The LPR/LPD printing system (and its successor LPRng) is the traditional method of printing under UNIX and Linux. The system comprises two elements:
- The LPD printer daemon, which runs on a print server and schedules print jobs from clients.
- The LPR protocol/command, which sends print jobs from the local machine to the LPD server.
On a standalone machine the LPD daemon would run locally and spool print jobs which were sent by the lpr command.
An important feature of LPR/LPD is the separation between the application program producing the print job and the printer driver itself. Applications using LPR to print have no way of obtaining information about the printer model being used, and thus cannot provide the user with configuration options beyond basic paper size and orientation.