Printing Files and Pipelines
Usually one or more printers exist on a UNIX system. The system administrator gives each printer a name so that users can specify the printer or group of printers to which they want their output to go. Users use the lp or lpr commands to print to the desired printer.
Introducing the UNIX Spooling System
What actually happens is that the text to be printed is saved in a system disk file, called a spool file. Each different print job gets its own spool file. The lp/lpr command actually completes very quickly because it does not take long to save all the text in a disk file. This process is called queuing up a printer request. A print scheduler program, which runs in the background, waits for the desired printer to ...