The Douro should not be unplugged from wall power prior to properly powering it off. Unexpected power loss could result in corruption of the tablet's hard drive and require replacement.
The machine should first be shut down by using a single press and release on the power button to the Aaeon tablet inside the door.
Please wait for a full shutdown, which includes the Lubuntu splash-screen, followed by a fully black screen. Then you may unplug from wall power.
The machine may be rebooted remotely with the 'ssu reboot' command.
To physically reboot the machine, press and release once on the tablet's power button, wait for full shutdown, then press once again to boot. Do not hold down the power button (long press) to reboot, as this results in a sudden loss of power.
To avoid data corruption from power loss, we recommend using an uninterruptible power supply (UPS), such as those by APC.
Resolving the GRUB boot loader screen
If the machine encounters an unexpected loss of power, upon the next boot it may present a text-based GRUB boot loader screen. To bypass this, connect a USB keyboard to the top of the tablet and press Enter on the first selection.
To bypass the screen permanently, see this article. However, this error screen serves as an indication of an improper shutdown that should be avoided.