Linux Interview Questions 2025 – 50 Most Asked Questions

Friends Linux is one of the most popular operating systems used in servers, cloud computing, and even in personal computers. If you are preparing for a Linux-related interview in 2025, it’s important to know the key concepts, commands, and troubleshooting techniques.

In this guide, we have listed the most common Linux Interview Questions 2025 along with simple explanations. Whether you are a beginner or someone looking to refresh your knowledge, these questions will help you feel confident in your interview. Let’s get started!

Linux Interview Questions 2025

10 Problem-Solving Linux Interview Questions (2025)

1. What is Linux?

Answer:
Linux is an open-source operating system based on Unix. It is widely used for servers, embedded systems, and cloud computing.

Explanation:
Linux is free to use and highly secure. It allows multiple users and multitasking, making it a popular choice for professionals.

2. What are the main components of Linux?

Answer:
The main components of Linux are:

• Kernel – The core of the OS that manages hardware and processes.
• Shell – The interface that takes user commands.
• File System – Organizes and stores files.
• System Libraries – Help applications interact with the kernel.

Explanation:
Each component plays a role in making Linux work smoothly. The kernel is the most important part, as it controls everything.

3. What is the difference between Linux and Unix?

Answer:
Linux is open-source and free, while Unix is a proprietary OS used mainly in large enterprises.

Explanation:
Linux is inspired by Unix but is more flexible. Many companies prefer Linux because of its cost-effectiveness and strong community support.

4. How do you check the current working directory in Linux?

Answer:
Use the pwd command.

pwd

Explanation:
This command prints the path of the directory you are currently in, helping you know where you are in the file system.

5. How do you list all files in a directory?

Answer:
Use the ls command.

ls

Explanation:
By default, ls shows files in the current directory. You can use options like ls -a to see hidden files.

6. How do you create a new file in Linux?

Answer:
Use the touch command.

touch filename.txt

Explanation:
The touch command creates an empty file if it doesn’t exist. You can also use echo or nano to create files.

7. How do you move or rename a file?

Answer:
Use the mv command.

mv oldname.txt newname.txt

Explanation:
The mv command is used to rename a file or move it to a different directory.

8. How do you delete a file in Linux?

Answer:
Use the rm command.

rm filename.txt

Explanation:
Be careful while using rm because deleted files cannot be recovered easily. To delete a directory, use rm -r directory_name.

9. How do you check system uptime in Linux?

Answer:
Use the uptime command.

uptime

Explanation:
This command shows how long the system has been running, along with the current time and system load.

10. How do you check disk usage in Linux?

Answer:
Use the df -h command.

df -h

Explanation:
This command shows available and used disk space in a human-readable format, making it easy to understand storage usage.

11. How do you check the Linux version installed on a system?

Answer:
Use the following command:

uname -r

or

cat /etc/os-release

Explanation:
uname -r shows the kernel version, while cat /etc/os-release provides detailed OS information, including the distribution name and version.

12. How do you create a new directory in Linux?

Answer:
Use the mkdir command.

mkdir new_folder

Explanation:
mkdir stands for “make directory.” It creates a new folder in the current location. You can also create nested directories using mkdir -p parent/child.

13. How do you copy a file from one location to another?

Answer:
Use the cp command.

cp file.txt /home/user/

Explanation:
The cp command copies files from one directory to another. To copy directories, use cp -r directory_name destination/.

14. How do you change file permissions in Linux?

Answer:
Use the chmod command.

chmod 755 filename

Explanation:
chmod (change mode) modifies file permissions. In 755, the numbers represent read (4), write (2), and execute (1) permissions for different user groups.

15. What command is used to check running processes in Linux?

Answer:
Use the ps or top command.

ps aux

or

top

Explanation:
ps aux lists all running processes, while top provides real-time monitoring of CPU and memory usage.

16. How do you find a specific word inside a file in Linux?

Answer:
Use the grep command.

grep "word" filename.txt

Explanation:
grep searches for a specific word or pattern in a file. It is useful for quickly locating information in large files.

17. How do you schedule a task in Linux?

Answer:
Use the cron job scheduler by editing the crontab file.

crontab -e

Example cron job to run a script every day at 5 AM:

0 5 * * * /path/to/script.sh

Explanation:
Cron jobs automate tasks like backups, system maintenance, or running scripts at scheduled times.

18. How do you switch users in Linux?

Answer:
Use the su command.

su username

Explanation:
The su (substitute user) command allows you to switch to another user account. To switch to the root user, use su - root.

19. How do you find the IP address of your Linux system?

Answer:
Use the ip or ifconfig command.

ip a

or

ifconfig

Explanation:
These commands display network interface details, including the system’s IP address, MAC address, and network status.

20. How do you stop a process in Linux?

Answer:
Use the kill or pkill command.

kill PID

or

pkill process_name

Explanation:
kill stops a process using its Process ID (PID). pkill terminates processes by name. To force kill, use kill -9 PID.

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

Answer:
Use the ls -lh or du command.

ls -lh filename

or

du -h filename

Explanation:
ls -lh shows file size in a human-readable format, while du -h (disk usage) provides detailed file size information.

22. How do you check the available memory in Linux?

Answer:
Use the free command.

free -h

Explanation:
The free command displays total, used, and available memory. The -h option makes the output more readable by showing sizes in MB or GB.

23. How do you change the hostname of a Linux system?

Answer:
Use the hostnamectl command.

sudo hostnamectl set-hostname new-hostname

Explanation:
The hostnamectl command allows you to change the system’s hostname permanently. You may need to restart the system for the changes to take effect.

24. What is the difference between hard links and soft links in Linux?

Answer:

• Hard Link: A duplicate file that shares the same inode.
• Soft Link (Symbolic Link): A shortcut that points to another file.

Example of creating a hard link:

ln original.txt hardlink.txt

Example of creating a soft link:

ln -s original.txt softlink.txt

Explanation:
Hard links remain even if the original file is deleted, while soft links break if the original file is removed.

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

Answer:
Use the cat, less, or more command.

cat filename.txt
less filename.txt
more filename.txt

Explanation:

• cat prints the entire file at once.
• less and more allow scrolling through large files.

26. How do you find a specific file in Linux?

Answer:
Use the find command.

find /path -name "filename"

Explanation:
The find command searches for files by name, type, or size. To search for all .txt files, use:

find /path -name "*.txt"

27. How do you check system logs in Linux?

Answer:
Use the journalctl or cat command.

journalctl -xe

or

cat /var/log/syslog

Explanation:
System logs help diagnose errors and monitor system activities. journalctl is used for systemd-based logs, while /var/log/syslog contains general logs.

28. How do you check the CPU usage in Linux?

Answer:
Use the top or htop command.

top

or

htop

Explanation:
top displays real-time CPU and memory usage. htop (if installed) provides a more user-friendly interface with colors and process management options.

29. How do you unzip a compressed file in Linux?

Answer:
Use the unzip or tar command.

unzip file.zip

For .tar.gz files:

tar -xvzf file.tar.gz

Explanation:
unzip extracts .zip files, while tar -xvzf is used for .tar.gz archives. The options stand for:

• x – Extract
• v – Verbose (show progress)
• z – Handle .gz compression
• f – File name follows

30. How do you restart a service in Linux?

Answer:
Use the systemctl restart command.

sudo systemctl restart service_name

Explanation:
This command restarts system services like Apache (apache2), MySQL (mysql), or SSH (ssh). To check if a service is running, use:

systemctl status service_name

31. Multiple Choice: Which command is used to display the current date and time in Linux?

A) date
B) time
C) clock
D) datetime

Answer: A) date

Explanation:
The date command prints the system’s current date and time. You can also format it using options like date +"%Y-%m-%d %H:%M:%S".

32. One-Word Answer: Which Linux command is used to count words in a file?

Answer: wc

Explanation:
The wc (word count) command counts the number of words, lines, and characters in a file. Example:

wc -w filename.txt

33. Multiple Choice: What is the default shell in most Linux distributions?

A) bash
B) sh
C) zsh
D) fish

Answer: A) bash

Explanation:
Bash (Bourne Again Shell) is the most commonly used shell in Linux. Other shells like zsh and fish provide additional features but are not the default.

34. Short Answer: How do you remove a directory in Linux?

Answer: Use the rm -r command.

rm -r directory_name

Explanation:
rm -r removes a directory and all its contents. Be careful while using it, as deleted files cannot be easily recovered.

35. One-Word Answer: Which command is used to display the manual pages of a command?

Answer: man

Explanation:
The man command provides detailed documentation for Linux commands. Example:

man ls

36. Multiple Choice: Which Linux directory contains system logs?

A) /home
B) /var/log
C) /etc/logs
D) /usr/logs

Answer: B) /var/log

Explanation:
The /var/log directory stores system logs, including authentication logs, kernel logs, and application logs.

37. Short Answer: How do you check the number of users currently logged in?

Answer: Use the who or w command.

who

or

w

Explanation:
who shows the logged-in users, while w provides additional details like system uptime and active processes.

38. One-Word Answer: Which Linux command is used to compress files?

Answer: gzip

Explanation:
gzip compresses files to reduce their size. Example:

gzip file.txt

39. Multiple Choice: Which of the following commands is used to shut down a Linux system?

A) shutdown -h now
B) poweroff
C) halt
D) All of the above

Answer: D) All of the above

Explanation:
All these commands can shut down the system:

• shutdown -h now shuts down immediately.
• poweroff turns off the system.
• halt stops the system without powering off.

40. Short Answer: How do you change the password for a user in Linux?

Answer: Use the passwd command.

passwd username

Explanation:
The passwd command allows users to change their password. Only the root user can change another user’s password.

10 Linux MCQs for Interviews (2025)

31. Which command is used to display the current working directory?

A) pwd
B) ls
C) cd
D) mkdir

Answer: A) pwd

Explanation:
The pwd (print working directory) command shows the full path of the current directory.

32. What is the default directory for user home directories in Linux?

A) /home
B) /usr
C) /root
D) /etc

Answer: A) /home

Explanation:
The /home directory stores personal files for regular users, while /root is for the system administrator.

33. Which command is used to delete a directory along with its contents?

A) rmdir
B) rm -r
C) delete
D) remove

Answer: B) rm -r

Explanation:
rm -r (recursive remove) deletes directories and their files. rmdir only works on empty directories.

34. Which Linux command is used to change file ownership?

A) chmod
B) chown
C) chgrp
D) mv

Answer: B) chown
Explanation:
The chown command changes the owner of a file. Example: chown user:group filename.

35. How can you display the contents of a text file one page at a time?

A) cat
B) less
C) nano
D) touch

Answer: B) less
Explanation:
less allows scrolling through large files, unlike cat, which prints everything at once.

36. What does the grep command do?

A) Finds a word in a file
B) Deletes a file
C) Moves a file
D) Copies a file

Answer: A) Finds a word in a file
Explanation:
grep "word" filename.txt searches for specific words or patterns inside a file.

37. Which command is used to see the list of active processes?

A) ps
B) jobs
C) top
D) Both A and C

Answer: D) Both A and C

Explanation:
ps shows a snapshot of processes, while top provides real-time monitoring of running processes.

38. What is the purpose of the df -h command?

A) Displays available disk space
B) Finds a file
C) Deletes a directory
D) Shows running services

Answer: A) Displays available disk space

Explanation:
df -h (disk free) shows disk usage in a human-readable format (MB, GB).

39. How do you switch to the root user in Linux?

A) sudo su
B) switch root
C) su root
D) Both A and C

Answer: D) Both A and C
Explanation:
su root switches to root, but sudo su is preferred for security reasons in some systems.

40. Which file stores the list of scheduled cron jobs?

A) /etc/crontab
B) /var/log/syslog
C) /etc/passwd
D) /home/cron

Answer: A) /etc/crontab
Explanation:
Cron jobs are scheduled tasks, and their settings are stored in /etc/crontab for system-wide use.

41. A process is consuming too much CPU. How do you identify and stop it?

Solution:

1. Identify high CPU usage: top or ps aux --sort=-%cpu | head -10
2. Find the process ID (PID).
3. Stop the process: kill PID or force stop: kill -9 PID

Explanation:
top and ps help locate resource-heavy processes. The kill command is used to terminate them safely.

42. You accidentally deleted an important file. How do you recover it?

Solution:

1. Check the Trash folder (for GUI-based Linux).
2. Use ls to check backups in /var/backups/.
3. If deleted from ext3/ext4 file systems, use extundelete: sudo extundelete /dev/sdX --restore-file /path/to/file

Explanation:
Recovering files depends on backups or recovery tools. extundelete works only if the disk space hasn’t been overwritten.

43. Your disk space is full. How do you find and delete large files?

Solution:

1. Find large files: du -ah / | sort -rh | head -10
2. Delete unnecessary files: rm filename
3. Clean package cache: sudo apt autoremove && sudo apt clean

Explanation:
du helps locate large files. apt autoremove cleans unnecessary packages.

44. How do you check which ports are in use on your Linux system?

Solution:

sudo netstat -tulnp

or

sudo lsof -i -P -n

Explanation:
These commands show active network connections and the services using them. This helps troubleshoot networking issues.

45. Your server is slow. How do you analyze and fix the issue?

Solution:

1. Check CPU and RAM usage: top free -h
2. Check disk I/O performance: iostat -x 1 5
3. Restart unnecessary services: sudo systemctl stop unused_service

Explanation:
top and free show system performance. iostat helps analyze disk bottlenecks.

46. A scheduled cron job is not running. How do you debug it?

Solution:

1. Check if the cron service is running: systemctl status cron
2. View the user’s cron jobs: crontab -l
3. Check logs for errors: cat /var/log/syslog | grep CRON

Explanation:
Cron jobs may fail due to syntax errors, permission issues, or a stopped cron service.

47. You need to monitor real-time logs of an application. How do you do it?

Solution:

tail -f /var/log/app.log

Explanation:
tail -f shows the latest log entries as they are written, useful for debugging live applications.

48. How do you find which user last modified a file?

Solution:

ls -ltu filename

or

stat filename

Explanation:
ls -ltu shows files sorted by last access time. stat gives detailed file metadata, including last modification time.

49. You want to block an IP address from accessing your server. How do you do it?

Solution:
Using iptables:

sudo iptables -A INPUT -s 192.168.1.100 -j DROP

Explanation:
iptables blocks unwanted IP addresses, preventing unauthorized access.

50. A Linux system is stuck or unresponsive. How do you troubleshoot?

Solution:

1. Switch to a different terminal: Ctrl + Alt + F2
2. Check system logs: journalctl -xe
3. Kill unresponsive processes: kill -9 PID
4. Reboot if necessary: sudo reboot

Explanation:
Switching terminals can help regain control. Logs provide error details, and killing processes may restore functionality without rebooting.