Learn the Basics of Linux and How It Can Be Used by Ethical Hackers

Linux has long been a favorite operating system among ethical hackers and security researchers. Its open-source nature, powerful command-line interface, and extensive collection of hacking tools make it an ideal platform for offensive security. In fact, a survey by Null Byte found that 82% of ethical hackers use Linux as their primary operating system for hacking.

In this comprehensive guide, we‘ll explore why Linux is so popular in the ethical hacking community and walk through the key concepts and tools every aspiring hacker should know. I‘ll share my perspective as a full-stack developer who has worked on application security teams and provide examples of how Linux can be used to assess and improve an organization‘s security posture. By the end of this article, you‘ll have a solid foundation for using Linux in your ethical hacking workflows.

The Rise of Linux in Ethical Hacking

To understand how Linux became the go-to operating system for hackers, it‘s helpful to look at its history. Linux was created in 1991 by Linus Torvalds as a free and open-source alternative to Unix. Unlike proprietary operating systems like Windows, Linux is built on the premise that users should have complete control over their computing environment and be free to modify and distribute the source code.

This ethos of freedom and openness aligned perfectly with the hacker community‘s values. In the early days of hacking, Unix systems were the primary target due to their dominance in academia, government, and business. As Linux matured and gained more advanced security features, hackers began switching over in droves.

The turning point came in 2006 with the release of BackTrack Linux, a Slackware-based distribution that contained hundreds of ethical hacking tools. For the first time, hackers had a pre-configured environment that included everything they needed to get started with security assessments and penetration testing. BackTrack eventually evolved into Kali Linux and sparked a wave of new Linux distributions for ethical hacking like Parrot Security OS and BlackArch Linux.

Today, Linux powers the vast majority of the world‘s servers, supercomputers, and embedded devices. According to a 2019 report by IDC, Linux has a 68% share of the worldwide server operating system market. Linux is also used by 100% of the world‘s top 500 supercomputers and dominates embedded devices like routers, smart TVs, and industrial control systems. This ubiquity means that being able to assess and secure Linux systems is a critical skill for ethical hackers.

Linux vs. Other Operating Systems for Hacking

While macOS and Windows have made strides in recent years, Linux still offers several unique advantages for ethical hacking:

Feature	Linux	macOS	Windows
Open-source	Yes	No	No
Command-line interface	Bash / ZSH	Bash / ZSH	PowerShell
Package management	APT / YUM / Pacman	Homebrew	Chocolatey
Filesystems	Ext4 / Btrfs / ZFS	APFS / HFS+	NTFS / ReFS
Customizability	High	Medium	Low
Low resource usage	Yes	No	No
Hacking tool availability	High	Medium	Low

As you can see, Linux beats out the competition in several key areas. Its open-source nature allows hackers to inspect the code for vulnerabilities and compile their own custom versions. The Bash command-line shell is more powerful and flexible than Windows‘ command prompt. Package managers like APT make it easy to install and update hacking tools.

Linux‘s wide range of supported filesystems and low resource usage also make it ideal for conducting resource-intensive security tasks like password cracking and vulnerability scanning. You can create a minimal virtual machine with just the tools you need and leave more resources for your host machine.

Finally, Linux simply has the best selection of hacking tools hands-down. While some tools have been ported to Windows and macOS, they often lag behind the Linux versions in terms of features and performance. Many tools are designed exclusively for Linux and take advantage of kernel features that aren‘t available on other operating systems.

Getting Started with Kali Linux

For beginners looking to get started with ethical hacking on Linux, I recommend installing Kali Linux in a virtual machine. Kali is a Debian-based Linux distribution that comes pre-loaded with over 600 penetration testing and security auditing tools. It‘s developed and maintained by Offensive Security, the same company behind the OSCP certification.

Here‘s a step-by-step guide to setting up Kali Linux in VirtualBox on a Windows host machine:

1. Download and install VirtualBox on your host machine.
2. Download the Kali Linux VirtualBox image (.ova) file from the official website.
3. Launch VirtualBox and select "File" > "Import Appliance".
4. Select the Kali Linux .ova file and click "Next".
5. Configure the virtual machine settings (e.g. RAM, CPU, disk space) and click "Import".
6. Once the import process finishes, select the new virtual machine and click "Start".
7. When prompted, log in with the default credentials (root / toor).
8. Launch a terminal and run apt update && apt full-upgrade to update Kali to the latest version.
9. Install VirtualBox Guest Additions for better performance by running apt install -y virtualbox-guest-x11.
10. Reboot the virtual machine and you‘re ready to start using Kali Linux!

Of course, this is just a simple example of installing Kali Linux on a single machine. In a real penetration testing environment, you might have multiple virtual machines connected in a lab network to simulate a real-world target environment. Building a home lab is a great way to practice your hacking skills safely and legally.

Key Linux Commands for Hacking

Once you have Kali Linux up and running, you should spend some time familiarizing yourself with the Linux command-line interface (CLI). While you can use the GUI tools in Kali for many tasks, the real power of Linux comes from the terminal.

Here are some essential Linux commands every ethical hacker should know:

Command	Description
ls	List files and directories
cd	Change current directory
pwd	Print current working directory
mkdir	Create a new directory
cp	Copy files and directories
mv	Move or rename files and directories
rm	Remove files and directories
cat	Display file contents
grep	Search for patterns in files
find	Search for files in a directory hierarchy
man	Display the manual page for a command
sudo	Execute a command with superuser privileges
apt	Package management utility for Debian-based systems

Take some time to practice using these commands and read through their manual pages to understand their full capabilities. You can also chain multiple commands together using pipes (|) to create powerful command-line pipelines.

For example, to search for all files containing the word "password" in the current directory and save the output to a file:

grep -r "password" . > password_files.txt

Essential Tools for Ethical Hacking on Linux

Kali Linux comes pre-installed with hundreds of tools for various ethical hacking tasks. Here are some of the most important tools to become familiar with:

Tool	Description
Nmap	Network exploration and security auditing
Metasploit Framework	Penetration testing platform for exploiting vulnerabilities
Burp Suite	Web application security testing platform
Wireshark	Network protocol analyzer for capturing and inspecting traffic
John the Ripper	Password cracking tool
Hashcat	Advanced password recovery utility
Hydra	Network logon cracker supporting many protocols
Aircrack-ng	Wireless network security assessment tools
Sqlmap	Automatic SQL injection and database takeover tool

These are just a few examples of the many tools available in Kali Linux. It‘s important to understand that each of these tools is complex and requires a significant amount of knowledge and practice to use effectively. Start by reading the documentation and running the tools in a lab environment before attempting to use them on real targets.

Here‘s an example of using Nmap to scan a target host for open ports and services:

nmap -sV -sC -p- 192.168.1.100

This command tells Nmap to perform a service version scan (-sV), run default scripts (-sC), and scan all ports (-p-) on the target host. The output will show which ports are open, what services are running on those ports, and any additional information gathered by the default scripts.

Linux Privilege Escalation Techniques

One of the most important skills for an ethical hacker is being able to escalate privileges on a compromised system. Linux systems often have misconfigurations and vulnerabilities that can allow an attacker to gain root access.

Here are some common Linux privilege escalation techniques:

• Exploiting kernel vulnerabilities
• Exploiting SUID/SGID binaries
• Exploiting writable files and directories
• Exploiting sudo misconfigurations
• Exploiting cron jobs
• Exploiting NFS shares
• Exploiting vulnerable services
• Exploiting password reuse and weak credentials

To practice these techniques safely, you can download vulnerable virtual machines from sites like VulnHub and exploit them in your lab environment. Be sure to document your findings and develop a methodology for privilege escalation that you can use on real engagements.

Linux Forensics and Anti-Forensics

In addition to offensive security skills, ethical hackers also need to understand forensics and anti-forensics techniques on Linux systems. This knowledge is important for conducting incident response and understanding how attackers can cover their tracks.

Some important Linux forensics concepts include:

• Collecting volatile data (e.g. memory dumps, running processes)
• Acquiring disk images with tools like dd and dcfldd
• Analyzing log files (e.g. /var/log/auth.log, /var/log/syslog)
• Identifying persistence mechanisms (e.g. cron jobs, systemd services)
• Recovering deleted files with tools like Extundelete and Foremost
• Identifying timestomping and other anti-forensics techniques

On the flip side, attackers may use anti-forensics techniques to make incident response more difficult. Some examples include:

• Disabling or modifying logging
• Clearing command history and logs
• Timestomping files to modify access, modify, and change times
• Using secure deletion tools like shred and srm
• Encrypting files and communications
• Hiding files with rootkits and steganography

Understanding these techniques can help you detect and respond to intrusions more effectively.

Getting Certified in Ethical Hacking

If you‘re serious about pursuing a career in ethical hacking, it‘s important to validate your skills with industry-recognized certifications. Here are some of the top certifications that test your knowledge of Linux and ethical hacking:

Certification	Description
Offensive Security Certified Professional (OSCP)	Hands-on penetration testing certification that requires passing a 24-hour practical exam
CompTIA PenTest+	Multiple-choice and performance-based assessment of penetration testing skills
Certified Ethical Hacker (CEH)	Demonstrates knowledge of ethical hacking techniques and tools
GIAC Penetration Tester (GPEN)	Certifies ability to conduct high-value penetration testing engagements
Offensive Security Experienced Penetration Tester (OSEP)	Advanced certification focusing on exploit development and custom code

Each of these certifications has different requirements and covers slightly different material. Research each one carefully to determine which aligns best with your career goals. Keep in mind that preparing for these certifications can be a significant investment of time and money.

In addition to certifications, it‘s important to continuously develop your skills through hands-on practice, reading blogs and whitepapers, attending conferences, and contributing to open-source projects. The ethical hacking field is constantly evolving, so it‘s important to stay up-to-date with the latest techniques and tools.

Conclusion

Linux is an essential tool for any ethical hacker or penetration tester. Its open-source nature, powerful command-line interface, and extensive collection of hacking tools make it the perfect platform for offensive security.

By following the steps outlined in this guide, you can set up a Kali Linux environment, learn essential commands and tools, and start practicing your skills safely and legally. Remember to always obtain written permission before conducting any security testing and to adhere to a strict code of ethics.

As you continue to develop your skills, consider pursuing industry certifications and connecting with the wider ethical hacking community. With dedication and practice, you can become a skilled ethical hacker and help make the digital world a safer place.