Nearest printer support

With the ThinLinc nearest printer feature, printer jobs are sent to a printer selected based on the physical address of the users terminal. This is typically used to implement printer queues based on physical proximity.

The nearest printer is implemented as an extra printer queue, on top of the real printers. Printer jobs sent to the nearest queue will be sent to the nearest printer backend. The backend is a program which is called by CUPS together with all needed information. The backend will look at the user name requesting the printout and ask the ThinLinc VSM server for more information about this user. The information includes which terminal the user is currently using. The backend then queries the information stored in Hiveconf for a list of printers that are considered near the terminal used by the printing user. When a printer is known the backend will place the job in that printer queue.

The nearest queue is added to the VSM master server by ThinLinc Setup. The recommended setup is to configure one nearest printer queue in the CUPS daemon on the VSM Server host, and then let all agents use this CUPS daemon. See Printer Configuration Overview for an overview of printer setup in a ThinLinc cluster.

Administration of the Nearest Printer Feature in ThinLinc

The nearest printer system needs information about groups of terminals, known as locations, which typically represents some physical layout. The information connects terminals to locations and also links printers to the locations. Available printers are automatically fetched from the underlying printing system and are available for assigment to locations and/or terminals.

Information about terminals, locations and their associated printers can be administrated using the ThinLinc Web Administration, see The Locations Module.

Each location should be entered with a name, and may have an optional description. A location can for example represent a classroom, a department, a house, and so on. Each location can be associated with one or more printers, including the special nearest and thinlocal printers. Typically it will include all printers available near that physical location the location represents. If the location is so big that different printers are close to different parts of the location, then you should probably divide the location into smaller parts, each represented by a separate location.

A location can be set to handle clients which are not defined using a terminal definition (“unknown terminals”).

Each terminal in the ThinLinc Web Administration represents one physical terminal in the installation and is defined by its terminal network interface hardware (MAC) address. The hardware address can be entered in many formats, but will be converted to all uppercase hexadecimal form separated by colon, i.e. 01:23:45:67:89:AB.

A terminal must be associated with a location.

Nearest Printer Selection Algorithm

If a terminal has a printer directly assigned to it in the terminals module in tlwebadm, that printer will be the nearest printer for that terminal. For terminals without a printer directly assigned (the normal situation), the first printer in the list of printers for the terminal’s location is selected when the user submits a printer job to the nearest queue.

If the client is not a known terminal, i.e. its hardware address was not found, it will use the printer for the location marked as handling unknown terminals. If not, there will be no printer available.

If a user is using multiple sessions, print jobs submitted via nearest printer will be redirected to the printer that is found starting from the client that made the last connection.

Printer Drivers

When printing via the nearest printer, the CUPS client can’t get hold of all information about the real printer where the job will actually be printed, because it doesn’t know that the printer job will be rerouted by the nearest driver. Therefore, the printing application has no way to know about the number of trays, the paper sizes available etc.). This is a problem for some applications, and it also adds to the number of applications that will be misconfigured, for example selecting the wrong paper size.

As a compromise, the nearest printer is configured with a PPD (Postscript Printer Definition) that covers a broad range of printer capabilities - it’s a Generic Postscript Printer driver. This makes it possible to configure default values for some of the settings, for example paper size, using the CUPS configuration interface.

If all the printers in your organisation are of the same type, it may be a good idea to replace the Generic Postscript PPD installed for the nearest queue with a PPD for the specific printer in use. That will let CUPS-aware applications select between the specific set of features available for the specific printer model.