lpr.exe: Windows Line Printer Remote

Overview

lpr.exe is a command-line utility in Windows operating systems that implements the Line Printer Remote (LPR) protocol. This protocol, defined in RFC 1179, is a legacy network printing protocol used to send print jobs to a print server or a network-connected printer that supports LPR. It's a relatively simple protocol, predating more modern and feature-rich printing protocols like IPP (Internet Printing Protocol). While less common today due to the prevalence of newer protocols, lpr.exe remains part of Windows for backward compatibility and specialized use cases.

Origin and Function

Origin: lpr.exe originates from the Unix world, where the LPR protocol and related utilities (like lpd, the Line Printer Daemon) were standard components of the printing system. Microsoft included it in Windows to provide interoperability with Unix-based print servers and network printers that still relied on LPR.
Function: The primary function of lpr.exe is to transmit a print job (usually a file) to a remote printer or print server that is configured to receive LPR requests. It acts as an LPR client, sending the print data along with basic control information to the specified destination.

Is it a Virus? Is it Vulnerable?

Is it a Virus?: No, lpr.exe is a legitimate Windows system file. It is not inherently malicious. However, like any executable, it could theoretically be replaced by a malicious file with the same name. This is unlikely in a properly secured system, but it's a general principle to be aware of. The genuine lpr.exe is typically located in C:\Windows\System32.
Vulnerabilities: While lpr.exe itself is not known to have specific, exploitable vulnerabilities, the LPR protocol it uses is inherently less secure than modern printing protocols. LPR lacks robust authentication and encryption, making it potentially susceptible to:
- Spoofing: A malicious actor could potentially send unauthorized print jobs to an LPR-enabled printer.
- Interception: Print data sent via LPR is typically unencrypted, meaning it could be intercepted and read by someone on the network.
- Denial of Service (DoS): A printer or print server could be overwhelmed with a flood of LPR requests, making it unavailable for legitimate users.
It's crucial to understand that these vulnerabilities are primarily associated with the LPR protocol itself, not specifically with the lpr.exe utility. Using lpr.exe on a network that is not properly secured or to a printer that is not properly configured could expose you to these risks. Because of these security concerns, LPR is generally discouraged for use on untrusted networks.

Usage (Tool Software Details)

lpr.exe is a command-line utility, meaning it is used from the Command Prompt or PowerShell. It does not have a graphical user interface. Here's a breakdown of its usage and common options:

Basic Syntax:

lpr -S <server> -P <printer> [-O <option>] <filename>

Parameters and Options:

-S <server>: (Required) Specifies the hostname or IP address of the print server or network-connected printer that supports LPR. This is the destination for the print job.
-P <printer>: (Required) Specifies the name of the printer queue on the print server, or the printer name as configured on the target device. The exact name required depends on the server's configuration. It is case-sensitive on some systems.
-O <option>: (Optional) Specifies additional options. The most common is -O l (lowercase L), which indicates that the file is already formatted for the printer and should be sent as raw data (binary). Without -O l, lpr.exe may attempt to perform text formatting, which can be undesirable for pre-formatted documents or PostScript files. Other less common options might be supported, depending on the specific Windows version and the print server. Refer to lpr /? for possible additional options (though they are rarely used).
<filename>: (Required) The path to the file you want to print. This can be a local file path or a UNC path.

Examples:

Print a text file to a printer named "MyPrinter" on a server with the IP address 192.168.1.100:

lpr -S 192.168.1.100 -P MyPrinter C:\Documents\MyTextFile.txt
Print a PostScript file (already formatted) to a printer named "LaserJet" on a server named "PrintServer," sending it as raw data:

lpr -S PrintServer -P LaserJet -O l C:\Documents\MyPostScriptFile.ps
Print a file with a space in its name: Enclose the filename in double quotes. lpr -S 192.168.1.100 -P MyPrinter "C:\My Documents\File with spaces.txt"

Troubleshooting:

"lpr is not recognized...": This usually means the "Print and Document Services" feature is not enabled.
1. Open "Control Panel."
2. Go to "Programs" -> "Turn Windows features on or off."
3. Expand "Print and Document Services."
4. Check the box for "LPD Print Service" and "LPR Port Monitor". It is possible that only "LPR Port Monitor" needs to be checked, however checking both will ensure the feature works properly.
5. Click "OK" and allow Windows to install the features. A reboot may be required.
"Unable to connect to the print server...": This can have several causes:
- Incorrect server address: Double-check the IP address or hostname of the print server.
- Network connectivity: Ensure your computer can communicate with the print server (e.g., try pinging the server).
- Firewall: A firewall on your computer, the print server, or in between might be blocking LPR traffic (port 515 is commonly used).
- Print server not running LPD: The print server must be configured to accept LPR requests (the LPD service must be running).
- Incorrect printer name: Verify that the printer name you specified with -P is correct.
"The printer is not accepting jobs...":
- Printer offline/error: Check the printer's status.
- Print queue paused: Check the print queue on the print server.
Print job garbled or incorrect:
- If printing a text file, and the output includes unexpected characters or formatting, try the -O l option to prevent lpr from reformatting.
- If printing something other than plain text (like a PDF or Postscript file), always use -O l.

Conclusion