Unix Operating System Commands For Interview With Examples

This guide explains UNIX commands with real-life examples, Unix Operating System Commands covering file management, system monitoring, permissions, pipes, SSH access, and interview essentials. It also includes a clear UNIX vs Linux comparison, Installation process.

UNIX examples

Practical examples categorized by use case:

File Searching and Discovery

Finding a specific file or piece of information in a sea of data.

• Scenario: You need to find all PDF files in your “Documents” folder.
  • Command: find ~/Documents -name "*.pdf"
• Scenario: You want to find every line in a file that contains the word “Error” regardless of capitalization.
  • Command: grep -i "error" server.log
• Scenario: You want to see the top 10 largest files in a directory.
  • Command: du -ah | sort -rh | head -n 10

Monitoring System Health

Checking if your computer is “breathing” correctly.

• Scenario: Checking how much RAM is being used right now.
  • Command: free -m (on Linux) or top (on all Unix).
• Scenario: Finding a “frozen” application to close it.
  • Command: ps -ef | grep "Chrome" (This gives you the Process ID or PID).
• Scenario: Checking if a website or server is reachable.
  • Command: ping google.com

Permission Management

UNIX uses a numeric or symbolic system to control who can touch what.

• Scenario: Making a script “executable” so you can run it as a program.
  • Command: chmod +x myscript.sh
• Scenario: Restricting a file so only you can read it, and no one else can even see it.
  • Command: chmod 600 private_notes.txt

Also read about Unix Operating System: Features, Benefits, Drawbacks & Types

The “Magic” of Pipes (|)

Piping allows the output of one command to become the input for another.

• Scenario: You have a long list of names in a file. you want to sort them alphabetically, remove duplicates, and save the result to a new file.
  • Command: cat names.txt | sort | uniq > clean_names.txt
• Scenario: You want to count how many files are in your current folder.
  • Command: ls -l | wc -l

Remote Access (SSH)

Unix is the king of remote management.

• Scenario: Logging into a server located in a different country to run commands.
  • Command: ssh username@192.168.1.10

Common Symbols

Symbol	Meaning	Example
>	Overwrite a file with output	ls > files.txt
>>	Append output to the end of a file	date >> log.txt
**`	`**	Send output to another command
*	Wildcard (matches everything)	rm *.tmp (removes all .tmp files)
..	The parent directory (one level up)	cd ..

Unix Operating System Commands

UNIX commands are short, case-sensitive, and designed to be combined.

Command	Purpose	Example
ls	List files in the current directory	ls -l (lists with details)
cd	Change directory	cd /home/user/Documents
pwd	Print Working Directory (Where am I?)	pwd
mkdir	Create a new folder	mkdir MyProject
rm	Remove/Delete a file	rm old_file.txt
cp	Copy a file or folder	cp file.txt backup.txt
mv	Move or Rename a file	mv old.txt new.txt
grep	Search for text within a file	grep "error" log.txt
chmod	Change file permissions	chmod 755 script.sh
man	Manual (Help for any command)	man grep

Also read about Linux File System Structure Explained: Root And Directories

Unix commands with examples

Every command follows a specific structure:

Example: ls -a /etc

• ls: The action (list).
• -a: The option (show all files, including hidden ones).
• /etc: The argument (look in the “etc” folder).

Installation Process

Although each system is slightly different, installing a UNIX-based operating system (such as Ubuntu) generally goes like this:

Step 1: Create Bootable Media

Use a program like Rufus or Etcher to “burn” the ISO file (image file) onto a USB flash drive after downloading it.

Step 2: Boot from USB

After restarting your computer, use F2, F12, or Del to access the BIOS/UEFI menu. To make the USB drive start first, change the boot order.

Step 3: Disk partitioning

The most important step is this one. You have to choose:

• Erase Disk: Installs UNIX and removes everything.
• Dual Boot: Installs both Windows and UNIX so you can select one at startup.

Step 4: Configuring the User

Create your primary user account and set your Root (Administrator) password. These passwords are essential to UNIX security.

Step 5: Following the Installation

After you’re done, disconnect the USB and restart. Open the terminal and run an update command: sudo apt update && sudo apt upgrade (for Ubuntu/Debian).

Unix operating system commands for interview

File and Directory Commands

Command	Purpose	Example
ls	List files and folders	ls -l
pwd	Show current directory	pwd
cd	Change directory	cd /home/user
mkdir	Create directory	mkdir test
rmdir	Delete empty directory	rmdir test
cp	Copy files	cp file1 file2
mv	Move/rename files	mv old.txt new.txt
rm	Delete files	rm file.txt
touch	Create empty file	touch demo.txt
tree	Show directory structure	tree /home

Also read about What Is A Shell Script In Linux? How It Works And Examples

File Viewing Commands

Command	Purpose
cat	Display file content
less	Scrollable file view
more	Page-by-page view
head	First 10 lines
tail	Last 10 lines
wc	Word/line count

Example:

bash

-n 20 log.txt

File Permissions & Ownership

Command	Purpose
chmod	Change permissions
chown	Change owner
chgrp	Change group

Example:

bash

chmod 755 script.sh

User & Process Management

Command	Purpose
who	Logged-in users
whoami	Current user
ps	Running processes
top	Live system processes
kill	Stop process
nice	Set priority

Example:

bash

kill -9 1234

Disk & System Information

Command	Purpose
df	Disk usage
du	Folder size
free	Memory usage
uptime	System running time
uname	System info
hostname	Machine name

Example:

bash

df -h

Also read about What Is Btrfs File System In Linux? And Btrfs Vs Ext4 Vs XFS

Networking Commands

Command	Purpose
ping	Check connectivity
ifconfig	Network config
netstat	Network status
ssh	Remote login
scp	Copy via network

Example:

bash

ssh user@192.168.1.1

Search & Text Processing

Command	Purpose
grep	Search text
find	Search files
sort	Sort data
uniq	Remove duplicates
cut	Extract columns
awk	Text processing
sed	Stream editor

Example:

bash

grep "error" log.txt

Compression & Archiving

Command	Purpose
tar	Archive files
gzip	Compress
gunzip	Decompress
zip	Zip files
unzip	Extract zip

Example:

bash

tar -cvf backup.tar folder/

Package & Software Commands

Command	Purpose
pkgadd	Install software
pkgrm	Remove software
pkginfo	Package info

Important Interview Concepts

Pipes and Redirection

bash

ls | grep txt

Input/Output

bash

command > output.txt
command < input.txt

Background Jobs

bash

command &

Most Asked Unix Interview Questions

Q1. Difference between rm and rmdir?

• rm deletes files
• rmdir deletes empty directories only

Q2. What is a pipe?

It sends output of one command to another.

Q3. What does chmod 777 mean?

Full permission to everyone (read, write, execute)

Q4. What is cron?

Scheduler for automatic tasks.

Also read about What Is Linux Kernel? Why It Is Important And Its Components

Top 10 Commands

1. ls
2. cd
3. pwd
4. ps
5. top
6. grep
7. find
8. chmod
9. tar
10. kill

UNIX vs Linux

Feature	UNIX	Linux
Definition	A family of proprietary operating systems originally developed at Bell Labs	An open-source UNIX-like operating system created by Linus Torvalds
Source Code	Mostly closed source and controlled by vendors	Completely open source and freely available
Cost	Usually paid and requires licenses	Free to use, modify, and distribute
Ownership	Owned by companies like Oracle (Solaris), IBM (AIX), HP (HP-UX)	Community-driven with contributions from individuals and companies
Development	Developed and maintained by specific vendors	Developed by a global open-source community
Customization	Limited customization options	Highly customizable
Hardware Support	Runs on specific certified hardware	Runs on almost any hardware
Security	Very secure and stable	Very secure with frequent updates
Stability	Extremely stable, used in enterprise systems	Very stable, widely used in servers
User Interface	Traditionally command-line focused	Both command-line and graphical desktops
Popularity	Less common today	Most popular server OS worldwide
Learning Curve	Steeper, requires professional training	Easier, large learning resources
Software Availability	Limited to vendor-supported software	Huge software repositories
Examples	Solaris, AIX, HP-UX, macOS	Ubuntu, Debian, Fedora, Red Hat, Linux Mint
Certification	Officially certified UNIX systems	Not officially UNIX, but UNIX-like
Updates	Controlled by vendor	Frequent community updates
Cloud Usage	Limited	Dominates cloud and container platforms
Community Support	Smaller, vendor-based	Massive global community