Karl's Code

and other code related stuff

Disabling the Webcam or USB Ports on Linux

Why disable a USB port?

You may just want to make sure that you webcam, usually connected to the internal USB bus, is turned off.

In my case my laptop webcam has become intermittently faulty. This has caused my laptop to hang on shutdown while the kernel tries to power down the device.

Clearly I want to disable the camera’s port without disabling all the other USB ports on the laptop…

Identify the port

The first step was to identify the camera’s port.

You can trawl through dmesg logs looking at all USB entries until you find the webcam, e.g.

$ dmesg
[    2.996705] usb 1-1.6: Product: Webcam SC-13HDL11624N

Here you can see that my webcam was on bus 1 - port 1 on the 6th device on that port e.g. 1-1.6

However Linux has some commands and a pseudo “sys” file system that make it easier, for instance you could use lsusb

$ lsusb -t
/:  Bus 03.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/2p, 5000M
/:  Bus 02.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/2p, 480M
    |__ Port 1: Dev 2, If 0, Class=Mass Storage, Driver=usb-storage, 480M
    |__ Port 2: Dev 3, If 0, Class=Human Interface Device, Driver=usbhid, 12M
    |__ Port 2: Dev 3, If 1, Class=Human Interface Device, Driver=usbhid, 12M
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/3p, 480M
    |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/6p, 480M
        |__ Port 2: Dev 3, If 0, Class=Human Interface Device, Driver=usbhid, 1.5M
        |__ Port 5: Dev 4, If 0, Class=Wireless, Driver=btusb, 12M
        |__ Port 5: Dev 4, If 1, Class=Wireless, Driver=btusb, 12M
        |__ Port 6: Dev 5, If 0, Class=Video, Driver=uvcvideo, 480M
        |__ Port 6: Dev 5, If 1, Class=Video, Driver=uvcvideo, 480M

If we walk this tree we can see bus 01 Port 1 is a USB hub and port 6 on the hub is a video device, which is my webcam… but this is a bit obtuse and confusing, and it doesn’t yield the literal string 1-1.6 that I’ll need to disable the webcam port.

A better method is to walk the sys pseudo file system that gives info on all devices attached to the kernel system.

$ for device in $(ls /sys/bus/usb/devices/*/product); do echo $device;cat $device;done
Dell USB Entry Keyboard
Webcam SC-13HDL11624N
Amazon Kindle
USB Receiver
EHCI Host Controller
xHCI Host Controller
xHCI Host Controller

Here we can see that the file /sys/bus/usb/devices/1-1.6/product contains the Webcam SC-13HDL11624N

So in this case the USB device (or port) we need is 1-1.6.

Because the Webcam is attached to the internal USB hub, it will always be listed at the same address, this is helpful as it means I can hard-code 1-1.6 where I need it rather than parsing the output of the command.

Turn off power to the Webcam

Now we know the USB device number, it is simple to turn off the camera using the sys file system.

By writing values to the “files” in the sys file system you can effect the devices that the file represents. Obviously you need to be root to do this, or be a user that has sudo permissions.

On Ubuntu

We can send a command to the USB driver to unbind a port,

$ echo '1-1.6' | sudo tee /sys/bus/usb/drivers/usb/unbind

Obviously replace “1-1.6” with whichever usb port your webcam is on (see above).

To turn it back on,

$ echo '1-1.6' | sudo tee /sys/bus/usb/drivers/usb/bind

This command pushed the USB device name, “1-1.6”, to a special socket that acts like a command API to the USB driver, in other words rather than directly control the power of the device we ask the USB driver to do it for us.

Run it at start-up

Now I have control over my USB ports I want to disable this port at start-up. Ubuntu uses the anacron cron daemon which allows a special syntax, @reboot, to hook a command to the reboot sequence.

Simple edit root’s crontab

$ sudo crontab -e

And then append the following

@reboot echo '1-1.6' > /sys/bus/usb/drivers/usb/unbind

Again edit ‘1-1.6’ to your usb device’s number.

And that’s it. My laptop can now shutdown without hanging.