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Top 100 Operating System Interview Questions and Answers

Top 100 Operating System Interview Questions and Answers

Contents show

1. What is an Operating System?

Answer:

An operating system is a software that manages computer hardware and provides services for computer programs. It acts as an intermediary between users/applications and the computer hardware.


2. Explain the main functions of an Operating System.

Answer:

  • Process Management: It manages processes (programs in execution) by scheduling them and ensuring they have necessary resources.
  • Memory Management: Allocates and manages the memory space for programs and data.
  • File System Management: Organizes and maintains files on storage devices.
  • Device Management: Controls and communicates with hardware devices.

3. What is a Process in an Operating System?

Answer:

A process is an instance of a program in execution. It has its own memory space, resources, and execution state.


4. How is a Process different from a Thread?

Answer:

A process is a standalone program in execution, while a thread is a unit within a process that can execute instructions independently. Threads share the same memory space within a process.


5. What is a Context Switch?

Answer:

A context switch is the process of saving the state of a running process and loading the saved state of another process. It’s essential for multitasking.


6. Explain Virtual Memory.

Answer:

Virtual memory is a technique that allows the execution of processes that may not entirely fit into physical memory. It uses a portion of the hard disk as an extension of RAM.


7. What is a File System?

Answer:

A file system is a way to organize, store, and retrieve files on a storage medium. It manages the naming, storing, retrieving, naming, and sharing of files.


8. Describe the Role of a Device Driver.

Answer:

A device driver is a software program that allows the operating system to interact with hardware devices. It serves as a bridge between the hardware and the OS.


9. How do you Create a New Process in Linux using Fork?

Answer:

#include <unistd.h>
#include <stdio.h>

int main() {
    pid_t pid = fork();
    if (pid == 0) {
        printf("This is the child process.\n");
    } else if (pid > 0) {
        printf("This is the parent process.\n");
    } else {
        perror("Fork failed");
        return 1;
    }
    return 0;
}

10. What is a Deadlock in Operating Systems?

Answer:

A deadlock is a situation where two or more processes are unable to proceed because each is waiting for another to release a resource, or more than two processes are waiting for resources in a circular chain.


11. Explain Process Synchronization.

Answer:

Process synchronization is the concept of coordinating the execution of multiple processes to ensure data consistency and integrity in shared resources.


12. How do you List all Files in a Directory using Command Line in Linux?

Answer:

ls /path/to/directory

13. Define Multi-programming.

Answer:

Multi-programming is a technique where multiple programs are loaded into the main memory at the same time and the CPU is switched among them.


14. What is a Kernel in an Operating System?

Answer:

The kernel is the core component of an operating system. It manages memory, processes, tasks, and provides low-level access to hardware.


15. How do you Kill a Process in Linux?

Answer:

Use the kill command followed by the process ID (PID).

kill PID

16. What is a Shell in Operating System?

Answer:

A shell is a user interface that provides access to the services of an operating system. It interprets user commands and passes them to the kernel for execution.


17. Explain the Difference between Hard Link and Soft Link in Linux.

Answer:

  • Hard Link: A hard link is a direct pointer to the file’s inode. It shares the same inode number as the original file and points directly to the data on the disk.
  ln source_file hard_link
  • Soft Link (Symbolic Link): A soft link is a file that points to the file name, not the inode. It acts as a shortcut to the target file or directory.
  ln -s source_file symbolic_link

18. What is a Zombie Process?

Answer:

A zombie process is a process that has completed execution but still has an entry in the process table. It no longer executes but its entry remains until the parent process reads its status.


19. How do you Change File Permissions in Linux?

Answer:

Use the chmod command followed by the permission codes.

chmod [permissions] file

Example:

chmod +x script.sh

20. Explain the Role of an I/O Scheduler in an Operating System.

Answer:

An I/O scheduler is responsible for deciding the order in which I/O operations are submitted to the storage devices. It aims to minimize seek times and optimize disk performance.


21. What is a Page Fault?

Answer:

A page fault occurs when a program tries to access a portion of memory that is currently not in physical RAM, but rather in secondary storage like a hard drive.


22. How do you Mount a File System in Linux?

Answer:

Use the mount command followed by the device and mount point.

mount /dev/sda1 /mnt

23. Explain the Role of the Swap Space in an Operating System.

Answer:

Swap space is a designated area on a disk used to supplement physical RAM. When the RAM is full, the operating system moves inactive data from RAM to the swap space.


24. How do you Check Disk Space in Linux?

Answer:

Use the df command to display disk space usage.

df -h

25. What is a Pipe in Linux?

Answer:

A pipe is a method for passing information from one program process to another. It allows the output of one command to serve as input to another command.

Example:

command1 | command2

26. What is the Purpose of the ‘top’ Command in Linux?

Answer:

The ‘top’ command is used to display system statistics in real-time. It provides information about CPU usage, memory usage, running processes, and more.


27. Explain the Difference between Process and Program.

Answer:

  • Program: A program is a set of instructions that can be executed by a computer. It is a passive entity stored on disk.
  • Process: A process is an instance of a program that is in execution. It has its own memory space, resources, and state.

28. What is a Kernel Panic?

Answer:

A kernel panic is a critical error that occurs when the kernel of an operating system encounters a problem it cannot recover from. It results in the system freezing or displaying an error message.


29. How do you View Running Processes in Linux?

Answer:

Use the ‘ps’ command to view running processes.

ps aux

30. Explain the Purpose of the ‘chroot’ Command in Linux.

Answer:

The ‘chroot’ command is used to change the root directory for a process. This provides a way to isolate processes and create a restricted environment.


31. What is a Semaphore?

Answer:

A semaphore is a synchronization construct that is used to control access to a common resource by multiple processes or threads. It is often used to prevent race conditions.


32. How do you Create a Directory in Linux?

Answer:

Use the ‘mkdir’ command followed by the directory name.

mkdir my_directory

33. Explain the Difference between Multiprogramming and Multitasking.

Answer:

  • Multiprogramming: It involves running multiple programs on a single processor by quickly switching between them.
  • Multitasking: It involves running multiple tasks simultaneously on multiple processors or processor cores.

34. What is a Zombie Process?

Answer:

A zombie process is a process that has completed execution but still has an entry in the process table. It no longer executes but its entry remains until the parent process reads its status.


35. How do you Change File Permissions in Linux?

Answer:

Use the ‘chmod’ command followed by the permission codes.

chmod [permissions] file

Example:

chmod +x script.sh

36. What is the Role of an Inode in a File System?

Answer:

An inode is a data structure in a file system that stores information about a file. It includes details like file type, size, ownership, permissions, and pointers to the actual data blocks.


37. How do you Find Files in Linux?

Answer:

Use the ‘find’ command followed by the search directory and criteria.

find /path/to/search -name "filename"

38. Explain the Purpose of the ‘grep’ Command in Linux.

Answer:

The ‘grep’ command is used for searching text within files. It allows you to specify patterns or regular expressions to match lines.

Example:

grep "pattern" file.txt

39. What is a System Call?

Answer:

A system call is a request made by a program to the operating system for a specific operation, such as reading or writing a file. It provides an interface between applications and the kernel.


40. How do you View System Logs in Linux?

Answer:

Use the ‘tail’ or ‘cat’ command to view system logs.

tail /var/log/syslog

41. Explain the Role of an Environment Variable.

Answer:

An environment variable is a dynamic value that can affect the way running processes will behave on a computer. It provides a way to influence the behavior of software.


42. How do you Kill a Process in Linux?

Answer:

Use the ‘kill’ command followed by the process ID (PID).

kill PID

43. What is a Page Table?

Answer:

A page table is a data structure used in computer operating systems to manage virtual memory. It maps virtual addresses to physical addresses.


44. Explain the Purpose of the ‘cron’ Service in Linux.

Answer:

The ‘cron’ service is a time-based job scheduler in Linux. It allows users to schedule jobs (commands or scripts) to run at specific times or intervals.


45. What is a Shell Script?

Answer:

A shell script is a series of commands written in a plain text file that can be executed by a shell. It allows for automation of tasks in the operating system.


46. Explain the Difference between a Process and a Program.

Answer:

  • Program: It is a set of instructions that can be executed by a computer. It is a passive entity stored on disk.
  • Process: It is an instance of a program in execution. It has its own memory space, resources, and state.

47. What is a Pipe in Linux?

Answer:

A pipe is a method for passing information from one program process to another. It allows the output of one command to serve as input to another command.

Example:

command1 | command2

48. What is the Purpose of the ‘top’ Command in Linux?

Answer:

The ‘top’ command is used to display system statistics in real-time. It provides information about CPU usage, memory usage, running processes, and more.


49. How do you Check Disk Space in Linux?

Answer:

Use the ‘df’ command to display disk space usage.

df -h

50. Explain the Purpose of the ‘chroot’ Command in Linux.

Answer:

The ‘chroot’ command is used to change the root directory for a process. This provides a way to isolate processes and create a restricted environment.


51. What is a Semaphore?

Answer:

A semaphore is a synchronization construct that is used to control access to a common resource by multiple processes or threads. It is often used to prevent race conditions.


52. How do you Create a Directory in Linux?

Answer:

Use the ‘mkdir’ command followed by the directory name.

mkdir my_directory

53. Explain the Difference between Multiprogramming and Multitasking.

Answer:

  • Multiprogramming: It involves running multiple programs on a single processor by quickly switching between them.
  • Multitasking: It involves running multiple tasks simultaneously on multiple processors or processor cores.

54. What is a Kernel Panic?

Answer:

A kernel panic is a critical error that occurs when the kernel of an operating system encounters a problem it cannot recover from. It results in the system freezing or displaying an error message.


55. How do you View Running Processes in Linux?

Answer:

Use the ‘ps’ command to view running processes.

ps aux

56. What is the Purpose of the ‘grep’ Command in Linux?

Answer:

The ‘grep’ command is used for searching text within files. It allows you to specify patterns or regular expressions to match lines.

Example:

grep "pattern" file.txt

57. Explain the Purpose of the ‘awk’ Command in Linux.

Answer:

The ‘awk’ command is a powerful text processing tool used for pattern scanning and processing. It allows for complex operations on text data.

Example:

awk '{print $1}' file.txt

58. How do you Find Files in Linux?

Answer:

Use the ‘find’ command followed by the search directory and criteria.

find /path/to/search -name "filename"

59. What is a System Call?

Answer:

A system call is a request made by a program to the operating system for a specific operation, such as reading or writing a file. It provides an interface between applications and the kernel.


60. How do you View System Logs in Linux?

Answer:

Use the ‘tail’ or ‘cat’ command to view system logs.

tail /var/log/syslog

61. Explain the Role of an Environment Variable.

Answer:

An environment variable is a dynamic value that can affect the way running processes will behave on a computer. It provides a way to influence the behavior of software.


62. How do you Kill a Process in Linux?

Answer:

Use the ‘kill’ command followed by the process ID (PID).

kill PID

63. What is a Page Table?

Answer:

A page table is a data structure used in computer operating systems to manage virtual memory. It maps virtual addresses to physical addresses.


64. Explain the Purpose of the ‘cron’ Service in Linux.

Answer:

The ‘cron’ service is a time-based job scheduler in Linux. It allows users to schedule jobs (commands or scripts) to run at specific times or intervals.


65. What is a Shell Script?

Answer:

A shell script is a series of commands written in a plain text file that can be executed by a shell. It allows for automation of tasks in the operating system.


66. What is the Purpose of the ‘sed’ Command in Linux?

Answer:

The ‘sed’ command is a stream editor used for text processing. It can perform search, find and replace, insert, and more operations on text streams.

Example:

sed 's/old/new/' file.txt

67. Explain the Role of the ‘umask’ Command in Linux.

Answer:

The ‘umask’ command is used to set default file permissions for newly created files and directories. It specifies which permissions should be subtracted from the default.

Example:

umask 022

68. How do you Check Network Connectivity in Linux?

Answer:

Use the ‘ping’ command followed by the target host or IP address.

ping google.com

69. What is a Daemon in Linux?

Answer:

A daemon is a background process that runs without any direct user interaction. It typically performs system-related tasks or provides services to other processes.


70. How do you Find and Replace Text in a File using Command Line in Linux?

Answer:

Use the ‘sed’ command for find and replace operations.

sed -i 's/old/new/g' file.txt

71. Explain the Purpose of the ‘tar’ Command in Linux.

Answer:

The ‘tar’ command is used for archiving files and directories. It allows for bundling multiple files into a single archive file.

Example:

tar -cvf archive.tar files/

72. What is a Hard Link in Linux?

Answer:

A hard link is a directory entry that associates a name with a file. It creates a new name for an existing file on the same filesystem.

Example:

ln /path/to/file hard_link

73. How do you Rename Files in Linux?

Answer:

Use the ‘mv’ command followed by the current file name and the new file name.

mv old_name new_name

74. Explain the Purpose of the ‘who’ Command in Linux.

Answer:

The ‘who’ command displays information about currently logged-in users. It shows usernames, terminal names, login times, and more.


75. What is the Purpose of the ‘passwd’ Command in Linux?

Answer:

The ‘passwd’ command is used to change a user’s password. It allows users to set or reset their login credentials.

Example:

passwd

76. How do you Compress and Decompress Files in Linux?

Answer:

  • Compression (using ‘gzip’):
gzip filename
  • Decompression:
gzip -d filename.gz

77. Explain the Purpose of the ‘du’ Command in Linux.

Answer:

The ‘du’ command is used to estimate file space usage. It provides information about the disk space used by files and directories.

Example:

du -sh directory/

78. What is a Symbolic Link in Linux?

Answer:

A symbolic link (symlink) is a special type of file that points to another file or directory. It acts as a shortcut or alias to the target file or directory.

Example:

ln -s /path/to/target symbolic_link

79. How do you View the Contents of a File in Linux?

Answer:

Use the ‘cat’ command to view the entire file content.

cat filename

For long files, you can use ‘less’ for paging.

less filename

80. Explain the Purpose of the ‘route’ Command in Linux.

Answer:

The ‘route’ command is used to view and modify the IP routing table. It shows the current routing table or allows you to add/remove routes.

Example (showing routes):

route -n

81. What is a Runlevel in Linux?

Answer:

A runlevel is a state or mode in which a Unix-based system operates. It defines the services and processes that are active and available in a given state.


82. How do you List Open Ports in Linux?

Answer:

Use the ‘netstat’ or ‘ss’ command to list open ports.

netstat -tuln

or

ss -tuln

83. Explain the Purpose of the ‘cron’ Tab File in Linux.

Answer:

The ‘cron’ tab file is a time-based job scheduler configuration file. It defines the schedule for executing recurring tasks or commands.

Example (edit cron tab for current user):

crontab -e

84. What is a Library in Linux?

Answer:

A library is a collection of pre-compiled routines, functions, and procedures that are referenced and used by a program during its execution.


85. How do you Display the Last Lines of a File in Linux?

Answer:

Use the ‘tail’ command to display the last lines of a file.

tail filename

86. What is the Purpose of the ‘ifconfig’ Command in Linux?

Answer:

The ‘ifconfig’ command is used to configure and display information about network interfaces on a system. It allows you to view and change network configurations.

Example (show network interfaces):

ifconfig

87. Explain the Role of the ‘ssh’ Command in Linux.

Answer:

The ‘ssh’ command is used for secure remote access to a system over a network. It provides a secure shell connection for executing commands or transferring files.

Example (connect to a remote server):

ssh username@remote_host

88. What is a Process Group in Linux?

Answer:

A process group is a collection of one or more processes that can be manipulated as a single entity. It allows for controlling and signaling multiple processes at once.


89. How do you View Hidden Files in Linux?

Answer:

Use the ‘-a’ option with the ‘ls’ command to view hidden files.

ls -a

90. Explain the Purpose of the ‘echo’ Command in Linux.

Answer:

The ‘echo’ command is used to display a line of text or a string on the standard output. It is often used in scripts for printing messages.

Example:

echo "Hello, World!"

91. What is the Purpose of the ‘touch’ Command in Linux?

Answer:

The ‘touch’ command is used to update the access and modification times of a file or create a new, empty file if it doesn’t exist.

Example (update file timestamp):

touch filename

92. How do you Determine the Current User in Linux?

Answer:

Use the ‘whoami’ command to display the current username.

whoami

93. Explain the Role of the ‘find’ Command in Linux.

Answer:

The ‘find’ command is used to search for files and directories within a specified directory hierarchy based on various criteria.

Example (find files by name):

find /path/to/search -name "filename"

94. What is a Core Dump File in Linux?

Answer:

A core dump file is a memory snapshot of a process at the time of a crash or abnormal termination. It helps in debugging and analyzing the cause of the crash.


95. How do you Change the Owner of a File in Linux?

Answer:

Use the ‘chown’ command followed by the new owner and the file/directory.

chown new_owner file

96. What is the Purpose of the ‘chmod’ Command in Linux?

Answer:

The ‘chmod’ command is used to change the file permissions of a file or directory, allowing or restricting access to it.

Example (give read and write permissions to owner):

chmod u+rw file

97. How do you Check the System Uptime in Linux?

Answer:

Use the ‘uptime’ command to display the system uptime.

uptime

98. Explain the Purpose of the ‘grep’ Command in Linux.

Answer:

The ‘grep’ command is used for searching text within files. It allows you to specify patterns or regular expressions to match lines.

Example:

grep "pattern" file.txt

99. What is a Pipe in Linux?

Answer:

A pipe is a method for passing information from one program process to another. It allows the output of one command to serve as input to another command.

Example:

command1 | command2

100. How do you Check Network Connectivity in Linux?

Answer:

Use the ‘ping’ command followed by the target host or IP address.

ping google.com