1. Introduction
If we’re working on a Linux system and need to toggle a USB port power supply, there are a few ways to do it.
In this tutorial, we’ll explore how to control the power supply of a USB port using Linux.
Notably, certain USB devices may have built-in protections or firmware settings that prevent unauthorized changes to their power settings for safety or operational reasons.
2. Using /sys/bus/usb
By writing specific values to the /sys pseudo-filesystem power/control file for a USB device, we can influence its power-related behavior. For example, we can turn on or off the USB port and toggle the autosuspend functionality.
Thus, we’ll use echo in combination with file redirection to write a value to the respective control file of a USB device.
First, let’s find the device’s USB port using dmesg and grep:
$ dmesg | grep "usb"
dmesg | grep "usb"
[ 0.325546] usbcore: registered new interface driver usbfs
[ 0.325589] usbcore: registered new interface driver hub
[ 0.325616] usbcore: registered new device driver usb
[ 0.487210] pci 0000:00:1d.0: quirk_usb_early_handoff+0x0/0x140 took 33353 usecs
[ 0.680250] usb usb1: New USB device found, idVendor=1d6b, idProduct=0002, bcdDevice= 5.14
[ 0.680263] usb usb1: New USB device strings: Mfr=3, Product=2, SerialNumber=1
[ 0.680276] usb usb1: Product: EHCI Host Controller
[ 0.680288] usb usb1: Manufacturer: Linux 5.14.0-299.el9.x86_64 ehci_hcd
...
[38484.380733] usb 1-3: USB disconnect, device number 10
[38614.274597] usb 1-3: new high-speed USB device number 11 using ehci-pci
[38614.406083] usb 1-3: New USB device found, idVendor=090c, idProduct=1000, bcdDevice=11.00
[38614.406097] usb 1-3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[38614.406099] usb 1-3: Product: USB Flash Disk
[38614.406100] usb 1-3: Manufacturer: P-net
[38614.406101] usb 1-3: SerialNumber: 0360915110000723
[38614.411735] usb 1-3:1.0: USB P-net Fan device detectedIn this example, we searched for lines in the kernel message log that contain the keyword usb. From the output, we got data about our USB port devices such as Manufacturer, SerialNumber, idVendor, and idProduct. In this case, 1-3:1.0 indicates that the USB fan device is connected to bus 1, port 3, and has a configuration or interface of 1.0.
Now, we can disable autosuspend of our USB device:
$ echo "0" > "/sys/bus/usb/devices/1-3:1.0/power/autosuspend_delay_ms"To be clear, autosuspend is a feature that allows the system to automatically suspend power to idle USB devices to save energy. By setting autosuspend to 0, we disable this behavior for our device. Importantly, 1-3:1.0 is the exact number we got from the previous step.
Then, we can turn off our USB device:
$ echo "auto" > "/sys/bus/usb/devices/1-3:1.0/power/control"Here, auto indicates that the power management should be handled automatically by the system or device driver. The system determines when to suspend or resume power for the USB device based on its activity or idle state.
Finally, we can check the status of our USB device by reading back the respective runtime_status file via cat:
$ cat /sys/bus/usb/devices/1-3:1.0/power/runtime_status
suspendedAs we can see, our USB device is suspended.
Now, we can turn our device on again:
$ echo "on" > "/sys/bus/usb/devices/1-3:1.0/power/control"Finally, let’s recheck the status:
$ cat /sys/bus/usb/devices/1-3:1.0/power/runtime_status
activeHere, we can see the USB device is active again.
3. Using uhubctl
uhubctl is a command-line utility that allows us to control the USB power of individual ports on smart USB hubs. uhubctl doesn’t directly control power to other types of USB devices such as flash drives or keyboards.
First, we install the uhubctl command via apt-get:
$ sudo apt-get install uhubctlThen, we run the uhubctl command to list available hubs and ports:
$ sudo uhubctl
Current status for hub 1-1 [046d:0821 Logitech Smart USB Hub, USB 2.0, 7 ports]
Port 1: 0100 power fan
Port 2: 0100 power
Port 3: 0100 power
Port 4: 0100 power
Port 5: 0100 power
Port 6: 0100 power
Port 7: 0100 powerIn this example, we can see all our smart USB hub ports are powered on and that a fan is connected to port 1.
So, let’s turn off the fan’s port:
$ sudo uhubctl -a off -p 1
Current status for hub 1-1 [046d:0821 Logitech Smart USB Hub, USB 2.0, 7 ports]
Port 1: 0100 power
Sent power off request
New status for hub 1-1 [046d:0821 Logitech Smart USB Hub, USB 2.0, 7 ports]
Port 1: 0000 offNotably, we used -a off to specify that our action is off. Moreover, -p determines the port. In this case, a power off request was sent to port 1, and the status changed to 0000 which means our port’s power supply is now off.
At this point, we can turn the port back on:
$ sudo uhubctl -a on -p 1
Current status for hub 1-1 [046d:0821 Logitech Smart USB Hub, USB 2.0, 7 ports]
Port 1: 0000 off
Sent power off request
New status for hub 1-1 [046d:0821 Logitech Smart USB Hub, USB 2.0, 7 ports]
Port 1: 0100 powerIn this case, a power on request was sent to port 1, and the current status of our port is back to 0100, meaning power is on.
4. Using Udev Rules
udev is a Linux utility that manages device events. Moreover, udev rules are custom configurations that define actions for specific devices based on their attributes. With udev rules, we can control USB power and perform various automated actions directly from the command line in Linux.
There are several ways to get information about connected USB devices such as dmesg, lsusb, and inspecting /usb/devices.
First, let’s get information about our USB device:
$ sudo lsusb
Bus 001 Device 014: ID 203a:fffc PARALLELS Virtual Mouse
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 010: ID 12d1:140c Huawei Technologies Co., Ltd. E180v
Bus 002 Device 009: ID 203a:fffe PARALLELS Virtual USB1.1 HUB
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hubHere, we can see the list of our USB devices. Moreover, the string after ID is the idVendor and idProduct. In this case, we have 12d1:140c for the device of interest: Huawei Technologies Co., Ltd. E180v.
Then, we can create a udev rule file using any text editor, such as nano:
$ nano /etc/udev/rules.d/usb-power.rulesNow, we can add this rule:
ACTION=="add", SUBSYSTEM=="usb", ATTR{idVendor}=="12d1", ATTR{idProduct}=="140c", ATTR{power/control}="auto"Let’s break down this rule:
- ACTION==”add” – defines the action that triggers the rule
- SUBSYSTEM==”usb” – matches the subsystem of the device
- ATTR{idVendor}==”12d1″ – idVendor of the USB device
- ATTR{idProduct}==”140c” – idProduct of the USB device
- ATTR{power/control}=”auto” – sets the value of the power or control attribute to auto
Then, we need to reload the udev rules for the changes to take effect:
$ sudo udevadm control --reload-rulesIn this case, we used udevadm, a command-line tool for managing and querying the udev device manager. Moreover, we used control –reload-rules to ask the udev daemon to reload the udev rules.
5. Using hub-ctrl
hub-ctrl is a Linux command-line utility that controls the power supply of USB hub ports, enabling users to programmatically turn USB devices on or off. Moreover, hub-ctrl simplifies USB power management, allowing for automation and customization according to user preferences.
5.1. Installation
First, we need to install dependencies:
$ sudo apt-get install libusb-dev gccThen, we can get hub-ctl via git:
$ git clone https://github.com/yy502/hub-ctrlNow, we’ll navigate to the hub-ctrl directory:
$ cd hub-ctrlThen, we’ll compile hub-ctrl using gcc:
$ gcc -o hub-ctrl hub-ctrl.c -lusb -std=c99Here, we compiled the hub-ctrl.c source code file and generated an executable binary file named hub-ctrl. Moreover, we used the -lusb option to use libusb library during the compilation process. Afterward, we used -std=c99 to set the C language standard to C99.
5.2. Control USB Power
Now, we can list hubs and ports directly with hub-ctrl instead of using another tool:
$ sudo ./hub-ctrl
Hub 0 (Bus 4, Dev 1) - ganged power switching
Hub 1 (Bus 3, Dev 1) - no power switching
├─ Port 1: power
└─ Port 2: power
Hub 2 (Bus 2, Dev 1) - no power switching
├─ Port 1: power
└─ Port 2: power
Hub 3 (Bus 1, Dev 1) - no power switching
├─ Port 1: power high-speed connect enable
...
├─ Port 14: power
└─ Port 15: powerThe output is a comprehensive tree view of the requested devices.
Finally, we can turn off the port of interest:
$ sudo ./hub-ctrl -H 3 -P 1 -p 0
> Hub:3 Bus:0 Devive:0 Port:1 power->offHere, we use several options:
- -H – hub number
- -P – port number
- -p 0 – turn off the power
Moreover, we can use bus, device, and port numbers:
$ sudo ./hub-ctrl -B 1 -D 1 -P 1 -p 0
> Hub:3 Bus:1 Devive:1 Port:1 power->offHere, we used -B to define the bus number and -D to set the device number.
Conversely, we can turn the power back on for the same USB port:
$ sudo ./hub-ctrl -B 1 -D 1 -P 1 -p 1
> Hub:3 Bus:1 Devive:1 Port:1 power->onAs we can see, the -p 1 option means turning on the power.
6. Conclusion
In this article, we looked at several methods for controlling USB port power supply on Linux systems. Firstly, we used the echo command to manipulate the power/control file of the USB device. In particular, we disabled autosuspend, and controlled the power state. Secondly, we used the uhubctl command to control USB port power on smart USB hubs individually.
Afterward, the third technique involved creating custom udev rules to automate actions based on specific USB device attributes. Lastly, we explored the hub-ctrl utility, which allowed for controlling power to individual ports on a USB hub.
To sum up, these methods offer flexibility and control over USB port power management, enabling us to customize our system’s behavior according to our specific requirements.