LPD controls everything about a host's printers. It is responsible for a number of things:
It controls access to attached printers and printers attached to other hosts on the network.
It enables users to submit files to be printed; these submissions are known as jobs.
It prevents multiple users from accessing a printer at the same time by maintaining a queue for each printer.
It can print header pages (also known as banner or burst pages) so users can easily find jobs they have printed in a stack of printouts.
It takes care of communications parameters for printers connected on serial ports.
It can send jobs over the network to a LPD spooler on another host.
It can run special filters to format jobs to be printed for various printer languages or printer capabilities.
It can account for printer usage.
Through a configuration file (/etc/printcap), and by providing the special filter programs, you can enable the LPD system to do all or some subset of the above for a great variety of printer hardware.
If you are the sole user of your system, you may be wondering why you should bother with the spooler when you do not need access control, header pages, or printer accounting. While it is possible to enable direct access to a printer, you should use the spooler anyway since:
LPD prints jobs in the background; you do not have to wait for data to be copied to the printer.
LPD can conveniently run a job to be printed through filters to add date/time headers or convert a special file format (such as a TeX DVI file) into a format the printer will understand. You will not have to do these steps manually.
Many free and commercial programs that provide a print feature usually expect to talk to the spooler on your system. By setting up the spooling system, you will more easily support other software you may later add or already have.
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