The Dizzying Display
Many modern laptops, 2-in-1 convertibles, and tablets running Ubuntu come equipped with internal accelerometers. By default, the GNOME desktop environment utilizes this hardware sensor to automatically change the screen orientation. If you tilt your laptop sideways, the screen immediately rotates 90 degrees into Portrait mode. While brilliant for reading long documents on a tablet, this feature is incredibly annoying if you are simply using your laptop in bed and shifting your posture, only to have your desktop, windows, and mouse controls violently rotate sideways.
Locking the Rotation
To ensure your desktop remains locked to your preferred layout and stop Ubuntu from automatically changing the screen orientation based on physical movement, you must lock the rotation settings.
The fastest way to lock the screen is directly from the system tray. Click on the group of icons in the extreme top-right corner of your screen (where your battery, Wi-Fi, and volume icons live) to open the Quick Settings menu. Look for the circular icon resembling a screen with a curved arrow—this is the Rotation Lock toggle. If it is grey, auto-rotation is active. Click it once so the icon turns solid (and usually changes to a padlock icon). This instantly freezes the screen in its current orientation. Alternatively, you can open the main Settings app, navigate to Displays, and explicitly toggle the Orientation setting from “Automatic” to “Landscape.”