Chroot on Android using Termux

Guide originally by ELWAER-M. Modified and added to by TuralTo.

Content

• Setting chroot up
  • Good to Mention
  • Setting termux up
  • Choosing a rootfs
  • Extracting the rootfs
  • Making a script to launch the chroot environment
  • Troubleshooting
    • Fixing apt under debian based ditros
    • Fixing network issues
  • Problems that you may encounter
• Additional Stuff
  • Setting audio up

Good to Mention

• You need a rooted device for chroot
• The device used here is a Samsung A20 phone running Android 11 Red Velvet Cake
• If you damage your device in any way, you are all responsible for it!

Setting termux up

You have to add root-repo and install tsu in order to get root access under the Termux environment:

$ apt install root-repo
$ apt update
$ apt install tsu

Choosing a rootfs

The rootfs architecture has to match with your device's architecture. In order to know what architecture your device has:

$ uname -m

(e.g. aarch64, armv7l).

You can get Debian rootfs matching your architecture from jubinson's repo for example. The most up-to-date rootfs I could find is Ubuntu Base at the time of writing and to my knowledge. You should be able to use any rootfs within this format.

Extracting the rootfs

Any location under /data should be good (because it is formatted as ext4) so you can use your termux home directory (because it's under /data too "/data/data/com.termux/files/home"), or /data/local

e.g.

$ mkdir chroot #or anything else
$ sudo tar xfp /sdcard/Download/rootfs.tar.xz -C ./chroot #to keep the files permissions

Making a script to launch the chroot environment

Use vim, nano or any text editor you like:

$ nano run-chroot.sh

A simple example:

#!/data/data/com.termux/files/usr/bin/sh

# fix /dev mount options
mount -o remount,dev,suid /data

mount --bind /dev ./chroot/dev
mount --bind /sys ./chroot/sys
mount --bind /proc ./chroot/proc
mount --bind /dev/pts ./chroot/dev/pts

# disable termux-exec
unset LD_PRELOAD

export PATH=/bin:/sbin:/usr/bin:/usr/sbin
export TERM=$TERM
export TMPDIR=/tmp

chroot ./chroot /bin/su - root

Then change the file permissions to executable:

$ chmod +x run-chroot.sh

Run it (as root):

$ sudo ./run-chroot.sh

Troubleshooting

Fixing network issues

You have to add a DNS to resolv.conf (The DNS server used here is Google's):

echo "nameserver 8.8.8.8" > /etc/resolv.conf

Then you need to add android root groups:

groupadd -g 3001 aid_bt
groupadd -g 3002 aid_bt_net
groupadd -g 3003 aid_inet
groupadd -g 3004 aid_net_raw
groupadd -g 3005 aid_admin

Add those groups to the user you are using (in this case root):

usermod -a -G aid_bt,aid_bt_net,aid_inet,aid_net_raw,aid_admin root

Fixing apt under debian based ditros

usermod -g 3003 _apt

You can only use this command after you've added the groups found in this section.

Problems that you may encounter

"Could not open session" when trying to start chroot

This error is bound to the rootfs, so it may or may not be present in the rootfs you are using. The solution usually (and in my case) is commenting out or removing this line in /etc/pam.d/su-l:

session optional pam_keyinit.so force revoke

Other solutions that people reported working:

• Deleting /var/log/btmp

Additional Stuff

Setting up audio (pulseaudio)

On the server side (chroot):

Before running the script make sure pulseaudio is running. If it isn't:

$ pulseaudio --start

Use your preffered text editor (in this case nano):

$ nano pashare

An example script to setup the server:

#!/bin/sh
case "$1" in
  start)
    $0 stop
    pactl load-module module-simple-protocol-tcp rate=48000 format=s16le channels=2 source=<source_name_here> record=true port=8000
    ;;
  stop)
    pactl unload-module `pactl list | grep tcp -B1 | grep M | sed 's/[^0-9]//g'`
    ;;
  *)
    echo "Usage: $0 start|stop" >&2
    ;;
esac

Make it executable:

$ chmod +x pashare

Run the scipt like this:

$ ./pashare start # replace with "stop" if you want to stop

The script is from this post.

On the client side (your phone):

• Install Simple protocol player, PulseDroid for Android.
• In the app set:
  • IP Address/Hostname/Server to 127.0.0.1.
  • Port to 8000(in this case. set by the script).
• And connect!