Print filters

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A default filter is provided with the print service to provide simple printer fault detection. It does not convert files or handle any of the special modes. It may, however, be adequate for your needs.

A filter is a program that you can use for the following purposes:

To convert a user file from one data format to another so that it can be printed correctly on a given printer
To handle the special modes of printing that users may request with the -y option to the lp command (such as two-sided printing, landscape printing, draft or letter-quality printing)
To detect printer faults and notify the print service of them, so that the print service can alert you

Not every filter can perform all three tasks. Given the printer-specific nature of these roles, the print service has been designed so that these roles can be implemented separately. This separation allows you or a printer manufacturer (or another source) to provide filters without having to change the print service.

Note: Adding, changing, or removing filters can cause print requests that are still queued to be canceled. This is because the print service evaluates all print requests still queued to see which are affected by the filter change. Requests that are no longer printable, because a filter has been removed or changed, are canceled (with notifications sent to the users who submitted them). There can also be delays in the responses to new or changed print requests when filters are changed, due to the many characteristics that must be evaluated for each print request still queued. These delays can become noticeable if there is a large number of requests that need to be filtered.
Because of this possible impact, make alterations to filters during periods when the print service is idle.