Linux Tips For Normal Users

By Gurjot Singh Saini , 07 Aug 2022

Linux Basics & Daily Usage – Beginner Friendly

This module builds a strong foundation for first-time Linux users. You will understand what Linux is, how it differs from Windows/macOS, and how to use Linux comfortably in daily life.

1.1 What Is Linux? History, Philosophy & Use Cases

Linux is a free and open-source operating system built around the Linux kernel.

Unlike Windows, Linux is community-driven, highly customizable, and used everywhere — from laptops and servers to Android phones and supercomputers.

💡 Linux is not a single OS — it comes in many distributions.

1.2 Linux vs Windows vs macOS (Real Differences)

Feature	Linux	Windows	macOS
Cost	Free	Paid	Included with Apple devices
Customization	Very High	Limited	Moderate
Security	Very Strong	Target of most malware	Strong

✅ Linux gives you control. Windows gives convenience.

1.3 Linux Distributions Explained (Ubuntu, Fedora, Mint)

Ubuntu: Beginner-friendly, large community
Linux Mint: Windows-like feel
Fedora: Modern and developer-focused

💡 A Linux distribution = Linux kernel + desktop + software.

1.4 Desktop Environment vs Window Manager

A Desktop Environment provides a complete visual experience (menus, settings, file manager), while a Window Manager only controls window behavior.

⚠️ Beginners should start with Desktop Environments like GNOME or Cinnamon.

1.5 Linux File System Basics (/home, /etc, /var)

/home – Your personal files
/etc – System configuration
/var – Logs and system data

✅ Linux uses a single unified file system — no C: or D: drives.

1.6 User Files, Hidden Files & Configuration Files

Files starting with a dot (.config, .bashrc) are hidden files used for settings.

💡 Press Ctrl + H to show hidden files.

1.7 Everyday Linux Usage for Normal Users

Web browsing & media
Office work
Software installation via app store
Updates without restarting constantly

🚀 Linux is stable, fast, and perfect for daily use.

Module 04 : Terminal & Command Line (Beginner)

This module introduces the Linux terminal - the powerful command-line interface that gives you complete control over your system. Learn essential commands, shortcuts, and best practices to become productive in the terminal.

4.1 What Is Terminal & Why Linux Uses It

The Terminal (also called console or command line) is a text-based interface to control your computer.

Unlike graphical interfaces, the terminal gives you direct access to the system, allowing you to perform complex tasks quickly with just a few keystrokes.

🎯 Why Terminal is Powerful:

Speed: Faster than clicking through menus
Automation: Script repetitive tasks
Power: Access advanced system features
Remote Access: Control servers over SSH
Consistency: Same commands work across different Linux systems

💡 Quick Tip: Open terminal with Ctrl + Alt + T (in most Linux distributions)

✅ Don't be intimidated! Terminal is just another way to talk to your computer - like learning a new language.

4.2 Understanding Shells (bash, zsh)

A Shell is the program that interprets your commands in the terminal. It's your interface to the operating system.

🐚 Common Shell Types:

Shell	Description	Best For	Default Color
bash	Bourne Again SHell - Most common, default on most systems	Beginners & compatibility	Blue prompt
zsh	Z Shell - Feature-rich with autocomplete & themes	Power users & customization	Green prompt
fish	Friendly Interactive SHell - User-friendly with syntax highlighting	Those who want modern features	Yellow prompt

🔍 How to Check Your Current Shell:

            # Check which shell you're using

            echo $SHELL

            # Output example: /bin/bash

            # See all available shells on your system

            cat /etc/shells

⚠️ Beginner Recommendation: Start with bash - it's everywhere and has the most learning resources.

💡 Pro Tip: Your shell prompt (e.g., user@computer:~$) shows your username, computer name, and current directory.

4.3 Basic Commands (ls, cd, pwd, clear)

These four commands are the foundation of Linux navigation. Master these, and you can explore anywhere!

🚀 The Essential Four:

Command	What It Does	Basic Usage	Common Options
`pwd`	Print Working Directory - Shows where you are	`pwd`	(no options)
`ls`	List files and directories	`ls`	`-l` (details), `-a` (all), `-h` (human readable)
`cd`	Change Directory - Move to different folder	`cd folder_name`	`cd ..` (go up), `cd ~` (go home)
`clear`	Clear screen - Makes terminal empty	`clear`	`Ctrl + L` (keyboard shortcut)

🎮 Hands-On Practice:

            # 1. See where you are

            pwd

            # Output: /home/your_username

            # 2. List files in current directory

            ls

            ls -la  # List all files with details

            # 3. Navigate to Documents folder

            cd Documents

            pwd  # Now shows: /home/your_username/Documents

            # 4. Go back home

            cd ~

            # OR simply: cd

            # 5. Clean up the screen

            clear

✅ Success Tip: Type these commands yourself! Muscle memory is key to learning terminal.

💡 Remember: Linux is case-sensitive! Documents ≠ documents ≠ DOCUMENTS

4.4 Working with Files & Directories

Now that you can navigate, let's learn how to create and organize your files and folders.

📁 File & Directory Management Commands:

Command	Purpose	Example	What Happens
`mkdir`	Make Directory (create folder)	`mkdir my_folder`	Creates "my_folder"
`touch`	Create empty file	`touch file.txt`	Creates "file.txt" (0 bytes)
`cat`	View file contents	`cat file.txt`	Shows file content
`nano`	Simple text editor	`nano notes.txt`	Opens editor to create/edit
`rmdir`	Remove empty directory	`rmdir empty_folder`	Deletes empty folder

🛠️ Practical Example - Organize Your Files:

            # Create a project structure

            mkdir my_project

            cd my_project

            # Create subfolders

            mkdir docs images code

            ls  # Shows: docs  images  code

            # Create files

            touch README.txt

            cd docs

            touch notes.txt

            # Add content to a file

            echo "Project started on $(date)" > notes.txt

            cat notes.txt  # View the content

            # Edit with nano

            nano notes.txt

            # Add more text, then Ctrl+X to save and exit

📝 Nano Editor Basics:

Nano Cheat Sheet:
• Ctrl + O : Save file
• Ctrl + X : Exit Nano
• Ctrl + K : Cut line
• Ctrl + U : Paste line
• Ctrl + W : Search
• Ctrl + \ : Replace
All shortcuts shown at bottom of screen

✅ Good Practice: Use meaningful names (avoid spaces - use underscores or hyphens instead)

4.5 Copy, Move & Delete Safely

These commands manipulate files. Be careful with delete - there's no "Recycle Bin" in terminal!

⚠️ Safety First - The Dangerous Commands:

Command	Purpose	Safe Version	Danger Level
`cp`	Copy files/directories	`cp -i file1 file2`	Low
`mv`	Move or rename files	`mv -i old new`	Medium
`rm`	Remove (delete) files	`rm -i file.txt`	HIGH
`rm -rf /`	NEVER USE THIS!	Just don't	SUICIDE

🔧 Safe Operations with Examples:

            # COPYING FILES

            cp file.txt file_backup.txt          # Basic copy

            cp -i file.txt file_backup.txt       # Ask before overwriting

            cp -r folder/ backup/                # Copy folder recursively

            # MOVING/RENAMING

            mv file.txt new_name.txt             # Rename file

            mv file.txt Documents/               # Move to folder

            mv -i old.txt new.txt                # Ask before overwrite

            # DELETING (BE CAREFUL!)

            rm file.txt                          # Delete single file

            rm -i important.txt                  # ASK before deleting

            rm -r old_folder/                    # Delete folder with contents

            rmdir empty_folder/                  # Delete ONLY if empty

🛡️ Safety Aliases (Add to ~/.bashrc):

            # Make commands ask before doing dangerous things

            alias cp='cp -i'     # Ask before overwriting copy

            alias mv='mv -i'     # Ask before overwriting move

            alias rm='rm -i'     # ASK before deleting anything

            # Prevent accidental deletion of system files

            alias rm='rm -I --preserve-root'

⚠️ CRITICAL WARNING: Never run rm -rf / or rm -rf /* - it will delete EVERYTHING on your system!

💡 Recovery Tip: If you accidentally delete something, check if it's in ~/.local/share/Trash (GUI deletions) or use file recovery tools immediately.

4.6 Command History, Autocomplete & Shortcuts

These productivity features will make you 10x faster in the terminal. Learn them early!

📜 Command History - Your Time Machine:

            # View command history

            history                    # Shows all commands you've typed

            history 10                 # Show last 10 commands

            !45                        # Run command #45 from history

            !!                         # Run last command again

            !ls                        # Run last 'ls' command

            Ctrl + R                   # Search history (reverse-i-search)

            # Type to search, press Enter to run, Ctrl+C to cancel

🚀 Tab Autocomplete - Your Best Friend:

Tab Key Magic:
• Type cd Docu then press Tab → completes to cd Documents/
• Press Tab twice → shows all possible completions
• Works for commands, files, folders, and options!

⌨️ Essential Keyboard Shortcuts:

Shortcut	Action	Why It's Useful
`Tab`	Auto-complete	Saves typing, prevents typos
`Ctrl + A`	Move cursor to beginning	Quick edit long commands
`Ctrl + E`	Move cursor to end	Add arguments quickly
`Ctrl + U`	Cut to beginning	Clear current command
`Ctrl + K`	Cut to end	Remove rest of line
`Ctrl + Y`	Paste cut text	Undo Ctrl+U/K cuts
`Ctrl + R`	Search history	Find old commands fast
`Ctrl + C`	Cancel/stop command	Stop running programs
`Ctrl + D`	Exit shell/logout	Close terminal session
`Ctrl + L`	Clear screen	Better than typing 'clear'
`↑ / ↓`	Navigate history	Cycle through past commands

💡 Pro Tip: Use Ctrl + R to find commands. Type a few letters of what you remember, and it will search your history.

🎮 Practice Exercise:

            # 1. Type this long command:

            echo "Hello this is a long command to practice shortcuts"

            # 2. Press Ctrl+A to go to beginning

            # 3. Press Ctrl+K to cut everything

            # 4. Type: ls -la

            # 5. Press Ctrl+Y to paste back the echo command

            # 6. Press Ctrl+C to cancel

            # Practice tab completion:

            cd /usr/share/  # Then press Tab multiple times

            ls /e  # Press Tab → completes to /etc/

✅ Mastery Goal: Use Tab for everything! It's the single biggest productivity boost in terminal.

4.7 Linux Aliases - Custom Command Shortcuts

Aliases are your personal command shortcuts - create custom names for frequently used commands!

🎯 Why Create Aliases?

Save Time: Shorten ls -la to just ll
Reduce Errors: Avoid typos in complex commands
Create Workflows: Chain multiple commands together
Personalize: Build your own command language

🔧 Creating Aliases:

            # Temporary alias (lasts only this session)

            alias ll='ls -la'

            ll  # Now works as ls -la!

            # Permanent alias (add to ~/.bashrc)

            nano ~/.bashrc

            # Add at bottom:

            alias ll='ls -la'

            alias update='sudo apt update && sudo apt upgrade'

            alias cl='clear'

            alias ..='cd ..'

            # Save (Ctrl+X, Y, Enter) then reload: source ~/.bashrc

🌟 Useful Beginner Aliases:

            # Navigation

            alias home='cd ~'

            alias ..='cd ..'

            alias ...='cd ../..'

            alias ....='cd ../../..'

            # Listing

            alias l='ls -CF'

            alias la='ls -A'

            alias ll='ls -la'

            alias lh='ls -lh'

            # Safety first!

            alias rm='rm -i'     # Ask before deleting

            alias cp='cp -i'     # Ask before overwriting

            alias mv='mv -i'     # Ask before moving

            # System info

            alias cpu='top -o %CPU'

            alias mem='top -o %MEM'

            alias disk='df -h'

            alias space='du -sh * | sort -h'

🛠️ Managing Your Aliases:

            # List all current aliases

            alias

            # OR: alias -p

            # Check specific alias

            type ll

            # Output: ll is aliased to `ls -la`

            # Remove an alias

            unalias ll

            # Create separate alias file (recommended)

            nano ~/.bash_aliases

            # Add all aliases here, then add this to ~/.bashrc:

            if [ -f ~/.bash_aliases ]; then

                . ~/.bash_aliases

            fi

🎮 Hands-On Exercise:

            # 1. Create a test alias

            alias greet='echo "Hello from your alias!"'

            greet  # Should show greeting

            # 2. Create update shortcut

            alias update-system='sudo apt update && sudo apt upgrade -y'

            # 3. Make it permanent

            echo 'alias ll="ls -la"' >> ~/.bashrc

            echo 'alias update="sudo apt update && sudo apt upgrade -y"' >> ~/.bashrc

            source ~/.bashrc  # Reload

            # 4. Test your new powers!

            ll ~/Documents

            # (Might need sudo for update if not Ubuntu/Debian)

✅ Alias Progression: Start with 2-3 aliases, add more as you discover commands you use frequently.

⚠️ Common Mistake: Aliases are user-specific. If you create a new user account, you need to set up aliases again.

4.8 Common Beginner Terminal Mistakes

Everyone makes mistakes when learning terminal. Here's how to avoid (and recover from) the most common ones.

🚫 Top 10 Terminal Mistakes & Solutions:

Mistake	Why It Happens	How to Avoid	How to Fix
`rm -rf /`	Thinking it will "remove folder root"	NEVER type this. Use aliases for safety	Too late. Reinstall OS.
Wrong case: `Documents` vs `documents`	Linux is case-sensitive	Use `Tab` to autocomplete	Check spelling and case
Spaces in file names without quotes	`touch my file.txt` creates TWO files	Use underscores: `my_file.txt`	Use quotes: `touch "my file.txt"`
Forgetting `sudo`	Need admin rights for system changes	Error will tell you "Permission denied"	Add `sudo` before command
Using wrong slash: `\` vs `/`	Windows uses backslash, Linux uses forward	Linux always uses `/`	Replace `\` with `/`
Command not found	Typo or package not installed	Use `Tab`, check spelling	Install package: `sudo apt install package_name`
Accidental `Ctrl + D`	Meant to cancel but exited terminal	Use `Ctrl + C` to cancel	Just reopen terminal
Forgetting to `cd` into folder	Running command in wrong directory	Always check with `pwd` first	`cd` to correct folder
Missing arguments	`rm` needs file name	Read error messages carefully	Add required arguments
Running command as wrong user	Need `sudo` or different user	Check who you are: `whoami`	Use `sudo` or switch user

🔧 Recovery Techniques:

                                 # 1. Stuck in a program?

                                 Press: Ctrl + C          # Cancel current command

                                 Press: Ctrl + Z          # Pause program (bg/fg to manage)

                                 Press: Ctrl + D          # Send EOF (may exit)

                                 # 2. Typed wrong command?

                                 Press: Ctrl + C          # Stop it immediately

                                 Use: history             # Find correct command

                                 Use: !!                  # Rerun last command

                                 # 3. Deleted wrong file?

                                 # Check trash: ls ~/.local/share/Trash/files/

                                 # Use recovery tools immediately (testdisk, photorec)

                                 # 4. Lost in filesystem?

                                 pwd                      # Where am I?

                                 cd ~                     # Go home

                                 cd /                     # Go to root

                                 cd -                     # Go to previous directory

🛡️ Preventive Safety Measures:

                                 # 1. Create safety aliases in ~/.bashrc

                                 alias rm='rm -i'          # Ask before delete

                                 alias cp='cp -i'          # Ask before overwrite

                                 alias mv='mv -i'          # Ask before move

                                 # 2. Backup important files regularly

                                 cp important.txt important.txt.backup

                                 # OR use version control: git init

                                 # 3. Test commands with echo first

                                 echo rm *.txt            # Shows what WOULD be deleted

                                 # Then remove 'echo' to actually run

                                 # 4. Use dry-run options when available

                                 rsync -nav source/ destination/  # -n = dry run

🎮 Practice - Making (Safe) Mistakes:

                                 # Create a safe practice area

                                 mkdir ~/terminal_practice

                                 cd ~/terminal_practice

                                 touch file1.txt file2.txt file3.txt

                                 # Practice common scenarios

                                 # 1. Case sensitivity

                                 ls FILE1.TXT             # Fails - wrong case

                                 ls file1.txt             # Works

                                 # 2. Spaces in names

                                 touch "my document.txt"   # Use quotes

                                 ls my\ document.txt       # OR use backslash

                                 # 3. Permission errors

                                 mkdir /system_folder      # Fails - need sudo

                                 sudo mkdir /system_folder # Works with sudo

                                 # 4. Tab completion

                                 ls f                 # Completes to file

                                 ls fi           # Shows all matches

                                 # Clean up

                                 cd ~

                                 rm -r terminal_practice/

✅ Golden Rule: If you're about to run a command with rm, format, or dd - STOP. Double-check everything.

💡 Learning Mindset: Every expert was once a beginner who made mistakes. The key is to make them in a safe environment and learn from them!

Internet, Browsers & Networking – Connectivity Mastery

This module covers everything about staying connected on Linux. You'll learn how to manage browsers, fix network issues, use Bluetooth devices, and secure your connection with firewalls and VPNs.

6.1 Browsers on Linux (Firefox, Chrome)

Linux supports all major browsers. Firefox is usually pre-installed and optimized for Linux, while Google Chrome and Chromium are available for download.

Firefox: Default on most distributions, privacy-focused
Chrome: Available as .deb or .rpm package
Chromium: Open-source version of Chrome
Brave: Privacy browser with built-in ad blocking

💡 Firefox on Linux supports hardware acceleration and Wayland for better performance.

6.2 Network Manager Explained

NetworkManager is the default networking service on most Linux distributions. It manages Wi-Fi, Ethernet, VPN, and mobile broadband connections through both GUI and CLI.

Tool	Purpose	How to Access
nm-applet	System tray network icon	Click system tray icon
nmtui	Text-based UI for terminal	Run `nmtui` in terminal
nmcli	Command-line interface	Run `nmcli` commands

✅ Use nmtui when GUI isn't working – it's a lifesaver!

6.3 Wi-Fi & Ethernet Troubleshooting

Network issues are common but usually easy to fix. Follow this troubleshooting checklist:

Check if Wi-Fi is enabled: Look for airplane mode or hardware switch
Verify driver installation: Run lspci -k | grep -A 2 -i network
Restart NetworkManager: sudo systemctl restart NetworkManager
Check connection details: ip addr show or ifconfig
Test DNS: ping 8.8.8.8 (if this works but websites don't, it's DNS)

⚠️ Some Wi-Fi cards need proprietary drivers. Use "Additional Drivers" tool on Ubuntu.

6.4 Bluetooth Setup & Troubleshooting

Linux has excellent Bluetooth support for headphones, speakers, mice, and keyboards. Most distributions include Bluez (the standard Bluetooth stack).

Quick Setup:

Ensure Bluetooth is enabled: Click system tray icon or check settings
Put your device in pairing mode
Search for devices and connect

Complete Bluetooth Installation & Setup:

Task	Command	Purpose
Install Bluetooth stack	`sudo apt install bluez*`	Install all Bluez packages
Install Bluetooth manager	`sudo apt install blueman`	GUI tool for Bluetooth management
Enable Bluetooth service	`sudo systemctl enable bluetooth.service`	Start Bluetooth on boot
Start Bluetooth service	`sudo systemctl start bluetooth.service`	Start Bluetooth immediately
Check service status	`sudo systemctl status bluetooth.service`	Verify Bluetooth is running

Common Issues & Fixes:

Problem	Solution	Description
Bluetooth not showing in GUI	`sudo systemctl start bluetooth`	Start the Bluetooth service
Device not found	`bluetoothctl` then `scan on`	Use command-line tool to search
Audio quality poor	`sudo apt install pulseaudio-module-bluetooth` `pulseaudio -k`	Install Bluetooth audio support & restart PulseAudio
Connection drops frequently	`sudo btmgmt power off` `sudo hciconfig hci0 up`	Disable power saving & bring interface up
Missing Bluetooth packages	`sudo apt install aptitude` `sudo aptitude install bluetooth`	Use aptitude for better dependency handling
Bluetooth service won't start	`sudo /etc/init.d/bluetooth restart` `service bluetooth restart`	Alternative service restart commands
Bluetooth not enabled at boot	`sudo systemctl enable bluetooth` Check: `systemctl is-enabled bluetooth`	Ensure Bluetooth starts automatically

Step-by-Step Troubleshooting Guide:

Check if Bluetooth adapter is detected:

lsusb | grep -i bluetooth
hciconfig -a
bluetoothctl list

Enable and start the service:

sudo systemctl enable bluetooth
sudo systemctl start bluetooth
sudo systemctl status bluetooth

Install missing packages:

sudo apt update
sudo apt install bluez blueman bluez-tools
sudo apt install pulseaudio-module-bluetooth

Using bluetoothctl (command-line tool):

bluetoothctl          # Enter Bluetooth control
power on              # Turn Bluetooth on
agent on              # Enable agent
default-agent         # Set as default
scan on               # Start scanning (wait 30 sec)
devices               # List found devices
pair XX:XX:XX:XX:XX   # Pair with device MAC
connect XX:XX:XX:XX:XX # Connect to device
trust XX:XX:XX:XX:XX  # Trust device for auto-connect
exit                  # Exit bluetoothctl

💡 Pro Tip: If bluetoothctl shows "No default controller available", run:
sudo rmmod btusb then sudo modprobe btusb to reload Bluetooth drivers.

⚠️ Important: Some systems use different service management:

For SysV init: sudo service bluetooth restart
For systemd: sudo systemctl restart bluetooth
Check your init system: ps -p 1 -o comm=

✅ Quick Fix Checklist:

Install packages: sudo apt install bluez blueman
Enable service: sudo systemctl enable --now bluetooth
Check adapter: hciconfig -a
Restart if needed: sudo systemctl restart bluetooth

6.5 Checking Network Using Terminal

The terminal provides powerful tools for diagnosing network issues. Here are essential commands:

Command	What It Does	Example
`ping`	Test connection to a server	`ping google.com`
`ip addr`	Show network interfaces & IPs	`ip addr show`
`nslookup`	Check DNS resolution	`nslookup google.com`
`traceroute`	Trace network path to server	`traceroute google.com`
`ss` or `netstat`	Show active connections	`ss -tulpn`

✅ ip command replaces old ifconfig - learn it for modern systems.

6.6 Firewall Basics (UFW Explained)

UFW (Uncomplicated Firewall) is an easy-to-use firewall for Linux. It's a frontend for iptables that simplifies firewall management.

Basic UFW Commands:

sudo ufw enable                 # Turn on firewall
sudo ufw disable                # Turn off firewall
sudo ufw status                 # Check status
sudo ufw allow ssh              # Allow SSH (port 22)
sudo ufw allow 80/tcp           # Allow HTTP
sudo ufw deny from 192.168.1.10 # Block specific IP

Common Use Cases:

Allow web server: sudo ufw allow 80,443/tcp
Allow specific application: sudo ufw allow OpenSSH
Deny all incoming, allow all outgoing (default)
Rate limiting: sudo ufw limit ssh

⚠️ Don't enable UFW without allowing SSH first if you're connecting remotely!

6.7 VPN Usage & Privacy on Linux

Using a VPN on Linux is straightforward. Most VPN providers offer Linux apps, or you can use NetworkManager's built-in VPN support.

VPN Setup Methods:

Official VPN apps: Many providers have .deb/.rpm packages
NetworkManager integration: Import .ovpn files
Command line: Use openvpn or wireguard tools
Browser extensions: For browser-only VPN

Popular Linux VPN Clients:

OpenVPN: Standard protocol with GUI (network-manager-openvpn)
WireGuard: Modern, fast, simple configuration
NordVPN/ExpressVPN: Official Linux clients available

💡 WireGuard is built into Linux kernel 5.6+ for excellent performance.

Privacy Tips:

Use DNS over HTTPS in Firefox/Chrome
Consider using Tor Browser for maximum anonymity
Regularly check for DNS leaks: dnsleaktest.com
Disable unnecessary network services

✅ Linux + VPN = Excellent privacy combination with full control.

Essential Linux Commands – Complete Reference & Daily Usage

This module provides a comprehensive reference of essential Linux commands organized by category. Each command includes syntax, options, practical examples, and real-world use cases.

💡 How to use this module: Bookmark this page and return whenever you need to understand a specific command. Each section is self-contained with command details, common options, and beginner-friendly explanations.

⚠️ Important: Commands marked with ⚡ require sudo or root privileges. Always understand a command before running it, especially with sudo.

10.1 File System Navigation Commands

These commands help you move around and explore the Linux file system. Mastering navigation is the first step to terminal confidence.

📁 pwd – Print Working Directory

Purpose: Shows the full path of your current directory.

pwd # Output: /home/username/Documents

Real-world use: When you're lost in the terminal and need to know exactly where you are.

📋 ls – List Directory Contents

Purpose: Displays files and directories in the current location.

Option	Description	Example
`ls -l`	Long format (permissions, size, date)	`ls -l /home`
`ls -a`	Show hidden files (starting with .)	`ls -la`
`ls -h`	Human-readable sizes	`ls -lh`
`ls -t`	Sort by modification time	`ls -lt`
`ls -R`	Recursive (show subdirectories)	`ls -R /etc`

💡 Pro tip: ls -la is the most commonly used combination.

🔄 cd – Change Directory

Purpose: Move between directories.

`cd /path`	Go to specific directory	`cd /var/log`
`cd ~` or `cd`	Go to home directory	`cd ~`
`cd ..`	Go up one level	`cd ../..` (up two levels)
`cd -`	Go to previous directory	`cd -`

🌳 tree – Display Directory Structure

Purpose: Shows directories and files in a tree-like format.

tree tree -L 2 # Limit to 2 levels deep tree -a # Include hidden files

Install if missing: sudo apt install tree

📌 pushd / popd – Directory Stack

Purpose: Navigate between multiple directories efficiently.

pushd /var/log # Save current dir and move to /var/log pushd /etc # Save and move to /etc popd # Return to previous directory dirs # Show directory stack

10.2 File & Directory Management Commands

Create, copy, move, rename, and delete files and directories safely.

📄 touch – Create Empty File / Update Timestamp

touch file.txt # Create new empty file touch -t 202502111430 file.txt # Set specific timestamp touch file{1..5}.txt # Create file1.txt through file5.txt

📂 mkdir – Create Directories

mkdir newfolder mkdir -p parent/child/grandchild # Create nested directories mkdir dir_{1..3} # Create dir_1, dir_2, dir_3 mkdir -m 755 securedir # Create with specific permissions

🗑️ rm – Remove Files & Directories

⚠️ Warning: Deletion is permanent! No recycle bin in terminal.

Command	Description	Example
`rm file.txt`	Remove single file	`rm old.txt`
`rm -r folder`	Remove directory and contents	`rm -r downloads/`
`rm -f file`	Force remove (no confirmation)	`rm -f log.txt`
`rm -rf /path`	⚠️ Dangerous: force recursive delete	`rm -rf temp/`
`rm -i *.txt`	Interactive (ask before each)	`rm -i *.log`

📋 cp – Copy Files & Directories

`cp source dest`	Copy file	`cp file.txt backup.txt`
`cp -r dir1 dir2`	Copy directory recursively	`cp -r /etc /etc-backup`
`cp -i file dest`	Interactive (ask before overwrite)	`cp -i data.txt /backup/`
`cp -p file dest`	Preserve permissions & timestamps	`cp -p config.conf /etc/`
`cp -a source dest`	Archive mode (preserve all attributes)	`cp -a /home/user /backup/`

✂️ mv – Move / Rename

mv oldname.txt newname.txt # Rename file mv file.txt /path/to/destination/ # Move file mv -i source dest # Interactive (ask before overwrite) mv -u source dest # Update - move only when source is newer mv folder1 folder2 # Rename or move directory

🔗 ln – Create Links

Hard link vs Soft link (symlink):

ln file.txt hardlink.txt # Hard link (same inode) ln -s /original/file symlink # Soft/symbolic link (shortcut) ln -s /usr/bin/python3 python # Create alias for command

💡 Symlinks break if original file is moved; hard links don't.

10.3 File Viewing & Editing Commands

View file contents without opening full editors, or edit directly in terminal.

👁️ cat – Concatenate & Display

cat file.txt # Display entire file cat file1.txt file2.txt > combined.txt # Merge files cat > newfile.txt # Create file (Ctrl+D to save) cat -n code.py # Show with line numbers

📖 less / more – Page Through Files

less is more powerful than more (backwards navigation allowed).

less /var/log/syslog dmesg | less # Pipe output to less

Navigation: Space (next page), b (previous), g (top), G (bottom), / (search), q (quit)

🔍 head / tail – View Beginning/End of Files

`head file.txt`	Show first 10 lines	`head -n 20 file.txt` (20 lines)
`tail file.txt`	Show last 10 lines	`tail -n 50 file.txt` (50 lines)
`tail -f logfile.log`	Follow mode (live updates)	`tail -f /var/log/syslog`
`tail -f -n 100 app.log`	Follow with initial 100 lines	Debugging applications

✅ Real-world use: tail -f is essential for watching log files in real-time.

📝 nano – Simple Terminal Text Editor

Best for beginners - intuitive and easy to use.

nano file.txt # Open file nano -l file.txt # Show line numbers nano -B file.txt # Create backup (.bak)

Shortcuts: Ctrl+O (save), Ctrl+X (exit), Ctrl+W (search), Ctrl+K (cut line)

⚡ vim – Advanced Text Editor

Powerful but has learning curve. Modes: Normal, Insert, Visual, Command.

vim file.txt # Open file vim +20 file.txt # Open at line 20 vimdiff file1.txt file2.txt # Compare files

Essential vim commands: i (insert), :w (save), :q (quit), :wq (save & quit), u (undo)

📊 stat – Display File Status

stat file.txt # Output includes: Size, Permissions, Access/Modify/Change timestamps, Inode

Useful for: Checking when file was actually modified vs changed permissions.

🔢 nl – Number Lines

nl script.sh # Show with line numbers nl -b a file.txt # Number all lines (including blank)

10.4 File Permissions & Ownership Commands

Control who can read, write, and execute files. Essential for security and multi-user systems.

📚 Permission Basics: r=4 (read), w=2 (write), x=1 (execute)
User(owner) | Group | Others → Example: 755 = rwxr-xr-x

🔐 chmod – Change File Permissions

Numeric mode (octal):

chmod 755 script.sh # rwxr-xr-x (owner: all, group/others: read/execute) chmod 644 file.txt # rw-r--r-- (owner: read/write, others: read only) chmod 600 private.key # rw------- (owner only, for SSH keys) chmod 777 file ⚠️ Dangerous: read/write/execute for everyone

Symbolic mode:

chmod u+x script.sh # Add execute for user chmod g-w file.txt # Remove write for group chmod o+r file.txt # Add read for others chmod a+x script.sh # Add execute for all (ugo) chmod -R 755 directory/ # Recursive change

👑 chown – Change File Owner

⚡ Requires sudo privileges.

sudo chown username file.txt # Change owner sudo chown username:groupname file.txt # Change owner and group sudo chown :groupname file.txt # Change only group sudo chown -R username:group directory/ # Recursive

💡 Example: sudo chown www-data:www-data /var/www/html - Set web server ownership

👥 chgrp – Change Group Ownership

sudo chgrp developers project/ # Change group to 'developers' sudo chgrp -R staff /shared/ # Recursive group change

🎭 umask – Set Default Permissions

Purpose: Determines default permissions for new files/directories.

umask # Show current umask (usually 0022) umask 077 # New files: 600, directories: 700 (private) umask 022 # New files: 644, directories: 755 (default)

Calculation: File permissions = 666 - umask, Directory = 777 - umask

🔒 chattr – Change File Attributes (Advanced)

⚡ Root privileges required. Sets immutable/append-only flags.

sudo chattr +i important.conf # Make file immutable (can't be deleted/modified) sudo chattr -i important.conf # Remove immutable flag sudo chattr +a logfile.log # Append-only mode lsattr file.txt # List attributes

⚠️ Even root cannot modify an immutable file until the flag is removed.

10.5 Process Management Commands

Monitor, control, and terminate running programs and processes.

📊 ps – Process Status

Purpose: Snapshot of current processes.

`ps`	Processes in current shell	`ps`
`ps aux`	All processes (BSD syntax)	`ps aux \| grep firefox`
`ps -ef`	All processes (standard syntax)	`ps -ef --forest` (tree view)
`ps -u username`	Processes for specific user	`ps -u www-data`
`ps -C command`	Processes by command name	`ps -C apache2`

Common columns: PID (Process ID), %CPU, %MEM, VSZ, RSS, TTY, STAT, START, TIME, COMMAND

📈 top / htop – Interactive Process Viewer

top # Default process viewer htop # Enhanced, color-coded, easier to use top -u username # Show only user's processes top -p 1234,5678 # Monitor specific PIDs

top shortcuts: q (quit), k (kill process), u (filter by user), 1 (show CPU cores)

✅ htop is better - install with sudo apt install htop

🛑 kill / pkill – Terminate Processes

Signal	Number	Purpose	Example
SIGTERM	15	Graceful termination (default)	`kill 1234`
SIGKILL	9	Force kill (cannot be ignored)	`kill -9 1234`
SIGHUP	1	Hangup (reload config)	`kill -1 1234`
SIGSTOP	19	Pause process	`kill -19 1234`
SIGCONT	18	Continue paused process	`kill -18 1234`

pkill - kill by name:

pkill firefox # Kill all firefox processes pkill -f "python script.py" # Kill by full command line pkill -u username # Kill all processes of user

⚠️ Always try kill (SIGTERM) before kill -9 (SIGKILL).

⚖️ nice / renice – Process Priority

Priority range: -20 (highest) to 19 (lowest). Default: 0.

nice -n 10 ./backup-script.sh # Start with lower priority sudo renice -5 -p 1234 # Change priority of PID 1234 (higher) sudo renice +5 -u username # Lower priority for user's processes

💡 Use nice for CPU-intensive background tasks.

⬇️⬆️ bg / fg – Job Control

command & # Start process in background Ctrl+Z # Suspend foreground process bg # Resume suspended job in background fg # Bring background job to foreground jobs # List background jobs kill %1 # Kill job number 1

🔄 nohup – Run Immune to Hangups

Purpose: Continue running after terminal closes.

nohup long-script.sh & # Run in background, survives logout nohup python server.py > output.log 2>&1 & # With custom log file

Output goes to nohup.out by default.

🖥️ screen / tmux – Terminal Multiplexers

screen (pre-installed on most systems):

screen -S session_name # Start named session Ctrl+A, D # Detach from session screen -ls # List sessions screen -r session_name # Reattach to session

tmux (more modern): sudo apt install tmux

tmux new -s session_name Ctrl+B, D # Detach tmux attach -t session_name

✅ Essential for remote servers - your processes survive disconnection!

10.6 System Information Commands

Get details about your Linux system, kernel, hardware, and environment.

🖥️ uname – System Information

uname -a # All system information (kernel, hostname, arch) uname -r # Kernel release version uname -m # Machine hardware (x86_64, aarch64) uname -n # Network node hostname

Example output: Linux mypc 5.15.0-91-generic #101-Ubuntu SMP x86_64

🏷️ hostname – System Hostname

hostname # Show current hostname sudo hostname new-name # Temporarily change hostname hostname -I # Show IP addresses (capital i) hostnamectl # Detailed hostname info (systemd)

Permanent change: Edit /etc/hostname and /etc/hosts

⏰ uptime – System Running Time

uptime # 14:23:01 up 3 days, 2:15, 3 users, load average: 0.08, 0.12, 0.10

Shows: Current time, uptime, logged-in users, load averages (1, 5, 15 minutes)

👤 whoami / id – User Identity

whoami # Current username id # User ID, group ID, groups id username # Info about specific user groups # Show groups for current user

📅 date / cal – Date & Calendar

date # Current date/time date +"%Y-%m-%d %H:%M:%S" # Custom format sudo date -s "2025-02-11 15:30:00" # Set date (requires sudo) cal # Current month calendar cal 2025 # Full year calendar cal -3 # Previous, current, next month

🧮 bc – Command Line Calculator

echo "12 * 5" | bc # Basic arithmetic echo "scale=2; 10/3" | bc # Decimal precision bc -l # Start interactive mode with math library

📢 echo – Display Text

echo "Hello World" echo $HOME # Show variable value echo -e "Line1\nLine2" # Enable escape sequences echo -n "No newline" # Suppress trailing newline

🌍 env – Environment Variables

env # Show all environment variables export MYVAR="value" # Set environment variable unset MYVAR # Remove variable echo $PATH # Show executable search path

💡 Add to ~/.bashrc to make environment variables permanent.

🔄 which / whereis – Locate Commands

which python # Show path to executable which -a python # Show all matches in PATH whereis python # Show binary, source, man pages

10.7 User Management Commands

Create, modify, and delete users and groups. ⚡ All commands require sudo.

👤 useradd / adduser – Create Users

useradd (low-level):

sudo useradd username # Create user (basic) sudo useradd -m -s /bin/bash username # Create with home dir and shell sudo useradd -u 1500 -g groupname username # Specific UID and primary group

adduser (friendly, recommended):

sudo adduser username # Interactive, creates home, prompts for password

✏️ usermod – Modify Users

sudo usermod -aG sudo username # Add user to sudo group (Ubuntu) sudo usermod -aG docker username # Add to docker group sudo usermod -s /bin/zsh username # Change default shell sudo usermod -l newname oldname # Change username sudo usermod -L username # Lock user account sudo usermod -U username # Unlock user account

⚠️ Always use -aG (append) with groups, never -G alone (removes other groups).

🗑️ userdel – Delete Users

sudo userdel username # Remove user sudo userdel -r username # Remove user and home directory sudo userdel -f username # Force removal (even if logged in)

🔑 passwd – Change Passwords

passwd # Change own password sudo passwd username # Change another user's password sudo passwd -l username # Lock password (disable login) sudo passwd -u username # Unlock password sudo passwd -e username # Expire password (force change on next login)

👥 groupadd / groupdel – Manage Groups

sudo groupadd groupname # Create new group sudo groupdel groupname # Delete group sudo groupmod -n newname oldname # Rename group sudo gpasswd -d username groupname # Remove user from group

📋 who / w / last – Login Information

who # Who is logged in w # More detailed: what users are doing last # Login history (reads /var/log/wtmp) last -n 10 # Last 10 logins lastb # Failed login attempts

🔄 su – Switch User

su - username # Switch to user with their environment su - # Switch to root (requires root password) sudo su - # Switch to root using sudo (Ubuntu style)

10.8 Network Commands

Configure, monitor, and troubleshoot network connections.

🌐 ip – Modern Network Configuration

Replacement for deprecated ifconfig.

ip addr show # Show IP addresses ip link show # Show network interfaces ip route show # Show routing table sudo ip addr add 192.168.1.100/24 dev eth0 # Add IP address sudo ip link set eth0 up/down # Enable/disable interface

📶 ping – Test Connectivity

ping google.com # Ping until Ctrl+C ping -c 4 8.8.8.8 # Send 4 packets ping -i 2 -c 10 example.com # 2 second intervals ping -s 1472 example.com # Set packet size

Return codes: 0 (host reachable), 1 (unreachable), 2 (other error)

📊 netstat / ss – Network Statistics

ss is faster, modern replacement for netstat.

ss -tuln # Show listening ports (tcp, udp, listening, numeric) ss -tup # Show established connections with process netstat -i # Interface statistics netstat -r # Routing table

✅ Use ss -tuln | grep :80 to check if web server is running.

🔍 nslookup / dig – DNS Lookup

nslookup google.com # Basic DNS query dig google.com # Detailed DNS information dig -x 8.8.8.8 # Reverse lookup (IP to hostname) dig @8.8.8.8 example.com # Use specific DNS server dig MX gmail.com # Query mail exchange records

🛤️ traceroute – Network Path

traceroute google.com # Show path packets take mtr google.com # Combined traceroute + ping (real-time) tracepath example.com # Similar, no root needed

📡 wget / curl – Download Files

wget https://example.com/file.zip # Download file wget -c https://example.com/large.zip # Resume download wget -r -np -nH --cut-dirs=1 https://site.com/files/ # Recursive download curl -O https://example.com/file.zip # Download (save as filename) curl -o custom.zip https://example.com/file.zip # Download with custom name curl -I https://example.com # Fetch HTTP headers only

📱 nmcli – NetworkManager CLI

For systems with NetworkManager (most desktop distros).

nmcli dev status # Device status nmcli con show # Show connections nmcli con up/down id "Connection Name" # Connect/disconnect nmcli dev wifi list # Scan WiFi networks nmcli dev wifi connect SSID password PASSWORD # Connect to WiFi

10.9 Package Management Commands

Install, update, and remove software on Debian/Ubuntu systems.

⚠️ These commands vary by distribution. This section covers Debian/Ubuntu (apt).

📦 apt – Advanced Package Tool

Modern, user-friendly package manager.

Command	Description	Example
`sudo apt update`	Update package lists	Always run first
`sudo apt upgrade`	Upgrade all packages	`sudo apt upgrade -y`
`sudo apt install package`	Install package	`sudo apt install vim`
`sudo apt remove package`	Remove package	`sudo apt remove firefox`
`sudo apt purge package`	Remove + config files	`sudo apt purge apache2`
`apt search keyword`	Search packages	`apt search pdf editor`
`apt show package`	Show package details	`apt show python3`
`apt list --installed`	List installed packages	`apt list --installed \| grep python`
`sudo apt autoremove`	Remove unused dependencies	Clean up orphaned packages
`sudo apt autoclean`	Remove old .deb files	Free disk space

💡 apt combines features from apt-get and apt-cache with better output.

🔧 dpkg – Debian Package Manager

Lower-level tool for working with .deb files.

sudo dpkg -i package.deb # Install local .deb file sudo dpkg -r package # Remove package dpkg -l # List installed packages dpkg -L package # List files installed by package dpkg -S /path/to/file # Find which package owns file sudo dpkg --configure -a # Fix interrupted installations

📱 snap / flatpak – Universal Packages

Sandboxed applications that work across distributions.

snap find searchterm # Search snaps sudo snap install package # Install snap snap list # List installed snaps sudo snap refresh package # Update snap flatpak search app # Search Flatpak flatpak install flathub app # Install Flatpak flatpak run app # Run Flatpak app

🔄 apt-get – Legacy Package Tool

Traditional command, still widely used in scripts.

sudo apt-get update sudo apt-get upgrade sudo apt-get dist-upgrade # Smart dependency resolution sudo apt-get install -f # Fix broken dependencies sudo apt-get clean # Clear package cache

10.10 Disk & Storage Commands

Monitor disk usage, partition drives, and manage filesystems.

💾 df – Disk Free Space

df -h # Human-readable sizes (GB, MB) df -T # Show filesystem type df -i # Inode usage (important for mail servers) df -h --total # Show total at end

Example output: /dev/sda1 100G 45G 55G 45% /

📊 du – Disk Usage

du -sh folder/ # Total size of directory du -h --max-depth=1 # Size of immediate subdirectories du -ah folder/ # Show size of each file du -sh * | sort -h # Sort by size (smallest to largest) du -sh * | sort -rh # Sort by size (largest first)

✅ Find largest files: du -ah /home 2>/dev/null | sort -rh | head -20

💽 lsblk – List Block Devices

lsblk # Tree view of disks and partitions lsblk -f # Include filesystem info lsblk -m # Show permissions and owner lsblk -o NAME,SIZE,TYPE,MOUNTPOINT,LABEL # Custom columns

🔧 fdisk / parted – Partition Tools

⚡ Require sudo and careful handling.

sudo fdisk -l # List all partitions sudo fdisk /dev/sdb # Interactive partition tool sudo parted -l # List partitions (more detailed) sudo parted /dev/sda print # Show partition table

⚠️ Partitioning can destroy data. Always backup and double-check device names.

🔌 mount / umount – Mount Filesystems

mount # Show all mounted filesystems sudo mount /dev/sdb1 /mnt/usb # Mount partition to directory sudo umount /mnt/usb # Unmount sudo mount -t ntfs /dev/sdb1 /mnt/usb # Specify filesystem type sudo mount -o ro /dev/sdb1 /mnt/usb # Mount read-only

🆔 blkid – Block Device Attributes

sudo blkid # Show UUID and filesystem type blkid -s UUID /dev/sda1 # Show only UUID

UUIDs are used in /etc/fstab for persistent mounting.

🩺 fsck – Filesystem Check

⚡ Filesystem must be unmounted.

sudo fsck /dev/sda1 # Check filesystem sudo fsck -f /dev/sda1 # Force check even if clean sudo fsck -y /dev/sda1 # Auto-repair (yes to all)

🔄 dd – Convert & Copy

Powerful low-level copying tool.

sudo dd if=/dev/sda of=/dev/sdb bs=4M status=progress # Clone disk sudo dd if=/dev/zero of=/tmp/test.img bs=1M count=100 # Create 100MB test file sudo dd if=/dev/sda of=backup.img bs=4M # Backup disk to image sudo dd if=backup.img of=/dev/sdb bs=4M # Restore from image

⚠️ dd is called "Disk Destroyer" for a reason. One wrong device and data is gone forever.

10.11 Compression & Archive Commands

Create and extract compressed archives.

📦 tar – Tape Archive

Most common archiving tool.

Operation	Command	Description
Create	`tar -czf archive.tar.gz folder/`	Create gzipped archive
Extract	`tar -xzf archive.tar.gz`	Extract gzipped archive
Create	`tar -cjf archive.tar.bz2 folder/`	Create bzip2 archive (smaller)
Extract	`tar -xjf archive.tar.bz2`	Extract bzip2 archive
List	`tar -tf archive.tar.gz`	View contents without extracting
Extract specific	`tar -xzf archive.tar.gz file.txt`	Extract single file
Verbose	`tar -xzvf archive.tar.gz`	Verbose output (show files)

Options explained: c=create, x=extract, t=list, f=file, z=gzip, j=bzip2, v=verbose

🗜️ gzip / gunzip – GNU Zip

gzip file.txt # Compress (creates file.txt.gz) gunzip file.txt.gz # Decompress gzip -l file.txt.gz # List compression info zcat file.txt.gz # View compressed file

📚 zip / unzip – ZIP Archives

zip archive.zip file1.txt file2.txt # Create ZIP zip -r archive.zip folder/ # Recursive (include subfolders) zip -e secure.zip file.txt # Encrypt with password unzip archive.zip # Extract ZIP unzip -l archive.zip # List contents unzip archive.zip -d /target/folder # Extract to directory

10.12 Search & Text Processing Commands

Find files and manipulate text data.

🔎 grep – Global Regular Expression Print

Search text using patterns.

grep "error" logfile.log # Search for string grep -i "warning" logfile.log # Case-insensitive grep -r "TODO" ~/project/ # Recursive search grep -v "exclude" file.txt # Invert (lines NOT matching) grep -c "pattern" file.txt # Count matches grep -n "error" file.txt # Show line numbers grep -l "config" *.conf # List only filenames grep -A2 -B2 "error" log.txt # Show 2 lines after/before

💡 Common pipeline: history | grep "git" - Find git commands in history

🔍 find – Search for Files

find . -name "*.txt" # Find by name find / -type f -size +100M # Files larger than 100MB find ~ -type d -name "Documents" # Directories named Documents find . -mtime -7 # Modified in last 7 days find . -user username # Owned by specific user find . -name "*.tmp" -delete # Find and delete find . -name "*.py" -exec python {} \; # Execute command on each

⚡ locate – Fast File Search

locate filename # Search database (instant) sudo updatedb # Update database locate -i "document.pdf" # Case-insensitive

vs find: locate is faster but database may be outdated.

✂️ cut – Extract Columns

cut -d: -f1 /etc/passwd # Usernames (field 1, delimiter :) cut -c1-5 file.txt # First 5 characters each line cut -f2,3 -d',' data.csv # Columns 2 and 3 from CSV

📊 sort / uniq – Sort & Unique

sort file.txt # Sort alphabetically sort -n numbers.txt # Sort numerically sort -r file.txt # Reverse order sort -u file.txt # Sort and unique uniq file.txt # Remove adjacent duplicates sort file.txt | uniq -c # Count occurrences sort file.txt | uniq -d # Show only duplicates

📝 wc – Word Count

wc file.txt # Lines, words, bytes wc -l file.txt # Line count wc -w file.txt # Word count ps aux | wc -l # Count processes

🔄 sed – Stream Editor

Find and replace text.

sed 's/old/new/' file.txt # Replace first occurrence per line sed 's/old/new/g' file.txt # Replace all occurrences sed -i 's/old/new/g' file.txt # Edit file in-place sed '5d' file.txt # Delete line 5 sed '2,5d' file.txt # Delete lines 2-5 sed 's/ *$//' file.txt # Remove trailing spaces

10.13 SSH & Remote Access Commands

Securely connect to remote systems and transfer files.

🔐 ssh – Secure Shell

ssh user@hostname # Connect to remote ssh -p 2222 user@hostname # Custom port ssh -i ~/.ssh/id_rsa user@hostname # Use specific key ssh -J jumpuser@jumpbox user@target # Jump host (proxy) ssh -X user@hostname # Forward X11 (GUI apps) ssh -L 8080:localhost:80 user@hostname # Local port forwarding

🔑 ssh-keygen – Generate SSH Keys

ssh-keygen -t rsa -b 4096 # Generate RSA key (4096 bit) ssh-keygen -t ed25519 # Modern, more secure ssh-keygen -f ~/.ssh/customkey # Custom filename

📤 scp / rsync – File Transfer

scp file.txt user@host:/path/ # Copy to remote scp user@host:/path/file.txt . # Copy from remote scp -r folder/ user@host:/path/ # Copy directory rsync -avz source/ user@host:/dest/ # Sync with compression rsync -av --delete source/ dest/ # Mirror (delete extras) rsync --progress largefile user@host:/path/ # Show progress

✅ rsync is better than scp for large transfers - it only transfers differences and can resume.

10.14 Date, Time & Scheduling Commands

Schedule tasks and manage system time.

⏰ crontab – Scheduled Tasks

Format: minute hour day month weekday command

crontab -e # Edit crontab crontab -l # List cron jobs crontab -r # Remove all jobs

Examples:

`0 5 * * * /script.sh`	Daily at 5:00 AM
`/15 * * * /check.sh`	Every 15 minutes
`0 0 * * 1 /weekly.sh`	Every Monday at midnight
`@reboot /startup.sh`	Run at system boot

⏱️ at – One-time Scheduled Task

at 14:30 # Schedule at specific time at now + 1 hour # One hour from now atq # List pending jobs atrm 5 # Remove job ID 5

👁️ watch – Execute Periodically

watch -n 2 df -h # Run df -h every 2 seconds watch -d free -h # Highlight differences watch 'ps aux | grep python' # Monitor Python processes

⏲️ timedatectl – System Time Control

timedatectl # Show current settings timedatectl list-timezones # List all timezones sudo timedatectl set-timezone America/New_York # Set timezone sudo timedatectl set-time "2025-02-11 14:30:00" # Set date/time sudo timedatectl set-ntp yes # Enable NTP sync

10.15 Hardware & Device Commands

View hardware information and manage devices.

🖥️ lspci – PCI Devices

lspci # List PCI devices lspci -v # Verbose lspci -nn # Show vendor/device IDs lspci | grep VGA # Graphics card lspci -s 00:02.0 -v # Specific device

🔌 lsusb – USB Devices

lsusb # List USB devices lsusb -v # Verbose lsusb -t # Tree view sudo lsusb -D /dev/bus/usb/001/002 # Device descriptor

🧠 lscpu – CPU Information

lscpu # CPU architecture, cores, threads cat /proc/cpuinfo # Detailed CPU info nproc # Number of processing units

Shows: Architecture, CPU op-modes, CPU(s), Thread(s) per core, Core(s) per socket, Model name, CPU MHz

💾 free – Memory Usage

free -h # Human-readable free -m # In MB free -s 2 # Repeat every 2 seconds vmstat 1 # Virtual memory stats

🧩 lsmod / modprobe – Kernel Modules

lsmod # List loaded modules sudo modprobe module_name # Load module sudo modprobe -r module_name # Remove module modinfo module_name # Show module info sudo depmod -a # Rebuild module dependencies

📟 dmesg – Kernel Ring Buffer

dmesg # All kernel messages dmesg | tail -20 # Recent messages dmesg -w # Follow (live) dmesg -l err,warn # Errors and warnings only

Useful for: Debugging hardware issues, USB device detection, driver problems.

🖥️ xrandr – Display Settings

xrandr # List displays and resolutions xrandr --output HDMI-1 --mode 1920x1080 # Set resolution xrandr --output eDP-1 --brightness 0.8 # Adjust brightness xrandr --output HDMI-1 --same-as eDP-1 # Mirror displays xrandr --output HDMI-1 --right-of eDP-1 # Extend displays

🎧 alsamixer – Sound Settings

alsamixer # Interactive sound mixer amixer set Master 70% # Set volume from terminal amixer set Master mute # Mute amixer set Master unmute # Unmute

🌡️ sensors – Temperature Monitoring

sensors # CPU/GPU temperatures sensors -f # Fahrenheit

Install: sudo apt install lm-sensors

📚 Quick Command Reference Card

Most commonly used commands for daily Linux usage:

Navigation:
pwd - Current location
ls -la - List all files
cd ~ - Go home
cd .. - Up one level

File Operations:
cp -r - Copy directory
mv - Move/rename
rm -r - Remove directory
mkdir -p - Create nested

Viewing:
cat - Display file
less - Page through
tail -f - Follow logs
head -n 20 - First 20 lines

Permissions:
chmod 755 - Executable
chmod 644 - Read/write
sudo - Admin rights

Processes:
ps aux - All processes
htop - Interactive
kill -9 PID - Force kill

Search:
grep -r - Search text
find . -name - Find files
locate - Fast search

⚠️ Safety Reminder

Commands to be extremely careful with:
rm -rf / - Deletes entire system
dd if=/dev/zero of=/dev/sda - Overwrites entire disk
chmod 777 / - Makes entire system world-writable
sudo without understanding what you're running

Module 10 Complete • Essential Linux Commands Reference • Bookmark this page for daily terminal work

Kali Linux Basics – Beginner & Safety Focused

This optional module introduces Kali Linux in a safe, ethical, and beginner-friendly way. You will understand what Kali Linux is, when to use it, how to run it safely using a USB pendrive, and how to avoid legal or beginner mistakes.

⚠️ This module focuses on learning, setup, and legal awareness. It does NOT teach hacking or illegal activities.

Kali Linux.1 What Is Kali Linux & Who Should Use It

Kali Linux is a Debian-based Linux distribution developed by Offensive Security. It is designed specifically for cybersecurity testing, ethical hacking, and digital forensics.

Unlike normal Linux systems (Ubuntu, Mint), Kali Linux comes pre-installed with hundreds of security-related tools. These tools are used to test systems you own or have permission to test.

🎯 Who Should Use Kali Linux?

Cybersecurity students
Ethical hackers (with permission)
Network administrators
Security researchers

🚫 Who Should NOT Use Kali Linux?

Normal daily computer users
Beginners without Linux knowledge
People looking for gaming or office work

💡 Important: Kali Linux is a learning and testing OS, not a replacement for Windows or Ubuntu.

Kali Linux.2 Is Kali Linux Legal? Important Rules

Kali Linux itself is 100% legal to download, install, and use. However, how you use it determines legality.

⚖️ Legal Usage

Practicing on your own computer
Learning Linux commands
Testing your own Wi-Fi or server
Lab platforms (TryHackMe, Hack The Box)

🚨 Illegal Usage

Hacking websites without permission
Attacking public Wi-Fi networks
Breaking into accounts or systems

⚠️ Unauthorized hacking is a crime in most countries and can lead to jail time, fines, and permanent records.

✅ Learn Kali Linux ethically and legally — skills matter more than shortcuts.

Kali Linux.3 Ways to Use Kali Linux (USB, Install, VM)

Kali Linux can be used in multiple ways depending on your experience and system setup.

Method	Description	Best For
Live USB	Run Kali from pendrive without installing	Beginners & safe testing
Full Installation	Install Kali on hard disk	Advanced users
Virtual Machine	Run Kali inside VirtualBox	Students & labs

💡 Recommended for beginners: Live USB or Virtual Machine

Kali Linux.4 Create Kali Linux Bootable Pendrive

A bootable pendrive allows you to run Kali Linux without installing it.

🧰 Requirements

USB drive (minimum 16GB)
Kali Linux ISO (official)
Rufus / BalenaEtcher

⬇️ Download Kali Linux (Official ISO Files)

Kali Linux provides different download formats depending on how you want to use it. Always download Kali Linux from official sources only.

1️⃣ Kali Linux Live USB (No Installation)

This version runs directly from a pendrive without installing Kali Linux. Note: The Live ISO is officially distributed via torrent only.

🔗 Official page: https://www.kali.org/get-kali/
Download type: Live → Installer → Torrent
Recommended for: Temporary use & safe testing

⚠️ Kali Linux Live ISO does not have a direct browser download link. Torrent is the official and recommended method.

2️⃣ Kali Linux Full Installation (Direct ISO)

This ISO can be downloaded directly in a browser and used to install Kali Linux or boot from USB.

🔗 Direct download (official): https://kali.download/base-images/kali-2025.4/kali-linux-2025.4-installer-amd64.iso
Best for: Beginners who want a simple setup

💡 This installer ISO works perfectly for USB boot and learning Kali Linux.

3️⃣ Kali Linux Virtual Machine (Easiest & Safest)

Pre-built Kali Linux virtual machines are available for VirtualBox and VMware. No ISO or USB is required.

🔗 Official VM downloads: https://www.kali.org/get-kali/#kali-virtual-machines
Supported: VirtualBox, VMware
Best for: Students & lab practice

✅ Recommended for beginners: Virtual Machine or Installer ISO USB

4️⃣ Download Kali Linux ISO (Direct Link for USB)

To create a Kali Linux bootable pendrive, you need the official Kali Linux Installer ISO. This file can be downloaded directly in your browser without using torrent.

🔗 Kali Linux Installer ISO (AMD64 – Official)
https://archive.kali.org/kali-images/kali-2025.4/kali-linux-2025.4-installer-amd64.iso

💡 This ISO works perfectly for:

Bootable USB (Rufus / BalenaEtcher)
Fresh Kali Linux installation
Learning & practice

⚙️ Steps (Using Rufus)

Insert USB drive
Open Rufus
Select Kali ISO
Partition scheme: GPT (UEFI)
Click Start

⚠️ All data on the USB will be erased.

✅ You now have a Kali Linux bootable pendrive.

Kali Linux.5 Boot Kali Linux & First-Time Setup

After creating the bootable USB, you can boot Kali Linux safely.

🚀 Boot Steps

Restart PC
Press Boot Menu key (F12 / Esc / F9)
Select USB device
Choose Live System

🔧 First-Time Setup

Set keyboard layout
Connect Wi-Fi
Update system (optional)

💡 Default username: kali | password: kali

✅ Kali Linux is now ready for learning and labs.

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