USB devices no longer show up in /dev

Product support
1

As of this week (?), dynamically plugged usb devices no longer show in /dev.

Setup:

  • multi-container app
  • Dockerfile for affected container sets “ENV UDEV=1” and does not override the ENTRYPOINT
  • It is run as “privileged”

When I connect a USB device (example is an ESP32 but I’ve tried many others with same result), it shows up in lsusb:

Bus 001 Device 005: ID 10c4:ea60 Cygnal Integrated Products, Inc. CP2102/CP2109 UART Bridge Controller [CP210x family]

dmesg even shows the port the device is attached to (ttyUSB0):

[  472.505837] usbcore: registered new interface driver cdc_acm
[  588.133495] usb 1-1.4: new full-speed USB device number 5 using xhci_hcd
[  588.244833] usb 1-1.4: New USB device found, idVendor=10c4, idProduct=ea60, bcdDevice= 1.00
[  588.253373] usb 1-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[  588.260848] usb 1-1.4: Product: CP2104 USB to UART Bridge Controller
[  588.267342] usb 1-1.4: Manufacturer: Silicon Labs
[  588.272167] usb 1-1.4: SerialNumber: 0160B5B8
[  588.540347] usbcore: registered new interface driver cp210x
[  588.546444] usbserial: USB Serial support registered for cp210x
[  588.564967] usb 1-1.4: cp210x converter now attached to ttyUSB0

If I plug in a second device, dmesg reports cp210x converter now attached to ttyUSB1.

However, neither list in /dev.

Possibly relevant is a recent change to no longer run the container as root, i.e. added

RUN useradd -m -s /bin/bash -G dialout,netdev -U -u 1000 iot \
 && echo 'iot ALL=(ALL) NOPASSWD:ALL' | EDITOR='tee -a' visudo

USER iot
WORKDIR /home/iot

CMD [ "/bin/bash", "/usr/local/bin/start.sh" ]

Maybe this “broke” the usb mount - if so, what’s the fix?

3

Yes, switching to a non-root user was the problem. Making the switch in start.sh instead fixed my issue.

I suspect the ENTRYPOINT script assumes the user is root.

5

Thanks for reaching out. It seems from your message you were able to resolve the issue via switching in start.sh. Anything we can help here answer for you?

6

Hi, are you still having issues accessing your USB devices? Let us know if there are still things that you need help with.

8

Everything works again after removing “USER iot” from my Dockerfile.
Perhaps this could be added to the documentation:

  • Privileged
  • UDEV=1
  • → add USER root

I switch the user in start.sh (run by CMD). The trick is to avoid inadvertently dropping back to root (exit, ^D).

Many thanks! I should say generally my experience with Balena.io has been excellent. It’s powerful and very reliable. Thanks!