Re: [Pyusb-users] USB control requires root access

[Andrew S. <str...@as...>]

Sarah,

I think the simplest way is to go through udev.

1) create a group named something like "tekscope"

2) Create a file in /etc/udev/rules.d (well, that's where it is on 
Ubuntu) something like:

SUBSYSTEM=="usb_device", ACTION=="add", SYSFS{idVendor}=="1234",
SYSFS{idProduct}=="5678", GROUP="tekscope", MODE="0660"

3) Restart udev to re-load the new rules, and voila, anyone in the 
tekscope group should be able to access the USB device created when the 
device is plugged in.

Sarah Messer wrote:
> Hello,
>
> I have a (working) USB interface to a Tektronix TDS-2014B oscilloscope 
> based around pyusb.  My issue is that it's only usable when I'm 
> SuperUser.  I'm doing support work for a company, and would rather not 
> require several different people to log in as root in order to 
> download data from the scopes.  Here's what I've figured out so far:
>
> 1)  The following python commands work the way one would expect if 
> logged in as root:
> > import usb
> > barn=usb.busses()
> >barn[1].devices
> (<usb.Device object at 0x80ee5f8>,)
>
> 2)  If I lack root access, the device list returns empty:
> ()
>
> 3)  I'm running SuSe 10.0 with python 2.4.1, pyusb 0.3.5, and 
> libusb-0.1.12 (with a minimal custom patch, see my posting on the 
> libusb group 
> <http://sourceforge.net/tracker/index.php?func=detail&aid=1633542&group_id=1674&atid=101674> 
> for details).
>
> If I understand things correctly, there are three different low-level 
> daemons / drivers which might be involved in establishing permissions 
> for the USB ports: HAL, udev, and hotplug.  I seem to have bits of all 
> three on the system, and I'm trying to figure out which one sets the 
> permissions:
>
> Things I've tried:
> 1) editted fstab to put the "users,dev,exec" flags on the usbfs line 
> (in addition to the "noauto" flag that was there already.  The full 
> listing is:
> usbfs   /proc/bus/usb   usbfs   noauto,users,dev,exec   0   0
> Despite this, rebooting mounts the usbfs with only the rw flag, not 
> the users flag and so on.  This makes me think that fstab doesn't 
> actually control mounting of usbfs.
> 2)  I tried editting the mount commands in /etc/hotplug/usb.rc, but 
> again this has no effect.  I made the first line of this file
> echo "Executing /etc/hotplug/usb.rc \a"
> but rebooting doesn't seem to produce either the bell or message.  
> This makes me think Hotplug isn't handling the USB communication either.
> 3)  lsmod and ps reveal the following potentially-relevant modules / 
> processes:  pci_hotplug, usblp, usbcore, ehci_hcd, uhci_hcd, hald, 
> hald-addon-acpi, hald-addon-stor, and udevd.
> 4)  If I run "chgrp users /dev/usbdev*" (as root), the affected 
> devices become available to non-root users.  However, if a device (or 
> the PC) is power-cycled, it becomes root-only again.
>
> Any ideas on how to tell whether I need to learn HAL or UDev or 
> something else?  Any clues on how to let pyusb talk to the scopes for 
> regular users?
>
> Thanks.
>
>
> -Sarah
>
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