Last modified on $Date$ To account for pages or eventually ink usage, you must plug your accounting system into CUPS. One way to do this without having to modify CUPS itself, is by using a filter. A filter is a computer program which takes data in one format as its input, and outputs the same data but transformed into another format. CUPS already contains many filters. For example there's one filter named pstops which accepts PostScript data as its input, and, as its name implies, outputs PostScript data too, but after having eventually rearranged the pages to fit several pages on a single sheet of paper, or other manipulations like that. The pstops filter described above is also in charge of doing basic page accounting, but PyKota currently doesn't use this facility since it may prove to be unreliable depending on the drivers used or if a paper jam occur for example. So to do its own accounting, PyKota has its own filter, named pykota, which you have to plug into the different set of filters used by CUPS. The procedure to install the pykota filter is described in the chapter. Currently the pykota filter is used at the very last stage of the print mechanism, just before the final data is sent to the printer, but it may eventually be used earlier with some modifications to CUPS's filtering configuration. This is not tested yet, but this may be the solution to use PyKota with printers which really needs to have a *cupsFilter line in their PPD file, i.e. non-postscript printers. The pykota filter really is the only thing which depends on CUPS, so it is probable that a next version of PyKota will support other printing environments.