The Disruptive Timeout
Ubuntu is designed with security in mind. By default, if you step away from your keyboard and leave your computer idle for a short period (usually 5 minutes), the operating system automatically blanks the screen and locks your session. To get back to work, you must wake the monitor and re-enter your user password. While this is a crucial security measure in a busy office or public library, it is incredibly annoying if you are using Ubuntu on a secure home desktop. If you are watching a long YouTube video, reading a lengthy document, or compiling code, having the screen constantly lock and demand a password disrupts your entire workflow.
Disabling the Security Lock
To ensure uninterrupted access to your session and stop Ubuntu from automatically locking the screen when idle, you must adjust the privacy and security settings associated with the screen blanker.
Open the main application launcher and search for Settings. In the left-hand navigation sidebar, scroll down and click on Privacy & Security (in older Ubuntu versions, this might just be “Privacy”). On the right-hand panel, click on the section explicitly named Screen or Screen Lock. You will see several options. The primary setting is the toggle switch labelled Automatic Screen Lock. Click this toggle to turn it completely Off. (Note: You can also leave the lock enabled but change the “Lock screen after blank for” dropdown to a much longer duration if you prefer a compromise). Once disabled, your screen may still go to sleep to save power (depending on your Power settings), but moving the mouse will instantly wake it up without ever asking for your password.