Unix Printing Basics

by
Dru Lavigne
, author of
BSD Hacks
07/08/2004
Somewhere there must be a theory stating that the amount of configuration knowledge required is directly proportional to the need for using said configured service. This is certainly often the case with printing.
True, the configuration interfaces have steadily improved in the past few years. However, administrators still need a fair bit of knowledge to understand which particular software bits they need to make the most of the features of a particular printer. Additionally, the vast array of software available often confuses new users. As an example, there are more than 300 print applications available in the ports collection. Where exactly does one start?
In the next few articles, I'll explain some basic printing terminology. I'll also discuss some of the available applications for each printing component and cover some of the pros and cons of each application. Throughout, I'll demonstrate applying this knowledge to an example printer.
If you haven't already, take some time and skim through
the printing section of the FreeBSD handbook
. While you may not understand everything, that section will still give you a good overview of the printing process on a Unix system. If you're new to hardware, you'll also find the "hardware setup" and "troubleshooting" subsections very helpful if you're having problems physically setting up your printer.
The Spooler
Let's start with the various components available when setting up your printer. Regardless of the operating system, the main printing software component will always be the spooler. This piece of software receives your print request, known as a print job, and places it in a print queue. As the name suggests, a queue is a lineup of jobs waiting for their turn to receive access to the hardware printer. The spooler monitors both the queue and the printer. As the printer becomes available, the spooler sends the next job for printing. Once the print successfully completes, the spooler removes the job from the queue and moves on to the next job.
Your FreeBSD system comes with lpd, the original Unix spooler. Another popular spooler,
LPRng
(LPR new generation), is available in the ports collection.
Both spoolers use the printer capability database located in /etc/printcap for configuration. Did you notice that the bulk of the printing section of the handbook deals with the proper configuration of this file? That's for good reason; all printing components rely on the spooler, which calls them based on their appearance in the spooler configuration file. Depending upon your particular printer, it may be easier to create this file manually or use a printer configuration tool to create the necessary /etc/printcap entries. I'll discuss both methods shortly.
Ghostscript
Technically, a configured spooler will allow you to access your printer. You'll often want additional components, though. After all, your printer isn't very useful if it can only print gobbledygook or unformatted text with all of the appeal of plain ASCII on a terminal. It's also rather disappointing if your particular printer model comes with a slew of features, none of which you can access.

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