Guide to Printers and Printing

Printer Terminology

The following list defines terms commonly used with printing.

Local Printer

When you attach a printer to a node or host, the printer is referred to as a local printer.

Print Job

A print job is a unit of work to be run on a printer. A print job can consist of printing one or more files, depending on how the print job is requested. The system assigns a unique job number to each job it runs.

Print Spooler

The spooler used for printing provides a generic spooling function that can be used for queuing various types of jobs, including print jobs queued to a printer.The spooler does not normally know what type of job it is queuing. When the system administrator defines a spooler queue, the purpose of the queue is defined by the spooler backend program that is specified for the queue. For example, if the spooler backend program is the piobe command (the printer I/O backend), the queue is a print queue.

Likewise, if the spooler backend program is a compiler, the queue is for compile jobs. When the spooler's qdaemon command selects a job from a spooler queue, it runs the job by invoking the backend program specified by the system administrator when the queue was defined.

The main spooler command is the enq command. Although you can invoke this command directly to queue a print job, three front-end commands are defined for submitting a print job: the lp, lpr, and qprt commands. A print request issued by one of these commands is first passed to the enq program, which then places the information about the file in the queue for the qdaemon to process.

Printer Backend

The printer backend is a collection of programs called by the spooler's qdaemon command to manage a print job that is queued for printing. The printer backend performs the following functions:

• Receives from the qdaemon command a list of one or more files to be printed.
• Uses printer and formatting attribute values from the database, overridden by flags entered on the command line
• Initializes the printer before printing a file
• Runs filters as necessary to convert the print data stream to a format supported by the printer
• Provides filters for simple formatting of ASCII documents
• Provides support for printing national language characters
• Passes the filtered print data stream to the printer device driver
• Generates header and trailer pages
• Generates multiple copies
• Reports paper out, intervention required, and printer error conditions
• Reports problems detected by the filters
• Cleans up after a print job is canceled
• Provides a print environment that a system administrator can customize to address specific printing needs

Printer/Plotter Device

A special file in the /dev directory for the device. This file can be used by redirection (for example, cat FileName > /dev/lp0). Settings for the device driver can be displayed and changed using Web-based System Manager (type wsm, then select Devices) or the lsdev and chdev commands. Before printer commands can access a printer device, a print queue must be created for the device or the printer must be configured in the printer backend in /etc/qconfig.

qdaemon

The qdaemon is a process that runs in the background controling the queues. It is generally started by the startsrc command when the system is turned on. startsrc is a command to the srcmstr daemon that is started from /etc/inittab.

The qdaemon keeps track of the print requests in the /var/spool/lpd/qdir directory and ensures that the jobs are sent to the proper printer at the proper time. It also keeps track of the status of the printers and stores printer usage data for system accounting purposes (for example, lpstat and enq -A commands). This information is held in the /var/spool/lpd/stat directory.

If the qdaemon is stopped, it will be restarted by the srcmstr.

Note: Do not stop the srcmstr process; it controls other daemons running on your system.

Queue

The queue is where you direct a print job. It is a stanza in the /etc/qconfig file whose name is the name of the queue. It points to the associated queue device. The following is a sample listing:

Msa1:
   device = lp0

Usually, queues are created through Web-based System Manager.

Queue Device

The queue device is the stanza in the /etc/qconfig file that usually follows the local queue stanza. It specifies the /dev file (printer device) that should be printed to and the backend that should be used. Following is a sample listing:

lp0:
   file = /dev/lp0
   header = never
   trailer = never
   access = both
   backend = /usr/lpd/piobe

In the previous example, lp0 is the device name, and the rest of the lines define how the device is used.

Adding a printer through Web-based System Manager (type wsm, then select Devices) creates a standard queue device entry to an existing queue.

Notes:

1. There can be more than one queue device associated with a single queue.
2. There will not be a file entry in the /etc/qconfig file when you are using a remote printer. The queue directs the file to the server.

Real Printer

A real printer is the printer hardware attached to a serial or parallel port at a unique hardware device address. The printer device driver in the kernel communicates with the printer hardware and provides an interface between the printer hardware and a virtual printer.

Remote Printer

A remote print system allows nodes that are not directly linked to a printer to have printer access.

To use remote printing facilities, the individual nodes must be connected to a network using the Transmission Control Protocol/Internet Protocol (TCP/IP) and must support the required TCP/IP applications.

Virtual Printers

Avirtual printer , usually called avirtual printer definition is a file containing a set of attribute values that describe a particular data stream for a particular printer. Before a print job can be placed in a queue, a virtual printer definition must exist for both the print queue and the queue device. See the mkvirprt command for more information.