1 | <!-- $Id: filterpykota.sgml 1454 2005-03-06 16:52:43Z jerome $ --> |
---|
2 | |
---|
3 | <chapter> |
---|
4 | <title id="filter">PyKota's internals</title> |
---|
5 | |
---|
6 | <para>Last modified on $Date: 2005-03-06 17:52:43 +0100 (dim, 06 mar 2005) $</para> |
---|
7 | |
---|
8 | <para> |
---|
9 | To account for pages or eventually ink usage |
---|
10 | <footnote> |
---|
11 | <para> |
---|
12 | PyKota doesn't currently account for ink usage, it only accounts |
---|
13 | pages. To account for ink usage, you should use PrintBill instead for now. |
---|
14 | </para> |
---|
15 | </footnote> |
---|
16 | , you must plug your accounting |
---|
17 | system somewhere into the printing system you use. One way to do this without having |
---|
18 | to modify the printing system itself, is by using a <firstterm>filter</firstterm>. |
---|
19 | </para> |
---|
20 | |
---|
21 | <para> |
---|
22 | A filter is a computer program which takes data in one format as its input, and outputs the |
---|
23 | same data but transformed into another format. <application>CUPS</application> already |
---|
24 | contains many filters. For example there's one filter named <command>pstops</command> which accepts |
---|
25 | PostScript data as its input, and, as its name implies, outputs PostScript data too, but after having |
---|
26 | eventually rearranged the pages to fit several pages on a single sheet of paper, or other manipulations |
---|
27 | like that. |
---|
28 | </para> |
---|
29 | |
---|
30 | <para> |
---|
31 | The <command>pstops</command> filter described above is also in charge of doing basic page |
---|
32 | accounting, but <application>PyKota</application> currently doesn't use this facility since it may |
---|
33 | prove to be unreliable depending on the drivers used or if a paper jam occurs for example. |
---|
34 | </para> |
---|
35 | |
---|
36 | <para> |
---|
37 | So to do its own accounting, <application>PyKota</application> has its own filters, for <application>CUPS</application> |
---|
38 | it's named <command>cupspykota</command>, which is in fact a <application>CUPS</application> backends wrapper. |
---|
39 | The procedure to plug the correct filter into your printing system is described in the |
---|
40 | <xref linkend="installation" endterm="installation"> chapter. |
---|
41 | </para> |
---|
42 | |
---|
43 | <para> |
---|
44 | Currently with <application>CUPS</application>' internal accounting mechanism, the <command>pstops</command> |
---|
45 | filter can be bypassed. That's why <application>PyKota</application> uses its own backend. |
---|
46 | The <command>cupspykota</command> backend wrapper ensures that jobs can't bypass it, so you can use |
---|
47 | any printer with any driver and any command line option, and you can be sure that your |
---|
48 | print job will be correctly accounted for. |
---|
49 | </para> |
---|
50 | |
---|
51 | <para> |
---|
52 | When using the <literal>hardware</literal> accounting method, |
---|
53 | <application>PyKota</application> launches the script you specified to |
---|
54 | ask the printer for its internal page counter at the start and at the end of the print job, and |
---|
55 | computes the values' difference to know the job's size. |
---|
56 | </para> |
---|
57 | |
---|
58 | <para> |
---|
59 | When using the <literal>software</literal> accounting method, |
---|
60 | the command you specified is launched with the job's data on its |
---|
61 | standard input. Your command must print the job's size in number of |
---|
62 | pages on a single line on its standard output. This number is then |
---|
63 | read by <application>PyKota</application> and used to update the current user's quota information. |
---|
64 | </para> |
---|
65 | |
---|
66 | <para> |
---|
67 | If a problem occurs, it is logged either to the filter's standard error or to the system logger, depending on |
---|
68 | your preferences in <application>PyKota</application>'s configuration files. Also if a print quota is reached |
---|
69 | you may choose if the administrator, the user, both or no-one will receive an email message explaining |
---|
70 | the situation and proposing a solution. You can even configure another action instead of sending email |
---|
71 | messages if you want. |
---|
72 | </para> |
---|
73 | |
---|
74 | </chapter> |
---|
75 | |
---|