find_yubikey() fails with ValueError: No backend available

[bhechinger]

I was trying to work with FreeIPA and YubiKey on CentOS 7, but the ipa otptoken-add-yubikey command was exploding. I tracked it down to being this module that has the actual issues.

Using python-yubico 1.3.1:

[root@ipa-yubikey-test ~]# python
Python 2.7.5 (default, Nov 20 2015, 02:00:19)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> import yubico
>>> yubikey = yubico.find_yubikey(debug=False)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/site-packages/yubico/yubikey.py", line 53, in find_key
    hid_device = YubiKeyHIDDevice(debug, skip)
  File "/usr/lib/python2.7/site-packages/yubico/yubikey_usb_hid.py", line 123, in __init__
    if not self._open(skip):
  File "/usr/lib/python2.7/site-packages/yubico/yubikey_usb_hid.py", line 317, in _open
    usb_device = self._get_usb_device(skip)
  File "/usr/lib/python2.7/site-packages/yubico/yubikey_usb_hid.py", line 367, in _get_usb_device
    find_all=True, idVendor=YUBICO_VID)]
  File "/usr/lib/python2.7/site-packages/usb/core.py", line 864, in find
    raise ValueError('No backend available')
ValueError: No backend available
>>>

The YubiKey (Standard) is definitely there:

[ 1955.426313] usb 2-2.2: USB disconnect, device number 7
[ 2489.666237] usb 2-2.2: new low-speed USB device number 8 using uhci_hcd
[ 2489.758404] usb 2-2.2: New USB device found, idVendor=1050, idProduct=0010
[ 2489.758407] usb 2-2.2: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[ 2489.758408] usb 2-2.2: Product: Yubico Yubikey II
[ 2489.758409] usb 2-2.2: Manufacturer: Yubico
[ 2489.766705] input: Yubico Yubico Yubikey II as /devices/pci0000:00/0000:00:11.0/0000:02:00.0/usb2/2-2/2-2.2/2-2.2:1.0/input/input8
[ 2489.818727] hid-generic 0003:1050:0010.0005: input,hidraw1: USB HID v1.11 Keyboard [Yubico Yubico Yubikey II] on usb-0000:02:00.0-2.2/input0

Also:

[root@ipa-yubikey-test ~]# lsusb | grep Yubikey
Bus 002 Device 008: ID 1050:0010 Yubico.com Yubikey

This is extremely frustrating!

[bhechinger]

Some additional information. If I run this without the key attached it does recognize that it isn't there:

>>> yubikey = yubico.find_yubikey(debug=False)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/site-packages/yubico/yubikey.py", line 65, in find_key
    raise YubiKeyError('No YubiKey found')
yubico.yubikey_base.YubiKeyError: <YubiKeyError instance at 0x7f0263fa0550: No YubiKey found>

Here's the output (with they key connected) with debug=True:

.................

Ok then. I do not understand this at all. I've been at this for hours and not once has this ever worked.

Just now it did.

>>> yubikey = yubico.find_yubikey(debug=False)
>>> print(yubikey.version())
2.4.2
>>>

This is extremely odd. :(

[afitzgerald]

I have the same error, but it never works.

[AnnaAnge]

same error here and it never works. What's the backend that it refers to actually? Thanks in advance guys!

[Ratler]

It sounds like libusb is missing on your system, which is the 'backend' it is looking for. If you are using CentOS try yum install libusb and then try again.

[AnnaAnge]

Hi again,
We've installed the package that you suggested and we've followed the instructions here: https://github.com/Yubico/python-yubico
but we still have an error: usb.core.USBError: [Errno 13] Access denied (insufficient permissions)
Could it be due to the fact that we use a macOS ? Do you have a workaround ?

Thanks in advance :)

[Ratler]

@AnnaAnge I'm afraid that you've run into a known issue on OS X/macOS, see #7. The issue is with libusb on OS X/macOS and as far as I know there is no known workaround.

[mdxs]

I think this issue can be closed; the original question was about CentOS and was reported to start working at one point in time (by @bhechinger as the original poster). While @Ratler added a note on 4 Jan 2017 that for this CentOS a particular step might be important (for anyone else hitting this on CentOS).

The remaining comments about permissions is to be addressed at #7 (as noted before by @Ratler).

Thus, this issue can be closed in my opinion.

[dainnilsson]

Agreed, closing.