I have a python script which employs pyusb to scan connected usb devices matching against a specific device 0403:6001 which is an FTDI USB to RS232 converter but this seems to require being run as root. Here is the portion of the script that fails:
if device != None:
handle = None
handle = device.open()
if handle != None:
print "Vendor: %s - %s" % (hex(device.idVendor), handle.getString(device.iManufacturer, 30))
print "Product: %s - %s" % (hex(device.idProduct), handle.getString(device.iProduct, 30))
print "Serial: %s" % handle.getString(device.iSerialNumber, 30)
Producing the following error:
Traceback (most recent call last):
File "test.py", line 28, in <module>
print "Vendor: %s - %s" % (hex(device.idVendor), handle.getString(device.iManufacturer, 30))
usb.USBError: error sending control message: Operation not permitted
As mentioned when running as root this works fine but I need it to run as a standard user. I have checked the permissions of the device with this:
$ ls -s /dev/ttyUSB*
crw-rw---- 1 root dialout 188, 0 2011-02-05 13:33 /dev/ttyUSB0
And the user account is a member of dialout (and tty, and plugdev) but still I get the permission denied error..
I have read about setting up udev rules for this and have tried many variations but it seems to have the correct permissions and groups anyway..?
I also read an article about modem-manager taking control of serial devices and that removing this may work but it didn't for me.. Any ideas?
Thanks

Ok so I figured out that it's related to file permissions in that doing the following then allowed the user to communicate with the device:
$ ls -l /dev/bus/usb/005/006
crw-rw-r-- 1 root root 189, 517 2011-02-05 17:44 /dev/bus/usb/005/006
So I temporarily granted other access and the script will run as a normal user:
$ sudo chmod o+rw /dev/bus/usb/005/006
Where as before I was trying to modify /dev/ttyUSB0 permissions.
I guess I need to sort out some udev rule for this now..

If anyone is interested.. fixed with udev rule:
SUBSYSTEM=="usb", ATTRS{idVendor}=="0403", GROUP="dialout"
then reloaded udev rules:
$ udevadm control --reload-rules