9.3. Building Custom Kali Live ISO Images
Kali Linux has a ton of functionality and flexibility right out of the box. Once Kali is installed, you can perform all sorts of amazing feats with a little guidance, creativity, patience, and practice. However, you can also customize a Kali build so that it contains specific files or packages (to scale up or scale down performance and features) and can perform certain functions automatically. For example, the Kali ISO of Doom and the Kali Evil Wireless Access Point are both excellent projects that rely on a custom-built implementation of Kali Linux. Let's take a look at the process of rolling a custom Kali Linux ISO image.
Official Kali ISO images are built with live-build, which is a set of scripts that allows for the complete automation and customization of all facets of ISO image creation. The live-build suite uses an entire directory structure as input for its configuration. We store this configuration and some associated helper scripts in a live-build-config Git repository. We will use this repository as a basis for building customized images.
Before going further, you must know that the commands shown in this section are meant to be run on an up-to-date Kali Linux system. They are very likely to fail if run on a non-Kali system or if the system is out of date.
The first step is to install the packages needed and to retrieve the Git repository with the Kali live-build configuration:
# apt install curl git live-build
# git clone https://gitlab.com/kalilinux/build-scripts/live-build-config.git
# cd live-build-config
auto bin build_all.sh build.sh kali-config README.md simple-cdd
At this point, you can already create an updated (but unmodified) Kali live ISO image just by running ./build.sh --verbose. The build will take a long time to complete as it will download all the packages to include. When finished, you will find the freshly created ISO image in the new images directory.
The build.sh live-build wrapper that we provide is responsible for setting up the config directory that live-build expects to find. It can put in place different configurations depending on its --variant option.
The wrapper creates the config directory by combining files from kali-config/common and kali-config/variant-X, where X is the name of a variant given with the --variant parameter. When the option is not explicitly given, it uses default as the name of the variant.
The kali-config directory contains directories for the most common desktop environments:
- e17 for Enlightenment;
- gnome for GNOME;
- i3wm for the corresponding window manager;
- kde for KDE;
- lxde for LXDE;
- mate for the Mate Desktop Environment;
- xfce for XFCE.
You can easily create a Kali live image using KDE as desktop environment with this single command:
./build.sh --variant kde --verbose
This concept of variant allows for some high-level pre-defined customizations but if you take the time to read through the Debian Live System Manual, you will discover many other ways to customize the images, just by changing the content of the appropriate sub-directory of kali-config. The following sections will provide some examples.
Once launched, live-build installs all the packages listed in package-lists/*.list.chroot files. The default configuration that we provide includes a package-lists/kali.list.chroot file, which lists kali-linux-default (the main metapackage pulling all the Kali packages to include). You can comment out this package and put another metapackage of your choice or include a precise set of other packages. You can also combine both approaches by starting with a metapackage and adding supplementary packages of your choice.
With package-lists, you can only include packages that are already available in the official Kali repository. But if you have custom packages, you can include them in the live image by placing the .deb files in a packages.chroot directory (for example kali-config/config-gnome/packages.chroot if you build the GNOME variant).
metapackages are empty packages whose sole purpose is to have many dependencies on other packages. They make it easier to install sets of packages that you often want to install together. The kali-meta source package builds all the metapackages provided by Kali Linux:
- kali-linux-core: the base system (it is pulled by all the other metapackages)
- kali-linux-headless: the default Kali Linux installation command line tools
- kali-linux-default: the default Kali Linux installation, both command line and graphical
- kali-linux-large: wider range set of tools, which are not as commonly used
- kali-linux-everything: metapackage of all the metapackages and other packages (almost everything that Kali provides so it is really huge!)
- kali-tools-top10: the ten most popular tools
- kali-tools-web: web applications assessment tools
- kali-tools-passwords: password cracking tools
- kali-tools-wireless: The collection of 802.11, Bluetooth, RFID and SDR wireless assessment and analysis tools
- kali-tools-forensic: forensic tools (finding evidence of what happened)
- kali-tools-802-11: wireless assessment and analysis tools
- kali-tools-bluetooth: Bluetooth focused tools
- kali-tools-crypto-stego: cryptography and steganography tools
- kali-tools-crypto-fuzzing: fuzzing attack tools
- kali-tools-gpu: GPU-powered tools (tools making use of the computing power available in your graphical card)
- kali-tools-hardware: tools designed to attacking hardware
- kali-tools-rfid: Radio Frequency IDentification (RFID) tools
- kali-tools-sdr: Software Defined Radio (SDR) tools
- kali-tools-voip: Voice Over IP tools
- kali-tools-windows-resources: Pre-compiled Microsoft Windows binaries
You can leverage these metapackages when you create custom package lists for live-build. The full list of available metapackages and the tools they include can be found at https://tools.kali.org/kali-metapackages
live-build offers hooks that can be executed at different steps of the build process. Chroot hooks are executable scripts that you install as hooks/live/*.chroot files in your config tree and that are executed within the chroot. While chroot is the command that lets you temporarily changes the operating system's root directory to a directory of your choice, it is also used by extension to designate a directory hosting a full (alternate) file system tree. This is the case here with live-build, where the chroot directory is the directory where the live file system is being prepared. Since applications started in a chroot can't see outside of that directory, the same goes with the chroot hooks: you can only use and modify anything available in that chroot environment. We rely on those hooks to perform multiple Kali specific customizations (see kali-config/common/hooks/live/kali-hacks.chroot).
Binary hooks (hooks/live/*.binary) are executed in the context of the build process (and not chrooted anywhere) at the end of the process. You can modify the content of the ISO image built but not of the live file system since at this point, it has already been generated. We use this feature in Kali to make some changes to the default isolinux configuration generated by live-build. For example, see kali-config/common/hooks/live/persistence.binary where we add the boot menu entries enabling persistence.
Another very common customization is to add files either in the live file system or in the ISO image.
You can add files to the live file system by putting them at their expected location below the includes.chroot config directory. For example, we provide kali-config/common/includes.chroot/usr/lib/live/config/0031-kali-password, which ends up as /usr/lib/live/config/0031-kali-password in the live file system.
You can add files to the ISO image by putting them at their expected location below the includes.binary config directory. For example, we provide kali-config/common/includes.binary/isolinux/splash.png to override the background image used by the Isolinux bootloader (which is stored in /isolinux/splash.png in the filesystem of the ISO image).