Why is Python pyusb usb.core access denied due to permissions and why won't the rules.d fix it?

Question

I have a USB device which I'm tring to talk to using pyusb 1.0.2 on linux (Linux tpad 4.15.0-38-generic #41~16.04.1-Ubuntu SMP Wed Oct 10 20:16:04 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux). Running python 3.5 I get the following error (full trace at bottom of this post):

usb.core.USBError: [Errno 13] Access denied (insufficient permissions)

Mounting the usb and using lsusb and then inspecting it:

udevadm info -a -p $(udevadm info -q path -n /dev/bus/usb/006/011)

shows

    looking at device '/devices/pci0000:00/0000:00:10.0/usb6/6-1':
        KERNEL=="6-1"
        SUBSYSTEM=="usb"
        DRIVER=="usb"
        ATTR{authorized}=="1"
        ATTR{avoid_reset_quirk}=="0"
        ATTR{bConfigurationValue}=="1"
        ATTR{bDeviceClass}=="00"
        ATTR{bDeviceProtocol}=="00"
        ATTR{bDeviceSubClass}=="00"
        ATTR{bMaxPacketSize0}=="8"
        ATTR{bMaxPower}=="98mA"
        ATTR{bNumConfigurations}=="1"
        ATTR{bNumInterfaces}==" 1"
        ATTR{bcdDevice}=="0111"
        ATTR{bmAttributes}=="80"
        ATTR{busnum}=="6"
        ATTR{configuration}==""
        ATTR{devnum}=="11"
        ATTR{devpath}=="1"
        ATTR{idProduct}=="0001"
        ATTR{idVendor}=="17a4"
        ATTR{ltm_capable}=="no"
        ATTR{manufacturer}=="Concept2"
        ATTR{maxchild}=="0"
        ATTR{product}=="Concept2 Performance Monitor 3 (PM3)"
        ATTR{quirks}=="0x0"
        ATTR{removable}=="unknown"
        ATTR{serial}=="300118412"
        ATTR{speed}=="12"
        ATTR{urbnum}=="12"
        ATTR{version}==" 1.10"

So I wrote a rule in /etc/udev/rules.d/10-local.rules like this (FYI -- I've also tried "user1" which is the user python shows it is running under and I've tried both ":=" and "="):

    SUBSYSTEMS=="usb", ATTRS{idVendor}=="17a4", ATTRS{idProduct}=="0001", GROUP:="users", MODE="0777"

Then I ran udevadm test /devices/pci0000:00/0000:00:10.0/usb6/6-1

which shows:

calling: test
version 229
This program is for debugging only, it does not run any program
specified by a RUN key. It may show incorrect results, because
some values may be different, or not available at a simulation run.

=== trie on-disk ===
tool version:          229
file size:         7049340 bytes
header size             80 bytes
strings            1759644 bytes
nodes              5289616 bytes
Load module index
timestamp of '/etc/systemd/network' changed
timestamp of '/lib/systemd/network' changed
Parsed configuration file /lib/systemd/network/99-default.link
Created link configuration context.
timestamp of '/etc/udev/rules.d' changed
Reading rules file: /etc/udev/rules.d/10-local.rules
Reading rules file: /lib/udev/rules.d/40-crda.rules
[removed long list of rule files...]
Skipping empty file: /etc/udev/rules.d/99-usbftdi.rules
rules contain 393216 bytes tokens (32768 * 12 bytes), 33403 bytes strings
25688 strings (211409 bytes), 22263 de-duplicated (181432 bytes), 3426 trie nodes used
GROUP 100 /etc/udev/rules.d/10-local.rules:1
MODE 0777 /etc/udev/rules.d/10-local.rules:1
value '[dmi/id]sys_vendor' is 'LENOVO'
value '[dmi/id]sys_vendor' is 'LENOVO'
IMPORT builtin 'usb_id' /lib/udev/rules.d/50-udev-default.rules:13
IMPORT builtin 'hwdb' /lib/udev/rules.d/50-udev-default.rules:13
MODE 0664 /lib/udev/rules.d/50-udev-default.rules:41
PROGRAM 'mtp-probe /sys/devices/pci0000:00/0000:00:10.0/usb6/6-1 6 11' /lib/udev/rules.d/69-libmtp.rules:1923
starting 'mtp-probe /sys/devices/pci0000:00/0000:00:10.0/usb6/6-1 6 11'
'mtp-probe /sys/devices/pci0000:00/0000:00:10.0/usb6/6-1 6 11'(out) '0'
Process 'mtp-probe /sys/devices/pci0000:00/0000:00:10.0/usb6/6-1 6 11' succeeded.
handling device node '/dev/bus/usb/006/011', devnum=c189:650, mode=0664, uid=0, gid=100
set permissions /dev/bus/usb/006/011, 020664, uid=0, gid=100
setting mode of /dev/bus/usb/006/011 to 020664 failed: Operation not permitted
setting owner of /dev/bus/usb/006/011 to uid=0, gid=100 failed: Operation not permitted
ACTION=add
BUSNUM=006
DEVNAME=/dev/bus/usb/006/011
DEVNUM=011
DEVPATH=/devices/pci0000:00/0000:00:10.0/usb6/6-1
DEVTYPE=usb_device
DRIVER=usb
ID_BUS=usb
ID_MODEL=Concept2_Performance_Monitor_3__PM3_
ID_MODEL_ENC=Concept2\x20Performance\x20Monitor\x203\x20\x28PM3\x29
ID_MODEL_FROM_DATABASE=Performance Monitor 3
ID_MODEL_ID=0001
ID_REVISION=0111
ID_SERIAL=Concept2_Concept2_Performance_Monitor_3__PM3__300118412
ID_SERIAL_SHORT=300118412
ID_USB_INTERFACES=:030000:
ID_VENDOR=Concept2
ID_VENDOR_ENC=Concept2
ID_VENDOR_FROM_DATABASE=Concept2
ID_VENDOR_ID=17a4
MAJOR=189
MINOR=650
PRODUCT=17a4/1/111
SUBSYSTEM=usb
TYPE=0/0/0
USEC_INITIALIZED=3850171749
Unload module index
Unloaded link configuration context.

However after doing this python still reports access errors to the USB device.

Traceback (most recent call last):
  File "/home/user1/PycharmProjects/PyRow/statshow.py", line 22, in <module>
    erg = pyrow.pyrow(ergs[0])
  File "/home/user1/PycharmProjects/PyRow/pyrow.py", line 61, in __init__
    usb.util.claim_interface(erg, INTERFACE)
  File "/home/user1/PycharmProjects/camera/venv/lib/python3.5/site-packages/usb/util.py", line 205, in claim_interface
    device._ctx.managed_claim_interface(device, interface)
  File "/home/user1/PycharmProjects/camera/venv/lib/python3.5/site-packages/usb/core.py", line 102, in wrapper
    return f(self, *args, **kwargs)
  File "/home/user1/PycharmProjects/camera/venv/lib/python3.5/site-packages/usb/core.py", line 159, in managed_claim_interface
    self.managed_open()
  File "/home/user1/PycharmProjects/camera/venv/lib/python3.5/site-packages/usb/core.py", line 102, in wrapper
    return f(self, *args, **kwargs)
  File "/home/user1/PycharmProjects/camera/venv/lib/python3.5/site-packages/usb/core.py", line 120, in managed_open
    self.handle = self.backend.open_device(self.dev)
  File "/home/user1/PycharmProjects/camera/venv/lib/python3.5/site-packages/usb/backend/libusb1.py", line 786, in open_device
    return _DeviceHandle(dev)
  File "/home/user1/PycharmProjects/camera/venv/lib/python3.5/site-packages/usb/backend/libusb1.py", line 643, in __init__
    _check(_lib.libusb_open(self.devid, byref(self.handle)))
  File "/home/user1/PycharmProjects/camera/venv/lib/python3.5/site-packages/usb/backend/libusb1.py", line 595, in _check
    raise USBError(_strerror(ret), ret, _libusb_errno[ret])
usb.core.USBError: [Errno 13] Access denied (insufficient permissions)

I'm out of ideas on how to fix this. Are there any suggestions?

Answer 1

given that this is the first result on google, and that i don't see the answer that fixed this issue for me, I figured i'd post.

the udev rules do not allow comments and seems to fail pretty much silently, so if you tried adding comments to keep track of your devices, you'll have broken the permissions for those devices.

SUBSYSTEMS=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="faf0", GROUP="plugdev", MODE="0777"

will work, but

SUBSYSTEMS=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="faf0", GROUP="plugdev", MODE="0777" # thorlabs KB101 motor controller

will not

Answer 2

Using this answer I found I could correct the permissions problem using the plugdev group.

So in a terminal I used

groups
groups [myuserid]

and verified plugdev was there and the user was part of that group. Then I put the following line in /etc/udev/rules.d/10-local.rules

SUBSYSTEMS=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="17a4", ATTRS{idProduct}=="0001", GROUP="plugdev", MODE="0777"

I'm not sure if the devtype and if 0777 or 0666 is proper, but this is what worked.

After making the changes I also ran the following commands to reset the rules for the system:

sudo udevadm control --reload
sudo udevadm trigger