Top 100+ Linux Interview Questions and Answers

Linux, an open-source, Unix-like operating system, has become integral to various computing environments, from servers and desktops to embedded systems. Its versatility, security, and robustness make it a preferred choice for many organizations. As a result, proficiency in Linux is highly sought after in the tech industry. Whether you’re a beginner or an experienced professional, preparing for a Linux interview requires a solid understanding of both fundamental and advanced concepts. This comprehensive guide presents over 100 Linux interview questions and answers, categorized by difficulty levels, to aid your preparation.​

Table of Contents

• Beginner-Level Linux Interview Questions
• Intermediate-Level Linux Interview Questions
• Advanced-Level Linux Interview Questions
• Linux Administration Interview Questions
• Linux Troubleshooting Interview Questions
• Linux Networking Interview Questions

Beginner-Level Linux Interview Questions

These questions cover the foundational aspects of Linux, suitable for individuals new to the operating system.​

1. What is Linux?

Linux is a free, open-source, Unix-like operating system kernel developed by Linus Torvalds. It serves as the foundation for various distributions designed for systems, servers, embedded devices, mobile devices, and mainframes. Linux supports major computer platforms such as ARM, x86, and SPARC. ​

2. Explain the basic features of the Linux OS.

Some fundamental features of Linux include:​

• Open Source: Freely available and modifiable by users.​
• Security: Utilizes security auditing and password authentication features, making it more secure than many other operating systems.​
• Software Repository: Offers a personal software repository for easy access to applications.
• Multilingual Support: Supports different language keyboards, catering to users worldwide.​
• User Interfaces: Provides both Command-Line Interface (CLI) and Graphical User Interface (GUI) to accommodate various user preferences. ​

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

Linux was created by Linus Torvalds in 1991. As a student at the University of Helsinki, Finland, Torvalds sought a free academic version of Unix, leading him to develop the Linux kernel. The initial version, 0.01, was released as open-source software under the GNU General Public License (GPL), inviting global contributions that have shaped Linux into a versatile operating system used in various applications, from server administration to network management.

4. What is the difference between Linux and Unix?

While Linux and Unix share similarities, key differences include:​

• Cost: Linux distributions are often free, whereas Unix systems may have associated costs.​
• User Interface: Linux primarily uses a GUI with an optional command-line interface, whereas Unix traditionally relies on the command-line interface.​
• Portability: Linux is portable across various hardware platforms; Unix is not as portable.​
• Development: Linux is developed by a global community; Unix was developed by AT&T developers.​
• Usage: Linux is commonly used in home-based PCs and phones; Unix is typically used in server systems.

5. What is the Linux Kernel?

The Linux Kernel is the core component of the Linux operating system. It acts as a bridge between software applications and hardware, managing system resources and hardware communication. The kernel handles tasks such as process management, memory management, and device drivers, ensuring system stability and efficiency. ​

6. What is BASH?

BASH (Bourne Again Shell) is a Unix shell and command processor written by Brian Fox for the GNU Project. It serves as a replacement for the Bourne Shell and is widely used as the default shell in many Linux distributions. BASH allows users to execute commands, run scripts, and automate tasks, providing a powerful interface for interacting with the operating system. ​

7. What is LILO?

LILO (Linux Loader) is a boot loader for Linux operating systems. It is responsible for loading the Linux kernel into memory and starting the operating system. LILO can boot Linux from hard disks and floppy disks and can also boot other operating systems, making it a versatile tool in multi-boot environments. ​

8. What is a Shell in Linux?

A shell in Linux is a command-line interpreter that provides a user interface for accessing the services of the operating system. It allows users to execute commands, run programs, and perform various tasks by typing commands into the terminal. Commonly used shells include BASH, Zsh, and Fish.

9. What is CLI?

CLI (Command-Line Interface) is a text-based user interface used to interact with the operating system. Users input commands as text, and the system responds with text-based output. CLI is powerful for performing administrative tasks, scripting, and automating processes, offering greater control over the operating system compared to graphical interfaces. ​

10. What is a Linux Distribution?

A Linux Distribution (distro) is a complete operating system package that includes the Linux kernel, system utilities, applications, and package management systems. Distributions are tailored for different purposes and user preferences.

11. What are some popular Linux distributions?

Some commonly used Linux distributions include:

• Ubuntu – User-friendly, widely used for desktops and servers.
• Debian – A stable distribution with a large repository of software packages.
• Fedora – A cutting-edge distribution with the latest features.
• CentOS – A free alternative to Red Hat Enterprise Linux (RHEL).
• Arch Linux – A lightweight and customizable distribution.
• Kali Linux – Specialized for penetration testing and security research.

12. What is the root user in Linux?

The root user is the superuser in Linux with complete administrative control over the system. The root user has permissions to modify system files, install software, create and remove users, and configure system settings.

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13. What is the difference between soft links and hard links?

• Hard Link: A direct reference to the original file’s data blocks. Even if the original file is deleted, the data remains accessible.
• Soft Link (Symbolic Link): A pointer to the original file. If the original file is deleted, the soft link becomes invalid.

ln original_file hard_link
ln -s original_file soft_link

14. What is a process in Linux?

A process is an instance of a running program. Linux assigns a unique Process ID (PID) to every running process. You can check running processes using:

ps aux

or

top

15. What are the different states of a process in Linux?

A process in Linux can be in one of the following states:

• Running (R) – Actively executing.
• Sleeping (S or D) – Waiting for a resource.
• Stopped (T) – Paused or suspended.
• Zombie (Z) – Completed execution but not removed from the process table.

16. How do you kill a process in Linux?

To terminate a process, you can use:

• kill command: bashCopy code

kill <PID>

pkill command (by name):

pkill process_name

killall command:

killall process_name

htop (interactive process manager)

17. What is a daemon process in Linux?

A daemon is a background process that runs continuously without user intervention. Common daemons include:

• cron – Schedules jobs.
• httpd – Apache web server.
• sshd – Secure Shell (SSH) server.

18. What is the difference between foreground and background processes?

• Foreground Process – Runs interactively and takes control of the terminal until it finishes.
• Background Process – Runs in the background without blocking terminal access.

To send a process to the background:

command &

To move a process to the foreground:

fg %job_id

19. How do you check system resource usage in Linux?

You can use the following commands:

• top – Displays real-time process and system information.
• htop – An enhanced version of top.
• vmstat – Shows CPU and memory usage.
• free -m – Displays memory usage.
• df -h – Shows disk space usage.
• du -sh /path – Displays directory size.

20. How do you change file permissions in Linux?

The chmod command is used to change file permissions. Permissions are represented as:

• r (read) = 4
• w (write) = 2
• x (execute) = 1

To give full permission (read, write, execute) to the owner:

chmod 755 filename

To give read and write permission to everyone:

chmod 666 filename

To remove write permission for others:

chmod o-w filename

21. What is the difference between absolute and relative file paths?

• Absolute Path: The full path from the root directory (/). Example:

/home/user/documents/file.txt

Relative Path: A path relative to the current directory. Example:

./documents/file.txt

22. How do you find a file in Linux?

You can use the following commands:

• find – Searches files based on name, type, size, etc.

find /path -name “filename”

locate – Searches using a pre-built database.

locate filename

which – Finds the location of executable commands.

which bash

23. What is the purpose of the /etc/passwd file?

The /etc/passwd file stores user account information, including:

• Username
• User ID (UID)
• Group ID (GID)
• Home directory
• Shell type

You can view its content using:

cat /etc/passwd

24. What is the difference between cron and at?

• cron – Schedules repetitive tasks at specific times.
• at – Schedules one-time tasks.

To list scheduled cron jobs:

crontab -l

To add a new cron job:

crontab -e

To schedule a one-time job with at:

at 5pm

Then enter the command to execute.

25. How do you check the Linux kernel version?

You can check the kernel version using:

uname -r

Alternatively, you can use:

cat /proc/version

26. What is grep in Linux?

grep is used to search for patterns in text files.

Example:

grep “error” logfile.txt

To search recursively in all files:

grep -r “error” /var/log/

27. What is awk in Linux?

awk is a powerful text processing tool used for pattern matching.

Example:

awk ‘{print $1}’ filename.txt

This prints the first column of a file.

28. How do you view the contents of a file in Linux?

You can use:

• cat filename – Displays the entire file.
• less filename – Allows scrolling through a file.
• head filename – Shows the first 10 lines.
• tail filename – Shows the last 10 lines.
• nano filename – Opens the file in a text editor.

29. How do you mount and unmount a device in Linux?

To mount a device:

mount /dev/sdb1 /mnt

To unmount:

umount /mnt

To view mounted devices:

df -h

30. What is the purpose of the ls command?

The ls command lists files and directories.

Common options:

ls -l # Long listing format
ls -a # Show hidden files
ls -lh # Human-readable sizes
ls -t # Sort by modification time

31 What is the difference between cp, mv, and rm commands?

• cp (Copy) – Copies files from one location to another. bashCopy codecp source_file destination/
• mv (Move/Rename) – Moves files or renames them. bashCopy codemv oldname newname
• rm (Remove/Delete) – Deletes files or directories. bashCopy coderm filename rm -r directory

32. What is the purpose of the df and du commands?

• df (Disk Free) – Displays disk space usage. bashCopy codedf -h
• du (Disk Usage) – Shows disk usage for files and directories. bashCopy codedu -sh /path

33. How do you change the hostname in Linux?

To temporarily change the hostname:

hostname new-hostname

To permanently change the hostname:

sudo nano /etc/hostname
sudo nano /etc/hosts  # Update the old hostname references

Then restart the system.

34. What are environment variables in Linux?

Environment variables are global settings affecting shell behavior.

To view environment variables:

printenv

To set an environment variable:

export VAR_NAME=value

35. How do you compress and extract files in Linux?

• Compress a file using tar bashCopy codetar -czvf archive.tar.gz filename/
• Extract a tar.gz file bashCopy codetar -xzvf archive.tar.gz
• Compress using zip bashCopy codezip archive.zip filename
• Extract a zip file bashCopy codeunzip archive.zip

36. What is the purpose of /etc/fstab?

The /etc/fstab file contains static information about file system mounts. It tells Linux which partitions should be automatically mounted at boot.

View its content using:

cat /etc/fstab

37. What is a swap partition?

A swap partition acts as virtual memory when physical RAM is full. It prevents system crashes by temporarily storing inactive processes.

To check swap usage:

swapon -s
free -m

38. How do you add a new user in Linux?

To add a new user:

sudo useradd -m username
sudo passwd username

To add a user to the sudo group:

sudo usermod -aG sudo username

39. How do you delete a user in Linux?

To remove a user but keep their home directory:

sudo userdel username

To remove the user along with their home directory:

sudo userdel -r username

40. What is the difference between su and sudo?

• su (Switch User) – Switches to another user’s account. bashCopy codesu username
• sudo (Superuser Do) – Runs commands with administrative privileges. bashCopy codesudo apt update

41. What is the /dev directory used for?

The /dev directory contains device files that represent hardware components. Examples:

• /dev/sda1 – First partition of the primary disk.
• /dev/null – A special file that discards any data written to it.

42. How do you list open ports in Linux?

You can check open ports using:

netstat -tulnp

or

ss -tulnp

43. What is the iptables command used for?

iptables is used to configure firewall rules in Linux.

To list firewall rules:

sudo iptables -L -v -n

To block an IP address:

sudo iptables -A INPUT -s 192.168.1.100 -j DROP

44. How do you check system logs in Linux?

System logs are stored in /var/log. Common logs include:

• /var/log/syslog – General system logs.
• /var/log/auth.log – Authentication logs.
• /var/log/dmesg – Kernel messages.

To view logs:

cat /var/log/syslog

45. What is crontab and how is it used?

crontab is used to schedule recurring tasks.

To edit a crontab file:

crontab -e

Example cron job (runs every day at midnight):

0 0 * * * /path/to/script.sh

46. What is the difference between apt and yum?

• apt (Advanced Package Tool) – Used in Debian-based distributions (Ubuntu, Debian).
• yum (Yellowdog Updater Modified) – Used in RHEL-based distributions (CentOS, Fedora).

Example:

sudo apt install package_name  # Debian
sudo yum install package_name  # RHEL

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47. How do you change a user’s password in Linux?

To change your own password:

passwd

To change another user’s password:

sudo passwd username

48. What is the sed command used for?

sed (Stream Editor) is used for text manipulation.

Example: Replace all occurrences of “old” with “new” in a file:

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

49. What is a symbolic link?

A symbolic link (or soft link) is a pointer to another file.

To create a symbolic link:

ln -s target_file link_name

50. How do you schedule a shutdown in Linux?

To shut down after 10 minutes:

shutdown -h +10

To cancel a scheduled shutdown:

shutdown -c

51. How do you reboot a Linux system from the terminal?

To reboot the system immediately:

sudo reboot

Or use:

sudo shutdown -r now

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52. What is the /proc directory used for?

The /proc directory contains virtual files that provide information about system processes and hardware. Examples:

• /proc/cpuinfo – CPU details
• /proc/meminfo – Memory usage
• /proc/uptime – System uptime

To check CPU info:

cat /proc/cpuinfo

53. What is the difference between hard links and soft links?

• Hard Link: Points directly to the data on disk, even if the original file is deleted.
• Soft Link (Symbolic Link): Points to the filename instead of data.

Example:

bashCopy codeln file1 hardlink
ln -s file1 softlink

54. How do you list all installed packages in Linux?

• Debian-based (Ubuntu, Debian): bashCopy codedpkg --list
• RedHat-based (RHEL, CentOS): bashCopy coderpm -qa

55. How do you find the process consuming the most CPU?

top

or

ps aux --sort=-%cpu | head

56. How do you find the process consuming the most memory?

ps aux --sort=-%mem | head

57. What is the difference between kill and pkill?

• kill – Terminates a process using its PID. bashCopy codekill 1234
• pkill – Terminates a process by its name. bashCopy codepkill firefox

58. How do you check the default run level in Linux?

Use the following command:

runlevel

59. What is the difference between /etc/passwd and /etc/shadow?

• /etc/passwd – Stores user account details.
• /etc/shadow – Stores encrypted user passwords.

60. How do you find which shell you are using?

echo $SHELL

61. How do you check system uptime?

uptime

62. What is the command to display disk usage by directory?

du -sh *

63. How do you check memory usage in Linux?

free -m

64. How do you check active network connections?

netstat -tulnp

or

ss -tulnp

65. How do you list open files used by a process?

bashCopy codelsof -p PID

66. How do you find the full path of a command?

which ls

or

whereis ls

67. How do you create an empty file in Linux?

touch filename

68. How do you change file permissions in Linux?

To give full permissions:

chmod 777 filename

To remove all permissions:

chmod 000 filename

69. What is the nohup command used for?

It allows a command to run even after logging out.

nohup command &

70. How do you find the size of a file in Linux?

ls -lh filename

71. How do you restart a service in Linux?

For systemd-based systems:

sudo systemctl restart service_name

72. What is the purpose of /etc/hosts?

It maps IP addresses to hostnames.

To add an entry:

sudo nano /etc/hosts

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73. How do you list all services running on Linux?

systemctl list-units --type=service

74. How do you create a tar archive?

bashCopy codetar -cvf archive.tar files/

75. How do you check the Linux kernel version?

uname -r

76. What is the rsync command used for?

It is used to copy/synchronize files efficiently.

rsync -av source/ destination/

77. How do you add a user to a group?

sudo usermod -aG group_name username

78. How do you find the MAC address of a network interface?

ip link show eth0

79. How do you clear the terminal screen?

clear

80. What is the difference between df and du?

• df – Shows disk space usage of partitions.
• du – Shows disk usage of directories.

81. What does the tee command do?

It reads input and writes to a file and standard output.

ls | tee file.txt

82. How do you rename a file in Linux?

mv oldfile newfile

83. How do you create a directory in Linux?

mkdir dirname

84. What is the command to display the last 10 lines of a file?

tail filename

85. How do you find a file by name in Linux?

bashCopy codefind / -name "filename"

86. What is chmod 755?

• Owner: Read, Write, Execute
• Group & Others: Read, Execute

87. How do you disable root login via SSH?

Edit the /etc/ssh/sshd_config file and set:

PermitRootLogin no

88. How do you remove duplicate lines from a file?

sort file.txt | uniq

89. How do you enable a service to start on boot?

sudo systemctl enable service_name

90. How do you check listening ports?

netstat -tulnp

91. How do you check DNS resolution?

nslookup google.com

92. What is df -h used for?

Displays disk space usage in human-readable format.

93. How do you check CPU temperature?

sensors

94. What is grub?

GRUB (Grand Unified Bootloader) is used to boot Linux.

95. How do you exit from vi editor?

• :q → Exit
• :q! → Exit without saving
• :wq → Save and exit

96. How do you kill all processes by name?

pkill process_name

97. How do you check network interface details?

ip a

98. What is the purpose of /etc/resolv.conf?

It configures DNS servers.

99. How do you find system information?

uname -a

100. How do you monitor real-time log updates?

tail -f /var/log/syslog