Top 50 Must Know Unix Interview Questions and Answers

Unix (UNiplexed Information Computing System) is an operating system widely used in enterprise-level computing, scientific research, and web servers. If you are preparing for your next Unix interview, this article is for you. We have mentioned the top Unix interview questions and answers. You can also enhance your job readiness with online Unix certification courses.

These Unix interview questions will help you confidently face the interview and answer questions effectively. You can also understand which type of questions can be asked and how to prepare for them.

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Q1. What is Unix, and what are its primary features?

This is one of the common Unix interview questions. Unix is a powerful multi-user operating system that was first developed in the 1970s. Its primary features include a hierarchical file system, a command-line interface, and support for multitasking and multiuser environments.

Q2. What is the difference between a command and a shell?

A command is a specific instruction or task that the user wants the computer to perform, while a shell is a program that provides a command-line interface for interacting with the computer's operating system.

Q3. How do you find out the size of a file in Unix?

This is one of the common Linux Unix interview questions. To determine the size of a file in Unix, you can employ the "ls" command, specifically with the "-l" option. This command provides a detailed listing of files, including their sizes in bytes, helping you easily ascertain the file's dimensions.

Q4. What is grep in Unix, and how is it used?

This is one of the basic unix interview questions to prepare for. Grep is a Unix command-line utility used to search for specific patterns in a file or set of files. It can be used to search for text strings, regular expressions, or other patterns.

Q5. What is a symbolic link in Unix, and how is it used?

This type of Unix interview questions and answers are important to remember. A symbolic link, also known as a soft link, is a special type of file that points to another file or directory. It can be used to create shortcuts or aliases for files or directories.

Q6. What is a daemon in Unix, and how is it used?

A daemon is a background process that runs independently of any user interaction. Daemons are commonly used to provide services such as web servers, email servers, and network services.

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Q7. What is a pipe in Unix, and how is it used?

A pipe is a method of connecting two or more Unix commands so that the output of one command becomes the input of another command. This allows for complex command sequences and can be used to automate repetitive tasks.

Q8. What is a signal in Unix, and how is it used?

This is one of the basic interview questions on Unix. A signal is a software interrupt which is sent to a Unix process to notify it of a particular event or condition. Signals can be used to control or manage running processes and can be sent using various Unix commands.

Q9. What is the purpose of the "chmod" command in Unix, and how is it used?

The "chmod" command is used to change the permissions of files and directories in Unix. It can be used to set or modify file permissions for users, groups, and other categories.

Q10. What is a cron job in Unix, and how is it used?

This is one of the basic Unix interview questions. A cron job is a Unix system daemon that allows the user to schedule recurring tasks or jobs at specified intervals. It can be used to automate repetitive tasks such as backups, system maintenance, and log file management.

Q11. What is SSH in Unix, and how is it used?

SSH (Secure Shell) is a cryptographic network protocol that provides secure access to Unix systems over an unsecured network. It can be used to encrypt network traffic, authenticate users, and provide secure remote access to Unix systems.

Q12. Explain what an inode is in Unix and why it is important.

An inode (index node) is a data structure in Unix-like file systems that stores metadata about a file, such as its size, ownership, permissions, timestamps, and data block pointers. Inodes are crucial for efficient file management and disk space allocation as they provide a way to represent and organise files and directories on disk.

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Q13. How do you change the owner of a file in Unix?

This is one of the interview questions for Unix commands. The "chown" command in Unix is used to change the owner of a file. For example, to change the owner of a file named "file.txt" to a user named "newowner," you would use the command: chown newowner file.txt.

Q14. What is a Unix shell script, and how is it different from a regular script?

A Unix shell script is a series of Unix commands and instructions saved in a text file with a ".sh" extension. It can be executed as a single unit, automating tasks and performing complex operations. The key difference is that shell scripts are interpreted and executed by the Unix shell, making them platform-independent and highly versatile.

Q15. Explain the purpose of the "tar" command in Unix and provide an example of how it is used.

This is one of the important interview questions on Unix for experienced professionals. The "tar" command in Unix is used to archive and compress files and directories into a single file, often referred to as a "tarball." For example, to create a tarball of a directory named "mydir," you would use the command: tar -cvf mydir.tar mydir.

Q16. What is a shell variable in Unix, and how can it be defined and used?

A shell variable in Unix is a symbolic name used to store data or values. It can be defined using the "variable_name=value" syntax. For example, to define a variable named "count" with a value of 10, you would use: count=10. You can access the value of a variable using the "$" symbol, such as echo $count.

Q17. How can you find all files larger than a specific size in Unix?

You can use the "find" command with the "-size" option to locate files larger than a specific size. For example, to find all files larger than 1MB in the current directory and its subdirectories, you would use the command: find . -type f -size +1M.

Q18. Explain what the "umask" command does in Unix and why it is important.

This is one of the common Unix interview questions and answers for experienced professionals. The "umask" command in Unix is used to set default file permissions for newly created files and directories.

The “umask” command subtracts the specified value from the maximum permissions (usually 666 for files and 777 for directories) to determine the default permissions. It is important for security and privacy as it ensures that files and directories are not created with overly permissive permissions by default.

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Q19. What is the purpose of the "awk" command in Unix, and how is it used?

The "awk" command in Unix is a powerful text processing tool that is used for pattern matching, data extraction, and text manipulation. It operates on structured text files and allows users to define custom actions based on patterns.

For example, to print the second field of a file separated by commas, you would use the command: awk -F',' '{print $2}' filename.

Q20. Explain the concept of Unix file permissions (rwx) and their significance.

This type of Unix interview question is frequently asked. Unix file permissions are represented by three sets of characters: user (owner), group, and others. Each set consists of three characters: read (r), write (w), and execute (x).

These permissions control who can read, write, and execute a file. They are crucial for security and access control, ensuring that only authorised users can perform specific actions on files and directories.

Q21. How can you search for a specific text pattern within multiple files in Unix using the "grep" command?

The "grep" command in Unix is used to search for a specific text pattern within one or more files. For example, to search for the word "searchterm" in all text files within the current directory and its subdirectories, you would use the command: grep -r "searchterm" *.txt.

Q22. What is a Unix shell and why is it essential for interacting with the Unix operating system?

A Unix shell is a command-line interface that allows users to interact with the Unix operating system by executing commands and scripts. It serves as a user-friendly interface to access system resources, manage files, run programs, and perform various tasks efficiently. Shells provide a powerful environment for automation, scripting, and system administration.

Q23. How can you redirect the output of a Unix command to a file instead of displaying it on the screen?

This is one of the easy Unix interview questions for freshers. You can use the ">" symbol to redirect the output of a Unix command to a file. For example, to redirect the output of a command named "commandname" to a file named "output.txt," you would use the command: commandname > output.txt.

Q24. Explain the purpose of the "cron" utility in Unix and how it is used for scheduling tasks.

The "cron" utility in Unix is used to schedule and automate recurring tasks or jobs at specified intervals. It operates on a predefined schedule, called a "cron schedule" or "cron tab," and can be configured to run scripts or commands at specific times or on specific days of the week or month.

The "cron" utility is essential for automating routine system maintenance, backups, and other scheduled activities.

Q25. What is the purpose of the "/etc/passwd" file in Unix, and what information does it contain?

This type of Unix interview questions and answers are important to practice. The "/etc/passwd" file in Unix is a system file that contains user account information.

Each line in the file represents a user and includes information such as the username, user ID (UID), group ID (GID), home directory, and the user's default shell. It plays a critical role in user authentication and system access control.

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Q26. How can you create a symbolic link (soft link) to a file in Unix?

To create a symbolic link to a file in Unix, you can use the "ln" command with the "-s" option, followed by the source file and the desired link name. For example, to create a symbolic link named "mylink" to a file named "myfile.txt," you would use the command: ln -s myfile.txt mylink.

Q27. What is the purpose of the "find" command in Unix, and how is it used to locate files and directories?

The "find" command in Unix is used to search for files and directories based on various criteria, such as name, size, type, and modification time. It is a powerful tool for locating files that match specific patterns or conditions.

For example, to find all files named "file.txt" in the current directory and its subdirectories, you would use the command: find . -name "file.txt".

Q28. What is the difference between a hard link and a symbolic link in Unix?

This is one of the interview questions for Unix commands. A hard link in Unix is a reference to the same inode (data structure) as the original file. It essentially creates multiple directory entries pointing to the same data blocks on disk.

In contrast, a symbolic link (soft link) is a separate file that contains a path or reference to the target file or directory. Hard links are limited to files on the same file system, while symbolic links can span file systems.

Q29. Explain the purpose of the "sudo" command in Unix and how it is used for privilege escalation.

This is one of the basic unix questions asked in interviews. The "sudo" command in Unix is used to temporarily elevate a user's privileges to perform tasks that require administrative or superuser access. Users can execute commands with higher privileges by prefixing them with "sudo."

This is essential for security and access control, allowing users to perform administrative tasks without having full superuser access.

Q30. What is the significance of the Unix "PATH" environment variable, and how does it work?

This is one of the frequently asked interview questions and answers on Unix. The Unix "PATH" environment variable is a list of directories that the shell searches when trying to execute a command. It determines where the system looks for executable files when a command is entered.

When a command is executed, the shell searches each directory in the "PATH" in order until it finds the executable file with the same name as the command.

Q31. How can you recursively copy a directory and its content in Unix using the "cp" command?

To recursively copy a directory and its contents in Unix using the "cp" command, you can use the "-r" or "-R" option. For example, to copy a directory named "sourcedir" and its contents to a destination directory named "destdir," you would use the command: cp -r sourcedir destdir.

Q32. What is the purpose of the "sed" command in Unix, and how is it used for text manipulation?

The "sed" (stream editor) command in Unix is used for text manipulation and editing. It allows users to perform text transformations on input text, such as search and replace operations, text filtering, and data manipulation. Users can specify editing commands in a script or interactively through the command line.

Q33. What is a Unix process ID (PID), and how is it useful in system administration?

This is one of the important interview questions for Unix commands. A Unix process ID (PID) is a unique identifier assigned to each running process in the Unix operating system.

PIDs are crucial for process management, as they allow system administrators to track, monitor, and control processes. They are used in commands like "kill" to terminate specific processes and in system logs for process identification.

Q34. Explain the purpose of the "df" command in Unix and how it is used to check disk space usage.

The "df" command in Unix is used to display information about disk space usage on mounted file systems. It provides details such as total disk space, used space, available space, and the percentage of space used. It helps users and administrators monitor the disk space of file systems and partitions.

Q35. What is a Unix shell prompt, and why is it important for user interaction?

This is one of the important interview questions on Unix for experienced individuals. A Unix shell prompt is a text or symbol displayed by the Unix shell to indicate that it is ready to accept commands from the user.

It typically includes information such as the user's name, hostname, current directory, and a delimiter (often "$" for regular users and "#" for the superuser). The prompt is essential for providing feedback to users and facilitating command entry and execution.

Q36. How can you terminate a running process in Unix using the "kill" command, and what are the common signals used?

The "kill" command in Unix is used to terminate a running process by sending it a signal. Common signals include:

SIGTERM (15): Terminate gracefully.

SIGKILL (9): Forceful termination.

SIGHUP (1): Hang up or restart the process.

To terminate a process with a specific PID, you would use the command: kill -SIGNAL PID.

Q37. What is the purpose of the "history" command in Unix, and how can it be used to review command history?

The "history" command in Unix is used to display a list of previously executed commands in the current session. It helps users review their command history, recall and repeat commands, and track their command usage. Users can also use command-line shortcuts, such as "!n" (where "n" is the command number), to rerun specific commands from history.

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Q38. What is the significance of the Unix "umask" value, and how does it affect file permissions?

This is one of the advanced Unix interview questions. The Unix "umask" value is a set of octal permissions that are subtracted from the default permissions when creating new files and directories. It determines which permissions are removed by default.

For example, a "umask" 022 would remove and write permissions for the group and others when creating new files. It is essential for controlling default file permissions and enhancing security.

Q39. Explain the purpose of the "tee" command in Unix and how it can be used for data redirection.

The "tee" command in Unix is used to read from standard input and write to standard output and one or more files simultaneously. It is often used to capture and display command output while saving it to a file for later analysis.

For example, to capture the output of a command named "mycommand" and save it to a file named "output.txt," you would use the command: mycommand | tee output.txt.

Q40. What is the purpose of the "at" command in Unix, and how is it used for scheduling one-time tasks?

This type of Unix interview questions is most asked during the interview. The "at" command in Unix is used to schedule one-time tasks to run at a specific time in the future.

Users can specify the exact time and date when a command or script should be executed. For example, to schedule a command to run at 3:30 PM, you would use the command: at 3:30 PM.

Q41. Explain the role of the "/etc/fstab" file in Unix and its significance in system booting.

The "/etc/fstab" (file system table) file in Unix serves as a pivotal configuration tool for file systems and disk partitions. This file meticulously outlines the specifics of how file systems are to be mounted during the system boot sequence.

It provides essential information such as mount points, device names, file system types, and associated options, facilitating the automated and seamless mounting of file systems as the system initializes, thus ensuring the system's smooth and efficient startup.

Q42. What is the purpose of the "grep" command with the "-i" option in Unix, and how does it differ from the regular "grep" command?

This is one of the must-know linux unix interview questions to prepare for. The "grep" command with the "-i" option in Unix is used to perform case-insensitive searches for text patterns in files.

It treats uppercase and lowercase characters as equivalent, making it useful for searches that need to match regardless of case. Unlike the regular "grep" command, which performs case-sensitive searches, "-i" makes the search case-insensitive.

Q43. What is the "sudoers" file in Unix, and how is it used to manage user privileges?

The "sudoers" file in Unix is a configuration file that defines which users or groups are allowed to execute commands with elevated privileges using the "sudo" command. It specifies the rules and permissions for privilege escalation. System administrators use the "sudoers" file to control who can perform administrative tasks and which commands they can run.

Q44. Explain the purpose of the "cut" command in Unix, and provide an example of how it can be used to extract specific fields from a text file.

The "cut" command in Unix is used to extract specific columns or fields from lines of text files. It is often used in conjunction with other commands like "echo," "cat," or "paste" to manipulate text data.

For example, to extract the second and third fields from a file named "data.txt" delimited by spaces, you would use the command: cut -d' ' -f2,3 data.txt.

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Q45. What is a Unix shell function, and how is it defined and used in shell scripting?

This is one of the important Unix interview questions and answers you must practice. A Unix shell function is a reusable block of code or a sequence of commands defined within a shell script or directly in the shell environment.

Functions are used to encapsulate logic, perform specific tasks, and make scripts more modular and readable. They can be defined using the "function" keyword or simply as a set of commands within parentheses.

Q46. What is the purpose of the "cron.d" directory in Unix, and how does it differ from the regular "cron" jobs?

The "cron.d" directory in Unix is a system directory that allows system administrators to place cron job configuration files for scheduled tasks. It differs from regular "cron" jobs, which are typically configured in the user's or system's "crontab" files.

The "cron.d" directory provides a more organised and centralised way to manage cron jobs, making it easier to maintain and track scheduled tasks.

Q47. How can you display the last few lines of a text file in Unix using the "tail" command?

The "tail" command in Unix is used to display the last few lines of a text file. By default, it shows the last 10 lines of the file. For example, to display the last 20 lines of a file named "logfile.txt," you can use the command: tail -n 20 logfile.txt.

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Q48. Explain the purpose of the "rsync" command in Unix, and how is it used for file synchronisation and backup.

This is one of the important Linux Unix interview questions. The "rsync" command in Unix is used for efficient file synchronisation and backup between local and remote systems.

It allows users to copy files and directories while minimising data transfer by only copying the differences between source and destination. It is often used for remote backups and mirroring data between systems.

Q49. What is a Unix shell variable scope, and how does it affect the visibility of variables within scripts?

In Unix, understanding the concept of variable scope is fundamental to effectively managing the visibility of variables within scripts. Variable scope dictates where a particular variable is accessible and where it isn't. Here's how variable scope works in Unix:

Local Scope: Variables defined within a specific function or script are said to have a local scope. This means that these variables are only accessible within the context of the function or script in which they are defined. They are isolated from the outside world and are, therefore, invisible to other parts of the script or the global scope.

This is essential for encapsulating data or values that are only relevant to a particular function or script and preventing unintended interference with other variables or scripts.

Global Scope: Variables defined outside of any function or script, often at the top of your script or in your shell environment, have global scope. Global variables are accessible and modifiable from anywhere within the script or session. They are shared across all functions and scripts running in that session.

Variable scope plays a pivotal role in ensuring code modularity, preventing variable naming clashes, and improving script readability and maintainability.

By using local scope for variables that are specific to a certain function or script and global scope for those that need to be accessed globally, you can structure your code more logically and reduce the risk of unintended side effects or errors.

Q50. How can you use the "cut" command in Unix to extract a specific range of characters from each line of a text file?

This can be one of the important Unix scenario-based interview questions. The "cut" command in Unix can be used to extract a specific range of characters from each line of a text file by specifying the starting and ending character positions using the "-c" option.

For example, to extract characters 5 to 10 from each line of a file named "textfile.txt," you can use the command: cut -c5-10 textfile.txt.

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Conclusion

It is important to note that Unix interview questions can be challenging, but with adequate preparation and practice, you can ace the interview. Remember to research the company and job position beforehand and tailor your answers accordingly.

Avoid common mistakes such as being unprepared or giving incomplete answers. Instead, demonstrate your knowledge of Unix concepts and show how you can apply them in real-world scenarios.

By following these tips for answering top Unix interview questions and preparing effectively for the interview process, you will be well on your way towards landing that dream job in a Unix-related field.