I had a problem with my scanner. Xsane worked only as root. Using it as normal user it didn't find any devices. Adding the user to the groups saned or scanner didn't help.
Finally I solved the problem by changing
# 'libusb' device nodes
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", MODE="0664"
to
# 'libusb' device nodes
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", MODE="0666"
in /lib/udev/rules.d/50-udev-default.rules
However I do not understand why this works and if it has any negative side effects. I guess that this gives write permissions to all users on any usb device, but I don't know if and why this is correct and why this solves the scanner problem.
Could anyone explain in detail why this works and wether it has any side effects.
My system is: ubuntu 12.04, the scanner is a HP PSC 1200 all in one device hplip is installed from the repository.
