Determine USB device file Path
How can i get USB device file path correctly in Linux. I used command: find / -iname "usb" and got the result as below:
/dev/bus/usb
/sys/bus/usb
/sys/bus/usb/drivers/usb
/sys/kernel/debug/usb
Under /dev/bus/usb i see:
001 002 003 004 005 006
But I think they aren't files as i need.
Under /sys/bus/usb/devices/:
sh-3.2# ls /sys/bus/usb/devices/
1-0:1.0 1-1:1.0 3-0:1.0 5-0:1.0 usb1 usb3 usb5
1-1 2-0:1.0 4-0:1.0 6-0:1.0 usb2 usb4 usb6
And Under /sys/bus/scsi/devices/ when i pluged an USB i see:
2:0:0:0 host0 host2 target2:0:0
And when i removed USB i see:
sh-3.2# ls
host0
So which device file is used for USB? How can i indentify it? I need to make a C program with USB device file...
Further more, could you explain to me the number 1-1:1.0? What does it mean?
Thank you.
Answer
So which device file is used for USB? How can i indentify it?
What you see behind /sys/ is mainly configuration/information about devices. /dev/bus/usb is what you are looking for. I think that the following article can help you
http://www.linuxjournal.com/article/7466?page=0,0
Is quite old, but still it can help you. (In the article they speak about /proc/bus/usb, today we have /dev/bus/usb)
Further more, could you explain to me the number 1-1:1.0? What does it mean?
The generic form is
X-Y.Z:A.B
Each field identify the connection point of your device. The first two field are mandatory:
- X is the USB bus of your motherboard where is connected the USB system.
- Y is the port in use on the bus system
So the USB device identified with the string 3-3 is the device connected on the port 3 of the bus 3.
If you connect an USB hub, you are extending the connection capability of a single USB port. The Linux kernel identify this situation by appending the Z field.
- Z is the port is use on an hub
So, the USB device identified with the string 1-2.5 is the device connected on the port 5 of the hub connected on the port 2 of the bus 1.
USB specification allow you to connect in cascade more then one USB hub, so the Linux kernel continue to append the port in use on the different hubs. So, the USB device identified with the string 1-2.1.1 is the device connected on the port 1 of the hub connected on the port 1 of the hub connected to the port 2 of the bus 1.
A fast way to retrieve these information is to read the kernel messages (if you can).
$ dmesg | grep usb
[... snip ...]
[ 2.047950] usb 4-1: new full-speed USB device number 2 using ohci_hcd
[ 2.202628] usb 4-1: New USB device found, idVendor=046d, idProduct=c318
[ 2.202638] usb 4-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[ 2.202643] usb 4-1: Product: Logitech Illuminated Keyboard
[ 2.202648] usb 4-1: Manufacturer: Logitech
[... snip ...]
Then, the last two fields of the pattern (after colon) identify an internal section of an USB device :
- A is the configuration number of the device
- B is the interface number of a configuration
So, the string 4-1:1.1 means: the interface 1, on configuration 1 that is connected on the port 1 of the bus 4.
You can retrieve these information with the command lsusb.