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What is LPR/LPD?

​LPR and LPD go together like left and right, front and back. LPR does the sending, and LPD does the receiving. Specifically, LPR sends print commands and queries, while LPD processes the commands and responds to the LPR queries.

What is LPR?

LPR stands for Line Print Requestor. It's the way you ask an LPD printer to print something for you. There are also status commands and a few others.

Synonyms for the LPR program include the client program or the print client. Nearly every computer system has at least one LPR print client. We have a page with sample setups for several print clients. However, we recommend you do a web search for the LPR setup on your target system. The search engines make it easy to find the setup options for any computing environment.

When you set up an outgoing LPR connection, there are two things at the minimum you need to set:

  • the hostname or IP address of the LPD server you send the print jobs to
  • the queue name, on that server, you want to process your print jobs

What is LPD?

LPD stands for Line Print Daemon. I realize this is a very outdated name! The term "daemon" predates my oldest daughter who now has a master's degree. A "daemon" is another name for a system service. Originally on Unix systems, it was a program that ran in the background. Linux systems still run their services, such as the print server or Apache web server, in the same way.

Your printer probably contains LPD software. Microsoft has a free program available for Windows.

Our product, RPM Remote Print Manager® ("RPM"), fully supports the LPD protocol as well as other print protocols and provides functionality sought by our customers since the 1990s. We actively support RPM, offering new features and updates regularly. For instance, we recently added bi-directional printer support, which has no connection to LPD whatsoever. We also have a folder watcher.

What is the LPD service?

The LPD service is the software that provides an LPD port to connect to and answers requests (including printing) from an LPR print client. RPM is an LPD service, and so is the Microsoft LPD Print Services.

A typical LPD service can print jobs, provide status, and remove print jobs that are still waiting to process.

The LPD service and the term LPD printer are synonymous.

The terms "LPD services" or "lpdsvc" also refer to the Microsoft LPD program.

What is an LPD printer?

An LPD printer is any hardware, or any software service, that runs an LPD service like we just described. The HP printer in my office is an LPD printer since the configuration listing shows it supports a couple of LPD queues. Our RPM product is software, and it is an LPD printer as well.

What is an LPD client?

An LPD client is the same thing as an LPR client. It is the client software that sends your print requests to an LPD server. You might think about LPD clients and servers as similar, in a way, to web clients and servers. The web client is where you make requests (by entering a URL or clicking on a link) to a web server, "somewhere" in the internet. While this is technically true, you usually call the web client your "web browser". It's just a habit. Similarly, the LPD client is usually called the LPR client, or the print client. 

What port does LPD use?

LPD uses TCP port 515. Typically port 515 is reserved on any networking computer for LPD printing. Sometimes you'll see it displayed in a network status window as "printer."

You may hear the term "listening port." In TCP/IP, a service listens on a port that has a number associated with it. Like we were saying above, port 515 is the LPD listening port.

What does LPR print mean?

LPR print means to send a print job to a specific computer, to the LPD port on that computer, and specifying which print queue to use for your print job.

If you are using a computer system such as an IBM AS/400 or an HP/UX system, when you print, you may not be using an attached printer. It's likely you direct your print jobs to a printer in your network. Often those print jobs go out using the LPR methodology supported by your vendor.

Similarly, if you use Windows and print from an application, you might use LPR print. Windows printers have a port definition. It's easy to edit an existing printer definition in Windows to use an LPR port. In this case, the Windows spooler sends your print job using LPR to a printer--which could be RPM. Many people use this to extend functionality for their prints, perhaps printing from multiple trays.

What is an LPR port?

There may not be an exact industry definition for LPR port. The common usage suggests it is a printer port intended to send print jobs using the LPR protocol we've been discussing. 

What is an LPR queue name?

As mentioned above in the section "what is LPR?" each request to an LPD printer includes a queue name. This way, you can use one service to process a wide variety of printing tasks, including entirely distinct setups for different operations. The admin sets up named queues, each with its separate processing steps.

What is an LPD port?

An LPD port listens for print requests from an LPR port. The LPD port is part of the LPD service, which does all the work the LPR port communicates. Port numbers are unique, so that you can be sure your request goes to the right software. The LPD port number is 515. On any given computer, port 515 receives print jobs.

About LPD printing

When I was a researcher in the eighties and nineties, the LPD print server we shared for printing tasks had an array of setups, each with a unique name. Each print server setup contained the instructions for printing our particular print jobs according to our requirements. Whenever we had a new type of print task, we'd edit the definition to add a new queue which did whatever we wanted.

The HP printers in our office today typically have two named queues, one for processing raw data already formatted for the printer, the other for accepting plain-text which the printer renders on its own.

RPM fully supports named queues, where you have as many as you want, each with its unique setup instructions. We do not have "default" queues because there is no standard for that. Each vendor has their preferences, so we remain neutral by offering a blank canvas.

We've noticed that our customers create distinctive queue names that capture the destination and the process to an extent. With RPM, anyone can use queue names the make sense to them.

For more information on the LPD protocol, please consult RFC 1179, Line Printer Daemon Protocol, dated August 1990, edited by L. McLaughlin III. You can find the RFC documents at http://www.ietf.org/rfc/

For more information on RPM, start at the RPM intro page, the virtual printer page, or download the 21-day free trial with pre-sales technical support, or contact us.