Printing on Air

Version 4.2 of iOS was the first to give the Apple iPad and iPhone the ability to print – but only on printers that support the technology known as AirPrint [1]. AirPrint devices are now available from all major manufacturers in every price and performance class, but many users are still wary of having to buy a new printer just to put something from their iPhone or iPad onto paper.

Luckily, if your home network includes a Linux machine, you have access to all the tools you need to share your printers on the network as AirPrint-enabled devices. AirPrint is based on the zero-configuration (Zeroconf) networking standard [2], which Apple markets under the brand name Bonjour. Linux has its own implementation of Zeroconf known as Avahi [3].

As early as 2011, Till Kamppeter modified the Common Unix Printer System (CUPS) implementation for the Ubuntu "Natty" and "Oneiric" versions so that connected AirPrint printers are directly available [4]. If your distro doesn't support direct configuration, it pays to know how to set up AirPrint support manually. In this article, I take a look at AirPrint with Linux.

CUPS

AirPrint is a technology that lets the device send PDF files to the printer. For this purpose, it sends information about the number of copies and page numbers that the user actually wants to print. A working installation of CUPS should be all you need to let iPad and iPhone find the network-shared printers and print to them.

Unfortunately, Apple has now removed some important features from CUPS that are not necessary on Mac OS X, because they are provided there by the Bonjour service [5]. Fortunately, Linux reintroduces these missing features through Avahi, which includes the necessary functions.

CUPS configuration in Linux is described by numerous web sources [6]. In this article, I assume a working version of CUPS is running on your system. Once the CUPS service is running, first check whether your printer is working by printing a test page. (Open a browser and enter the URL http://<hostname>:631.) You can reach this page from any other computer on the network. In the Printers tab below Management, you will see the command for outputting the test page.)

To share the printer on the network, make sure the /etc/cups/cupsd.conf file contains the appropriate entries. Listing 1 shows an example from the test system. The first two lines are important here; they allow any client to access the server. These lax permissions facilitate attacks on the service. It is thus important to consider any changes you make.

Change the file accordingly and restart the CUPS system. On openSUSE, you can do the following:

sudo systemctl restart cups.service

On Ubuntu and other Debian systems, however, use the following command:

sudo /etc/init.d/cups restart

Now you should be able to find the printer from a Windows computer. To do this, Add a new network printer in the Control Panel and then type the address of the CUPS server and the name of the printer as the name of the shared printer (Figure 1).

Figure 1: If you additionally want to use the shared printer on Windows, set up a new network printer on the system in question.

Windows asks for the printer model to install the correct driver. If you see an Unable to connect message here, check your CUPS installation and the network share for the printer again.

Avahi

For Apple devices to be able to recognize the printer, you need to advertise it via a Bonjour broadcast on the network. To do this, set up an Avahi service. The configuration files for these services can be found in the /etc/ahavi/services directory. Listing 2 shows the AirPrint HP1220C.service file on our lab system.

Admittedly, creating and modifying these service files manually for each printer on the system might not be everybody's idea of fun. Luckily, developer Timothy J. Fontaine implemented a small Python script (Listing 3), that automatically creates these files for all CUPS printers on the system [7].

wget https://github.com/tjfontaine/airprint-generate/zipall/master
unzip master
cd tjfontaine-airprint-generate-fb98c1d/
./airprint-generate.py
mv AirPrint-HP1220C.service /etc/avahi/services
sudo systemctl restart avahi-daemon.service
sudo systemctl restart cups.service

The steps are easy enough: Just run the script without any parameters once for each printer; this gives you a file that you then copy to the /etc/avahi/services directory. After restarting Avahi and CUPS, you should be able to print from Apple devices without any problems.

Creating MIME Types

What we have looked at thus far will fail if you happen to have iOS version 6 or newer installed on your device. In this case, you also need to create new MIME types to associate incoming data correctly. This is fairly straightforward (Listing 4).

echo "image/urf urf string(0,UNIRAST<00>)" > /usr/share/cups/mime/airprint.types
echo "image/urf application/pdf 100 pdftoraster" > /usr/share/cups/mime/airprint.convs