If you are unable to access your Preseem appliance using the root password, it is possible to reset the root password from the console. To connect to console, please refer to the article on how to do it.
We assume that you now have a terminal window open. Power off the Preseem appliance, and power it back on. In a few seconds, you should see the boot menu, which will look like this:
Press the "e" key. You should see a menu like this:
Use the Down arrow key to scroll down the line starting with "linux16". This was line 13 on the appliance we used, but it may vary. Use the arrow keys to go to the end of the line, or press Ctrl+E to get there instantly.
At the end of the line, add a space and then "rw init=/bin/bash" without the quotes. It should look like the picture below.
Press Ctrl+X to start the appliance with that configuration. In a few seconds, you should get a root prompt (#).
Type "passwd" and press enter, and you will be prompted for a new password.
Next, type the following command:
Then reboot the system:
When the system next boots, it will take a few minutes to relabel the system.
Once that process is complete, it will reboot itself once more and then you should be able to login as root with the new password.