[Nut-upsuser] Still trying to make nut work, failing miserably

Charles Lepple clepple at gmail.com
Wed Nov 12 03:35:58 UTC 2014

On Nov 11, 2014, at 9:41 PM, Gene Heskett <gheskett at wdtv.com> wrote:

> Can't claim USB device [050d:0751]: could not detach kernel driver from 
> interface 0: Operation not permitted
> Driver failed to start (exit status=1)
> In /dev/ttyUSB0 is owned by root. /dev/usb/hiddev3, the last one, has a 
> slow data marching out of it if I sudo cat /etc/dev/usb/hiddev3

Hi Gene,

I wish we had a good way to print a more specific error message (libusb doesn't return enough information to do so), but it's none of the above.

The Linux box only has a serial UPS attached at the moment, but we'll pretend my mouse is the UPS:

$ lsusb -d 046d:
Bus 001 Device 008: ID 046d:c03d Logitech, Inc. M-BT96a Pilot Optical Mouse

(In your case, you would run "lsusb -d 050d:0751")

The "Bus 001 Device 008" part maps to names under /dev/bus/usb. In this case:

$ ls -l /dev/bus/usb/001/008
crw-rw-r-T 1 root root 189, 7 Nov  4 19:53 /dev/bus/usb/001/008

This is the /dev node that needs to be owned by the NUT user.

There is a udev rules file that, when installed to someplace like /etc/udev/rules.d, should change the permissions of the /dev/bus/usb file automatically. I can never keep track of what needs to be unplugged and/or restarted to get that to work, though. The FAQ suggests that unplugging and re-plugging the USB cable after installing the udev file should be sufficient, but older udev daemons might need to be restarted.

Charles Lepple
clepple at gmail

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