After spending some time learning what the rootbackends-worldreadable.dpatch in expermental does, and learning what the code behind it does, I understand the problem.
I neither add a USB or parallel printer nor print to one in cups 1.3.8-1lenny2. Apparently the reason for this is that the relevant backends are apparently not running with permissions to access the relevant devices. crw-rw---- 1 root lp 6, 0 2008-11-18 08:10 /dev/lp0 crw-rw---- 1 root dialout 4, 64 2008-11-18 08:09 /dev/ttyS0 crw-rw---- 1 root dialout 4, 65 2008-11-18 08:09 /dev/ttyS1 crw-rw---- 1 root dialout 4, 66 2008-11-18 08:09 /dev/ttyS2 crw-rw---- 1 root dialout 4, 67 2008-11-18 08:09 /dev/ttyS3 crw-rw---- 1 root lp 180, 0 2008-11-18 08:09 /dev/usb/lp0 These permissions are set in /etc/udev/rules.d/91-permissions.rules CUPS default permissions for running filters (including the backends) is to run in group lpadmin. If I change the group that filters run in (adding the line "Group lp" in /etc/cups/cupsd.conf) then I can make the usb and parallel backends work. (But I can't make usb and parallel work at the same time as serial because they require different groups to run) If I change the permissions on the parallel, usb, and serial backends from 755 to 700, then cups will run them as root (this is the behavior that rootbackends-worldreadable.dpatch was dealing with, but not really fixing in this instance) and they will all work. -- Ken (Chanoch) Bloom. PhD candidate. Linguistic Cognition Laboratory. Department of Computer Science. Illinois Institute of Technology. http://www.iit.edu/~kbloom1/
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