First, you need to jailbreak your iPad. How to do this is beyond the scope of this document, but an internet search for "jailbreak ipad" will produce useful results.

Once your iPad is jailbroken, you will have a new program called Cydia.

Installing OpenSSH

Run Cydia and tap the "Search" tab.

In the text box, enter "openssh" and search. Tap on the result that is found.

If no result is found when you search for "openssh", you probably have Cydia in "User" mode. Tap the "Manage" tab, then "Settings", then choose either "Hacker" or "Developer". Then come back and search again.

Tap "Install".

Tap "Confirm".

Wait for the installation to complete, then press the Home button to exit Cydia.

Securing your iPad

At this stage, your iPad SSH server is installed, but your system has the Apple-default password "alpine". To protect your iPad from other people accessing it, is strongly recommended that you change your password.

First, we need to find the IP address of your iPad on the Wi-Fi network. Read this FAQ to learn how to find it.

On Windows, you will need to download PuTTY. Download and run "putty.exe" (you don't need the full installer).

Enter the IP address of your iPad, ensure SSH is selected, then click "Open".

On Linux or Mac OS X, simply open a terminal and type ssh -l root <ip address>.

The username is "root", and the default password is "alpine".

Type passwd root to change the root password. You will be prompted to enter it twice, followed by Enter.

Then type passwd mobile to change the mobile user password.

Your iPad is now secure.