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 Touch seeded packages, which is subscribed to cups in Ubuntu. https://bugs.launchpad.net/bugs/1738432 Title: Regression, poor user experience, print dialogs garbled by unidentifiable driverless printers Status in cups package in Ubuntu: Incomplete Bug description: Recently, my print dialogs have started to include network discoverd printers in addition to those configured in cups even if the cups- browsed service is disabled and the BrowseRemoteProtocols option is set to none. There does not seem to be any way to disable this behavior apart from disabling avahi or its ability to talk to dbus, which causes side effects on the system. Yet, in some environments this behavior is a definite regression over the old one and leads to an extremely poor user experience. On some networks: - The print dialogs takes 3-10 sec to open which is a huge amount of time for an action that is expected to be instantaneous and for which there is no visual feedback. - The print dialog contains many tens of printer entries, all identified by weird hex strings that cannot be related to any useful location, that do not help identifying which entry corresponds to which printer and that only mess up the list making it hard to find the printers that are actually useful. For instance, suppose that you work at some office that has recently purchased a batch of new printers all the same model. In the print dialog you may get many entries like: HP_Laserjet_Pro_Mxxxdw_21ACF2 which only vary in the final hex string. How is one suppose to know what is where? Please make it possible to disable this driverless printer madness. ProblemType: Bug DistroRelease: Ubuntu 17.10 Package: libcups2 2.2.4-7ubuntu3 ProcVersionSignature: Ubuntu 4.13.0-19.22-generic 4.13.13 Uname: Linux 4.13.0-19-generic x86_64 ApportVersion: 2.20.7-0ubuntu3.6 Architecture: amd64 CupsErrorLog: E [15/Dec/2017:12:41:45 +0100] [Client 6] Returning IPP client-error-bad-request for Create-Printer-Subscriptions (/) from localhost CurrentDesktop: KDE Date: Fri Dec 15 16:22:07 2017 EcryptfsInUse: Yes InstallationDate: Installed on 2013-12-12 (1463 days ago) InstallationMedia: Kubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1) MachineType: Notebook W740SU Papersize: a4 ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.13.0-19-generic root=/dev/mapper/zagar_ssd--vg-root ro quiet splash resume=/dev/zagar_ssd-vg/swap_1 acpi_backlight=vendor vt.handoff=7 SourcePackage: cups UpgradeStatus: Upgraded to artful on 2017-10-26 (50 days ago) dmi.bios.date: 10/02/2013 dmi.bios.vendor: American Megatrends Inc. dmi.bios.version: 4.6.5 dmi.board.asset.tag: Tag 12345 dmi.board.name: W740SU dmi.board.vendor: Notebook dmi.board.version: Not Applicable dmi.chassis.asset.tag: No Asset Tag dmi.chassis.type: 9 dmi.chassis.vendor: Notebook dmi.chassis.version: N/A dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr4.6.5:bd10/02/2013:svnNotebook:pnW740SU:pvrNotApplicable:rvnNotebook:rnW740SU:rvrNotApplicable:cvnNotebook:ct9:cvrN/A: dmi.product.family: Not Applicable dmi.product.name: W740SU dmi.product.version: Not Applicable dmi.sys.vendor: Notebook To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/cups/+bug/1738432/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : [email protected] Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
