There are different methods for auto-discovering driverless IPP network printers.
First, all these printers advertise themselves via DNS-SD, so that clients (computers, phones, TVs, ...) find them. The first step which then happens in your computer is that avahi-daemon picks up the printer's broadcasts. Therefore avahi-browse shows the printers. Every other program, like CUPS, cups-browsed, or print dialogs communicate with avahi-daemon to be able to list the printers. If you stop avahi- daemon the printers will disappear for sure, but other types of remote devices which your computer discovers will disappear, too. For getting the printers from avahi-daemon to the final print dialog there are three methods currently (in the order of how I assume that they appeared): 1. cups-browsed: This one I wrote when CUPS 1.6 came out and dropped its own broadcasting/browsing system to automatically make printers from CUPS servers appear on CUPS clients. CUPS replaced this by the same DNS- SD method which the the driverless IPP printers use but they did not do the client part, print dialogs were supposed to use it. But as in Linux GUI there is certain inertia in development and usually no one taking care of printing, I created cups-browsed to assure continuity in the functionality of Ubuntu. In the beginning cups-browsed did nothing more than picking up DNS-SD broadcasts of remote CUPS printers (with the help of avahi-daemon) and created local CUPS queues to make the printers listed locally and to be able to print on them. During the years I added more functionality, especially also creating local queues for driverless IPP printers. cups-browsed removes its local queues when the remote printer disappears or on (cups-browsed) daemon shutdown. This way I have overcome the lack of the print dialog's functionality and users die not complain about missing remote printers. 2. CUPS: Recently, CUPS added a mechanism to automatically have access to remote IPP printers (both driverless network printers and remote CUPS queues) by listing the printers even without having a local queue and auto-creating a temporary queue when trying to access the printer. The temporary queue is removed after 1 minute being idle or on (CUPS) daemon shutdown. Problem of this approach is that clients, like print dialogs need to use the correct CUPS API to see these printers. As not all of them do so I am keeping cups-browsed in the default installation of Ubuntu. 3. Print dialogs can follow the original idea of the time of CUPS 1.6, grabbing the DNS-SD broadcasts of the printers on its own (using only avahi-daemon) and this way list the printers. Now I do not know how exactly each print dialog is working and which of the three methods leads to the dialog listing the IPP printers. As you have already turned off cups-browsed as a first step, it must be (2) or (3) for the Qt dialog. You can try to turn off CUPS now, but only for testing as this way most probably printing will not work. If the dialog still shows the printers, the Qt dialog uses (3) for sure. Try to print even with CUPS still turned off. Does this work? Does the GTK dialog (for example evince) behave the same? Does also the print dialog of LibreOffice behave the same? Perhaps the dialogs behave all different. We have developed a new methods in which the dialogs stop accessing printers on their own and use GUI-independent print dialog backends. This new method (4) will hopefully soon make it into the Linux distributions. By the way, with your observation on Qt print dialog showing the printers as driverless only with cups-browsed running is due to how cups-browsed works. It creates local queues and marks them as "driverless" which the dialog shows. The dialog has a mechanism determining whether a remote printer has already a local queue to avoid duplicate listings. So you see the queue from cups-browsed if cups- browsed is running and you see the printer entry from CUPS or from the dialog itself if cups-browsed is not running. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1738432 Title: Regression, poor user experience, print dialogs garbled by unidentifiable driverless printers To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/cups/+bug/1738432/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
