How to fix the UVC camera DEVICE ID

[Jskim]

Hi Support Team,

[This is an inquiry regarding a UVC camera.]
We are using the voxl-mini as shown below.

• hw platform: M0104
• voxl-suite: 1.4.5
• SKU: TF-M0104-6-V1-C6
• video codec(voxl-streamer): h.264
• Web camera: uvc(YUY2) format

[Inquiry]

1. We are using a web camera.
2. The Device ID changes when the camera is turned back on (see figure below).
   
   Therefore, we execute the command "systemctl restart voxl-uvc-server" every time.
3. Please tell me how to fix the Device ID.???

Thank you.
Kim.

[Jskim]

Hi Support team,

I would like to know how to resolve the issue regarding the DEVICE ID change.

Could you please provide a solution for the above?

e.g., Will creating a udev rule file resolve the issue?

Thank you.

Kim,

[Alex Kushleyev]

@Jskim , you should check dmesg to see maybe there are some warnings. Perhaps the device is not de-initialized properly (how are you powering it off?) and next time the OS allocates a new Device ID.

Either way, using udev rule should help resolve the issue, however make sure there is no resource leak as a result of the device on/off. Also, if you keep turning the device on/off, does the device ID increment indefinitely?

Alex

[Jskim]

The Device ID continues to increase.

We are using a webcam with a built-in SD card.
We switch between SD card mode and Webcam mode by pressing a button.
When power is supplied to the camera, SD card mode is set by default, and pressing the button switches it to Webcam mode.
The DEVICE ID number increases every time the camera is connected.

Thank you.
Kim

[Alex Kushleyev]

@Jskim , maybe it's ok that the Device ID is increasing, however it could mean the USB device is not de-initializing properly (according to the Kernel). Perhaps the device is still open / in use by voxl-uvc-server when you power the camera off (switch to the SD card mode).

Please see some more information below that may be helpful.

Fix 1: Configure voxl-uvc-server to identify the camera by Vendor/Product ID

Instead of relying on the device index, tell voxl-uvc-server to always find your camera by its USB VID:PID. This is the most robust approach.

Step 1: Find your camera's Vendor ID and Product ID

lsusb

Look for your UVC webcam in the output. The ID is in VENDOR:PRODUCT hex format, e.g.:

Bus 001 Device 003: ID 090c:337b  <-- vendor=090c, product=337b

You can also use the ModalAI helper script:

show-video-device-info.sh

Step 2: Update the voxl-uvc-server service to pass VID/PID

Edit the systemd service override so the server always targets your specific camera:

mkdir -p /etc/systemd/system/voxl-uvc-server.service.d/
cat > /etc/systemd/system/voxl-uvc-server.service.d/override.conf << EOF
[Service]
ExecStart=
ExecStart=/usr/bin/voxl-uvc-server -v <your-vendor-id> -p <your-product-id>
EOF
systemctl daemon-reload
systemctl restart voxl-uvc-server

Replace <your-vendor-id> and <your-product-id> with the hex values from lsusb. With this in place, voxl-uvc-server will find the camera by identity rather than by device node index, so it will survive power cycles without needing a manual restart.

---

Fix 2: Create a udev rule for a persistent /dev symlink

This assigns a stable name (e.g., /dev/uvc_cam) to your camera regardless of enumeration order:

cat > /etc/udev/rules.d/99-uvc-camera.rules << EOF
SUBSYSTEM=="video4linux", ATTRS{idVendor}=="<your-vendor-id>", ATTRS{idProduct}=="<your-product-id>", SYMLINK+="uvc_cam", MODE="0660"
EOF
udevadm control --reload-rules
udevadm trigger

After this, /dev/uvc_cam will always point to your camera. You can reference this stable symlink in any configuration.

---

Fix 3: Check dmesg for resource leak warnings

If the device ID keeps incrementing (e.g., /dev/video0 → /dev/video1 → /dev/video2...) rather than re-using the same node, there may be an underlying resource leak from improper de-initialization:

dmesg | grep -i "uvc\|video\|usb" | tail -50

Look for warnings about disconnection or failed cleanup. If the ID increments indefinitely, this points to a kernel-side resource not being released properly on power-off — that may require a deeper fix or a systemctl stop voxl-uvc-server before powering down the camera.

---

Summary

Step	Action
1	Run lsusb to get your camera's Vendor ID and Product ID
2	Pass -v <vid> -p <pid> to voxl-uvc-server via a systemd override
3	Optionally create a udev rule for a stable /dev/uvc_cam symlink
4	Check dmesg for warnings if the device ID keeps incrementing

The vendor/product ID approach (Fix 1) should eliminate the need for the manual systemctl restart workaround entirely.

[Jskim]

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