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Common Unix Printing System turns into Apple's Printing System

The Common UNIX Printing System (CUPS) is a widely used suite of software and protocols used for printing documents and organising printer queues. CUPS is superior to the LPR system commonly used on UNIX® systems in the past. CUPS is developed by Apple since 2007. CUPS features its own network protocol and discovery of neighbouring CUPS servers (called „CUPS browsing“). This is about to change for some of CUPS' features will be dropped beginning with release 1.6. The mechanism will be moved to using DNS-SD instead of UDP broadcasts. If you rely on CUPS printer discovery, then you are in for a change.

In theory using DNS-SD for local resource discovery is not a bad idea. Multicast has its advantages over broadcasts. However just adding Avahi on GNU/Linux system won't do the trick. You still need the proper service definitions on machines providing these services. Getting the proper file for putting it into /etc/avahi/services/ can be a very frustrating experience. Even Mac OS X needs manual intervention to discover printers on the local network, contrary to all the rumours about its „point-and-click“ approach and user friendliness. And we haven't talked about Microsoft Windows® yet where the discovery of services works differently. You can install the Bonjour implementation for Windows®, but according to our tests it works worse than on GNU/Linux or Mac OS X.

If you do not deploy multicast routing or have all your clients in the same multicast segment, then you will miss CUPS browsing. A classic example being road-warriors connecting via VPN. Unless there is bridging involved, you won't get the list of printer queues. Of course, you can deploy DNS-SD routing or proxying. The question is why, because CUPS browsing can be configured to use HTTP and fetch all queues from your master CUPS server.

It's a small step for Apple, but it's a giant leap backwards for many others. Maybe the reason for the changes is the essence of this statement taken from the changes announcement on the Fedora development mailing list: „Apple is removing some filters from CUPS as they are not needed for Mac OS X.“ If it's of no use to OS X, then drop it. Let other deal with non-OS X stuff: „These filters will be maintained in a new "cups-filters" project at OpenPrinting.“ Interesting idea, but quite a deviation from a common printing system.