The Common UNIX Printing System (CUPS), which manages all printing duties on Ubuntu Linux, is designed to be as “plug-and-play” as possible. If you are connected to a large corporate or university Wi-Fi network, CUPS will constantly scan the network for shared printers using protocols like IPP or Bonjour. When it discovers a new, available printer, Ubuntu has a nasty habit of automatically changing your system’s Default Printer to match the newly discovered device.
If you have a dedicated, high-quality laser printer sitting on your desk that you use for 99% of your work, this automatic switching is infuriating. You might press Ctrl+P to print a critical document, only to realize seconds later that Ubuntu silently changed your default printer and just routed your confidential document to a random inkjet printer three floors below you.
You can lock your default printer in place by modifying the CUPS configuration.
How to Stop CUPS from Changing the Default Printer
You can configure CUPS via a local web interface built into Ubuntu.
- Open your web browser (e.g., Firefox).
- In the address bar, type
localhost:631and press Enter. This will open the CUPS web administration page. - Click on the Administration tab at the top of the page.
- Under the “Server” section on the right, look at the list of checkboxes.
- Uncheck the box labeled Show printers shared by other systems.
- Click the Change Settings button to apply the change. (You may be prompted to enter your Ubuntu administrator username and password).
By preventing CUPS from seeing randomly shared network printers, Ubuntu will no longer have any alternative devices to switch to. Your manually selected default printer will remain locked in place indefinitely, ensuring your documents always print exactly where you expect them to.