Kali Linux

What is Kali Linux?

Kali Linux is a Debian-based Linux distribution maintained by OffSec and built specifically for penetration testing, security auditing, digital forensics and reverse engineering. Its real value is not magic: it ships hundreds of security tools that are already packaged, configured and kept up to date in its own repositories, including Nmap, Burp Suite, Metasploit, Wireshark, John the Ripper, Hashcat and Aircrack-ng. Instead of spending an afternoon fighting dependencies, you open a terminal and get to work.

Kali is a rolling release, so there is no need to reinstall for every new version; you simply upgrade with apt. For several years it has used a regular (non-root) user by default and zsh as its shell, which is worth knowing if you are following older tutorials.

What Kali Linux is used for

• A pentesting workstation: reconnaissance, exploitation, post-exploitation and reporting from a single machine.
• Labs and CTFs: it is the distribution most platforms assume, including Hack The Box and TryHackMe.
• Certification prep such as OffSec's OSCP or the eJPT.
• Forensics: the Live USB forensic mode does not auto-mount disks, so evidence is not altered.
• Auditing your own network: Wi-Fi, exposed services and weak passwords on your devices.

Kali is a toolbox, not a licence. Only use it against your own systems, labs, CTFs or infrastructure you have written permission to test.

How to install Kali Linux

There are several ways to run Kali, and each one suits a different situation. Always download images from kali.org and check the SHA256 hash published next to each file.

Option 1: virtual machine (best for beginners)

Kali provides prebuilt images for VirtualBox and VMware: unpack and import. The default credentials are kali / kali; change them straight away with passwd. Give it at least 2 cores and 4 GB of RAM if you can, and take a clean snapshot before you change anything, so a broken system is a few seconds away from being fixed. For labs, prefer NAT or an isolated internal network over bridged mode.

Option 2: WSL on Windows

On Windows 10/11 you can run Kali without a full VM through the Windows Subsystem for Linux:

wsl --install -d kali-linux

The WSL install is minimal and has almost no tools, so add them yourself. If you want a graphical desktop, install Win-KeX:

sudo apt update && sudo apt full-upgrade -y
sudo apt install -y kali-linux-default
sudo apt install -y kali-win-kex
kex --win -s

Be aware of the limits: direct hardware access (for example putting a Wi-Fi card into monitor mode) does not work the way it does on a native install, and some network tools behave differently.

Option 3: Live USB (with or without persistence)

Booting from USB lets you use Kali on any computer without touching its disk. Write the "Live" ISO with balenaEtcher or Rufus (DD mode), or from Linux:

sudo dd if=kali-linux-live-amd64.iso of=/dev/sdX bs=4M status=progress conv=fsync

Replace /dev/sdX with your USB drive and double-check it with lsblk, because dd overwrites without asking. Changes are lost on shutdown by default; the official docs explain how to add a persistence partition, optionally encrypted.

Other options

There are also bare-metal installs (single or dual boot), ARM images for the Raspberry Pi, cloud images, Docker containers (docker run -it kalilinux/kali-rolling) and Kali NetHunter for Android.

How to use Kali Linux: practical first steps

1. Update the system

sudo apt update
sudo apt full-upgrade -y

Do this regularly. Security tools move fast, and plenty of "bugs" are just outdated versions.

2. Understand metapackages

Kali groups tools into metapackages so you install exactly what you need:

Metapackage	What it contains
kali-linux-core	Minimal base system
kali-linux-headless	Default tools without a GUI
kali-linux-default	The standard selection in official images
kali-linux-large	A broader selection
kali-linux-everything	Everything (very large)

There are also themed metapackages such as kali-tools-web, kali-tools-wireless, kali-tools-passwords and kali-tools-forensics:

sudo apt install -y kali-tools-web
apt-cache search kali-tools

3. Find and install specific tools

apt search gobuster
sudo apt install -y gobuster seclists

Wordlists live in /usr/share/wordlists and SecLists in /usr/share/seclists. The well-known rockyou.txt ships compressed; extract it with sudo gunzip /usr/share/wordlists/rockyou.txt.gz.

4. Organise your work

mkdir -p ~/labs/box01/{nmap,loot,notes}
cd ~/labs/box01
nmap -sC -sV -oA nmap/initial 10.10.10.10

One folder per target, every output saved and notes from minute one: that is the difference between a solid report and not remembering what you did.

Pro tips

• Do not use Kali as your daily driver for browsing, email or banking. It is a work environment; treat it like one.
• Snapshot before every big change: major upgrades, driver installs, experiments.
• Use kali-tweaks to configure repositories, the shell and metapackages from a menu.
• Learn Linux properly: permissions, processes, networking, bash. Wargames like OverTheWire are perfect for this.
• Get an external Wi-Fi adapter that supports monitor mode if you plan to audit your own wireless network from a VM.
• Do not add third-party repositories (such as Ubuntu's) unless you know exactly why: it is the quickest way to break Kali.

Pros and cons

Pros	Cons
Hundreds of ready-to-use tools	Overkill if you only use a handful of tools
Free, well documented, huge community	Not designed as an everyday OS
Many install options (VM, WSL, USB, ARM, cloud)	Rolling release: an upgrade can occasionally break things
De facto standard in courses, CTFs and certs	Makes it easy to run tools without understanding them

Kali Linux alternatives

• Parrot OS: also Debian-based, lighter, with a privacy-focused Home edition.
• BlackArch: Arch-based with a massive tool repository; better for experienced users.
• Exegol: a Docker-based pentesting environment, handy for keeping several clean setups.
• A regular distro (Debian, Ubuntu, Fedora) with only the tools you need: more control, less noise.

Frequently asked questions

Is Kali Linux free?

Yes. It is free and open source, and every official image can be downloaded from kali.org at no cost.

Is it legal to use Kali Linux?

Installing and using it is legal. Attacking systems without permission is what can be a crime. Stick to your own machines, labs, CTFs and engagements authorised in writing.

VM, WSL or Live USB: which should I start with?

A virtual machine. It is isolated, supports snapshots and puts nothing at risk. WSL is convenient for command-line tools, and a Live USB is useful for carrying Kali around or for forensics.

What are the default username and password?

On the VM and Live images it is kali / kali. With the installer, whatever you choose during setup.

Do I need Kali to learn ethical hacking?

It is not mandatory, but it saves a lot of time and most courses assume it. What matters is understanding the techniques, not the distribution.

Want a solid start? The Hackers en Acción Academy has hands-on Linux and pentesting lessons and challenges.