SSH into Termux over USB

In this tutorial, I’m going to provide a step-by-step tutorial on connecting to a Termux shell through SSH by a USB connection.

Prerequisites

• An Android phone running Termux
• A Linux system
• OpenSSH, android-tools/adb installed in the Linux system

Termux setup

• Install openssh in your Termux enviornment by running pkg install openssh
• Verify it works by running sshd. If it does not show any particular errors then it’s working.
• Stop sshd with killall sshd so we can edit it’s configuration file.
• In $PREFIX/etc/ssh/sshd_config, make sure you have the following keys set to their respective values.

  Port 8022
  PubkeyAuthentication no
  PasswordAuthentication yes
  PermitEmptyPasswords yes
  KbdInteractiveAuthentication no
  

  Or if you have the sshd_config.patch file, you can patch it with patch $PREFIX/etc/ssh/sshd_config < sshd_config.patch

• After saving the file, we need to set the user password. To do this, run passwd and set a password. If you already have a password set up, skip this step.
• Finally, run sshd

Client setup

• Connect your phone to your Linux machine through a USB cable.
• Make sure you have enabled USB debugging in your phone.
• Run adb devices to make sure it is connected and is being detected properly.
• Run adb forward tcp:8022 tcp:8022 to forward the ssh port from your phone to your Linux system
• Finally, run ssh localhost -p 8022 to ssh into your system.
• If it asks for a password, enter the password you previously created in the Termux setup step.

Troubleshooting

• If you’re getting any errors related to man-in-the-middle attacks then you should edit or delete the file at ~/.ssh/known_hosts

Security

For the sake of simplicity, I’m not using any certificate based login here. But as we’re connecting over a local network between our phone and the Linux system, the password-based authentication should be fine. But again, I’m not guaranteeing it to be very secure.