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Unix Interview Questions

Last Updated on October 31, 2023 by Ankit Kochar

UNIX, an operating system with a rich history dating back to the 1960s, continues to be a fundamental part of the computing world. For job seekers in fields like system administration, software development, and DevOps, UNIX skills are highly sought after. To help you prepare for UNIX-related interviews, here are the top 25 UNIX interview questions.

Unix Interview Questions and Answers

Unix Interview Questions and Answers are discussed below:

1. What is UNIX?
UNIX is a family of multitasking, multiuser computer operating systems originally developed in the 1960s at AT&T’s Bell Labs. It’s known for its robustness, security, and versatility and has been the basis for various operating systems, including Linux and macOS.

2. Explain the difference between UNIX and Linux.
While both UNIX and Linux are Unix-like operating systems, UNIX typically refers to commercial versions, while Linux is open source. Linux is a UNIX-like operating system that is freely available and has many distributions, like Ubuntu and CentOS.

3. What are some common UNIX flavors?
Common UNIX flavors include AIX (IBM), Solaris (formerly Sun Microsystems, now Oracle), HP-UX (Hewlett Packard), and macOS (Apple). Additionally, there are various Linux distributions, such as Ubuntu, CentOS, and Debian.

4. What is a shell in UNIX?
A shell is a command-line interface that allows users to interact with the UNIX operating system. Popular shells include Bash (Bourne-Again Shell), Zsh (Z Shell), and Korn (KornShell).

5. How do you list files in a directory in UNIX?
The ls command is used to list files and directories in UNIX. For example, ls -l displays detailed information about files and directories in the current directory.

6. What is a PID in UNIX?
PID stands for Process Identifier. It is a unique number assigned to each running process in UNIX. PIDs are used to manage and identify processes, making it easier to start, stop, or monitor them.

7. Explain the chmod command in UNIX.
The chmod command is used to change file permissions in UNIX. It allows you to specify who can read, write, or execute a file. For example, chmod 755 file.txt grants read, write, and execute permissions to the owner and read and execute permissions to others.

8. How do you search for a file in UNIX?
The find command is used to search for files and directories in UNIX. For instance, find /path/to/search -name filename searches for a file named "filename" under the specified path.

9. What is a symbolic link in UNIX?
A symbolic link (or symlink) is a reference to another file or directory. It acts as a pointer, allowing you to access the target file or directory from multiple locations. The ln -s command creates symbolic links.

10. Explain the purpose of the /etc/passwd file in UNIX.
The /etc/passwd file stores user account information, including usernames, user IDs (UIDs), home directories, and default shells. It is essential for user authentication and system administration.

11. What is the grep command used for in UNIX?
The grep command is used for text searching and manipulation. It searches for patterns in text files and displays matching lines. For instance, grep "pattern" file.txt searches for "pattern" in the file "file.txt."

12. What is the purpose of the /etc/hosts file in UNIX?
The /etc/hosts file maps hostnames to IP addresses. It is used for local DNS resolution, allowing users to specify custom host-to-IP mappings.

13. Explain the concept of a pipe (|) in UNIX.
A pipe is used to connect the standard output of one command to the standard input of another. For example, command1 | command2 takes the output of command1 and feeds it as input to command2.

14. What is a shell script in UNIX?
A shell script is a series of UNIX commands saved in a script file. It can be executed as a single command, automating repetitive tasks and complex operations.

15. What is the purpose of the cron utility in UNIX?
Cron is a time-based job scheduler in UNIX. It allows users to schedule tasks to run at specified intervals, such as daily, weekly, or monthly.

16. Explain the significance of tar in UNIX.
The tar command is used for archiving files and directories in UNIX. It can create, extract, and compress archive files. For example, tar -cvf archive.tar files/ creates an archive of the "files" directory.

17. What is SSH in UNIX?
SSH (Secure Shell) is a network protocol used to secure remote access to UNIX-like systems. It provides encrypted communication for secure login, file transfer, and remote command execution.

18. How do you check system resource usage in UNIX?
The top command displays real-time information about system resource usage, including CPU, memory, and processes. Pressing ‘q’ exits the top command.

19. Explain the purpose of /dev/null in UNIX.
/dev/null is a special file that discards data written to it. It is often used to suppress output or as a placeholder for unwanted data.

20. What is the significance of the passwd command in UNIX?
The passwd command is used to change a user’s password in UNIX. Users can use it to set or update their passwords securely.

21. What is the purpose of the umask command in UNIX, and how does it work?
The umask command is used to set the default file permissions for newly created files and directories. It subtracts the specified permissions from the maximum permissions (usually 777 for directories and 666 for files) to determine the default permissions.

22. Explain the concept of environment variables in UNIX. How can you set and display environment variables?
Environment variables are values that can be accessed by processes and shell scripts to customize the behavior of the environment. You can set environment variables using the export command, and you can display them using the echo $VARIABLE_NAME command.

23. What is a daemon in UNIX, and why are daemons important?
In UNIX, a daemon is a background process that runs independently of the user’s session and performs various system tasks. Daemons are crucial for tasks like managing hardware, network services, and scheduling jobs, as they operate without user intervention.

24. What is the purpose of the awk command in UNIX, and how can it be used?
awk is a versatile text-processing tool used for pattern scanning and processing. It is commonly used for tasks like data extraction, manipulation, and reporting. You can use it to specify patterns and actions to perform on matching lines of text in files or data streams.

25. How can you check the disk space usage in UNIX, and what command would you use to identify directories consuming the most space?
You can check disk space usage in UNIX using the df command, which displays file system disk space usage. To identify directories consuming the most space, you can use the du (disk usage) command with options like -h (human-readable) and -s (summary).

UNIX is a timeless and influential operating system that has shaped the computing landscape for decades. For job seekers and professionals in various IT domains, knowledge of UNIX is indispensable. In this article, we covered 25 key UNIX interview questions, spanning a wide range of topics from basic commands to advanced concepts. Preparing for these questions can help you stand out during UNIX-related interviews and pave the way for a successful career in fields like system administration, software development, and DevOps.

Frequently Asked Questions Related to Unix Interview Questions

Some frequently asked questions (FAQs) related to UNIX are:

1. Is UNIX the same as Linux?
No, UNIX and Linux are not the same. UNIX is a family of operating systems that includes commercial variants like AIX, Solaris, and HP-UX, while Linux is an open-source Unix-like operating system with various distributions.

2. What are some popular UNIX shells besides Bash?
Besides Bash, other popular UNIX shells include Zsh (Z Shell), Korn (KornShell), and Csh (C Shell).

3. Can you run graphical applications in a UNIX environment?
Yes, UNIX environments support graphical applications through X Window System (X11) or display protocols like SSH X11 forwarding.

4. How can you kill a process in UNIX?
You can use the kill command followed by the process ID (PID) or send a specific signal to terminate a process. The default signal is SIGTERM (15), which requests a graceful termination, while SIGKILL (9) forcefully terminates a process.

5. What is the purpose of the /etc/shadow file in UNIX?
The /etc/shadow file stores secure password information for user accounts, including encrypted passwords and password expiration details. It enhances password security compared to the older /etc/passwd file.

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