Kali Linux is the operating system of choice for ethical hackers. Almost every hacking tool runs on Linux. This lesson gets you comfortable with the command line — your most powerful interface as a security professional.

Why Linux?

Linux is open-source, highly customizable, and runs on most servers in the world. Kali Linux comes pre-loaded with 600+ security tools. As a hacker, you’ll spend most of your time in the terminal — understanding Linux is not optional.

Essential Linux Commands

Navigation & Files:

• pwd — Print working directory (where am I?)
• ls -la — List all files including hidden ones with permissions
• cd /path/to/dir — Change directory
• cp file.txt /destination/ — Copy a file
• mv file.txt newname.txt — Move or rename a file
• rm -rf folder/ — Delete folder and contents (use carefully!)
• find / -name ‘passwords.txt’ — Search the entire filesystem
• cat file.txt — Display file contents
• grep ‘password’ file.txt — Search for text in a file
• chmod 755 script.sh — Change file permissions
• sudo command — Run as superuser (administrator)

Networking Commands in Linux

• ifconfig / ip a — Show network interfaces and IP addresses
• netstat -tulnp — Show open ports and listening services
• curl https://example.com — Make an HTTP request from terminal
• wget https://file.com/tool.zip — Download a file
• ssh user@192.168.1.1 — Connect to a remote server securely
• nmap 192.168.1.1 — Quick port scan (we’ll cover this in depth later)

File Permissions Explained

In Linux, every file has three permission types: Read (r=4), Write (w=2), Execute (x=1). Permissions are set for Owner, Group, and Others. Example: chmod 755 means owner can read/write/execute (7), group can read/execute (5), others can read/execute (5).

Basic Bash Scripting

A bash script automates repetitive tasks. Create a file called scan.sh:

• #!/bin/bash (shebang — tells system to use bash)
• echo ‘Starting scan…’
• for ip in 192.168.1.{1..254}; do ping -c 1 -W 1 $ip &> /dev/null && echo “$ip is alive”; done
• Make it executable: chmod +x scan.sh then run: ./scan.sh

Practical Exercise

Practical Exercise: Linux Command Drill

1. Step 1: Boot into Kali Linux (VM or live USB). Open a terminal.
2. Step 2: Navigate to /etc/ and read the passwd file: cat /etc/passwd
3. Step 3: Create a directory called ‘hacking_practice’, navigate into it, and create 3 text files.
4. Step 4: Use grep to search for the word ‘root’ inside /etc/passwd.
5. Step 5: Write a bash script that pings 5 different IP addresses and reports which ones are alive.
6. Step 6: Use chmod to set different permission levels on your script and test the difference.

Tools Used in This Lesson