Specifications

6-23
System V Printer Configuration
file. Try to find a set of filters that take (as input types) all the different files your users
may want printed and converts those files directly into types your printers can handle.
• Printer types: A list of printer types into which the filter can convert files.
For most filters, this list is identical to the list of output types.
For example, you may have a printer that is given a single type for purposes of
initialization, see Printer Types on page 6-28, but which can recognize several different
types of files. In essence, this printer has an internal filter that converts the various types
into one that it can handle. Thus, a filter may produce one of several output types that
match the file types that the printer can handle. Label the filter as working with that
printer type.
As another example, you may have two different models of printers that are listed as
accepting the same types of files. However, due to slight differences in manufacture, one
printer deviates in the results it produces. You label the printers as being of different
printer types, say A and B, where B is the one that deviates. You create a filter that
adjusts files to account for the deviation produced by printers of type B. Because this
filter is needed only for those printer types, you list it as working only on type B printers.
For most printers and filters, you can leave this part of the filter definition blank.
• Printers: You may have some printers that, although they are of the correct type for a
filter, are in other ways not adequate for the output that the filter produces.
For example, you may want to dedicate one printer for fast turnaround. Only files that the
printer can handle without filtering will be sent to that printer. Other printers, of identical
type, you allow to be used for files that may need extensive filtering before they can be
printed. In this case, label the filter as working with only the latter group of printers.
In most cases, a filter works with all printers that accept its output, so you can usually
skip this part of the filter definition.
• Filter type: The print service recognizes fast filters and slow filters.
Fast filters are labeled fast because they incur little overhead in preparing a file for
printing and because they must have access to the printer when they run. A filter that is
to detect printer faults must be a fast filter. A filter that uses the PRINTER keyword as a
filter option must be installed as a fast filter.
Slow filters are filters that incur a lot of overhead in preparing a file and do not require
access to a printer. The print service runs slow filters in the background, without tying up
a printer. This allows files that do not need slow filtering to move ahead. Printers will not
be left idle while a slow filter works on a file if other files can be printed simultaneously.
Slow filters that are invoked by modes (using the –y option), must be run on the
computer where the print request was issued. The print service cannot pass values for
modes to server machines. It can, however, match a file content type (specified after the
–T option of the lp command) to a content type on a server machine. Therefore, to
activate special modes on a server machine, you must specify content types that will
allow the print service to match input types and output types.
• Options: Options specify how different types of information is transformed into
command line arguments to the filter command.
This information may include specifications from a user (with the print request), the
printer definition, and the specifications implemented by any filters used to process the
request.
There are 13 sources of information, each of which is represented by a keyword. Each
option is defined in a template, which is a statement in the following format:
keyword pattern = replacement
This type of statement is interpreted by the print service to mean: ”When the information
referred to by keyword has the value matched by pattern, take the replacement string,