Exercise 4-5: Kali Linux ARM chroot

You'll begin with the SD card from a previous exercise. In this example, we are using the image from the previous exercise (Exercise 4) -- our custom build. First, install qemu cross compiling tools and related tools into Kali:

apt-get install qemu qemu-user qemu-user-static

Let's make a /mnt/sd directory to keep our directories we're working on organized:

mkdir /mnt/sd

Pick up your /dev/sd drive assignment by inserting the Pi's SD card (ours is /dev/sdc). Your USB-SD adapter makes a difference. We are going to pick up all the physical drive mounts in one shot.

root@kali:~# mount /dev/sdc2 /mnt/sd/
root@kali:~# ls -l /mnt/sd
total 88
drwxr-xr-x  2 root root  4096 Aug  5 11:36 bin
drwxr-xr-x  2 root root  4096 Jul 18 03:08 boot
drwxr-xr-x  4 root root  4096 Aug  5 11:15 dev
drwxr-xr-x 71 root root  4096 Mar  1 16:43 etc
drwxr-xr-x  2 root root  4096 Jul 18 03:08 home
drwxr-xr-x 13 root root  4096 Aug  5 12:11 lib
drwx------  2 root root 16384 Aug  5 11:39 lost+found
drwxr-xr-x  2 root root  4096 Aug  5 11:15 media
drwxr-xr-x  2 root root  4096 Aug  5 11:15 mnt
drwxr-xr-x  2 root root  4096 Aug  5 11:15 opt
drwxr-xr-x  2 root root  4096 Jul 18 03:08 proc
drwx------  2 root root  4096 Mar  1 16:43 root
drwxr-xr-x  4 root root  4096 Aug  5 11:15 run
drwxr-xr-x  2 root root  4096 Aug  5 11:36 sbin
drwxr-xr-x  2 root root  4096 Aug  5 11:15 srv
drwxr-xr-x  2 root root  4096 Jul 18 03:08 sys
drwxrwxrwt  7 root root  4096 Mar  1 18:40 tmp
drwxr-xr-x 10 root root  4096 Aug  5 11:15 usr
drwxr-xr-x 11 root root  4096 Aug  5 11:15 var

Did you notice how all the Raspberry Pi's SD card directories are now mapped on your system under /mnt/sd?

Mount up all 'special filesystems' under /mnt/sd. Notice that we will be overriding mount options from /etc/fstab on some that are already mapped with the -o option:

mount -t proc none /mnt/sd/proc
mount -t sysfs none /mnt/sd/sys
mount -o bind /dev /mnt/sd/dev
mount -o bind /dev/pts /mnt/sd/dev/pts

Let's pull the emu cross-compiling tools over. We need these to compile the ARM stuff since our target is ARM!

cp /usr/bin/qemu-arm-static /mnt/sd/usr/bin

Time to enter a chroot! Once inside the chroot, all commends we execute will assume that /mnt/sd is our root filesystem. It's a pretty cool trick. Note that we set LAN=C to suppress locale warnings in your chroot:

LANG=C chroot /mnt/sd/

Let's make some changes to the Pi's filesystem. This is the cool part. All this is happening on your Pi's filesystem!

# apt-get update
# apt-get install mlocate
# apt-get install net-tools
# apt-get install hostapd dnsmasq

Continue configuration as necessary. Once done, exit the chroot and unmount the SDcard.

root@kali:~# exit

We need to unmount all the directories we mounted:

umount /mnt/sd/dev/pts
umount /mnt/sd/dev/
umount /mnt/sd/sys
umount /mnt/sd/proc
umount /mnt/sd

Lastly, insert the SD card into the Pi, and launch!