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Writing UDEV rules to get a SCSI scanner working on Ubuntu

Aug 17, 2009, 03:01 (0 Talkback[s])
(Other stories by jhansonxi)

[ Thanks to jhansonxi for this link. ]

"SCSI scanners pretty much ruled in the days before USB as they were much faster than parallel ports. However, they were a pain to configure and required heavy (and usually short) cables which made them difficult to fit into your work area. I tested a Microtek ScanMaker E3 (MRS-600E3) and UMAX Vista S8 scanner first. They worked without problems although the former was picky about termination. Unfortunately a Hewlett-Packard ScanJet 6100C (Q2950A) didn't work at all.

"Checking the kernel messages indicated that it was represented by /dev/sg7 but the permissions were 0660 root:root so sane couldn't access it. Changing the permissions solved the problem but the /dev directory is a virtual filesystem controlled by udev and the changes are lost after reboot. I could just put a chmod comand in /etc/rc.local but that is the wrong way to fix it. A search on launchpad found bug #378989 which describes the problem with this model. I'm not sure if the fault lies with udev or HAL but creating a udev rule is a simple enough way to fix it for now. I'll describe how to create such a rule using this as an example but udev rules can do much more than just change device permissions."

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