Running Arch Linux in Chroot on Android ARM

Hey guys!
In this tutorial I'll show you how to run Arch Linux (ARM edition) within Android in a chroot environment.

Undue Credit

This post was a base for mine. Do check it out! :)

 

Things you'll need

• (Recommended) A Linux distribution on your PC (If you don't have any PC at hand, continue with all steps using a terminal emulator)
• ADB (Android Debugging Bridge)
• A rooted Android phone
• The Arch Linux ARM rootfs tar.gz for specific phone architecture (ARM v5, v6 or v7 or AArch64. Download the multi-arch version for your specific architecture) Get Here
• Any Terminal Emulator on Android (Suggestion: JuiceSSH)
• a 1GB or greater microSD card (recommended atleast 2GB for the entire distro)
• A basic knowledge of using ADB
• An interest for commandline-fu

 

Reasons for choosing Arch Linux

Arch Linux (due to its rolling release) can support the quite old 3.0.101 kernel running on my device. Other distros seem to require a higher minimum kernel version.

Also, arch is a really minimal distro and so, it's a perfect fit for Android devices where storage space and RAM is frequently constrained (I have mine running on my 512MB RAM device quite smoothly)

 

Notations

I'll use a few notations for clarity:

$ - PC normal user terminal

# - Device root terminal 

/emmc/ - External SDCard

/sdcard/ - Internal Storage

arch.tar.gz - Arch Linux rootfs in tar.gz

 

Method

1. Download the Arch rootfs and transfer to your device
2. Create a disk image file for the distro.
1. If you're on your PC, enter the following in a terminal:
        $ truncate --size 1024M arch.img 
   The above creates a 1GB (1 * 1024MB) disk image. If you want more, increase the 1024 part (SIZE_IN_GB * 1024)
2. If on the device, use dd (EXERCISE EXTREME CAUTION WHEN USING DD!)
        # dd if=/dev/zero of=arch.img bs=1048576 count=1024
   Again, the above creates a 1GB file (For those who are wondering what "bs" is, it's block size and in the above command, it is set to 1MB [1024 * 1KB]). If you need a bigger image, change the "count=..." and set it equal to (SIZE_IN_GB * 1024)
3. Make an ext4 file system on the disk image by entering:
        $ mkfs.ext4 arch.img
4. Transfer the image file to the device (Use the external storage if possible)
5. Open a terminal, connect to the device using ADB and open a root shell (or if you're already using a terminal emulator, continue). Then, mount the disk image by typing:
        # mkdir /data/chroot
     # losetup /dev/block/loop7 /emmc/arch.img
     # mount -t ext4 /dev/block/loop7 /data/chroot
6. Now, extract the Arch Linux rootfs by entering:
        # cd /data/chroot/
     # tar xf /emmc/arch.tar.gz
7. Next, set it up by issuing:
        # rm /data/chroot/etc/resolv.conf
     # echo "nameserver 8.8.8.8" > /data/chroot/etc/resolv.conf
     # echo "export HOME=/root" >> /data/chroot/etc/profile
     # echo "unset LD_PRELOAD" >> /data/chroot/etc/profile
     # echo "cd /root" >> /data/chroot/etc/profile
8. Finally, enter the chroot by these final commands:
        # mount -o bind /dev/ /data/chroot/dev/
     # mount -t proc proc /data/chroot/proc/
     # mount -t sysfs sysfs /data/chroot/sys/
     # mount -t tmpfs tmpfs /data/chroot/tmp/
     # mount -t devpts devpts /data/chroot/dev/pts/
     # chroot /data/chroot/ /bin/bash -l
9. If successful, the terminal should read [root@localhost ~]

Congratulations, Your Arch Linux chroot is up and running!

 

After Setup

• Update the entire distro by issuing "pacman -Syu". Wait for it to finish
• Remove the linux kernel and firmware files from the chroot by issuing "pacman -Rs linux-<architecture>" where <architecture> is one among armv5, armv6, armv7 and aarch64. This can save a considerable 200MB of space.
• If you're planning to use the chroot for penetration testing, install the BlackArch Repository for an ocean of tools.
• Here's a tiny script to automate the mounting and starting process:
  --------------START OF SCRIPT---------------------- 
#!/bin/sh
losetup /dev/block/loop7 /emmc/arch.img
mount -t ext4 /dev/block/loop7 /data/chroot/
mount -o bind /dev/ /data/chroot/dev/
mount -t proc proc /data/chroot/proc/
mount -t sysfs sysfs /data/chroot/sys/
mount -t tmpfs tmpfs /data/chroot/tmp/
chroot /data/chroot/ /bin/bash -l
---------------------END OF SCRIPT---------------------- 
• You can install a VNC server to enable a GUI (Package: tigervnc)

As always, please do comment, follow and share my posts! :)
Cheers!
-Technohacker