Controlling a USB power supply (on/off) with Linux

Question

Note. The information in this answer is relevant for the older kernels (up to 2.6.32). See tlwhitec's answer for the information on the newer kernels.

# disable external wake-up; do this only once
echo disabled > /sys/bus/usb/devices/usb1/power/wakeup 

echo on > /sys/bus/usb/devices/usb1/power/level       # turn on
echo suspend > /sys/bus/usb/devices/usb1/power/level  # turn off

(You may need to change usb1 to usb n)

Source: Documentation/usb/power-management.txt.gz

According to the docs, there were several changes to the USB power management from kernels 2.6.32, which seem to settle in 2.6.38. Now you'll need to wait for the device to become idle, which is governed by the particular device driver. The driver needs to support it, otherwise the device will never reach this state. Unluckily, now the user has no chance to force this. However, if you're lucky and your device can become idle, then to turn this off you need to:

echo "0" > "/sys/bus/usb/devices/usbX/power/autosuspend"
echo "auto" > "/sys/bus/usb/devices/usbX/power/level"

or, for kernels around 2.6.38 and above:

echo "0" > "/sys/bus/usb/devices/usbX/power/autosuspend_delay_ms"
echo "auto" > "/sys/bus/usb/devices/usbX/power/control"

This literally means, go suspend at the moment the device becomes idle.

So unless your fan is something "intelligent" that can be seen as a device and controlled by a driver, you probably won't have much luck on current kernels.

PowerTOP from Intel allows you to toggle devices such as usb peripherals in real-time. These are called 'tunables'.

sudo apt install powertop
sudo powertop

• Tab over to 'tunables'.
• Scroll down to your device.
• Hit enter to toggle power saving mode (Good/Bad)

Note that Bad means the device is always on. Toggling to Good will turn off the device after the preset inactive saving time (default is 2000ms).

See the PowerTOP docs for details on how to make these changes permanent.
It generates the config scripts for you (pretty much as described by other posters on this thread).

NOTE: These scripts do not affect USB pin power (which is always on).
These only send the driver protocol to activate and deactivate a device.

If you want to control pin power, you could use either a supported smart USB hub, or better yet a microcontroller.

I have found these solutions that at least work for properly configured Terminus FE 1.1 USB hub chip:

1.To turn off power on all USB ports of a hub, you may unbind the hub from kernel using:

echo "1-4.4.4" > /sys/bus/usb/drivers/usb/unbind

to turn power back on - you may bind it back using

echo "1-4.4.4" > /sys/bus/usb/drivers/usb/bind

2.Switching power at each port individually is trickier: I was able to use hubpower to control each port - but it comes with a downside: hubpower first disconnects the usbdevfs wich causes all of the USB devices to disconect from system, at least on ubuntu:

usb_ioctl.ioctl_code = USBDEVFS_DISCONNECT;
rc = ioctl(fd, USBDEVFS_IOCTL, &usb_ioctl);

With this ioctl disabled I was able to switch off individual port power without detaching all devices - but the power goes back on immediately (probably due to kernel seeing an uninitialized device) which causes USB device just to do a "cold restart" which is what I generally wanted to do. My patched hubpower is here

You could use my tool uhubctl to control USB power per port for compatible USB hubs.

I wanted to do this, and with my USB hardware I couldn't. I wrote a hacky way how to do it here:

http://pintant.cat/2012/05/12/power-off-usb-device/ .

In a short way: I used a USB relay to open/close the V_CC of another USB cable...

echo '2-1' |sudo tee /sys/bus/usb/drivers/usb/unbind

works for ubuntu