Although you can download pre-rolled Kali ARM images from our download area, there may be applications which will require building your own custom bootstrapped Kali rootfs for ARM.

The following procedure shows an example of building a fairly generic Kali armhf rootfs. If you wish to build for armel, use that value rather than “armhf” when you export the architecture environment variable.

The intention in this article is more to provide a high-level overview of how the build scripts work than an actual manual procedure (although it’s completely possible to walk through this example at the command line). The style mimics that used in the build scripts used to create the pre-rolled images. Specifically, you’ll see a construct in several places that looks like:

kali@kali:~$ cat <<EOF > kali-$architecture/etc/apt/sources.list
deb http://http.kali.org/kali kali-rolling main contrib non-free non-free-firmware
EOF

This simply amounts to creating a new file, ~/arm-stuff/rootfs/kali-armhf/etc/apt/sources.list, with the contents:

deb http://http.kali.org/kali kali-rolling main contrib non-free non-free-firmware

Before we walk through our example, it’s probably good to see how a custom ARM build would actually be accomplished. Typically, to do a local build of an image for, e.g., Raspberry Pi, the process would be something like the following. As an initial one-time set-up, clone the ARM build scripts repository on GitHub and install the build prerequisites:

kali@kali:~$ cd ~/
kali@kali:~$ git clone https://gitlab.com/kalilinux/build-scripts/kali-arm.git
kali@kali:~$ dpkg --add-architecture i386
kali@kali:~$ sudo apt update
kali@kali:~$ sudo apt install -y debootstrap qemu-user-static device-tree-compiler lzma lzop u-boot-tools libncurses5:i386 pixz

To do an ARM build, you must enable cross-compilation for your current shell session:

kali@kali:~$ export ARCH=arm
kali@kali:~$ mkdir -p ~/arm-stuff/kernel/toolchains/
kali@kali:~$ cd ~/arm-stuff/kernel/toolchains/
kali@kali:~$ git clone git://gitlab.com/kalilinux/packages/gcc-arm-eabi-linaro-4-6-2.git
kali@kali:~$ export CROSS_COMPILE=~/arm-stuff/kernel/toolchains/gcc-arm-eabi-linaro-4.6.2/bin/arm-eabi-

Then simply invoke the build script for the specific platform. So, for a Raspberry Pi build of Kali Linux 2016.2, execute the commands:

kali@kali:~$ cd ~/
kali@kali:~$ kali-arm-build-scripts/rpi.sh 2016.2

The ARM build scripts are all completely self-contained, aside from the initial one-time installation of the build prerequisites. The first time you run one of the ARM build scripts, it is extremely important that you inspect the output for any errors such as missing tools, etc., correct them, and then re-run the script until you get a clean build. Only at that point can you go ahead to make any customizations you want to the basic build script to create the specific “recipe” you’re after.

It’s possible to speed up your builds by caching the packages you download, using a caching proxy such as approx (recommended) or apt-cacher-ng, as described in the previous article. Note that this can break some of the standard build scripts unless you uncomment certain lines before building - they’re noted in the scripts themselves. If you’re using approx or apt-cacher-ng, make sure you check your scripts for any necessary changes.

For reliable and predictable results, build your Kali Linix ARM chroot from within a pre-existing and up-to-date Kali Linux environment. This guide assumes that you have already set up your ARM cross-compilation environment.

The build described here is both minimal and generic. A small number of basic packages are included, and the fuller configuration needed for a real-world platform is omitted for the sake of clarity. Use this example as a reference for understanding what’s going on in the official ARM build scripts and as a high-level guide for writing your own build scripts. It can be successfully followed as a stand-alone tutorial from the command line, but the image produced is not likely to run on any particular device. Use the pre-rolled build scripts, either as-is or with your own customizations, to produce working images for concrete hardware.

This is a general set-up task, and should only ever need to be done once:

kali@kali:~$ sudo apt install -y debootstrap qemu-user-static

In order to enable the Linaro cross-compilation, you will need to set these environment variable at the beginning of every session:

kali@kali:~$ export ARCH=arm
kali@kali:~$ export CROSS_COMPILE=~/arm-stuff/kernel/toolchains/gcc-arm-eabi-linaro-4.6.2/bin/arm-eabi-

This is where you define some environment variables for your required ARM architecture (armel vs armhf) and list the packages to be installed in your image. These will be used throughout this article, so make sure to modify them to your needs:

kali@kali:~$ export packages="xfce4 kali-menu wpasupplicant kali-defaults initramfs-tools u-boot-tools nmap openssh-server"
kali@kali:~$ export architecture="armhf"

As our starting point, we’ll create a standard directory structure and use debootstrap to install a base ARM rootfs from the Kali Linux repositories. We then copy over qemu-arm-static, an ARM emulator, from our host machine into the rootfs in order to initiate the 2nd stage chroot:

kali@kali:~$ mkdir -p ~/arm-stuff/kernel # should have already been created when setting up x-compilation
kali@kali:~$ mkdir -p ~/arm-stuff/rootfs
kali@kali:~$ cd ~/arm-stuff/rootfs/
kali@kali:~$
kali@kali:~$ debootstrap --foreign --arch $architecture kali-rolling kali-$architecture http://http.kali.org/kali
kali@kali:~$ cp /usr/bin/qemu-arm-static kali-$architecture/usr/bin/

First, we’ll chroot into our newly-created base rootfs, use debootstrap a second time to construct our second-stage rootfs, and configure base image settings such as repositories (in /etc/apt/sources.list), host name (in /etc/hostname), default network interfaces and behavior (in /etc/network/interfaces and /etc/resolv.conf), etc. Change these to suit your requirements:

kali@kali:~$ cd ~/arm-stuff/rootfs/
kali@kali:~$ LANG=C chroot kali-$architecture /debootstrap/debootstrap --second-stage
kali@kali:~$
cat <<EOF > kali-$architecture/etc/apt/sources.list
deb http://http.kali.org/kali kali-rolling main contrib non-free non-free-firmware
EOF
kali@kali:~$
kali@kali:~$ echo "kali" > kali-$architecture/etc/hostname
kali@kali:~$
kali@kali:~$ cat <<EOF > kali-$architecture/etc/network/interfaces
auto lo
iface lo inet loopback
auto eth0
iface eth0 inet dhcp
EOF
kali@kali:~$
kali@kali:~$ cat <<EOF > kali-$architecture/etc/resolv.conf
nameserver 8.8.8.8
EOF

Now, we’re ready to assemble our third-stage chroot.

This is where your specific customizations come in. Your $packages list is installed, as are keymaps, a default kali user password of “kali” is set, and other configuration changes and fixes are applied:

kali@kali:~$ export MALLOC_CHECK_=0 # workaround for LP: #520465
kali@kali:~$ export LC_ALL=C
kali@kali:~$ export DEBIAN_FRONTEND=noninteractive
kali@kali:~$
kali@kali:~$ mount -t proc proc kali-$architecture/proc
kali@kali:~$ mount -o bind /dev/ kali-$architecture/dev/
kali@kali:~$ mount -o bind /dev/pts kali-$architecture/dev/pts
kali@kali:~$
kali@kali:~$ cat <<EOF > kali-$architecture/debconf.set
console-common console-data/keymap/policy select Select keymap from full list
console-common console-data/keymap/full select en-latin1-nodeadkeys
EOF

Here, we’ll create the script to do the third-stage chroot

kali@kali:~$ cat <<EOF > kali-$architecture/third-stage
#!/bin/sh
dpkg-divert --add --local --divert /usr/sbin/invoke-rc.d.chroot --rename /usr/sbin/invoke-rc.d
cp /bin/true /usr/sbin/invoke-rc.d

apt-get update
apt-get install -y locales-all
#locale-gen en_US.UTF-8

debconf-set-selections /debconf.set
rm -f /debconf.set
apt-get update
apt-get install -y locales-all
apt-get install -y git-core binutils ca-certificates initramfs-tools u-boot-tools
apt-get install -y locales console-common less vim git
echo "kali:kali" | chpasswd
sed -i -e 's/KERNEL\!=\"eth\*|/KERNEL\!=\"/' /lib/udev/rules.d/75-persistent-net-generator.rules
rm -f /etc/udev/rules.d/70-persistent-net.rules
apt-get install -y --force-yes ${packages}

rm -f /usr/sbin/invoke-rc.d
dpkg-divert --remove --rename /usr/sbin/invoke-rc.d

rm -f /third-stage
EOF

Now, we’ll run it from within our second-stage chroot:

kali@kali:~$ chmod +x kali-$architecture/third-stage
kali@kali:~$ LANG=C chroot kali-$architecture /third-stage

If you need to make any further modifications in your rootfs environment, you can do so by manually chrooting into it with the following command and making any needed changes:

kali@kali:~$ LANG=C chroot kali-$architecture

Once you’ve completed your modifications, leave the chroot’ed rootfs with the command

kali@kali:~$ exit

Lastly, we create and run a cleanup script in our chroot to free up space used by cached files and run any other cleanup jobs we may require, and unmount the directories we were using in our rootfs:

kali@kali:~$ cat <<EOF > kali-$architecture/cleanup
#!/bin/sh
rm -rf /root/.bash_history
apt-get update
apt-get clean
rm -f cleanup
EOF
kali@kali:~$
kali@kali:~$ chmod +x kali-$architecture/cleanup
kali@kali:~$ LANG=C chroot kali-$architecture /cleanup
kali@kali:~$
kali@kali:~$ umount kali-$architecture/proc
kali@kali:~$ umount kali-$architecture/dev/pts
kali@kali:~$ umount kali-$architecture/dev/
kali@kali:~$
kali@kali:~$ cd ../

Congratulations! Your custom Kali ARM rootfs is located in the ~/arm-stuff/rootfs/kali-$architecture directory. You can now tar up this directory or convert it to an image file for further work.