Connect to Android using SSH and Termux

This guide explains how to connect to your Android device from a Linux desktop using SSH (Secure Shell), with the help of the Termux app. SSH allows you to securely access your phone's command-line environment remotely from another machine on the same network.

Step 1: Install and Configure SSH in Termux

Open the Termux app on your Android phone.
Update and upgrade Termux packages:
```
pkg update && pkg upgrade
```
Install the OpenSSH package:
```
pkg install openssh
```
Start the SSH daemon:
```
sshd
```
To stop the server later, run:
```
pkill sshd
```

Step 2: Find Your Android Device's IP Address

Make sure your Android phone and Linux desktop are connected to the same Wi-Fi network.
In Termux, run:
```
ip address
```
Look for the inet address under the wlan0 interface (typically something like 192.168.x.x or 10.0.x.x).

Step 3: Connect to Your Phone from a Linux Desktop

On your Linux desktop, open a terminal.
Connect to the Android device using:
```
ssh -p 8022 username@192.168.x.x
```
Replace username with the output of the whoami command from Termux (usually u0_aXXX) or set a password using:
```
passwd
```
Enter the Termux password when prompted.

Optional: Set Up SSH Key-Based Authentication

To avoid entering your password each time and improve security, set up SSH key-based authentication.

Generate an SSH Key Pair on Linux

Run the following command on your Linux desktop:

ssh-keygen -t ed25519

Alternatively:

ssh-keygen -t rsa -b 4096

Accept the default file location.
Choose whether to set a passphrase.

This creates two files in ~/.ssh/:

id_ed25519 or id_rsa: private key
id_ed25519.pub or id_rsa.pub: public key

Copy the Public Key to Your Android Device

Run the following command on your desktop:

ssh-copy-id -p 8022 username@192.168.x.x

If ssh-copy-id fails, you can do it manually:

On your Linux desktop:
```
cat ~/.ssh/id_ed25519.pub
```
Copy the key to clipboard.
Connect to Termux:
```
ssh -p 8022 username@192.168.x.x
```

Inside Termux:

mkdir -p ~/.ssh
chmod 700 ~/.ssh
nano ~/.ssh/authorized_keys

Paste the public key, save and exit.
Set permissions:
```
chmod 600 ~/.ssh/authorized_keys
```

Final Step: Connect Using SSH Key

Use the same SSH command:

ssh -p 8022 username@192.168.x.x

If you set a passphrase, it will be prompted; otherwise, you will be logged in directly.

Summary Table

Step	Command Example
Install OpenSSH	`pkg install openssh`
Start SSH server	`sshd`
Get IP address	`ip address`
Set password	`passwd`
SSH into device	`ssh -p 8022 username@192.168.x.x`
Generate SSH keys	`ssh-keygen -t ed25519`
Copy SSH key automatically	`ssh-copy-id -p 8022 username@192.168.x.x`

This setup allows your Android device to function like a lightweight and secure remote-access terminal.