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You may just want to make sure that you webcam, or any other USB device, usually connected to the internal USB bus, is turned off.
In our case our laptop webcam has become intermittently faulty. This has caused our laptop to hang on shutdown while the kernel tries to power down the device.
Nww, in a hypotetical scenario, we 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, for example:
$ dmesg ... [ 2.996705] usb 1-1.6: Product: Webcam JN5284HD831 ...
Here you can see that our webcam was on bus 1 - port 1 on the 6th device on that port, for example 1-1.6
However, Linux distros has some commands and a pseudo “sys” file system that make it easier, for instance we 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 our 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 /sys/bus/usb/devices/1-1.2/product Dell USB Entry Keyboard /sys/bus/usb/devices/1-1.6/product Webcam SC-13HDL11624N /sys/bus/usb/devices/2-1/product Amazon Kindle /sys/bus/usb/devices/2-2/product USB Receiver /sys/bus/usb/devices/usb1/product EHCI Host Controller /sys/bus/usb/devices/usb2/product xHCI Host Controller /sys/bus/usb/devices/usb3/product xHCI Host Controller
Here we can see that the file /sys/bus/usb/devices/1-1.6/product contains the webcam JN5284HD831.
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 we can hard-code 1-1.6 where we 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.
Driver binding is the process of associating a device with a device driver that can control it. Bus drivers have typically handled this because there have been bus-specific structures to represent the devices and the drivers. With generic device and device driver structures, most of the binding can take place using common code.
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.
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 (bind):
$ 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 we have control over our USB ports we 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.