network bonding, or NIC teaming, is the process of combining multiple network interfaces into a single logical interface. It enhances network performance, provides fault tolerance, and ensures continuous network connectivity.

44. What are the different network bonding modes used in Linux?

    • Answer: Different network bonding modes in Linux include Round Robin, Active-Backup, XOR, Broadcast, 802.3ad (LACP), and Adaptive Load Balancing (ALB).

45. Name default ports used for DNS, SMTP, FTP, SSH, DHCP, and Squid.

    • Answer: Default ports are:

      • DNS: 53

      • SMTP: 25

      • FTP: 21

      • SSH: 22

      • DHCP: 67 and 68

      • Squid: 3128

46. What is SSH? How can we connect to a remote server via SSH.

    • Answer: SSH (Secure Shell) is a cryptographic network protocol used for secure communication over an unsecured network. To connect to a remote server, use the command ssh username@remote_server_ip in the terminal.

47. Write the difference between Soft and Hard links?

    • Answer: Soft links (or symbolic links) are pointers to the file's inode, while hard links are additional references to the same inode. Deleting a soft link does not affect the original file, but deleting the last hard link removes the file.

48. Name three standard streams in Linux.

    • Answer: Three standard streams in Linux are:

      • Standard Input (stdin): Represented by file descriptor 0 (fd 0)

      • Standard Output (stdout): Represented by file descriptor 1 (fd 1)

      • Standard Error (stderr): Represented by file descriptor 2 (fd 2)

49. How to copy a file in Linux?

    • Answer: The cp command is used to copy a file in Linux. For example, cp source_file destination_directory.

50. How to terminate a running process in Linux?

    • Answer: The kill command is used to terminate a running process in Linux. Find the process ID (PID) using ps or top and then use kill PID to terminate it.

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Conclusion:

It's important to recognize that the realm of Linux is incredibly vast, and the questions covered here only scratch the surface. While this set provides a solid foundation, there's so much more to explore and learn in the ever-evolving world of Linux.

Aspiring Linux enthusiasts should view these questions as a starting point, realizing that expertise in Linux goes beyond what's covered here. Interviews might delve into specific distributions, advanced configurations, and niche scenarios. The richness of Linux invites further exploration into areas like automation, containerization, and cloud integration.

In essence, this compilation is a guide, not the final destination. Continuous learning and hands-on experience are key to mastering Linux, especially considering its dynamic nature. So, while this serves as a good intro, be ready for the exciting journey of ongoing discovery and growth in the Linux landscape.

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