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Line Printer Daemon protocol
The Line Printer Daemon protocol (or LPR, LPD) also known as the Berkeley printing system, is a set of programs that provide printer spooling and network print server functionality for Unix-like systems. The most common implementations of LPD are the official BSD UNIX operating system and the LPRng project. The Common Unix Printing System (or CUPS), which is more common on modern Linux distributions, borrows heavily from LPD.
The official LPD protocol defines the following commands:
- lpr—Assign a job to a queue.
- lpq—Display the jobs assigned to a queue and their print status.
- lprm—Remove a job from a queue.
- lpc—Control a queue.
The lpd program provides the daemon and queues with which the aforementioned commands interface.
In order that a system provide print functionality using LPD, the lpd program must be configured and started. Based upon its configuration, it will create the necessary queues and address the printers available to users of the system. Once started, it listens for local messages from the lpr, lpq, lprm, and lpc programs, as well as for network messages from remote clients who also implement the LPD protocol.
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