Running Linux, 5th Edition - Matthias Kalle Dalheimer [268]
Basic Linux Printing Commands
The lpr command prints a document in Linux. You might not always invoke this command directly—you may just press a Print button on some glitzy drag-and-drop graphical interface—but ultimately, printing is handled by lpr and the other print management utilities we describe here.
If you want to print a program listing, you might enter the following:
$ lpr myprogram.c
Input is also often piped to lpr from another command, as described later. The lpr program starts the printing process by storing the data temporarily to a directory called a print spool . Other parts of the print management system, which we show you how to set up in "Managing Print Services" later in this chapter remove files from the print queue in the correct order, process the files for printing, and control the flow of data to the printer.
There is at least one print queue for each printer on the system, but each system has one print queue that's marked as the default. (In the old LPD printing systems, this queue was traditionally called lp, but this naming convention is less common with computers that run CUPS.) If you need to specify a queue of a different name, just include a -P option, as in lpr -Pepson myprogram.c. If you forget the name of a queue, you can look at queue names in the /etc/printcap file, access the CUPS web configuration tool (as described in "Managing Print Services"), or type lpstat -a to see the status of all the queues.
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Tip
A printer that can be used in different modes of operation, such as for printing faxes as well as letters, may have a separate print queue for each purpose. You can also create multiple queues for a single printer in order to use different resolutions, paper sizes, or other features.
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As a user, you do not see whether a printer is connected directly to your computer or somewhere else on the network; all you see and need to know is the name of the printer queue. If you use a printer queue that points to a printer on another machine, the file to print will first be spooled on your machine, then transmitted to the appropriate queue of the machine connected to the printer, and finally be printed. "Managing Print Services" tells you more about setting up printer queues.
Some programs look to the PRINTER environment variable to determine what queue to use. Thus, if you want to use a particular printer for most of your printing needs, you can set this environment variable. For instance, if you are using the bash shell, you could make epson_360 your personal default queue by putting this command in your .bashrc file:
$ export PRINTER=epson_360
This procedure doesn't work for all programs, though; many ignore the PRINTER environment variable. Some complex programs enable you to set a default queue in some other way, such as in a GUI dialog box. Consult your program's documentation for details. In any event, if you use lpr for printing, directly or indirectly, and can change how lpr is called, you can use the -P option to lpr to set the destination queue. This option overrides the PRINTER environment variable.
Once you know how to print a file, the next problem you might face is finding out what is happening if your file doesn't instantly print as you expect. You can find out the status of files in the print queue by using the lpq command. To find out the status of files sent to your default printer, enter:
$ lpq
epson_360 is ready and printing
Rank Owner Job File(s) Total Size
1st rodsmit 440 (stdin) 2242560 bytes
2nd rodsmit 441 (stdin) 5199872 bytes
3rd lark 442 (stdin) 1226752 bytes
You see that the printer is running, but large jobs are queued ahead of yours (if you are lark). If you just can't wait, you might decide to remove the job from the print queue. You can use the job number of the printing task