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Old 05-05-2011, 01:48 PM
Veli-Matti Lintu
 
Default CUPS printer filtering on LTSP fat clients

Hello everyone,

I'd have a quick question about the CUPS printer filtering patch that is in the Ubuntu CUPS version (the patch can be found at least here: http://patches.ubuntu.com/by-release/extracted/ubuntu/c/cups/1.4.1-5ubuntu2/printer-filtering.dpatch)

If I understand correctly, it is used on LTSP systems by adding LDM_PRINTER_LIST setting in lts.conf which is then turned to PRINTER_LIST environment variable when the user logs in. The patch above then filters not listed printers out from the user's printer list.

As here we are running quite a few fat clients that have their own local USB printers, we changed from configuring fat clients to use LTSP server's cups via /etc/cups/client.conf and instead run a local CUPS server on the fat clients. The CUPS server on the LTSP server broadcasts printer information to the LTSP network and the local CUPS processes on the fat clients then pick up the printers from the broadcasts. CUPS adds local USB printers automatically and they don't need to be configured through server lts.conf. Of course they are not usable by other users in the network, but it's not a problem.

This works nicely as long as we want to show all printers to the user. In bigger environments where a cluster of servers serves many schools, this doesn't work so nicely and that's where the LDM_PRINTER_LIST setting helps. The problems come when we want to show also the local USB printers that CUPS configures automatically when they are attached. As the LDM_PRINTER_LIST doesn't include the local printers, they are always filtered out from the printer list.

We've been now doing some test patches to filter out only printers that are not local, but I'd be interested to know if anyone else has tried using a setup like this? The same filtering could be also applied to laptops if the PRINTER_LIST env variable is set somewhere when the user logs in.

Ideas? Comments?

Veli-Matti

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