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Termux

How to setup an SSH server on an Android device

This does not require root access.

Install and open Termux on your phone.

You'll see a terminal, a welcome message and a command prompt.

Install OpenSSH:

pkg install openssh

If needed, or the package wasn't found, try updating the registry and upgrading existing packages first:

pkg upgrade

Note: You may be prompted to confirm the operation. Enter y to confirm. You may also be prompted to decide to update configurations files (y) or keep as is (n, the default). Either is fine. This may happen several times.

Install Nmap:

pkg install nmap

Run Nmap to verify an SSH server is not running:

nmap localhost

Note: There shouldn't be any ports opened listed.

Start an SSH server in your phone:

sshd

Verify it's running:

nmap localhost

Note: You should now see the port 8022 opened.

Get the IP address of the device. We'll use this address to connect to the SSH server from an external machine on the same network:

ifconfig wlan0

Note: You can also try with ifconfig and look for it there if the above doesn't yield anything. Local IP addresses usually start with 192.168, e.g. 192.168.100.10

To securely log into the SSH server we'll setup public key authentication.

On your machine (where you'll connect to your device), open a terminal and enter:

cd ~/.ssh
ssh-keygen -t rsa -b 4096 -f termux

Enter a passphrase for your new key when prompted.

This will generate an RSA key with 4096 bits named termux.

Note: The above assumes you have OpenSSH installed on your machine, i.e. ssh-keygen binary and ~/.ssh folder exist

Copy the new key from your machine to your device:

ssh-copy-id -p 8022 -i termux IP_ADDRESS

Where IP_ADDRESS should be the local IP address of the device.

Note: If the command failed, try copying and pasting the contents of termux.pub (from your machine) into ~/.ssh/authorized_keys (in your device)

On your device, restart the SSH server for the changes to take effect:

pkill sshd
sshd

On your machine, connect to the SSH server:

ssh -i ~/.ssh/termux -p 8022 IP_ADDRESS

You should have successfully logged into your Android device from your machine using SSH.

To log out of your session enter:

exit

Further security

In addition to the above, and to avoid risks, you should disable password authentication (enabled by default).

To do this edit the SSHD configuration file on your device located at $PREFIX/etc/ssh/sshd_config:

nano $PREFIX/etc/ssh/sshd_config

And change yes to no:

-PasswordAuthentication yes
+PasswordAuthentication no

Save the file, and restart the SSH server.

How to simplify the connection

Remembering the exact ssh command with its parameters and options may be cumbersome.

You can leverage the SSH configuration file to help with that

On your machine, edit your configuration file at ~/.ssh/config and add something like:

+Host android
+	HostName 192.168.100.10
+	IdentityFile ~/.ssh/termux
+	Port 8022

Where:

  • android is an alias for the hostname
  • 192.168.100.10 is the local IP address of the device
  • ~/.ssh/termux is the path to your (Termux SSH) public key
  • 8022 is the port of the SSH server

You can then log into your device by entering:

ssh android

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